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[1]  arXiv:1612.02424 [pdf, ps, other]
Title: VLBI studies of TANAMI radio galaxies
Authors: Roberto Angioni (MPIfR), Florian Rösch (U. Würzburg), Eduardo Ros (MPIfR, U. Valencia), Matthias Kadler (U. Würzburg), Roopesh Ojha (NASA GSFC), Cornelia Müller (U. Nijmegen), Robert Schulz (ASTRON) for the TANAMI collaboration
Comments: Submitted to the proceedings of the 13th EVN Symposium and Users Meeting held in St. Petersburg, Russia, 20-23 September 2016. Contributed talk: 6 pages, 1 figure
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Radio galaxies are relatively faint at $\gamma$-ray energies, where they make up only 1-2% of all AGN detected by Fermi-LAT. However, they offer a unique perspective to study the intrinsic properties of AGN jets. For this reason, the combination of $\gamma$-ray and multi-wavelength data with high-resolution VLBI monitoring is a powerful tool to tackle the basic unanswered questions about AGN jets. Here we present preliminary results from a sample study of radio galaxies in the Southern hemisphere observed by the TANAMI VLBI monitoring program. We obtain high-resolution maps at 8.4 and 22.3 GHz, and study the jet kinematics using multi-epoch data. We present a preliminary kinematic analysis for the peculiar $\gamma$-ray AGN PKS 0521$-$36.

[2]  arXiv:1612.02425 [pdf, ps, other]
Title: Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b
Comments: 13 pages, 10 colour figures, 5 tables. Submitted on 2016/12/05
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Detecting the atmospheres of low-mass low-temperature exoplanets is a high-priority goal on the path to ultimately detect biosignatures in the atmospheres of habitable exoplanets. High-precision HST observations of several super-Earths with equilibrium temperatures below 1000 K have to date all resulted in featureless transmission spectra, which have been suggested to be due to high-altitude clouds. We report the detection of an atmospheric feature in the atmosphere of a 1.6 Mearth transiting exoplanet, GJ 1132b, with an equilibrium temperature of ~600 K and orbiting a nearby M dwarf. We present observations of nine transits of the planet obtained simultaneously in the griz and JHK passbands. We find an average radius of 1.44 +/- 0.21 Rearth for the planet, averaged over all the passbands, which can be decomposed into a "surface radius" at ~1.35 Rearth, and higher contributions in the z and K bands. The z-band radius is 4 sigma higher than the continuum, suggesting a strong detection of an atmosphere. We deploy a suite of tests to verify the reliability of the transmission spectrum, which are greatly helped by the existence of repeat observations. The large z-band transit depth indicates strong opacity from H2O and/or CH4 or an hitherto unconsidered opacity. A surface radius of 1.35 +/- 0.21 Rearth allows for a wide range of interior compositions ranging from a nearly Earth-like rocky interior, with ~70% silicate and ~30% Fe, to a substantially H2O-rich water world. New observations with HST and existing ground-based facilities would be able to confirm the present detection and further constrain the atmospheric composition of the planet.

[3]  arXiv:1612.02426 [pdf, ps, other]
Title: The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
Authors: Michael C. Liu (IfA/Hawaii), Trent J. Dupuy (UT Austin), Katelyn N. Allers (Bucknell)
Comments: ApJ, in press, 138 pages including 33 figures and 15 tables. Compilation of young ultracool dwarfs and young substellar (brown dwarf and exoplanet) companions available at the Database of Ultracool Parallaxes (see this http URL)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

(Abridged) We present a large, uniform analysis of young (~10-150 Myr) ultracool dwarfs, based on new high-precision IR parallaxes for 68 objects. We find that low-gravity (VL-G) late-M and L dwarfs form a continuous sequence in IR color-magnitude diagrams, separate from field objects and current theoretical models. VL-G objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting the two populations have a different range of physical properties. In contrast, at the L/T transition, young, old, and peculiar objects all span a narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid/late-L dwarfs (fainter than the field). Overall, low-gravity (VL-G) objects have the most uniform photometric behavior while intermediate-gravity (INT-G) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group memberships for all young ultracool dwarfs with parallaxes, changing/refuting the status of 23 objects and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and find a declining frequency of VL-G objects relative to INT-G objects with increasing age. Notable objects in our sample include high-velocity INT-G objects; very red, late-L dwarfs with high surface gravities; candidate disk-bearing members of the MBM20 cloud and beta Pic moving group; and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of 102 young ultracool dwarfs, found in the field and as substellar companions to young stars.

[4]  arXiv:1612.02428 [pdf, other]
Title: HI-to-H2 Transition Layers in the Star-Forming Region W43
Comments: 5 pages, 2 figures. ApJ accepted. Comments welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The process of atomic-to-molecular (HI-to-H$_2$) gas conversion is fundamental for molecular-cloud formation and star formation. 21 cm observations of the star-forming region W43 revealed extremely high HI column densities, of 120-180 M$_{\odot}$ pc$^{-2}$, a factor of 10-20 larger than predicted by HI-to-H$_2$ transition theories. We analyze the observed HI with an HI-to-H$_2$ transition theoretical model, and show that the theory-observation discrepancy cannot be explained by the intense radiation in W43, nor by variations of the assumed volume density or H$_2$ formation-rate coefficient. We show that the large observed HI columns are naturally explained by several ($9-22$) HI-to-H$_2$ transition layers, superimposed along the sightlines of W43. We discuss other possible interpretations such as a non-steady-state scenario, and inefficient dust absorption. The case of W43 suggests that HI thresholds reported in extra-galactic observations are probably not associated with a single HI-to-H$_2$ transition, but are rather a result of several transition layers (clouds) along the sightlines, beam-diluted with diffuse inter-cloud gas.

[5]  arXiv:1612.02429 [pdf, other]
Title: Obscured Active Galactic Nuclei triggered in compact star-forming galaxies
Comments: Accepted for publication in MNRAS Letter
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present a structural study of 182 obscured Active Galactic Nuclei (AGNs) at z<=1.5, selected in the COSMOS field from their extreme infrared to X-ray luminosity ratio and their negligible emission at optical wavelengths. We fit optical to far-infrared spectral energy distributions and analyze deep HST imaging to derive the physical and morphological properties of their host galaxies. We find that such galaxies are more compact than normal star-forming sources at similar redshift and stellar mass, and we show that it is not an observational bias related to the emission of the AGN. Based on the distribution of their UVJ colors, we also argue that this increased compactness is not due to the additional contribution of a passive bulge. We thus postulate that a vast majority of obscured AGNs reside in galaxies undergoing dynamical compaction, similar to processes recently invoked to explain the formation of compact star-forming sources at high redshift.

[6]  arXiv:1612.02430 [pdf, other]
Title: Turbulent magnetic relaxation in pulsar wind nebulae
Comments: Submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present a model for magnetic energy dissipation in a pulsar wind nebula. Better understanding of this process is required to assess the likelihood that certain astrophysical transients may be powered by the spin-down of a "millisecond magnetar." Examples include superluminous supernovae, gamma-ray bursts, and anticipated electromagnetic counterparts to gravitational wave detections of binary neutron star coalescence. Our model leverages recent progress in the theory of turbulent magnetic relaxation to specify a dissipative closure of the stationary magnetohydrodynamic (MHD) wind equations, yielding predictions of the magnetic energy dissipation rate throughout the nebula. Synchrotron losses are treated self-consistently. To demonstrate the model's efficacy, we show that it can reproduce many features of the Crab Nebula, including its expansion speed, radiative efficiency, peak photon energy, and mean magnetic field strength. Unlike ideal MHD models of the Crab (which lead to the so-called sigma problem) our model accounts for the transition from ultra to weakly magnetized plasma flow, and for the associated heating of relativistic electrons. We discuss how the predicted heating rates may be utilized to improve upon models of particle transport and acceleration in pulsar wind nebulae. We also discuss implications for the Crab Nebula's gamma-ray flares, and point out potential modifications to models of astrophysical transients invoking the spin-down of a millisecond magnetar.

[7]  arXiv:1612.02431 [pdf, other]
Title: Accretion and Magnetic Reconnection in the Classical T Tauri Binary DQ Tau
Comments: Accepted to ApJ, 17 pages, 11 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Binary star-formation theory predicts that close binaries (a<100 AU) will experience periodic pulsed accretion events as streams of material form at the inner edge of a circumbinary disk, cross a dynamically cleared gap, and feed circumstellar disks or accrete directly onto the stars. The archetype for the pulsed-accretion theory is the eccentric, short-period, classical T Tauri binary DQ Tau. Low-cadence (~daily) broadband photometry has shown brightening events near most periastron passages, just as numerical simulations would predict for an eccentric binary. Magnetic reconnection events (flares) during the collision of stellar magnetospheres near periastron could, however, produce the same periodic, broadband behavior when observed at a one-day cadence. To reveal the dominate physical mechanism seen in DQ Tau's low-cadence observations, we have obtained continuous, moderate-cadence, multi-band photometry over 10 orbital periods, supplemented with 27 nights of minute-cadence photometry centered on 4 separate periastron passages. While both accretion and stellar flares are present, the dominant timescale and morphology of brightening events are characteristic of accretion. On average, the mass accretion rate increases by a factor of 5 near periastron, in good agreement with recent models. Large variability is observed in the morphology and amplitude of accretion events from orbit-to-orbit. We argue this is due to the absence of stable circumstellar disks around each star, compounded by inhomogeneities at the inner edge of the circumbinary disk and within the accretion streams themselves. Quasi-periodic apastron accretion events are also observed, which are not predicted by binary accretion theory.

[8]  arXiv:1612.02432 [pdf, ps, other]
Title: Kepler Transit Depths Contaminated by a Phantom Star
Comments: 11 pages, 10 figures, 5 tables. Accepted for publication in AJ. Transit light curves will be available from AJ as DbF
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We present ground-based observations from the Discovery Channel Telescope (DCT) of three transits of Kepler-445c---a supposed super-Earth exoplanet with properties resembling GJ 1214b---and demonstrate that the transit depth is approximately 50 percent shallower than the depth previously inferred from Kepler Spacecraft data. The resulting decrease in planetary radius significantly alters the interpretation of the exoplanet's bulk composition. Despite the faintness of the M4 dwarf host star, our ground-based photometry clearly recovers each transit and achieves repeatable 1-sigma precision of approximately 0.2 percent (2 millimags). The transit parameters estimated from the DCT data are discrepant with those inferred from the Kepler data to at least 17-sigma confidence. This inconsistency is due to a subtle miscalculation of the stellar crowding metric during the Kepler pre-search data conditioning (PDC). The crowding metric, or CROWDSAP, is contaminated by a non-existent "phantom star" originating in the USNO-B1 catalog and inherited by the Kepler Input Catalog (KIC). Phantom stars in the KIC are likely rare, but they have the potential to affect statistical studies of Kepler targets that use the PDC transit depths for a large number of exoplanets where individual follow-up observation of each is not possible. The miscalculation of Kepler-445c's transit depth emphasizes the importance of stellar crowding in the Kepler data, and provides a cautionary tale for the analysis of data from the Transiting Exoplanet Survey Satellite (TESS), which will have even larger pixels than Kepler.

[9]  arXiv:1612.02433 [pdf, ps, other]
Title: Chromospherically Active Stars in the RAVE Survey. II. Young dwarfs in the Solar neighborhood
Comments: 21 pages, 14 figures, accepted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

A large sample of over 38,000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a catalog of field stars in the Solar neighborhood with an excess emission flux in the calcium infrared triplet wavelength region. The central result of this work is the calibration of the age--activity relation for the main sequence dwarfs in a range from a few $10 \; \mathrm{Myr}$ up to a few Gyr. It enabled an order of magnitude age estimation of the entire active sample. Almost 15,000 stars are shown to be younger than $1\;\mathrm{Gyr}$ and $\sim$2000 younger than $100\;\mathrm{Myr}$. The young age of the most active stars is confirmed by their position off the main sequence in the $J-K$ versus $N_{UV}-V$ diagram showing strong ultraviolet excess, mid-infrared excess in the $J-K$ versus $W_1-W_2$ diagram and very cool temperatures ($J-K>0.7$). They overlap with the reference pre-main sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo generating magnetic fields in cool stars. 50\% of the RAVE objects from DR5 are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE's radial velocities directly useful as a tracer of the very recent large-scale star formation history in the Solar neighborhood. The data are available online in the Vizier database.

[10]  arXiv:1612.02435 [pdf, other]
Title: Impact of $(α,n)$ reactions on neutrino-driven wind nucleosynthesis
Comments: 15 pages, 8 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)

After a successful core-collapse supernova, a neutrino-driven wind develops where it is possible to synthesize lighter heavy elements ($30<Z<45$). In the early galaxy, the origin of these elements is associated to the r-process and to an additional process. Here we assume the additional process corresponds to the weak r-process or alpha-process taking place in neutrino-driven winds. Based on a trajectory obtained from hydrodynamical simulations we study the astrophysics and nuclear physics uncertainties with our main focus on the \alphan reactions. These are critical to redistribute the matter and allow to further move it from light to heavy elements after nuclear statistical equilibrium freezes out. In this first sensitivity study, we vary all \alphan reactions by given constant factors which are justified based on the uncertainties of the statistical model and its nuclear physics input, mainly alpha optical potentials under the conditions found in the wind. Our results show that \alphan reactions are indeed very important to predict abundances. Therefore, further studies will follow to identify individual critical reactions. Since the nucleosynthesis path is close to stability, these reactions can be measured in the near future. This will uniquely allow to reduce the nuclear physics uncertainties and thus to use observations to constrain and understand the astrophysical conditions in the wind.

[11]  arXiv:1612.02440 [pdf, other]
Title: Co-moving stars in Gaia DR1: An abundance of very wide separation co-moving pairs
Comments: submitted to AAS Journals; A web visualization of the result is available at this http URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

The primary sample of the Gaia Data Release 1 is the Tycho-Gaia Astrometric Solution (TGAS): $\approx$ 2 million Tycho-2 sources with improved parallaxes and proper motions relative to the initial catalog. This increased astrometric precision presents an opportunity to find new binary stars and moving groups. We search for high-confidence co-moving pairs of stars in TGAS by identifying pairs of stars consistent with having the same 3D velocity using a marginalized likelihood ratio test to discriminate candidate co-moving pairs from the field population. Although we perform some visualizations using (bias-corrected) inverse-parallax as a point-estimate of distance, the likelihood ratio is computed with a probabilistic model that includes the covariances of parallax and proper motions, and marginalizes the (unknown) true distances and 3D velocities of the stars. We find 13,085 co-moving star pairs among 10,606 unique stars with separations as large as 10 pc (our search limit). Some of these pairs form larger groups through mutual co-moving neighbors: many of these pair networks correspond to known open clusters and OB associations, but we also report the discovery of several new co-moving groups. Most surprisingly, we find a large number of very wide ($>1$ pc) separation co-moving star pairs, the number of which increases with increasing separation and cannot be explained purely by false-positive contamination. Our key result is a catalog of high-confidence co-moving pairs of stars in TGAS. We discuss the utility of this catalog for making dynamical inferences about the Galaxy, testing stellar atmosphere models, and validating chemical abundance measurements.

[12]  arXiv:1612.02441 [pdf, ps, other]
Title: Absolute dimensions of the eccentric eclipsing binary V541 Cygni
Authors: G. Torres (1), C.D. McGruder (1,2), R.J. Siverd (3), J.E. Rodriguez (1), J. Pepper (4), D.J. Stevens (5), K.G. Stassun (6,7), M.B. Lund (6), D. James (8) ((1) CfA, (2) Univ. of Tennessee, (3) LCOGT, (4) Lehigh Univ., (5) Ohio State Univ., (6) Vanderbilt Univ., (7) Fisk Univ., (8) Univ. of Washington)
Comments: 11 pages in emulateapj format, including figures and tables. Accepted for publication in the Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We report new spectroscopic and photometric observations of the main-sequence, detached, eccentric, double-lined eclipsing binary V541 Cyg (P = 15.34 days, e = 0.468). Using these observations together with existing measurements we determine the component masses and radii to better than 1% precision: M1 = 2.335 +0.017/-0.013 MSun, M2 = 2.260 +0.016/-0.013 MSun, R1 = 1.859 +0.012/-0.009 RSun, and R2 = 1.808 +0.015/-0.013 RSun. The nearly identical B9.5 stars have estimated temperatures of 10650 +/- 200 K and 10350 +/- 200 K. A comparison of these properties with current stellar evolution models shows excellent agreement at an age of about 190 Myr and [Fe/H] approximately -0.18. Both components are found to be rotating at the pseudo-synchronous rate. The system displays a slow periastron advance that is dominated by General Relativity (GR), and has previously been claimed to be slower than predicted by theory. Our new measurement, dw/dt = 0.859 +0.042/-0.017 deg/century, has an 88% contribution from GR and agrees with the expected rate within the uncertainties. We also clarify the use of the gravity darkening coefficients in the light-curve fitting program EBOP, a version of which we use here.

[13]  arXiv:1612.02443 [pdf, ps, other]
Title: Binaries among low-mass stars in nearby young moving groups
Comments: 12 pages, 3 figures, accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The solar galactic neighbourhood contains a number of young co-moving associations of stars (so-called `young moving groups') with ages of ~10--150 Myr, which are prime targets for a range of scientific studies, including direct imaging planet searches. The late-type stellar population of such groups still remain in their pre-main sequence phase, and are thus well suited for purposes such as isochronal dating. Close binaries are particularly useful in this regard, since they allow for a model-independent dynamical mass determination. Here we present a dedicated effort to identify new close binaries in nearby young moving groups, through high-resolution imaging with the AstraLux Sur Lucky Imaging camera. We surveyed 181 targets, resulting in the detection of 61 companions or candidates, of which 38 are new discoveries. An interesting example of such a case is 2MASS J00302572-6236015 AB, which is a high-probability member of the Tucana-Horologium moving group, and has an estimated orbital period of less than 10 years. Among the previously known objects is a serendipitous detection of the deuterium burning boundary circumbinary companion 2MASS J01033563-5515561 (AB)b in the z'-band, thereby extending the spectral coverage for this object down to near-visible wavelengths.

[14]  arXiv:1612.02449 [pdf, ps, other]
Title: Cosmological constant vis-a-vis dynamical vacuum: bold challenging the $Λ$CDM
Authors: Joan Sola
Comments: 31 pages, 2 tables, 9 figures. arXiv admin note: text overlap with arXiv:1605.06104
Journal-ref: Int.J.Mod.Phys. A31 (2016) 1630035
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

Next year we will celebrate 100 years of the cosmological term, $\Lambda$, in Einstein's gravitational field equations, also 50 years since the cosmological constant problem was first formulated by Zeldovich, and almost about two decades of the observational evidence that a non-vanishing, positive, $\Lambda$-term could be the simplest phenomenological explanation for the observed acceleration of the Universe. This mixed state of affairs already shows that we do no currently understand the theoretical nature of $\Lambda$. In particular, we are still facing the crucial question whether $\Lambda$ is truly a fundamental constant or a mildly evolving dynamical variable. At this point the matter should be settled once more empirically and, amazingly enough, the wealth of observational data at our disposal can presently shed true light on it. In this short review I summarize the situation of some of these studies. It turns out that the $\Lambda=$const. hypothesis, despite being the simplest, may well not be the most favored one when we put it in hard-fought competition with specific dynamical models of the vacuum energy. Recently it has been shown that the overall fit to the cosmological observables $SNIa+BAO+H(z)+LSS+BBN+CMB$ do favor the class of "running" vacuum models (RVM's) -- in which $\Lambda=\Lambda(H)$ is a function of the Hubble rate -- against the "concordance" $\Lambda$CDM model. The support is at an unprecedented level of $\sim4\sigma$ and is backed up with Akaike and Bayesian criteria leading to compelling evidence in favor of the RVM option and other related dynamical vacuum models. I also address the implications of this framework on the possible time evolution of the fundamental constants of Nature.

[15]  arXiv:1612.02454 [pdf, other]
Title: Separate Universes beyond General Relativity
Comments: 14 pages, submitted to PRD
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We establish purely geometric or metric-based criteria for the validity of the separate universe ansatz, under which the evolution of small-scale observables in a long-wavelength perturbation is indistinguishable from a separate Friedmann-Robertson-Walker cosmology in their angle average. In order to be able to identify the local volume expansion and curvature in a long-wavelength perturbation with those of the separate universe, we show that the lapse perturbation must be much smaller in amplitude than the curvature potential on a time slicing that comoves with the Einstein tensor. Interpreting the Einstein tensor as an effective stress energy tensor, the condition is that the effective stress energy comoves with freely falling synchronous observers who establish the local expansion, so that the local curvature is conserved. By matching the expansion history of these synchronous observers in cosmological simulations, one can establish and test consistency relations even in the nonlinear regime of modified gravity theories.

[16]  arXiv:1612.02474 [pdf, other]
Title: Optimizing future experiments of cosmic far-infrared background: a principal component approach
Comments: 12 pages, 4 figures, 2 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The anisotropies of cosmic far-infrared background (CFIRB) probe the star-formation rate (SFR) of dusty star-forming galaxies as a function of dark matter halo mass and redshift. We explore how future CFIRB experiments can optimally improve the SFR constraints beyond the current measurements of Planck. We introduce a model-independent, piecewise parameterization for SFR as a function of halo mass and redshift, and we calculate the Fisher matrix and principal components of these parameters to estimate the SFR constraints of future experiments. We investigate how the SFR constraints depend on angular resolution, number and range of frequency bands, survey coverage, and instrumental sensitivity. We find that the angular resolution and the instrumental sensitivity play the key roles. Improving the angular resolution from 20 to 4 arcmin can improve the SFR constraints by 1.5 to 2.5 orders of magnitude. With the angular resolution of Planck, improving the sensitivity by 10 or 100 times can improve the SFR constraints by 1 or 2 orders of magnitude, and doubling the number of frequency bands can also improve the SFR constraints by an order of magnitude. We find that survey designs like the Cosmic Origins Explorer (CORE) are very close to the optimal design for improving the SFR constraints at all redshifts, while survey designs like LiteBIRD and CMB-S4 can significantly improve the SFR constraints at z>3.

[17]  arXiv:1612.02475 [pdf, ps, other]
Title: The interpretation of the multi-wavelength afterglow emission of short GRB 140903A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

GRB 140903A, a short duration $\gamma-$ray burst (SGRB) detected by {\it Swift}, is characterized by its long-lasting radio emission among SGRBs. In addition to the $\sim 10^{6}$ s radio afterglow emission, the afterglow of GRB 140903A displays a plateau from $10^3$ s to $7 \times 10^3 $ s in the X-rays. In this work, we attribute the X-ray plateau to the energy injection into the decelerating blast wave and then model the later radio/optical/X-ray afterglow emission within the standard fireball afterglow model. The afterglow emission has been well reproduced with reasonable physical parameters, including a jet half-opening angle $\sim 0.05$. We also compare the physical properties of SGRBs with and without radio afterglow detections and find that nearby SGRBs are brighter and easier to be detected in radio. Such a phenomena has been interpreted within the afterglow model.

[18]  arXiv:1612.02501 [pdf, ps, other]
Title: Direct and Inverse Cascades in the Acceleration Region of the Fast Solar Wind
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)

Alfv\'{e}n waves are believed to play an important role in the heating and acceleration of the fast solar wind emanating from coronal holes. Nonlinear interactions between the dominant ${\bf z}_{+}$ waves and minority ${\bf z}_{-}$ waves have the potential to transfer wave energy either to smaller perpendicular scales ("direct cascade") or to larger scales ("inverse cascade"). In this paper we use reduced magnetohydrodynamic (RMHD) simulations to investigate how the cascade rates $\epsilon_{\pm}$ depend on perpendicular wavenumber and radial distance from Sun center. For models with a smooth background atmosphere we find that an inverse cascade ($\epsilon_{+} < 0$) occurs for the dominant waves at radii between 1.4 and 2.5 $R_\odot$ and dimensionless wavenumbers in the inertial range ($15 < a_\perp < 44$), and a direct cascade ($\epsilon_{+} > 0$) occurs elsewhere. For a model with density fluctuations there are multiple regions with inverse cascade. In both cases the cascade rate $\epsilon_{+}$ varies significantly with perpendicular wavenumber, indicating that the cacsade is a highly non-local process. As a result of the inverse cascades, the enery dissipation rates are much lower than expected from a phenomenological model, and are insufficient to maintain the temperature of the background atmosphere. We conclude that RMHD models are unable to reproduce the observed properties of the fast solar wind.

[19]  arXiv:1612.02507 [pdf, other]
Title: Asteroseismic Constraints on the Models of Hot B Subdwarfs: Convective Helium-Burning Cores
Comments: 10 pages, 3 figures, proceedings of the Joint TASC2 - KASC9 Workshop - SPACEINN - HELAS8 Conference "Seismology of the Sun and the Distant Stars 2016". To be published by the EPJ Web of Conferences
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Asteroseismology of non-radial pulsations in Hot B Subdwarfs (sdB stars) offers a unique view into the interior of core-helium-burning stars. Ground-based and space-borne high precision light curves allow for the analysis of pressure and gravity mode pulsations to probe the structure of sdB stars deep into the convective core. As such asteroseismological analysis provides an excellent opportunity to test our understanding of stellar evolution. In light of the newest constraints from asteroseismology of sdB and red clump stars, standard approaches of convective mixing in 1D stellar evolution models are called into question. The problem lies in the current treatment of overshooting and the entrainment at the convective boundary. Unfortunately no consistent algorithm of convective mixing exists to solve the problem, introducing uncertainties to the estimates of stellar ages. Three dimensional simulations of stellar convection show the natural development of an overshooting region and a boundary layer. In search for a consistent prescription of convection in one dimensional stellar evolution models, guidance from three dimensional simulations and asteroseismological results is indispensable.

[20]  arXiv:1612.02510 [pdf, other]
Title: ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907
Comments: Accepted for publication in A&A. 8 pages, 7 figures, plus appendix
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Yellow hypergiants are rare and represent a fast evolutionary stage of massive evolved stars. That evolutionary phase is characterised by a very intense mass loss, the understanding of which is still very limited. Here we report ALMA Compact Array observations of a 50$"$-mosaic toward the Fried Egg nebula, around one of the few Galactic yellow hypergiants IRAS 17163-3907. The emission from the $^{12}$CO J=2-1 line, H30$\alpha$ recombination line, and continuum is imaged at a resolution of $\sim$8$"$, revealing the morphology of the molecular environment around the star. The continuum emission is unresolved and peaks at the position of the star. The radio recombination line H30$\alpha$ shows unresolved emission at the star, with an approximately gaussian spectrum centered on a velocity of 21$\pm$3~km/s with a width of 57$\pm$6~km/s. In contrast, the CO 2-1 emission is complex and decomposes into several components beyond the contamination from interstellar gas in the line of sight. The CO spectrum toward the star is a broad plateau, centered at the systemic velocity of +18 km/s and with an expansion velocity of 100$\pm$10 km/s. Assuming isotropic and constant mass-loss, we estimate a mass-loss rate of 8$\pm$1.5 $\times10^{-5}$~M$_\odot$ yr$^{-1}$. At a radius of 25$"$ from the star, we detect CO emission associated with the dust ring previously imaged by {\it Herschel}. The kinematics of this ring, however, is not consistent with an expanding shell, but show a velocity gradient of $v_{sys} \pm$20 km/s. In addition, we find a puzzling bright feature radially connecting the star to the CO ring, at a velocity of +40 km/s relative to the star. This spur feature may trace a unidirectional ejection event from the star. Our ACA observations reveal the complex morphology around IRAS 17163 and illustrate the breakthroughs that ALMA will bring to the field of massive stellar evolution.

[21]  arXiv:1612.02529 [pdf, other]
Title: Primordial black holes from supersymmetry in the early universe
Comments: 5 pages, 4 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Supersymmetric extensions of the standard model generically predict that in the early universe a scalar condensate can form and fragment into Q-balls before decaying. If the Q-balls dominate the energy density for some period of time, the relatively large fluctuations in their number density can lead to formation of primordial black holes (PBH). Other scalar fields, unrelated to supersymmetry, can play a similar role. For a general scalar field, this robust mechanism can generate black holes with masses from $10^{15}$g to $10^3 \text{ M}_\odot$, with a sufficient abundance to account for all dark matter. In the case of supersymmetry the mass range is limited from above by $10^{20}$g. We also comment on the role that topolgical defects can play for PBH formation in a similar fashion.

[22]  arXiv:1612.02532 [pdf, other]
Title: Galactic Shapiro Delay to the Crab Pulsar and limit on Einstein's Equivalence Principle
Comments: 3 pages, 1 figure
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We calculate the total galactic Shapiro delay to the Crab pulsar by including the contributions from the dark matter as well as baryonic matter along the line of sight. The total delay due to dark matter potential is about 3.4 days. For baryonic matter, we included the contributions from both the bulge and the disk, which are approximately 0.12 and 0.32 days respectively. The total delay from all the matter distribution is therefore 3.84 days. We also calculate the limit on violations of Einstein's equivalence principle by using observations of "nano-shot" giant pulses from the Crab pulsar with time-delay $<0.4$ ns as well as using time differences between radio and optical photons observed from this pulsar. Using the former, we obtain a limit on violation of Einstein's equivalence principle in terms of the PPN parameter $\Delta \gamma < 2.41\times 10^{-15}$. From the time-difference between simultaneous optical and radio observations, we get $\Delta \gamma < 1.54\times 10^{-9}$.

[23]  arXiv:1612.02535 [pdf, other]
Title: A Hot Companion to a Blue Straggler in NGC188 as Revealed by the Ultra-violet Imaging Telescope (UVIT) on ASTROSAT
Authors: Subramaniam Annapurni (1), Sindhu N. (1,2), Tandon S.N. (1,3), Rao N. Kameswara (1), Postma J. (4), Cot'e Patrick (5), Hutchings J. (5), Ghosh S.K. (6,7), George K. (1), Girish V. (8), Mohan R. (1), Murthy J. (1), Sankarasubramanian K. (1,8,9), Stalin C.S. (1), Sutaria F. (1), Mondal C. (1), Sahu S. (1) ((1) Indian Institute of Astrophysics, Koramangala II Block, Bangalore-560034, India, (2) School of Advanced Sciences, VIT University, Vellore 632014, India, (3) Inter-University Center for Astronomy and Astrophysics, Pune, India, (4) University of Calgary, Canada, (5) National Research Council, Canada, (6) National Centre for Radio Astrophysics, Pune, India, (7) Tata Institute of Fundamental Research, Mumbai, India, (8) ISRO Satellite Centre, HAL Airport Road, Bangalore 560017, (9) Center of Excellence in Space Sciences India, Indian Institute of Science Education and Research (IISER), Kolkata, Mohanpur 741246, West Bengal, India)
Comments: 6 pages, 3 figures, two tables, To appear in ApJ Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We present early results from the Ultra-Violet Imaging Telescope (UVIT) onboard the ASTROSAT observatory. We report the discovery of a hot companion associated with one of the blue straggler stars (BSSs) in the old open cluster, NGC188. Using fluxes measured in four filters in UVIT's Far-UV (FUV) channel, and two filters in the near-UV (NUV) channel, we have constructed the spectral energy distribution (SED) of the star WOCS-5885, after combining with flux measurements from GALEX, UIT, UVOT, SPITZER, WISE and several ground-based facilities. The resulting SED spans a wavelength range of 0.15~${\mu}$m to 7.8~${\mu}$m. This object is found to be one of the brightest FUV sources in the cluster. An analysis of the SED reveals the presence of two components. The cooler component is found to have a temperature of 6,000$\pm$150~K, confirming that it is a BSS. Assuming it to be a main-sequence star, we estimate its mass to be $\sim$ 1.1 - 1.2M$_\odot$. The hotter component, with an estimated temperature of 17,000$\pm$500~K, has a radius of $\sim$ 0.6R$_\odot$ and L $\sim$ 30L$_\odot$. Bigger and more luminous than a white dwarf, yet cooler than a sub-dwarf, we speculate that it is a post-AGB/HB star that has recently transferred its mass to the BSS, which is known to be a rapid rotator. This binary system, which is the first BSS with a post-AGB/HB companion identified in an open cluster, is an ideal laboratory to study the process of BSS formation via mass transfer.

[24]  arXiv:1612.02544 [pdf, other]
Title: Starspots, Stellar Cycles and Stellar Flares: Lessons from Solar Dynamo Models
Comments: 30 pages, 16 figures, invited review published in Science China - Physics, Mechanics & Astronomy
Journal-ref: Sci. China-Phys. Mech. Astron. 60, 019601 (2017)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In this review, we discuss whether the present solar dynamo models can be extrapolated to explain various aspects of stellar activity. We begin with a summary of the following kinds of data for solar-like stars: (i) data pertaining to stellar cycles from Ca H/K emission over many years; (ii) X-ray data indicating hot coronal activity; (iii) starspot data (especially about giant polar spots); and (iv) data pertaining to stellar superflares. Then we describe the current status of solar dynamo modelling---giving an introduction to the flux transport dynamo model, the currently favoured model for the solar cycle. While an extrapolation of this model to solar-like stars can explain some aspects of observational data, some other aspects of the data still remain to be theoretically explained. It is not clear right now whether we need a different kind of dynamo mechanism for stars having giant starspots or producing very strong superflares.

[25]  arXiv:1612.02554 [pdf, other]
Title: MultiView High Precision VLBI Astrometry at Low Frequencies
Comments: Submitted for Publication in AJ (Nov. 4, 2016)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The arrival of the Square Kilometer Array (SKA) will revitalise all aspects of Very Long Baseline Interferometry (VLBI) astronomy at the lower frequencies. In the last decade there have been huge strides towards routinely achieving high precision VLBI astrometry at frequencies dominated by the tropospheric contributions, most notably at 22GHz, using advanced phase referencing techniques. Nevertheless to increase the capability for high precision astrometric measurements at low radio frequencies (<8GHz) an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. Observations at low frequencies are dominated by distinct direction dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase referencing calibrator.
The MultiView technique holds the key to the compensation of atmospheric spatial-structure errors, by using observations of multiple calibrators and 2-D interpolation. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phase-referencing techniques.
MultiView calibration provides an order of magnitude improvement in astrometry with respect to conventional phase referencing, achieving ca. 100 micro-arcseconds astrometry errors in a single epoch of observations, effectively reaching the thermal noise limit.
MultiView will achieve its full potential with the enhanced sensitivity and multibeam capabilities of SKA and the pathfinders, which will enable simultaneous observations of the target and calibrators. Our demonstration indicates that the 10 micro-arcseconds goal of astrometry at ~1.6GHz using VLBI with SKA is feasible using the MultiView technique.

[26]  arXiv:1612.02556 [pdf, other]
Title: The Two Rigid Body Interaction using Angular Momentum Theory Formulae
Authors: Gwenaël Boué
Comments: 13 pages, 1 figure, submitted to CeMDA on September 28, 2016
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

This work presents an elegant formalism to model the evolution of the full two rigid body problem. The equations of motion, given in a Cartesian coordinate system, are expressed in terms of spherical harmonics and Wigner D-matrices. The algorithm benefits from the numerous recurrence relations satisfied by these functions allowing a fast evaluation of the mutual potential. Moreover, forces and torques are straightforwardly obtained by application of ladder operators taken from the angular momentum theory and commonly used in quantum mechanics. A numerical implementation of this algorithm is made. Tests show that the present code is significantly faster than those currently available in literature.

[27]  arXiv:1612.02558 [pdf, other]
Title: Complete spin and orbital evolution of close-in bodies using a Maxwell viscoelastic rheology
Comments: 31 pages, 5 figures
Journal-ref: Celestial Mechanics and Dynamical Astronomy, Volume 126, Issue 1-3, pp. 31-60 (2016)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

In this paper, we present a formalism designed to model tidal interaction with a viscoelastic body made of Maxwell material. Our approach remains regular for any spin rate and orientation, and for any orbital configuration including high eccentricities and close encounters. The method is to integrate simultaneously the rotation and the position of the planet as well as its deformation. We provide the equations of motion both in the body frame and in the inertial frame. With this study, we generalize preexisting models to the spatial case and to arbitrary multipole orders using a formalism taken from quantum theory. We also provide the vectorial expression of the secular tidal torque expanded in Fourier series. Applying this model to close-in exoplanets, we observe that if the relaxation time is longer than the revolution period, the phase space of the system is characterized by the presence of several spin-orbit resonances, even in the circular case. As the system evolves, the planet spin can visit different spin-orbit configurations. The obliquity is decreasing along most of these resonances, but we observe a case where the planet tilt is instead growing. These conclusions derived from the secular torque are successfully tested with numerical integrations of the instantaneous equations of motion on HD 80606b. Our formalism is also well adapted to close-in super-Earths in multiplanet systems which are known to have non-zero mutual inclinations.

[28]  arXiv:1612.02560 [pdf, ps, other]
Title: Detection of a pair of prominent X-ray cavities in Abell 3847
Authors: Nilkanth D. Vagshette (1), Sachindra Naik (1), Madhav. K. Patil (2), Satish S. Sonkamble (2) ((1) Physical Research Laboratory, Navrangpura, Ahmedabad (2) School of Physical Sciences, Swami Ramanand Teerth Marathwada University, Nanded)
Comments: 13 Pages, 10 Figures, 3 Tables. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present results obtained from a detailed analysis of a deep Chandra observation of the bright FR II radio galaxy 3C~444 in Abell~3847 cluster. A pair of huge X-ray cavities are detected along North and South directions from the centre of 3C 444. X-ray and radio images of the cluster reveal peculiar positioning of the cavities and radio bubbles. The radio lobes and X-ray cavities are apparently not spatially coincident and exhibit offsets by ~61 kpc and ~77 kpc from each other along the North and South directions, respectively. Radial temperature and density profiles reveal the presence of a cool core in the cluster. Imaging and spectral studies showed the removal of substantial amount of matter from the core of the cluster by the radio jets. A detailed analysis of the temperature and density profiles showed the presence of a rarely detected elliptical shock in the cluster. Detection of inflating cavities at an average distance of ~55 kpc from the centre implies that the central engine feeds a remarkable amount of radio power (~6.3 X 10^44 erg/s) into the intra-cluster medium over ~10^8 yr, the estimated age of cavity. The cooling luminosity of the cluster was estimated to be ~8.30 X 10^43 erg/s, which confirms that the AGN power is sufficient to quench the cooling. Ratios of mass accretion rate to Eddington and Bondi rates were estimated to be ~0.08 and 3.5 X 10^4, respectively. This indicates that the black hole in the core of the cluster accretes matter through chaotic cold accretion.

[29]  arXiv:1612.02563 [pdf, ps, other]
Title: Pulse profiles and timing of PSR J1757$-$2421
Comments: 9 pages, 8 figures, 5 tables, Accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Pulse arrival time measurements over fourteen years with the Nanshan 25-m and Parkes 64-m radio telescopes have been used to determine the average profile and timing properties for PSR J1757$-$2421 (B1754$-$24). Analysis of the radio profile data shows a large variation of spectral index across the profile and an unusual increase in component separation with increasing frequency. The timing observations show that PSR B1754$-$24 underwent a large glitch with a fractional increase in spin frequency of $\Delta\nu_{\rm g}/\nu\sim 7.8\times10^{-6}$ in May 2011. At the time of the glitch there was a large permanent jump in the rotational frequency accompanied by two exponential recovery terms with timescales of 15(6) and 97(15) days, respectively.

[30]  arXiv:1612.02568 [pdf, ps, other]
Title: Chemical abundances in Galactic planetary nebulae from faint emission lines
Authors: Jorge García-Rojas (1,2) ((1) Instituto de Astrofísica de Canarias, Spain, (2) Univ. La Laguna, Spain)
Comments: Invited review in workshop "Chemical abundances in ionized nebulae" held in Campos do Jordao, Brazil between 3-5 November 2016. To be published in BAAA. G. H\"agele, M. Cardaci and E. P\'erez-Montero eds. 10 pages, 2 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Deep spectrophotometry has proved to be a fundamental tool to improve our knowledge on the chemical content of planetary nebulae. With the arrival of very efficient spectrographs installed in the largest ground-based telescopes, outstanding spectra have been obtained. These data are essential to constrain state-of-the-art nucleosynthesis models in asymptotic giant branch stars and, in general, to understand the chemical evolution of our Galaxy. In this paper we review the last advances on the chemical composition of the ionized gas in planetary nebulae based on faint emission lines observed through very deep spectrophotometric data.

[31]  arXiv:1612.02578 [pdf, other]
Title: Cosmogenic neutrinos and gamma-rays and the redshift evolution of UHECR sources
Comments: submitted for the proceedings of the Neutrino Oscillation Workshop, 4-11 September 2016, Otranto, Italy
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

If ultra-high-energy cosmic rays (UHECRs) have extragalactic origins, as is widely assumed to be the case at least for the majority of cosmic rays with energies above a few EeV, secondary neutrinos and photons can be expected to be produced during the propagation of UHECRs through intergalactic space via interactions with cosmic background photons. The fluxes of such secondary particles are strongly dependent on the redshift evolution of the emissivity (number density times luminosity) of UHECR sources. We show how cosmic rays, neutrinos, and gamma rays can potentially provide complementary information about UHECR source evolution.

[32]  arXiv:1612.02588 [pdf, ps, other]
Title: Long period variable stars in NGC 147 and NGC 185. I. Their star formation histories
Comments: Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda galaxy (M 31). Close together in the sky, of similar mass and morphological type dE, they possess different amounts of interstellar gas and tidal distortion. The question therefore is, how do their histories compare? Here we present the first reconstruction of the star formation histories of NGC 147 and NGC 185 using long-period variable stars. These represent the final phase of evolution of low- and intermediate-mass stars at the asymptotic giant branch, when their luminosity is related to their birth mass. Combining near-infrared photometry with stellar evolution models, we construct the mass function and hence the star formation history. For NGC 185 we found that the main epoch of star formation occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate. In the case of NGC 147, the star formation rate peaked only 7 Gyr ago, staying intense until ~ 3 Gyr ago, but no star formation has occurred for at least 300 Myr. Despite their similar masses, NGC 147 has evolved more slowly than NGC 185 initially, but more dramatically in more recent times. This is corroborated by the strong tidal distortions of NGC 147 and the presence of gas in the centre of NGC 185.

[33]  arXiv:1612.02598 [pdf, other]
Title: Hiding neutrino mass in modified gravity cosmologies
Comments: Submitted to JCAP
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Cosmological observables show a dependence with the neutrino mass, which is partially degenerate with parameters of extended models of gravity. We study and explore this degeneracy in Horndeski generalized scalar-tensor theories of gravity. Using forecasted cosmic microwave background and galaxy power spectrum datasets, we find that a single parameter in the linear regime of the effective theory dominates the correlation with the total neutrino mass. For any given mass, a particular value of this parameter approximately cancels the power suppression due to the neutrino mass at a given redshift. The extent of the cancellation of this degeneracy depends on the cosmological large-scale structure data used at different redshifts. We constrain the parameters and functions of the effective gravity theory and determine the influence of gravity on the determination of the neutrino mass from present and future surveys.

[34]  arXiv:1612.02599 [pdf, other]
Title: $^3$He Abundances in Planetary Nebulae
Comments: 4 pages, 2 figures, Proceedings IAU Symposium No. 323, 2017
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The $^3$He isotope is important to many fields of astrophysics, including stellar evolution, chemical evolution, and cosmology. The isotope is produced in stars which evolve through the planetary nebula phase. Planetary nebulae are the final evolutionary phase of low- and intermediate-mass stars, where the extensive mass lost by the star on the asymptotic giant branch is ionised by the emerging white dwarf. This ejecta quickly disperses and merges with the surrounding ISM. The abundance of $^3$He can only be derived from the hyperfine transition of the ionised $^3$He, which is represented as $^3$He$^+$, these transition can be observed in the radio at the rest frequency of 8.665 GHz. $^3$He abundances in PNe can help test models of the chemical evolution of the Galaxy. Many hours have been put into trying to detect this line, using telescopes like Effelsberg a 100m dish from the Max Planck Institute for Radio Astronomy, the National Radio Astronomy Observatory (NRAO) 140-foot telescope, the NRAO Very Large Array, the Arecibo antenna, the Green Bank Telescope, and only just recently, the Deep Space Station 63 antenna from the Madrid Deep Space Communications Complex.

[35]  arXiv:1612.02610 [pdf, ps, other]
Title: Statistical properties of the Bipolar Magnetic Regions
Authors: Dong Li
Comments: 19 pages, 12 figures, and 2 tables, accepted for publication in RAA
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Using the observations from Michelson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (SOHO), we develop a computational algorithm to automatically identify the bipolar magnetic regions (BMRs) in the active regions, and then study their statistical properties. The individual magnetic (positive or negative) pole of the BMR is determined from the region with an absolute strength above 55 G and with an area above 250 pixel^2 (495 Mm^2), while a BMR is identified as a pair of positive and negative poles with a shortest area-weight distance between them. Based on this method, 2234 BMRs are identified from the MDI synoptic magnetograms between the Carrington Rotation 1909 (1996 May 06) and 2104 (2010 December 10). 1005 of them are located in the northern hemisphere, while the other 1229 are in the southern hemisphere.We find that the BMR paraments (e.g., latitudes, separations, fragments, and strength) are similar to those of active regions (ARs). Moreover, based on the maximum likelihood estimation (MLE)method, the frequency distributions of these BMRs occurrence as functions of area size and magnetic flux exhibit a power-law behavior. We also find that their orientation angles follow the Hale's Polarity Laws and deviate slightly to the solar equator direction. Consistent with the previous findings, we obtain the orientation angles dependence on the latitudes for the normal BMRs during the 23rd solar cycle. The north-south asymmetry of these BMRs is also detected here.

[36]  arXiv:1612.02626 [pdf, ps, other]
Title: Physical properties of centaur (54598) Bienor from photometry
Comments: 12 pages, 3 figures, 13 tables, accepted in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We present time series photometry of Bienor in four observation campaigns from 2013 to 2016 and compare them with previous observations in the literature dating back to 2000. The results show a remarkable decline in the amplitude of the rotational light curve and in the absolute magnitude. This suggests that the angle between the rotation axis and the line of sight has changed noticeably during the last 16 years as Bienor orbits the Sun. From the light curve amplitude data we are able to determine the orientation of the rotation axis of Bienor ($\beta_p=50\pm3^{\circ}$, $\lambda_p=35\pm8^{\circ}$). We are also able to constrain the $b/a$ axial ratio of a triaxial Jacobi ellipsoidal body (with semi-axis $a>b>c$). The best fit is for $b/a=0.45\pm0.05$, which corresponds to a density value of $594^{+47}_{-35}$ kg$\,$m$^{-3}$ under the usual assumption of hydrostatic equilibrium and given that Bienor's rotational period is 9.17 h. However, the absolute magnitude of Bienor at several epochs is not well reproduced. We tested several explanations such as relaxing the hydrostatic equilibrium constraint, a large North-South asymmetry in the surface albedo of Bienor or even a ring system. When a ring system of similar characteristics to those of Chariklo and Chiron is included, we can fit both the light curve amplitude and absolute magnitude. In this case the derived axial ratio is modified to $b/a=0.37\pm0.10$. The implied density is $678^{+209}_{-100}$ kg$\,$m$^{-3}$. Also the existence of a ring is consistent with the spectroscopic detection of water ice on Bienor. Nevertheless the other explanations cannot be discarded.

[37]  arXiv:1612.02632 [pdf, ps, other]
Title: Millimeter Spectral Line Mapping Observations Toward Four Massive Star Forming HII Regions
Comments: 32 pages, 11 figures, 8 tables, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present spectral line mapping observations toward four massive star-forming regions (Cepheus A, DR21S, S76E and G34.26+0.15), with the IRAM 30 meter telescope at 2 mm and 3 mm bands. Totally 396 spectral lines from 51 molecules, one helium recombination line, ten hydrogen recombination lines, and 16 unidentified lines were detected in these four sources. An emission line of nitrosyl cyanide (ONCN, 14$_{0,14}$-13$_{0,13}$) was detected in G34.26+0.15, as first detection in massive star-forming regions. We found that the $c$-C$_{3}$H$_{2}$ and NH$_{2}$D show enhancement in shocked regions as suggested by evidences of SiO and/or SO emission. Column density and rotational temperature of CH$_{3}$CN were estimated with the rotational diagram method for all four sources. Isotope abundance ratios of $^{12}$C/$^{13}$C were derived using HC$_{3}$N and its $^{13}$C isotopologue, which were around 40 in all four massive star-forming regions and slightly lower than the local interstellar value ($\sim$65). $^{14}$N/$^{15}$N and $^{16}$O/$^{18}$O abundance ratios in these sources were also derived using double isotopic method, which were slightly lower than that in local interstellar medium. Except for Cep A, $^{33}$S/$^{34}$S ratio in the other three targets were derived, which were similar to that in the local interstellar medium. The column density ratios of N(DCN)/N(HCN) and N(DCO$^{+}$)/N(HCO$^{+}$) in these sources were more than two orders of magnitude higher than the elemental [D]/[H] ratio, which is 1.5$\times$10$ ^{-5}$. Our results show the later stage sources, G34.26+0.15 in particular, present more molecular species than earlier stage ones. Evidence of shock activity is seen in all stages studied.

[38]  arXiv:1612.02634 [pdf, other]
Title: Late time cosmology with LISA: probing the cosmic expansion with massive black hole binary mergers as standard sirens
Authors: Nicola Tamanini
Comments: 7 pages, 4 figures, 2 tables; prepared for the proceedings of the 11th International LISA Symposium
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

This paper summarises the potential of the LISA mission to constrain the expansion history of the universe using massive black hole binary mergers as gravitational wave standard sirens. After briefly reviewing the concept of standard siren, the analysis and methodologies of Ref. [1] are briefly outlined to show how LISA can be used as a cosmological probe, while a selection of results taken from Refs. [1,2] is presented in order to estimate the power of LISA in constraining cosmological parameters.

[39]  arXiv:1612.02645 [pdf, other]
Title: Polypolar spherical harmonic decomposition of galaxy correlators in redshift space: Toward cosmic isotropy and homogeneity tests
Comments: 12 pages, 2 figures, 2 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We propose an efficient way to test statistical isotropy and homogeneity in the cosmological perturbations by use of galaxy correlation functions. In symmetry-breaking cases, the galaxy power spectrum can have extra angular dependence in addition to the usual one due to the redshift-space distortion, $ \hat{k} \cdot \hat{x}$. We confirm that, via the decomposition into not the usual Legendre basis ${\cal L}_\ell(\hat{k} \cdot \hat{x})$ but the bipolar spherical harmonic one $\{Y_{\ell}(\hat{k}) \otimes Y_{\ell'}(\hat{x})\}_{LM}$, the symmetry-breaking signal can be completely distinguished from the usual isotropic and homogeneous one since the former yields nonvanishing $L \geq 1$ modes but the latter is confined to the $L = 0$ one. As a demonstration, we analyze the signatures due to primordial-origin symmetry breakings such as the well-known quadrupolar-type and dipolar-type power asymmetries and find nonzero $L = 2$ and $1$ modes, respectively. Fisher matrix forecasts of their constraints indicate that the $Planck$-level sensitivity could be achieved by the SDSS or BOSS-CMASS data, and an order-of-magnitude improvement is expected in a near future survey as PFS or Euclid by virtue of an increase in accessible Fourier mode. Our methodology is model-independent and hence applicable to the searches for various types of statistically anisotropic and inhomogeneous fluctuations.

[40]  arXiv:1612.02648 [pdf, other]
Title: Constraints and prospects on GW and neutrino emissions using GW150914
Comments: 8 pages, 4 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

Recently, the LIGO observatory reported the first direct observation of gravitational waves, with a signal consistent with the merger of a binary black hole. This detection triggered several follow-up searches for coincident emission in electromagnetic waves as well as neutrinos. In this article, the implications of the non-detection of counterpart neutrinos are investigated in a model-independent way. The results are interpreted with a parameter denoting the energy emitted in neutrinos relative to the energy emitted in gravitational waves. The bound on this parameter from the diffuse astrophysical neutrino flux detected by the IceCube Neutrino Observatory is discussed. It is found that, currently, the non-detection of counterpart neutrinos puts a bound comparable to the one from the diffuse astrophysical neutrino flux given the binary black hole merger rate. The detection of one of more neutrinos from a single merger in the near future would strongly constrain the source population and evolution. Finally, the same method is used to investigate the sensitivity to this parameter in future gravitational wave observation runs. While the method presented here is shown for binary black hole mergers, it can be used for other classes of gravitational wave sources as well.

[41]  arXiv:1612.02652 [pdf, ps, other]
Title: Operations in the era of large distributed telescopes
Comments: 4 pages; to be published in ADASS XXVI (held October 16-20, 2016) proceedings. Recording can be found here
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Other Computer Science (cs.OH)

The previous generation of astronomical instruments tended to consist of single receivers in the focal point of one or more physical reflectors. Because of this, most astronomical data sets were small enough that the raw data could easily be downloaded and processed on a single machine.
In the last decade, several large, complex Radio Astronomy instruments have been built and the SKA is currently being designed. Many of these instruments have been designed by international teams, and, in the case of LOFAR span an area larger than a single country. Such systems are ICT telescopes and consist mainly of complex software. This causes the main operational issues to be related to the ICT systems and not the telescope hardware. However, it is important that the operations of the ICT systems are coordinated with the traditional operational work. Managing the operations of such telescopes therefore requires an approach that significantly differs from classical telescope operations.
The goal of this session is to bring together members of operational teams responsible for such large-scale ICT telescopes. This gathering will be used to exchange experiences and knowledge between those teams. Also, we consider such a meeting as very valuable input for future instrumentation, especially the SKA and its regional centres.

[42]  arXiv:1612.02655 [pdf]
Title: What sparks the radio-loud phase of nearby quasars?
Comments: To be published in Monthly Notices of the Royal Astronomical Society, 25 pages with 16 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

To better constrain the hypotheses proposed to explain why only a few quasars are radio loud (RL), we compare the characteristics of 1958 nearby $(z\le 0.3)$ SDSS quasars, covered by the FIRST and NVSS radio surveys. Only 22\% are RL with $\log(L_{1.4{\rm GHz}}) \ge 22.5$ W Hz$^{-1}$, the majority being compact (C), weak radio sources (WRS), with $\log(L_{1.4{\rm GHz}}) < 24.5$ W Hz$^{-1}$. 15\% of the RL quasars have extended radio morphologies: 3\% have a core and a jet (J), 2\% have a core with one lobe (L), and 10\% have a core with two lobes (T), the majority being powerful radio sources (PRS), with $\log(L_{1.4{\rm GHz}}) \ge 24.5$ W Hz$^{-1}$. In general, RL quasars have higher bolometric luminosities and ionisation powers than radio quiet (RQ) quasars. The WRS have comparable black hole (BH) masses as the RQ quasars, but higher accretion rates or radiative efficiencies. The PRS have higher BH masses than the WRS, but comparable accretion rates or radiative efficiencies. The WRS also have higher $FWHM_{\rm [OIII]}$ than the PRS, consistent with a coupling of the spectral characteristics of the quasars with their radio morphologies. Inspecting the SDSS images and applying a neighbour search algorithm reveal no difference between the RQ and RL quasars of their host galaxies, environments, and interaction. Our results prompt the conjecture that the phenomenon that sparks the radio-loud phase in quasars is transient, intrinsic to the AGN, and stochastic, due to the chaotic nature of the accretion process of matter onto the BHs.

[43]  arXiv:1612.02669 [pdf, ps, other]
Title: Magnetic field structure in single late-type giants: The weak G-band giant 37 Comae from 2008 to 2011
Comments: Accepted in A&A, 14 pages, 10 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

This work studies the magnetic activity of the late-type giant 37 Com. This star belongs to the group of weak G-band stars that present very strong carbon deficiency in their photospheres. The paper is a part of a global investigation into the properties and origin of magnetic fields in cool giants.
We use spectropolarimetric data, which allows the simultaneous measurement of the longitudinal magnetic field $B_{l}$, line activity indicators (H$\alpha$, Ca\,{\sc ii} IRT, S-index) and radial velocity of the star, and consequently perform a direct comparison of their time variability. Mean Stokes V profiles are extracted using the least squares deconvolution (LSD) method. One map of the surface magnetic field of the star is reconstructed via the Zeeman Doppler imaging (ZDI) inversion technique.
A periodogram analysis is performed on our dataset and it reveals a rotation period of 111 days. We interpret this period to be the rotation period of 37 Com. The reconstructed magnetic map reveals that the structure of the surface magnetic field is complex and features a significant toroidal component. The time variability of the line activity indicators, radial velocity and magnetic field $B_{l}$ indicates a possible evolution of the surface magnetic structures in the period from 2008 to 2011. For completeness of our study, we use customized stellar evolutionary models suited to a weak G-band star. Synthetic spectra are also calculated to confirm the peculiar abundance of 37 Com.
We deduce that 37 Com is a 6.5~$M_{\odot}$ weak G-band star located in the Hertzsprung gap, whose magnetic activity is probably due to dynamo action.

[44]  arXiv:1612.02677 [pdf, ps, other]
Title: Quasi-periodic pulsations with periods that change depending on whether the pulsations have thermal or nonthermal components
Comments: 4 pages, 5 figures, 1 table, accepted for publication in the Letters of A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context. Quasi-periodic pulsations (QPPs) typically display periodic and regular peaks in the light curves during the flare emissions. Sometimes, QPPs show multiple periods at the same wavelength. However, changing periods in various channels are rare. Aims. We report QPPs in a solar flare on 2014 October 27. They showed a period change that depended on whether thermal or nonthermal components were included. The flare was simultaneously observed by many instruments. Methods. Using the fast Fourier transform (FFT), we decomposed the light curves at multiple wavelengths into slowly varying and rapidly varying signals. Then we identified the QPPs as the regular and periodic peaks from the rapidly varying signals. The periods are derived with the wavelet method and confirmed based on the FFT spectra of the rapidly varying signals. Results. We find a period of 50 s from the thermal emissions during the impulsive phase of the flare, that is, in the soft X-ray bands. At the same time, a period of about 100 s is detected from the nonthermal emissions, such as hard X-ray and microwave channels. The period ratio is exactly 2.0, which might be due to the modulations of the magnetic reconnection rate by the fundamental and harmonic modes of magnetohydrodynamic waves. Our results further show that the 100 s period is present over a broad wavelength, such as hard X-rays, extreme-UV/UV, and microwave emissions, indicating the periodic magnetic reconnection in this flare. Conclusions. To our knowledge, this is the first report about period changes from thermal to nonthermal components in a single flare that occur at almost the same time. This new observational finding could be a challenge to the theory of flare QPPs.

[45]  arXiv:1612.02688 [pdf, other]
Title: Search for Interstellar monohydric Thiols
Comments: 13 pages, 4 figures, Accepted for publication in The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR); Chemical Physics (physics.chem-ph)

It has been pointed out by various astronomers that very interesting relationship exists between interstellar alcohols and the corresponding thiols (sulfur analogue of alcohols) as far as the spectroscopic properties and chemical abundances are concerned. Monohydric alcohols such as methanol and ethanol are widely observed and 1-propanol is recently claimed to have been seen in Orion KL. Among the monohydric thiols, methanethiol (chemical analogue of methanol), has been firmly detected in Orion KL and Sgr B2(N2) and ethanethiol (chemical analogue of ethanol) has been claimed to be observed in Sgr B2(N2) though the confirmation of this detection is yet to come. It is very likely that higher order thiols could be observed in these regions. In this paper, we study the formation of monohydric alcohols and their thiol analogues. Based on our quantum chemical calculation and chemical modeling, we find that `Tg' conformer of 1-propanethiol is a good candidate of astronomical interest. We present various spectroscopically relevant parameters of this molecule to assist its future detection in the Interstellar medium (ISM).

[46]  arXiv:1612.02693 [pdf, other]
Title: Highly inclined and eccentric massive planets. II. Planet-planet interactions during the disc phase
Comments: 13 pages, 14 figures, Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We aim to investigate the influence of the eccentricity and inclination damping due to planet-disc interactions on the final configurations of the systems, generalizing previous studies on the combined action of the gas disc and planet-planet scattering during the disc phase. Instead of the simplistic $K$-prescription, our n-body simulations adopt the damping formulae for eccentricity and inclination provided by the hydrodynamical simulations of our companion paper. We follow the evolution of $11000$ numerical experiments of three giant planets in the late stage of the gas disc, exploring different initial configurations, planetary mass ratios and disc masses. The dynamical evolutions of the planetary systems are studied along the simulations, with emphasis on the resonance captures and inclination-growth mechanisms. Most of the systems are found with small inclinations ($\le10^{\circ}$) at the dispersal of the disc. Even though many systems enter an inclination-type resonance during the migration, the disc usually damps the inclinations on a short timescale. Although the majority of the multiple systems in our results are quasi-coplanar, $\sim5\%$ of them end up with high mutual inclinations ($\ge10^{\circ}$). Half of these highly mutually inclined systems result from two- or three-body MMR captures, the other half being produced by orbital instability and/or planet-planet scattering. When considering the long-term evolution over $100$ Myr, destabilization of the resonant systems is common, and the percentage of highly mutually inclined systems still evolving in resonance drops to $30\%$. Finally, the parameters of the final system configurations are in very good agreement with the semi-major axis and eccentricity distributions in the observations, showing that planet-planet interactions during the disc phase could have played an important role in sculpting planetary systems.

[47]  arXiv:1612.02725 [pdf, ps, other]
Title: An Empirical Fitting Method for Type Ia Supernova Light Curves. II. Estimating the First-Light Time and Rise Time
Authors: WeiKang Zheng (UCB), Patrick L. Kelly (UCB), Alexei V. Filippenko (UCB)
Comments: submitted
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We investigate a new empirical fitting method for the optical light curves of Type Ia supernovae (SNe~Ia) that is able to estimate the first-light time of SNe~Ia, even when they are not discovered extremely early. With an improved ability to estimate the time of first light for SNe Ia, we compute the rise times for a sample of 56 well-observed SNe~Ia. We find rise times ranging from 10.5 to 20.5 days, with a mean of 16.0 days, and confirm that the rise time is generally correlated with the decline rate $\Delta m_{15}(B)$, but with large scatter. The rise time could be an additional parameter to help classify SN~Ia subtypes.

[48]  arXiv:1612.02740 [pdf, other]
Title: 3D Radiation Non-ideal Magnetohydrodynamical Simulations Of The Inner Rim In Protoplanetary Disks
Comments: accepted for ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Many planets orbit within an AU of their stars, raising questions about their origins. Particularly puzzling are the planets found near the silicate sublimation front. We investigate conditions near the front in the protostellar disk around a young intermediate-mass star, using the first global 3-D radiation non-ideal MHD simulations in this context. We treat the starlight heating; the silicate grains sublimation and deposition at the local, time-varying temperature and density; temperature-dependent Ohmic dissipation; and various initial magnetic fields. The results show magnetorotational turbulence around the sublimation front at 0.5 AU. The disk interior to 0.8 AU is turbulent, with velocities exceeding 10% of the sound speed. Beyond 0.8 AU is the dead zone, cooler than 1000 K and with turbulence orders of magnitude weaker. A local pressure maximum just inside the dead zone concentrates solid particles, favoring their growth. Over many orbits, a vortex develops at the dead zones inner edge, increasing the disks thickness locally by around 10%. We synthetically observe the results using Monte Carlo transfer calculations, finding the sublimation front is near-infrared bright. The models with net vertical magnetic fields develop extended, magnetically-supported atmospheres that reprocess extra starlight, raising the near-infrared flux 20%.The vortex throws a nonaxisymmetric shadow on the outer disk. At wavelengths > 2 micron, the flux varies several percent on monthly timescales. The variations are more regular when the vortex is present. The vortex is directly visible as an arc at ultraviolet through near-infrared wavelengths, given sub-AU spatial resolution.

[49]  arXiv:1612.02764 [pdf, other]
Title: Charged current neutrino interactions in hot and dense matter
Comments: 19 pages, 4 figures. Submitted to Physical Review C
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)

We derive the charged current absorption rate of electron and anti-electron neutrinos in dense matter using a fully relativistic approach valid at arbitrary matter degeneracy. We include mean field energy shifts due to nuclear interactions and the corrections due to weak magnetism. The rates are derived both from the familiar Fermi's Golden Rule, and from the techniques of finite temperature field theory, and shown to be equivalent. In various limits, these results can also be used to calculate neutral current opacities. We find that some pieces of the response have been left out in previous derivations and their contribution at high density can be significant. Useful formulae and detailed derivations are presented and we provide a new open source implementation of these opacities for use in radiation hydrodynamic simulations of core-collapse supernovae and neutron star mergers.

[50]  arXiv:1612.02765 [pdf, other]
Title: In-vacuo-dispersion features for GRB neutrinos and photons
Comments: 12 pages, latex. arXiv admin note: text overlap with arXiv:1609.03982
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

Over the last 15 years there has been considerable interest in the possibility of quantum-gravity-induced in-vacuo dispersion, the possibility that spacetime itself might behave essentially like a dispersive medium for particle propagation. Two very recent studies have exposed what might be in-vacuo dispersion features for GRB (gamma-ray-burst) neutrinos of energy in the range of 100 TeV and for GRB photons with energy in the range of 10 GeV. We here show that these two features are roughly compatible with a description such that the same effects apply over 4 orders of magnitude in energy. We also characterize quantitatively how rare it would be for such features to arise accidentally, as a result of (still unknown) aspects of the mechanisms producing photons at GRBs or as a result of background neutrinos accidentally fitting the profile of a GRB neutrino affected by in-vacuo dispersion.

[51]  arXiv:1612.02768 [pdf, other]
Title: X-ray flux variability of active galactic nuclei observed using NuSTAR
Comments: 16 pages, 8 figures, 10 tables, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We present results on a systematic study of flux variability on hourly time scales in a large sample of active galactic nuclei (AGN) in the 3-79 keV band using data from NuSTAR. Our sample consists of 4 BL Lac objects (BL Lacs), 3 flat spectrum radio quasars (FSRQs) 24 Seyfert 1, 42 Seyfert 2 and 8 narrow line Seyfert 1 (NLSy1) galaxies. We find that in the 3-79 keV band, about 65% of the sources in our sample show significant variations on hourly time scales. Using Mann-Whitney U-test and Kolmogorov-Smirnov test, we find no difference in the variability behaviour between Seyfert 1 and 2 galaxies. The blazar sources (FSRQs and BL Lacs) in our sample, are more variable than Seyfert galaxies that include Seyfert 1 and Seyfert 2 in the soft (3-10 keV), hard (10-79 keV) and total (3-79 keV) bands. NLSy1 galaxies show the highest duty cycle of variability (87%), followed by BL Lacs (82%), Seyfert galaxies (56%) and FSRQs (23%). We obtained flux doubling/halving time in the hard X-ray band less than 10 min in 13 sources. For PKS 2155-304, we find the shortest flux doubling time of 1.65 \pm 0.16 min the shortest known in the hard X-ray band from any blazar. The flux variations between the hard and soft bands in all the sources in our sample are consistent with zero lag.

[52]  arXiv:1612.02774 [pdf, other]
Title: The distribution of radioactive $^{44}$Ti in Cassiopeia A
Comments: 14 pages, 13 figures (6 3D animations in the online journal). Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The distribution of elements produced in the inner-most layers of a supernova explosion is a key diagnostic for studying the collapse of massive stars. Here we present the results of a 2.4 Ms \textit{NuSTAR} observing campaign aimed at studying the supernova remnant Cassiopeia A (Cas A). We perform spatially-resolved spectroscopic analyses of the $^{44}$Ti ejecta which we use to determine the Doppler shift and thus the three-dimensional (3D) velocities of the $^{44}$Ti ejecta. We find an initial $^{44}$Ti mass of 1.54 $\pm$ 0.21 $\times 10^{-4}$ M$_{\odot}$ which has a present day average momentum direction of 340$^{\circ}$ $\pm$ 15$^{\circ}$ projected on to the plane of the sky (measured clockwise from Celestial North) and tilted by 58$^{\circ}$ $\pm$ 20$^{\circ}$ into the plane of the sky away from the observer, roughly opposite to the inferred direction of motion of the central compact object. We find some $^{44}$Ti ejecta that are clearly interior to the reverse shock and some that are clearly exterior to the reverse shock. Where we observe $^{44}$Ti ejecta exterior to the reverse shock we also see shock-heated iron; however, there are regions where we see iron but do not observe $^{44}$Ti. This suggests that the local conditions of the supernova shock during explosive nucleosynthesis varied enough to suppress the production of $^{44}$Ti in some regions by at least a factor of two, even in regions that are assumed to be the result of processes like $\alpha$-rich freezeout that should produce both iron and titanium.

[53]  arXiv:1612.02776 [pdf, other]
Title: Discovery of XO-6b: a hot Jupiter transiting a fast rotating F5 star on an oblique orbit
Comments: 13 pages, 11 figures, Accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Only a few hot Jupiters are known to orbit around fast rotating stars. These exoplanets are harder to detect and characterize and may be less common than around slow rotators. Here, we report the discovery of the transiting hot Jupiter XO-6b, which orbits a bright, hot, and fast rotating star: V = 10.25, Teff = 6720 +/- 100 K, v sin i = 48 +/- 3 km/s. We detected the planet from its transits using the XO instruments and conducted a follow-up campaign. Because of the fast stellar rotation, radial velocities taken along the orbit do not yield the planet's mass with a high confidence level, but we secure a 3-sigma upper limit Mp < 4.4 MJup. We also obtain high resolution spectroscopic observations of the transit with the SOPHIE spectrograph at the 193-cm telescope of the Observatoire de Haute-Provence and analyze the stellar lines profile by Doppler tomography. The transit is clearly detected in the spectra. The radii measured independently from the tomographic analysis and from the photometric lightcurves are consistent, showing that the object detected by both methods is the same and indeed transits in front of XO-6. We find that XO-6b lies on a prograde and misaligned orbit with a sky-projected obliquity lambda = -20.7 +/- 2.3 deg. The rotation period of the star is shorter than the orbital period of the planet: Prot < 2.12 days, Porb = 3.77 days. Thus, this system stands in a largely unexplored regime of dynamical interactions between close-in giant planets and their host stars.

[54]  arXiv:1612.02787 [pdf, ps, other]
Title: The metallic winds in dwarf galaxies
Comments: 13 pages, 7 figures, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present results from models of galactic winds driven by energy injected from nuclear (at the galactic center) and non-nuclear starbursts. The total energy of the starburst is provided by very massive young stellar clusters,which can push the galactic interstellar medium and produce an important outflow. Such outflow can be a well, or partially mixed wind, or a highly metallic wind. We have performed adiabatic 3D N-Body/Smooth Particle Hydrodynamics simulations of galactic winds using the GADGET-2 code. The numerical models cover a wide range of parameters, varying the galaxy concentration index, gas fraction of the galactic disk, and radial distance of the starburst. We show that an off-center starburst in dwarf galaxies is the most effective mechanism to produce a significant loss of metals (material from the starburst itself). At the same time a non-nuclear starburst produce a high efficiency of metal loss, in spite of having a moderate to low mass loss rate.

[55]  arXiv:1612.02790 [pdf, other]
Title: Six winters of photometry from Dome C, Antarctica: challenges, improvements, and results from the ASTEP experiment
Comments: 10 pages, 6 figures, SPIE conference proceedings, Ground-based and Airborne Instrumentation for Astronomy VI, 2016
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

ASTEP (Antarctica Search for Transiting ExoPlanets) is a pilot project that aims at searching and characterizing transiting exoplanets from Dome C in Antarctica and to qualify this site for photometry in the visible. Two instruments were installed at Dome C and ran for six winters in total. The analysis of the collected data is nearly complete. We present the operation of the instruments, and the technical challenges, limitations, and possible solutions in light of the data quality. The instruments performed continuous observations during the winters. Human interventions are required mainly for regular inspection and ice dust removal. A defrosting system is efficient at preventing and removing ice on the mirrors. The PSF FWHM is 4.5 arcsec on average which is 2.5 times larger than the specification, and is highly variable; the causes are the poor ground-level seeing, the turbulent plumes generated by the heating system, and to a lower extent the imperfect optical alignment and focusing, and some astigmatism. We propose solutions for each of these aspects that would largely increase the PSF stability. The astrometric and guiding precisions are satisfactory and would deserve only minor improvements. Major issues are encountered with the camera shutter which did not close properly after two winters; we minimized this issue by heating the shutter and by developing specific image calibration algorithms. Finally, we summarize the site testing and science results obtained with ASTEP. Overall, the ASTEP experiment will serve as a basis to design and operate future optical and near-infrared telescopes in Antarctica.

[56]  arXiv:1612.02804 [pdf, ps, other]
Title: Study of Dark-Matter Admixed Neutron Stars using the Equation of State from the Rotational Curves of Galaxies
Authors: Z. Rezaei
Comments: 18 pages, 18 figures, 8 tables. Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

In this work, we employ the dark matter equations of state (DMEOSs) obtained from the rotation curves of galaxies as well as the fermionic DMEOS with m = 1.0 GeV to study the structure of dark matter admixed neutron stars (DMANSs). Applying the equation of state in the Skyrme framework for the neutron matter, we calculate the mass-radius relation for different DMANSs with various DMEOSs and central pressure of dark matter to neutron matter ratios. Our results show that for some DMEOSs, the mass-radius relations are in agreement with the new observations, e.g. EXO 1745-248, 4U 1608-52, and 4U 1820-30, which are inconsistent with the normal neutron stars. We conclude that both DMEOS and central pressure ratio of dark matter to neutron matter affect the slope of the mass-radius relation of DMANS. This is because of the interaction between dark matter and neutron matter which leads to gravitationally or self bound DMANSs. We study the radius of the neutron matter sphere as well as the radius of the dark matter halo for different DMANSs. The results confirm that in some cases, the neutron matter sphere with a small radius is surrounded by a halo of dark matter having a larger radius. Our calculations verify that due to the different degrees of dark matter domination in DMANSs, with a value of the visible radius of star two possible DMANSs with different masses can be exist. The gravitational redshift is also calculated for DMANSs with different DMEOSs and central pressure ratios. The results explain that the existence of dark matter in the DMANS leads to higher values for the gravitational redshift of the star.

[57]  arXiv:1612.02805 [pdf, other]
Title: Exploring the limitations and capabilities of shock-cooling models: new results for Type II SNe observed by the Kepler mission
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Shock-cooling models provide robust predictions for the early time emission from core-collapse SNe. Modern surveys have begun discovering and following SNe shortly after first light---providing first measurements of the rise of Type II SNe. We explore how shock cooling models can constrain the progenitor's radius, explosion velocity, and local host extinction. We fit synthetic photometry in several realistic observing scenarios and find that ultraviolet observations can constrain the progenitor's radius to a statistical uncertainty of $\pm10-15\%$, with a systematic uncertainty of $\pm 20\%$. With these observations the local host extinction can be constrained to $\pm0.05$ mag and the velocity to $\pm 5\%$ with a systematic uncertainty of $\pm 10\%$. We also re-analyze the SN light curves presented in Garnavich et al (2016) and find that KSN2011a can be fit by a BSG model with a progenitor radius of $R_s = 10_{-7{\rm (stat)}}^{+37 {\rm (stat)}} \phantom{}_{-1 {\rm (sys)}}^{+8 {\rm (sys)}}$ R$_\odot$, while KSN2011d can be fit with a RSG model with a progenitor radius of $R_s = 140_{-47 {\rm (stat)}}^{+91 {\rm (stat)}} \phantom{}_{-28 {\rm (sys)}}^{+23 {\rm (sys)}}$ R$_\odot$. Our results do not agree with those of Garnavich et al (2016). Moreover, we re-evaluate their claims and find that there is no statistically significant evidence for shock breakout in the light curve of KSN 2011d.

[58]  arXiv:1612.02809 [pdf, other]
Title: Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs II: Properties of 11 T-dwarfs
Comments: Submitted to ApJ. Constructive comments encouraged
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

Brown dwarf spectra are rich in information revealing of the chemical and physical processes operating in their atmospheres. We apply a recently developed atmospheric retrieval tool to an ensemble of late T-dwarf (600-800K) near infrared spectra. With these spectra we are able to place direct constraints the molecular abundances of H$_2$O, CH$_4$, CO, CO$_2$, NH$_3$, H$_2$S, and Na+K, gravity, thermal structure (and effective temperature), photometric radius, and cloud optical depths. We find that ammonia, water, methane, and the alkali metals are present and well constrained in all 11 objects. From the abundance constraints we find no significant trend in the water, methane, or ammonia abundances with temperature, but find a very strong ($>$25$\sigma$) increasing trend in the alkali metal abundances with effective temperature, indicative of alkali rainout. We also find little evidence for optically thick clouds. With the methane and water abundances, we derive the intrinsic atmospheric metallicity and carbon-to-oxygen ratios. We find in our sample, that metallicities are typically sub solar and carbon-to-oxygen ratios are somewhat super solar, different than expectations from the local stellar population. We also find that the retrieved vertical thermal profiles are consistent with radiative equilibrium over the photospheric regions. Finally, we find that our retrieved effective temperatures are lower than previous inferences for some objects and that our radii are larger than expectations from evolutionary models, possibly indicative of un-resolved binaries. This investigation and methodology represents a paradigm in linking spectra to the determination of the fundamental chemical and physical processes governing cool brown dwarf atmospheres.

[59]  arXiv:1612.02810 [pdf, other]
Title: The BRAVE Program - I: Improved Bulge Stellar Velocity Dispersion Estimates for a Sample of Active Galaxies
Comments: 13 pages, 7 figures, Submitted to ApJ. Will be updated with final version upon acceptance
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present new bulge stellar velocity dispersion measurements for 10 active galaxies with secure $M_{BH}$ determinations from reverberation-mapping. These new velocity dispersion measurements are based on spatially resolved kinematics from integral-field (IFU) spectroscopy. In all but one case, the field of view of the IFU extends beyond the effective radius of the galaxy, and in the case of Mrk 79 the field of view extends to almost one half the effective radius. This combination of spatial resolution and field of view allows for secure determinations of stellar velocity dispersion within the effective radius for all 10 target galaxies. Spatially resolved maps of the first (V) and second ($\sigma_{\star}$) moments of the line-of-sight velocity distribution (LOSVD) indicate the presence of kinematic substructure in most cases. In future projects we plan to explore methods of correcting for the effects of kinematic substructure in the derived bulge stellar velocity dispersion measurements.

[60]  arXiv:1612.02815 [pdf, other]
Title: Recalibration of the $M_{BH}-σ_{\star}$ Relation for AGN
Comments: 7 pages, 3 figures. Submitted to ApJL, will be updated with the final version upon acceptance
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a re-calibration of the $M_{BH}-\sigma_{\star}$ relation for AGN, based on a sample of 16 reverberation-mapped galaxies with newly determined bulge stellar velocity dispersions ($\sigma_{\star}$) from integral-field (IFU) spectroscopy. IFU spectroscopy provides a spatially resolved view of the stellar kinematics within the bulge of each target galaxy, from which significantly improved $\sigma_{\star}$ determinations can be made. This method accounts for variations in the stellar kinematics resulting from the presence of substructure (e.g.\ bars), and avoids many of the biases that are known to be present in long slit and single aperture spectroscopy. The sample covers three orders of magnitude in black hole mass, and is approximately evenly split between early- and late-type galaxies, and barred and unbarred galaxies. We find a best fitting slope of $\beta=3.77\pm0.99$ for the full sample, which is consistent with recent estimates of the relation for active galaxies, and shallower than recent estimates of the relation for quiescent galaxies. We find that our best-fit relationship is not sensitive to galaxy morphology. We recalculate the virial scaling factor $f$ required to bring the reverberation-mapped AGN sample into agreement with the fit for quiescent galaxies, and find $f=3.39\pm1.28$.