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J.P. Magué & B. Ménard



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[1]  arXiv:1410.4841 [pdf, ps, other]
Title: High-Resolution X-Ray Spectroscopy of the Bursting Pulsar GRO J1744-28
Comments: Accepted for publication in ApJ Letters, 6 pages, 4 figures, 1 table
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The bursting pulsar GRO J1744-28 is a Galactic low-mass X-ray binary that distinguishes itself by displaying type-II X-ray bursts: brief, bright flashes of X-ray emission that likely arise from spasmodic accretion. Combined with its coherent 2.1 Hz X-ray pulsations and relatively high estimated magnetic field, it is a particularly interesting source to study the physics of accretion flows around neutron stars. Here we report on Chandra/HETG observations obtained near the peak of its bright 2014 accretion outburst. Spectral analysis suggests the presence of a broad iron emission line centered at E_l ~ 6.7 keV. Fits with a disk reflection model yield an inclination angle of i ~ 52 degrees and an inner disk radius of R_in ~ 85 GM/c^2, which is much further out than typically found for neutron star low-mass X-ray binaries. Assuming that the disk is truncated at the magnetospheric radius of the neutron star, we estimate a magnetic field strength of B ~ (2-6)E10 G. Furthermore, we identify an absorption feature near ~6.85 keV could correspond to blue-shifted Fe xxv and point to a fast disk wind with an outflow velocity of v_out ~ (7.5-8.2)E3 km/s (~0.025c-0.027c). If the covering fraction and filling factor are large, this wind could be energetically important and perhaps account for the fact that the companion star lost significant mass while the magnetic field of the neutron star remained strong.

[2]  arXiv:1410.4843 [pdf, ps, other]
Title: Prospects for Characterizing Host Stars of the Planetary System Detections Predicted for the Korean Microlensing Telescope Network
Comments: 15 pages, 8 figures, submitted to ApJ. For a brief video explaining the key results of this paper, please visit: this http URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

I investigate the possibility of constraining the flux of the lens (i.e., host star) for the types of planetary systems the Korean Microlensing Telescope Network is predicted to find. I examine the potential to obtain lens flux measurements by 1) imaging a lens once it is spatially resolved from the source, 2) measuring the elongation of the point spread function of the microlensing target (lens+source) when the lens and source are still unresolved, and 3) taking prompt follow-up photometry. In each case I simulate observing programs for a representative example of current ground-based adaptive optics (AO) facilities (specifically NACO on VLT), future ground-based AO facilities (GMTIFS on GMT), and future space telescopes (NIRCAM on $JWST$). Given the predicted distribution of relative lens-source proper motions, I find that the lens flux could be measured to a precision of $\sigma_{H_{\ell}} \leq 0.1$ for $\gtrsim$60$\%$ of planet detections $\geq$5 years after each microlensing event, for a simulated observing program using GMT that images resolved lenses. NIRCAM on $JWST$ would be able to carry out equivalently high-precision measurements for $\sim$28$\%$ of events $\Delta t$ = 10 years after each event by imaging resolved lenses. I also explore the effects various blend components would have on the mass derived from prompt follow-up photometry, including companions to the lens, companions to the source, and unassociated interloping stars. I find that undetected blend stars would cause catastrophic failures (i.e., $>$50$\%$ fractional uncertainty in the inferred lens mass) for $\lesssim$(16$\cdot f_{\rm bin})\%$ of planet detections, where $f_{\rm bin}$ is the binary fraction, with the majority of these failures occurring for host stars with mass $\lesssim$0.3$M_{\odot}$.

[3]  arXiv:1410.4845 [pdf, ps, other]
Title: A Search For Star Formation in the Smith Cloud
Comments: 9 pages, 7 figures, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Motivated by the idea that a subset of HVCs trace dark matter substructure in the Local Group, we search for signs of star formation in the Smith Cloud, a nearby ~2x10^6 Msun HVC currently falling into the Milky Way. Using GALEX NUV and WISE/2MASS NIR photometry, we apply a series of color and apparent magnitude cuts to isolate candidate O and B stars that are plausibly associated with the Smith Cloud. We find an excess of stars along the line of sight to the cloud, but not at a statistically significant level relative to a control region. The number of stars found in projection on the cloud after removing an estimate of the contamination by the Milky Way implies an average star formation rate surface density of 10^(-4.8 +/- 0.3) Msun yr^(-1) kpc^(-2), assuming the cloud has been forming stars at a constant rate since its first passage through the Milky Way ~70 Myr ago. This value is consistent with the star formation rate expected based on the average gas density of the cloud. We also discuss how the newly discovered star forming galaxy Leo P has very similar properties to the Smith Cloud, but its young stellar population would not have been detected at a statistically significant level using our method. Thus, we cannot yet rule out the idea that the Smith Cloud is really a dwarf galaxy.

[4]  arXiv:1410.4850 [pdf, ps, other]
Title: Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron
Comments: Submitted to the Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Instrumentation and Methods for Astrophysics (astro-ph.IM); Atomic Physics (physics.atom-ph)

We describe the influence of electron-impact multiple ionization (EIMI) on the ionization balance of collisionally ionized plasmas. We are unaware of any previous ionization balance calculations that have included EIMI, which is usually assumed to be unimportant. Here, we incorporate EIMI cross-section data into calculations of both equilibrium and non-equilibrium charge-state distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small effect and can usually be ignored. However, for non-equilibrium plasmas the influence of EIMI can be important. In particular, we find that for plasmas in which the temperature oscillates there are significant differences in the CSD when including versus neglecting EIMI. These results have implications for modeling and spectroscopy of impulsively heated plasmas, such as nanoflare heating of the solar corona.

[5]  arXiv:1410.4860 [pdf, other]
Title: The CMB Power Spectrum of Nambu-Goto cosmic strings
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We improve predictions of the CMB power spectrum induced by cosmic strings by using source terms obtained from Nambu-Goto network simulations in an expanding universe. We use three high-resolution cosmic string simulations that cover the entire period from recombination until late-time $\Lambda$ domination to calculate unequal time correlators (UETCs) for scalar, vector and tensor components of the cosmic-string energy-momentum tensor. We calculate the CMB angular power spectrum from strings in two ways: first, to aid comparison with previous work, we fit our simulated UETCs to those obtained from different parameter combinations from the unconnected segment model and then calculate the CMB power spectra using these parameters to represent the string network. Secondly and more accurately, we decompose the UETCs into their corresponding eigenvalues and eigenvectors and input them directly into an Einstein-Boltzmann solver to calculate the power spectrum for each of the three simulation time periods. We combine the three simulations together, using each of them in its relevant redshift range and we obtain overall power spectra in temperature and polarisation channels. Finally, we use the power spectra obtained with the latest Planck and BICEP2 likelihoods to obtain constraints on the cosmic string tension.

[6]  arXiv:1410.4864 [pdf, other]
Title: BANYAN. V. A Systematic All-Sky Survey for New Very Late-Type Low-Mass Stars and Brown Dwarfs in Nearby Young Moving Groups
Comments: 37 pages, 27 figures, Accepted for publication in the Astrophysical Journal (Oct 16 2014)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present the BANYAN All-Sky Survey (BASS) catalog, consisting of 228 new late-type (M4-L6) candidate members of nearby young moving groups (YMGs) with an expected false-positive rate of ~ 13%. This sample includes 79 new candidate young brown dwarfs and 22 planetary-mass objects. These candidates were identified through the first systematic all-sky survey for late-type low-mass stars and brown dwarfs in YMGs. We cross-matched the 2MASS and ALLWISE catalogs outside of the galactic plane to build a sample of 98 970 potential $\geq$ M5 dwarfs in the solar neighborhood and calculated their proper motions with typical precisions of 5-15 mas yr$^{-1}$. We selected highly probable candidate members of several YMGs from this sample using the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II). We used the most probable statistical distances inferred from BANYAN II to estimate the spectral type and mass of these candidate YMG members. We used this unique sample to show tentative signs of mass segregation in the AB Doradus moving group and the Tucana-Horologium and Columba associations. The BASS sample has already been successful in identifying several new young brown dwarfs in earlier publications, and will be of great interest in studying the initial mass function of YMGs and for the search of exoplanets by direct imaging; the input sample of potential close-by $\geq$ M5 dwarfs will be useful to study the kinematics of low-mass stars and brown dwarfs and search for new proper motion pairs.

[7]  arXiv:1410.4870 [pdf, other]
Title: External Photoevaporation of the Solar Nebula: Jupiter's Noble Gas Enrichments
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We present a model explaining elemental enrichments in Jupiter's atmosphere, particularly the noble gases Ar, Kr, and Xe. While He, Ne and O are depleted, seven other elements show similar enrichments ($\sim$3 times solar, relative to H). Being volatile, Ar is difficult to fractionate from ${\rm H}_{2}$. We argue that external photoevaporation by far ultraviolet (FUV) radiation from nearby massive stars removed ${\rm H}_{2}$, He, and Ne from the solar nebula, but Ar and other species were retained because photoevaporation occurred at large heliocentric distances where temperatures were cold enough ($\lt 30$ K) to trap them in amorphous water ice. As the solar nebula lost H it became relatively and uniformly enriched in other species. Our model improves on the similar model of Guillot \& Hueso (2006). We recognize that cold temperatures alone do not trap volatiles; continuous water vapor production also is necessary. We demonstrate that FUV fluxes that photoevaporated the disk generated sufficient water vapor, in regions $\lt 30$ K, to trap gas-phase species in amorphous water ice, in solar proportions. We find more efficient chemical fractionation in the outer disk: whereas the model of Guillot \& Hueso (2006) predicts a factor of 3 enrichment when only $< 2\%$ of the disk mass remains, we find the same enrichments when 30\% of the disk mass remains. Finally, we predict the presence of $\sim 0.1 \, M_{\oplus}$ of water vapor in the outer solar nebula and in protoplanetary disks in H II regions.

[8]  arXiv:1410.4875 [pdf, ps, other]
Title: Evolution of the specific Star Formation Rate Function at z<1.4 - Dissecting the mass-SFR plane in COSMOS and GOODS
Comments: 24 pages, 15 figures, 3 tables, submitted to A&A, comments are welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The relation between the stellar mass and the star formation rate characterizes how the instantaneous star formation is determined by the galaxy past star formation history and by the growth of the dark matter structures. We deconstruct the M-SFR plane by measuring the specific SFR functions in several stellar mass bins from z=0.2 out to z=1.4. Our analysis is primary based on a MIPS 24$\mu m$ selected catalogue combining the COSMOS and GOODS surveys. We estimate the SFR by combining mid- and far-infrared data for 20500 galaxies. The sSFR functions are derived in four stellar mass bins within the range 9.5<log(M/Msun)<11.5. First, we demonstrate the importance of taking into account selection effects when studying the M-SFR relation. Secondly, we find a mass-dependent evolution of the median sSFR with redshift varying as $sSFR \propto (1+z)^{b}$, with $b$ increasing from $b=2.88$ to $b=3.78$ between $M=10^{9.75}Msun$ and $M=10^{11.1}Msun$, respectively. At low masses, this evolution is consistent with the cosmological accretion rate and predictions from semi-analytical models (SAM). This agreement breaks down for more massive galaxies showing the need for a more comprehensive description of the star-formation history in massive galaxies. Third, we obtain that the shape of the sSFR function is invariant with time at z<1.4 but depends on the mass. We observe a broadening of the sSFR function ranging from 0.28 dex at $M=10^{9.75}Msun$ to 0.46 dex at $M=10^{11.1}Msun$. Such increase in the scatter of the M-SFR relation suggests an increasing diversity of SFHs as the stellar mass increases. Finally, we find a gradual decline of the sSFR with mass as $log(sSFR) \propto -0.17M$. We discuss the numerous physical processes, as gas exhaustion in hot gas halos or secular evolution, which can gradually reduce the sSFR and increase the SFH diversity.

[9]  arXiv:1410.4892 [pdf, other]
Title: STARS: A software application for the EBEX autonomous daytime star cameras
Comments: 14 pages, 6 figures, SPIE conference proceedings
Journal-ref: Proceedings of the SPIE, Volume 9152, id. 915212 14 pp. (2014)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The E and B Experiment (EBEX) is a balloon-borne telescope designed to probe polarization signals in the CMB resulting from primordial gravitational waves, gravitational lensing, and Galactic dust emission. EBEX completed an 11 day flight over Antarctica in January 2013 and data analysis is underway. EBEX employs two star cameras to achieve its real-time and post-flight pointing requirements. We wrote a software application called STARS to operate, command, and collect data from each of the star cameras, and to interface them with the main flight computer. We paid special attention to make the software robust against potential in-flight failures. We report on the implementation, testing, and successful in flight performance of STARS.

[10]  arXiv:1410.4898 [pdf, ps, other]
Title: PSR J1738+0333: The First Millisecond Pulsar + Pulsating White Dwarf Binary
Comments: MNRAS Letters, in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We report the discovery of the first millisecond pulsar with a pulsating white dwarf companion. Following the recent discoveries of pulsations in extremely low-mass (ELM, <0.3 Msol) white dwarfs (WDs), we targeted ELM WD companions to two millisecond pulsars with high-speed Gemini photometry. We find significant optical variability in PSR J1738+0333 with periods between roughly 1790-3060 s, consistent in timescale with theoretical and empirical observations of pulsations in 0.17 Msol He-core ELM WDs. We additionally put stringent limits on a lack of variability in PSR J1909-3744, showing this ELM WD is not variable to <0.1 per cent amplitude. Thanks to the accurate distance and radius estimates from radio timing measurements, PSR J1738+0333 becomes a benchmark for low-mass, pulsating WDs. Future, more extensive time-series photometry of this system offers an unprecedented opportunity to constrain the physical parameters (including the cooling age) and interior structure of this ELM WD, and in turn, the mass and spin-down age of its pulsar companion.

[11]  arXiv:1410.4923 [pdf, ps, other]
Title: The phase-space of boxy-peanut and X-shaped bulges in galaxies II. The relation between face-on and edge-on boxiness
Comments: 12 pages, 13 figures, accepted for publication in the MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Dynamical Systems (math.DS); Chaotic Dynamics (nlin.CD)

We study the dynamical mechanisms that reinforce the formation of boxy structures in the \textit{inner} regions, roughly in the middle, of bars observed nearly \textit{face-on}. Outer boxiness, at the ends of the bars, is usually associated with orbits at the inner, radial 4:1 resonance region and can be studied with 2D dynamics. However, in the middle of the bar dominate 3D orbits that give boxy/peanut bulges in the edge-on views of the models. In the present paper we show that 3D quasi-periodic, as well as 3D chaotic orbits sticky to the x1v1 and x1v1$^{\prime}$ tori, especially from the Inner Lindblad Resonance (ILR) region, have boxy projections on the equatorial plane of the bar. The majority of vertically perturbed 2D orbits, initially on the equatorial plane in the ILR resonance region, enhance boxy features in face-on bars. Orbits that build a bar by supporting sharp "{\sf X}" features in their side-on views at energies \textit{beyond} the ILR, may also have a double boxy character. If populated, the extent of the inner boxiness along the major axis is about the same with that of the peanut supporting orbits in the side-on views. At any rate these orbits do not obscure the observation of the boxy orbits of the ILR region in the face-on views, as they contribute more to the surface density at the sides of the bar than to their central parts.

[12]  arXiv:1410.4933 [pdf, ps, other]
Title: The Properties of the Tilts of Bipolar Solar Regions
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We investigate various properties associated with the tilt of isolated magnetic bipoles in magnetograms taken at the solar surface. We show that bipoles can be divided into two groups which have tilts of opposite signs, and reveal similar properties with respect to bipole area, flux and bipolar moment. Detailed comparison of these physical quantities shows that the dividing point between the two types of bipoles corresponds to a bipole area of about 300 millionths of the solar hemisphere (MHS). The time-latitude distribution of small bipoles differs substantially from that for large bipoles. Such behaviour in terms of dynamo theory may indicate that small and large bipoles trace different components of the solar magnetic field. The other possible viewpoint is that the difference in tilt data for small and large bipoles is connected with spectral helicity separation, which results in opposite tilts for small and large bipoles. We note that the data available do not provide convincing reasons to prefer either interpretation.

[13]  arXiv:1410.4937 [pdf, other]
Title: Galaxy stellar mass assembly: the difficulty to match observations and semi-analytical predictions
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Semi-analytical models (SAMs) are currently the best way to understand the formation of galaxies within the cosmic dark-matter structures. While they fairly well reproduce the local stellar mass functions, correlation functions and luminosity functions, they fail to match observations at high redshift (z > 3) in most cases, particularly in the low-mass range. The inconsistency between models and observations indicates that the history of gas accretion in galaxies, within their host dark-matter halo, and the transformation of gas into stars, are not well followed. Hereafter, we briefly present a new version of the GalICS semi-analytical model. We explore the impacts of classical mechanisms, such as supernova feedback or photoionization, on the evolution of the stellar mass assembly. Even with a strong efficiency, these two processes cannot explain the observed stellar mass function and star formation rate distribution and some other relations. We thus introduce an ad-hoc modification of the standard paradigm, based on the presence of a \textit{no-star-forming} gas component, and a concentration of the star-forming gas in galaxy discs. The main idea behind the existence of the no-star-forming gas reservoir is that only a fraction of the total gas mass in a galaxy is available to form stars. The reservoir generates a delay between the accretion of the gas and the star formation process. This new model is in much better agreement with the observations of the stellar mass function in the low-mass range than the previous models, and agrees quite well with a large set of observations, including the redshift evolution of the specific star formation rate. However, it predicts a large fraction of no-star-forming baryonic gas, potentially larger than observed, even if its nature has still to be examined in the context of the missing baryon problem.

[14]  arXiv:1410.4938 [pdf, other]
Title: Toward a new modelling of gas flows in a semi-analytical model of galaxy formation and evolution
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present an extended version of the semi-analytical model, GalICS. As its predecessor, eGalICS applies a post-treatment of the baryonic physics on pre-computed dark-matter merger trees extracted from a N-body simulation. We review all the mechanisms that affect, at a given time, the formation and evolution of a galaxy in its host dark-matter halo. We mainly focus on the gas cycle, from the smooth cosmological accretion to feedback processes. To follow with a high accuracy this cycle we introduce some novel prescriptions: i) a smooth baryonic accretion with two phases: a cold mode and a hot mode built on the continuous dark-matter accretion. In parallel to this smooth accretion we implement the standard photoionisation modelling to reduce the input gas flow on the smallest structures. ii) a complete monitoring of the hot gas phase. We compute the evolution of the core density, the mean temperature and the instantaneous escape fraction of the hot atmosphere by considering that the hot gas is in hydrostatic equilibrium in the dark matter potential well, and by applying a principle of conservation of energy on the treatment of gas accretion, supernovae and super massive black hole feedback iii) a new treatment for disc instabilities based on the formation, the migration and the disruption of giant clumps. The migration of such clumps in gas-rich galaxies allows to form \textit{pseudo}-bulges. The different processes in the gas cycle act on different time scales, and we thus build an adaptive time-step scheme to solve the evolution equations. The model presented here is compared in detail to the observations of stellar-mass functions, star formation rates, and luminosity functions, in a companion paper (Cousin et al. 2014).

[15]  arXiv:1410.4946 [pdf, ps, other]
Title: 1/1 resonant periodic orbits in three dimensional planetary systems
Comments: Accepted for publication in the proceedings of IAU Symposium 310: Complex Planetary Systems
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We study the dynamics of a two-planet system, which evolves being in a $1/1$ mean motion resonance (co-orbital motion) with non-zero mutual inclination. In particular, we examine the existence of bifurcations of periodic orbits from the planar to the spatial case. We find that such bifurcations exist only for planetary mass ratios $\rho=\frac{m_2}{m_1}<0.0205$. For $\rho$ in the interval $0<\rho<0.0205$, we compute the generated families of spatial periodic orbits and their linear stability. These spatial families form bridges, which start and end at the same planar family. Along them the mutual planetary inclination varies. We construct maps of dynamical stability and show the existence of regions of regular orbits in phase space.

[16]  arXiv:1410.4949 [pdf, ps, other]
Title: Spontaneous Magnetization of Solid Quark-cluster Stars
Authors: X. Y. Lai (XJU, XAO), R. X. Xu (PKU, KIAA)
Comments: 5 pages, 1 figure
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Pulsar-like compact stars have strong magnetic fields, with the strength from $\sim 10^9$ to $\sim 10^{12}$ Gauss. How can such strong magnetic fields be generated and maintained is still an unsolved problem, and in principle it is related to the interior structure of compact stars. In this paper we propose that, under the Coulomb repulsion, the electrons in solid quark-cluster stars could spontaneously magnetized, and hence electrons could contribute non-zero net magnetic momentum to the whole star. We find that, for most cases in solid quark-cluster stars, the amount of net magnetic momentum, which is proportional to spin polarization $\xi=(n_+-n_-)/n_e$ and depends on the number density of electrons $n_e=n_++n_-$, could be significant with non-zero $\xi$, and the corresponding magnetic moment per unit mass could be higher than $10^{-4}$ Gauss cm$^3$ g$^{-1}$. Therefore the net magnetic moments of electron system in solid quark-cluster stars could be large enough to induce the observed magnetic fields for pulsars.

[17]  arXiv:1410.4960 [pdf, other]
Title: Overview of Non-Liquid Noble Direct Detection Dark Matter Experiments
Authors: J. Cooley
Comments: 19 pages, 1 figure. In Proceedings of the 13th International Conference on Topics in Astroparticle and Underground Physics, TAUP 2013
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Instrumentation and Detectors (physics.ins-det)

In the last few years many advances have been made in the field of dark matter direct detection. In this article I will review the progress and status of experiments that employ detection techniques that do not use noble liquids. First, I will give an introduction to the field of dark matter and discuss the background challenges that confront all dark matter experiments. I will also discuss various detection techniques employed by the current generation and the next generation of dark matter experiments. Finally, I will discuss recent results and the status of current and future direct detection experiments.

[18]  arXiv:1410.4968 [pdf, other]
Title: Theoretical implications of detecting gravitational waves
Comments: 21 pages
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

This paper is the third in a series of theorems which state how cosmological observations can provide evidence for an early phase of acceleration in the universe. Previous theorems demonstrated that the observed power spectrum for scalar perturbations forces all possible alternative theories of inflation to theories other than General Relativity. It was shown that generically, without a phase of accelerated expansion, these alternatives have to break at least one of the following tenets of classical general relativity: the Null Energy Condition (NEC), subluminal signal propagation, or sub-Planckian energy densities. In this paper we prove how any detection of primordial gravitational waves at large scales can provide independent evidence to support a phase of accelerated expansion. This proof does not rely on the spectral index for tensor modes. Our approach, like in the case of scalars, is proof by contradiction: we investigate the possibility of a detectable tensor signal sourced by vacuum fluctuations in a non-accelerating, sub-Planckian universe using cosmological perturbation theory (based on quantum field theory in curved space time) and derive contradictory limits on cosmological dynamics. The contradiction implies that one or more of our axioms for early universe must have been broken. The bound from tensor perturbations is not only independent of, but also stronger than the one obtained from scalar power spectrum.

[19]  arXiv:1410.4971 [pdf, ps, other]
Title: The Impact of Chromospheric Activity on Observed Initial Mass Functions
Authors: Keivan G. Stassun (1,2), Aleks Scholz (3), Trent Dupuy (4), Kaitlin Kratter (5), ((1) Vanderbilt University, (2) Fisk University, (3) University of St. Andrews, (4) University of Texas, (5) University of Arizona)
Comments: Accepted by ApJ, 9 pages, 2 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Using recently established empirical calibrations for the impact of chromospheric activity on the radii, effective temperatures, and estimated masses of active low-mass stars and brown dwarfs, we reassess the shape of the initial mass function (IMF) across the stellar/substellar boundary in the Upper Sco star-forming region (age 5-10 Myr). We adjust the observed effective temperatures to warmer values using the observed strength of the chromospheric H$\alpha$ emission, and redetermine the estimated masses of objects using pre--main-sequence evolutionary tracks in the H-R diagram. The effect of the activity-adjusted temperatures is to shift the objects to higher masses by 3-100%. While the slope of the resulting IMF at substellar masses is not strongly changed, the peak of the IMF does shift from ~0.06 to ~0.11 Msun. Moreover, for objects with masses ~0.2 Msun, the ratio of brown dwarfs to stars changes from ~80% to ~33%. These results suggest that activity corrections are essential for studies of the substellar mass function, if the masses are estimated from spectral types or from effective temperatures.

[20]  arXiv:1410.4997 [pdf, other]
Title: Evidence of cross-correlation between the CMB lensing and the gamma-ray sky
Comments: 6 pages, 2 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

We report the measurement of the angular power spectrum of cross-correlation between the unresolved component of the Fermi-LAT gamma-ray sky-maps and the CMB lensing potential map reconstructed by the Planck satellite. The matter distribution in the Universe determines the bending of light coming from the last scattering surface. At the same time, the matter density drives the growth history of astrophysical objects, including their capability at generating non-thermal phenomena, which in turn give rise to gamma-ray emissions. The Planck lensing map provides information on the integrated distribution of matter, while the integrated history of gamma-ray emitters is imprinted in the Fermi-LAT sky maps. We report here the first evidence of their correlation (at 3.2$\sigma$ C.L.). We find that the multipole dependence of the cross-correlation measurement is in agreement with current models of the gamma-ray luminosity function for AGN and star forming galaxies. Moreover, its amplitude can in general be matched only assuming that these extra-galactic emitters are also the bulk contribution of the measured isotopic gamma-ray background (IGRB) intensity. This leaves little room for a big contribution from galactic sources to the IGRB measured by Fermi-LAT, pointing toward a direct evidence of the extragalactic origin of the IGRB.

[21]  arXiv:1410.5046 [pdf, other]
Title: Constraints on the Nambu-Goto cosmic string contribution to the CMB power spectrum in light of new temperature and polarisation data
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Cosmic strings generate vector and tensor modes in the B-channel of polarization, as well as the usual temperature power spectrum and E-mode polarization spectrum. We use the power spectrum obtained from high-resolution Nambu-Goto cosmic string simulations together with the Planck and BICEP2 likelihoods to explore the degeneracies appearing between cosmic strings and other cosmological parameters in different inflationary scenarios, as well as the constraints that can be imposed on cosmic strings in each of these situations. In standard $\Lambda$CDM, the Planck likelihood yields an upper limit $G\mu<1.49 \times 10^{-7}$ (95\% confidence). We also analyse the possibility of explaining the BB power spectrum signal recently detected by the BICEP2 probe. We find that cosmic strings alone are able to explain only part of the B-mode polarization signal. Apart from the standard $\Lambda$CDM model, we look at the following non-minimal parameters: the running of the spectral index, non-zero tensor-to-scalar ratio, additional degrees of freedom ($N_{eff}$) and sterile neutrinos. We find that in both Planck and BICEP2 scenarios adding $N_{eff}$ induces degeneracies between cosmic strings and $N_{eff}$ and other $\Lambda$CDM parameters. With $N_{eff}$ a larger contribution from cosmic strings is allowed, even favoured, but after combining with large-scale structure data such as BAOs strings remain strongly constrained.

[22]  arXiv:1410.5048 [pdf, ps, other]
Title: Activity and quiescence in galaxies at redshifts 1.4<z<3.5. The role of the starburst temperature
Authors: M. Contini
Comments: 5 pages, 3 figures, in press in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We investigate 'activity' and 'quiescence' in galaxies at relatively high redshifts by modelling the line(and continuum) spectra of each object. The models account consistently for photoionization and shocks. We claim that the starburst effective temperature, the flux from an AGN, and the shock velocity are critical to activity. The results confirm that two sample galaxies show intense starburst activity with temperatures reaching Ts=2x10^5K and shock velocities Vs> 250 km/s, while for the remaining galaxies of our sample the models show quiescent star formation with Ts< 7x10^4K. A Seyfert 2 like AGN is proposed in one galaxy. The O/H relative abundances derived by the detailed modelling of the spectra are nearly solar for all the sample galaxies, in contrast to those obtained by direct methods.

[23]  arXiv:1410.5070 [pdf, other]
Title: Towards SiPM camera for current and future generations of Cherenkov telescopes
Comments: 4 pages, 5 figures, Proc. of 33rd ICRC, Rio de Janeiro, Brazil, 2013
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Instrumentation and Detectors (physics.ins-det)

So far the current ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs) have energy thresholds in the best case in the range of ~30 to 50 GeV (H.E.S.S. II and MAGIC telescopes). Lowest energy gamma-ray showers produce low light intensity images and cannot be efficiently separated from dominating images from hadronic background. A cost effective way of improving the telescope performance at lower energies is to use novel photosensors with superior photon detection efficiency (PDE). Currently the best commercially available superbialkali photomultipliers (PMTs) have a PDE of about 30-33%, whereas the silicon photomultipliers (SiPMs, also known as MPPC, GAPD) from some manufacturers show a photon detection efficiency of about 40-45%. Using these devices can lower the energy threshold of the instrument and may improve the background rejection due to intrinsic properties of SiPMs such as a superb single photoelectron resolution. Compared to PMTs, SiPMs are more compact, fast in response, operate at low voltage, and are insensitive to magnetic fields. SiPMs can be operated at high background illumination, which would allow to operate the IACT also during partial moonlight, dusk and dawn, hence increasing the instrument duty cycle. We are testing the SiPMs for Cherenkov telescopes such as MAGIC and CTA. Here we present an overview of our setup and first measurements, which we perform in two independent laboratories, in Munich, Germany and in Barcelona, Spain.

[24]  arXiv:1410.5073 [pdf, other]
Title: Upgrade of the MAGIC telescopes
Comments: 4 pages, 7 figures, Proc. of 33rd ICRC, Rio de Janeiro, Brazil, 2013
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The MAGIC telescopes are two Imaging Atmospheric Cherenkov Telescopes (IACTs) located on the Canary island of La Palma. With 17m diameter mirror dishes and ultra-fast electronics, they provide an energy threshold as low as 50 GeV for observations at low zenith angles. The first MAGIC telescope was taken in operation in 2004 whereas the second one joined in 2009. In 2011 we started a major upgrade program to improve and to unify the stereoscopic system of the two similar but at that time different telescopes. Here we report on the upgrade of the readout electronics and digital trigger of the two telescopes, the upgrade of the camera of the MAGIC I telescope as well as the commissioning of the system after this major upgrade.

[25]  arXiv:1410.5084 [pdf, other]
Title: The Main-Belt Comets: The Pan-STARRS1 Perspective
Comments: 38 pages, 14 figures; accepted for publication in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We analyze 760475 observations of 333026 main-belt objects obtained by the Pan-STARRS1 (PS1) survey telescope between 2012 May 20 and 2013 November 9, a period during which PS1 discovered two main-belt comets, P/2012 T1 (PANSTARRS) and P/2013 R3 (Catalina-PANSTARRS). PS1 comet detection procedures currently consist of the comparison of the point spread functions (PSFs) of moving objects to those of reference stars, and the flagging of objects that show anomalously large radial PSF widths. Based on the number of missed discovery opportunities among comets discovered by other observers, we estimate an upper limit comet discovery efficiency rate of ~70% for PS1. Additional analyses that could improve comet discovery yields in future surveys include linear PSF analysis, modeling of trailed stellar PSFs for comparison to trailed moving object PSFs, searches for azimuthally localized activity, comparison of point-source-optimized photometry to extended-source-optimized photometry, searches for photometric excesses in objects with known absolute magnitudes, and crowd-sourcing. Analysis of PS1 survey statistics indicates an expected fraction of 59 MBCs per 10^6 outer main-belt asteroids, and a 95% confidence upper limit of 96 MBCs per 10^6 outer main-belt asteroids. We note that more sensitive future surveys could detect many more MBCs than estimated here. We find an excess of high eccentricities (0.1 < e < 0.3) among all known MBCs relative to the background asteroid population. Theoretical calculations show that, given these eccentricities, the sublimation rate for a typical MBC is orders of magnitude larger at perihelion than at aphelion, providing a plausible physical explanation for the observed behavior of MBCs peaking in observed activity strength near perihelion.

[26]  arXiv:1410.5109 [pdf, other]
Title: Mass Transfer from Giant Donors
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

The stability of mass transfer in binaries with convective giant donors remains an open question in modern astrophysics. There is a significant discrepancy between what the existing methods predict for a response to mass loss of the giant itself, as well as for the mass transfer rate during the Roche lobe overflow. Here we show that the recombination energy in the superadiabatic layer plays an important and hitherto unaccounted-for role in he donor's response to mass loss, in particular on its luminosity and effective temperature. Our improved optically thick nozzle method to calculate the mass transfer rate via $L_1$ allows us to evolve binary systems for a substantial Roche lobe overflow. We propose a new, strengthened criterion for the mass transfer instability, basing it on whether the donor experiences overflow through its outer Lagrangian point. We find that with the new criterion, if the donor has a well-developed outer convective envelope, the critical initial mass ratio for which a binary would evolve stably through the conservative mass transfer varies from $1.5$ to $2.2$, which is about twice as large as previously believed. In underdeveloped giants with shallow convective envelopes this critical ratio may be even larger. When the convective envelope is still growing, and in particular for most cases of massive donors, the critical mass ratio gradually decreases to this value, from that of radiative donors.

[27]  arXiv:1410.5113 [pdf, other]
Title: Scaling of Observable Properties in Rapidly Rotating Stars
Comments: Published in ApJ, October 10 2014
Journal-ref: 2014 ApJ 794 13
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The spectral energy distribution as a function of inclination is computed using 2D rotating stellar models and NLTE plane parallel stellar atmospheres. These models cover the range from $1.875M_{\odot}$ to $3.0M_{\odot}$. The deduced effective temperature is determined by B-V computed from the spectral energy distribution, and the deduced luminosity is computed as the integral of the spectral energy distribution over all frequencies, assuming the distance and reddening are known. These deduced quantities are obtained from the observed spectral energy distribution assuming the objects are spherically symmetric, and thus the results are dependent on the inclination. Previous work has shown that the surface properties between two rotating stellar models with the same surface shape scale, and this is also true for the deduced effective temperature and luminosity over this limited mass range.

[28]  arXiv:1410.5114 [pdf, other]
Title: Combining power spectrum and bispectrum measurements to detect oscillatory features
Comments: 20 pages, 14 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The simplest inflationary models present us with few observable parameters to discriminate between them. A detection of features in the spectra of primordial density perturbations could provide valuable insights and lead to stringent tests of models of the early universe. So far, searches for oscillatory features have not produced statistically significant results. In this work we consider a combined search for features in the power spectrum and bispectrum. We show that possible dependencies between the estimates of feature model amplitudes based on the two and three-point correlators are largely statistically independent under the assumption of the null hypothesis of a nearly Gaussian featureless CMB. Building on this conclusion we propose an optimal amplitude estimator for a combined search and study the look-elsewhere effect in feature model surveys. In particular we construct analytic models for the distribution of amplitude estimates that allow for a reliable assessment of the significance of potential findings. We also propose a well behaved integrated statistic that is designed to detect evidence for models exhibiting features at multiple frequencies.

[29]  arXiv:1410.5120 [pdf, ps, other]
Title: Black Holes in 4 Nearby Radio Galaxies
Comments: to appear in ApSS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the velocity dispersion profiles of the nuclei of NGC 1326, 2685, 5273 and 5838 in the CO first overtone band. There is evidence for a black hole (BH) in NGC 1326 and 5838. Gas is seen flowing out of the nuclear region of NGC 5273. We put upper limits on the nuclear BHs responsible for its activity and that of NGC 2685.

[30]  arXiv:1410.5125 [pdf, ps, other]
Title: Gamma/hadron segregation for a ground based imaging atmospheric Cherenkov telescope using machine learning methods: Random Forest leads
Authors: Mradul Sharma (BARC), J. Nayak (ISI), M. K. Koul (BARC), S.Bose (BARC), Abhas Mitra (BARC)
Comments: Accepted to RAA
Journal-ref: Research in Astronomy and Astrophysics 14 (2014) 1491-1503
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

A detailed case study of $\gamma$-hadron segregation for a ground based atmospheric Cherenkov telescope is presented. We have evaluated and compared various supervised machine learning methods such as the Random Forest method, Artificial Neural Network, Linear Discriminant method, Naive Bayes Classifiers,Support Vector Machines as well as the conventional dynamic supercut method by simulating triggering events with the Monte Carlo method and applied the results to a Cherenkov telescope. It is demonstrated that the Random Forest method is the most sensitive machine learning method for $\gamma$-hadron segregation.

[31]  arXiv:1410.5136 [pdf, ps, other]
Title: Probability distribution function for inclinations of merging compact binaries detected by gravitational wave interferometers
Authors: Naoki Seto
Comments: 8 pages, 6 figures, accepted for publication in MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We analytically discuss probability distribution function (PDF) for inclinations of merging compact binaries whose gravitational waves are coherently detected by a network of ground based interferometers. The PDF would be useful for studying prospects of (1) simultaneously detecting electromagnetic signals (such as gamma-ray-bursts) associated with binary mergers and (2) statistically constraining the related theoretical models from the actual observational data of multi-messenger astronomy. Our approach is similar to Schutz (2011), but we explicitly include the dependence of the polarization angles of the binaries, based on the concise formulation given in Cutler and Flanagan (1994). We find that the overall profiles of the PDFs are similar for any networks composed by the second generation detectors (Advanced-LIGO, Advanced-Virgo, KAGRA, LIGO-India). For example, 5.1% of detected binaries would have inclination angle less than 10 degree with at most 0.1% differences between the potential networks. A perturbative expression is also provided for generating the PDFs with a small number of parameters given by directional averages of the quantity $\epsilon$ that characterises the asymmetry of network sensitivities to incoming two orthogonal polarization modes.

[32]  arXiv:1410.5141 [pdf, ps, other]
Title: VIMAP: an Interactive Program Providing Radio Spectral Index Maps of Active Galactic Nuclei
Authors: Jae-Young Kim, Sascha Trippe (Seoul National University)
Comments: 5 pages, 4 figures, 2 tables; to appear in JKAS (received September 5, 2014; accepted October 10, 2014)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)

We present a GUI-based interactive Python program, VIMAP, which generates radio spectral index maps of active galactic nuclei (AGN) from Very Long Baseline Interferometry (VLBI) maps obtained at different frequencies. VIMAP is a handy tool for the spectral analysis of synchrotron emission from AGN jets, specifically of spectral index distributions, turn-over frequencies, and core-shifts. In general, the required accurate image alignment is difficult to achieve because of a loss of absolute spatial coordinate information during VLBI data reduction (self-calibration) and/or intrinsic variations of source structure as function of frequency. These issues are overcome by VIMAP which in turn is based on the two-dimensional cross-correlation algorithm of Croke and Gabuzda (2008). In this paper, we briefly review the problem of aligning VLBI AGN maps, describe the workflow of VIMAP, and present an analysis of archival VLBI maps of the active nucleus 3C 120.

[33]  arXiv:1410.5184 [pdf, other]
Title: Deriving extinction laws with O stars: from the IR to the UV
Comments: To appear in Highlights of Spanish Astrophysics VIII, Proceedings of the XI Scientific Meeting of the Spanish Astronomical Society held on September 8-12, 2014, in Teruel, Spain
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We have recently derived a family of extinction laws for 30 Doradus that provides better fits to the optical photometry of obscured stars in the Galaxy and the LMC. Simultaneously, we are extending our Galactic O-Star Spectroscopic Survey (GOSSS) to fainter, more extinguished stars to obtain accurate spectral types for massive stars with more than 6 magnitudes of $V$-band extinction. I have combined both lines of research with 2MASS, WISE, and Spitzer photometry to obtain the 1-10 micron extinction law for O stars in the solar neighborhood. I present these results and compare them with the extinction laws in the same wavelength range derived from late-type stars and H II regions. I also discuss plans to extend the newly derived optical-IR extinction laws to the UV.

[34]  arXiv:1410.5193 [pdf, ps, other]
Title: A classical and a relativistic law of motion for spherical supernovae
Authors: L. Zaninetti
Comments: 15 figures and 34 pages
Journal-ref: The Astrophysical Journal , (2014) , 195, 80
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

In this paper we derive some first order differential equations which model the classical and the relativistic thin layer approximations. The circumstellar medium is assumed to follow a density profile of Plummer type, or of Lane--Emden ($n=5$) type, or a power law. The first order differential equations are solved analytically, or numerically, or by a series expansion, or by recursion. The initial conditions are chosen in order to model the temporal evolution of SN 1993J over ten years and a smaller chi-squared is obtained for the Plummer case with eta=6. The stellar mass ejected by the SN progenitor prior to the explosion, expressed in solar mass, is identified with the total mass associated with the selected density profile and varies from $0.217 $ to $0.402 $ when the central number density is $10^7 $ particles per cubic centimeter. The Full width at half maximum of the three density profiles, which can be identified with the size of the Pre-SN 1993J envelope, varies from 0.0071 pc to 0.0092 pc.

[35]  arXiv:1410.5203 [pdf, other]
Title: Spin-orbit angle in compact planetary systems perturbed by an inclined companion. Application to the 55 Cancri system
Comments: Accepted for publication in the proceedings of IAU Symposium 310: Complex Planetary Systems
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The stellar spin orientation relative to the orbital planes of multiplanet systems are becoming accessible to observations. For example, 55 Cancri is a system composed of 5 planets orbiting a member of a stellar binary for which a projected obliquity of 72+-12 deg relative to the orbit of the innermost planet has been reported (Bourrier & Hebrard 2014). This large obliquity has been attributed to the perturbation induced by the binary. Here we describe the secular evolution of similar systems and we discuss the case of the 55 Cancri system more deeply. We provide two different orbital configurations compatible with the currently available observations.

[36]  arXiv:1410.5205 [pdf, other]
Title: The ultra luminous X-ray source NuSTAR J095551+6940.8: A magnetar in a high mass X-ray binary
Comments: 3 pages, 1 figure
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The recent detection of pulsations from the ultra luminous X-ray source (ULX) NuSTAR J095551+6940.8 in M82 by Bachetti et al.\ indicates that the object is an accreting neutron star in a high mass X-ray binary (HMXB) system. The super-Eddington luminosity of the object implies that the magnetic field is sufficiently strong to suppress the scattering cross-section unless its beam is viewed at a favourable angle. We show that the torque equilibrium condition for the pulsar indicates the dipole magnetic field of the neutron star is $\sim 10^{14}$ G, two orders of magnitude higher than that estimated by Bachetti et al., and further point to the possibility that even stronger magnetic fields could well be in the higher multipoles. This supports the recent view that magnetars descent from HMXBs.

[37]  arXiv:1410.5208 [pdf, ps, other]
Title: Fermi-LAT Detection of Pulsed Gamma-rays Above 50 GeV from the Vela Pulsar
Comments: 14 pages, 4figures, accepted by ApJ Letter
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The First \fermi-LAT Catalog of Sources Above 10 GeV reported evidence of pulsed emission above 25 GeV from 12 pulsars, including the Vela pulsar, which showed evidence of pulsation at $>37$ GeV energy bands. Using 62 months of \fermi-LAT data, we analyzed the gamma-ray emission from the Vela pulsar and searched for pulsed emission above 50 GeV. Having confirmed the significance of the pulsation in 30-50 GeV with the H-test (p-value $\sim10^{-77}$), we extracted its pulse profile using the Bayesian block algorithm and compared it with the distribution of the 5 observed photons above 50 GeV using the likelihood ratio test. Pulsation was significantly detected for photons above 50 GeV with p-value $=3\times10^{-5}$ ($4.2\sigma$). The detection of pulsation is significant above $4\sigma$ at $>79$ GeV and above $3\sigma$ at $>90$ GeV energy bands, making this the highest energy pulsation significantly detected by the LAT. We explore non-stationary outer gap scenario of the very high-energy emissions from the Vela pulsar.

[38]  arXiv:1410.5216 [pdf, ps, other]
Title: Comparing the spectral lag of short and long gamma-ray bursts and its relation with the luminosity
Comments: 11 pages, 6 figures, 2 tables, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We investigated the rest frame spectral lags of two complete samples of bright long (50) and short (6) gamma-ray bursts (GRB) detected by Swift. We analysed the Swift/BAT data through a discrete cross-correlation function (CCF) fitted with an asymmetric Gaussian function to estimate the lag and the associated uncertainty. We find that half of the long GRBs have a positive lag and half a lag consistent with zero. All short GRBs have lags consistent with zero. The distributions of the spectral lags for short and long GRBs have different average values. Limited by the small number of short GRBs, we cannot exclude at more than 2 sigma significance level that the two distributions of lags are drawn from the same parent population. If we consider the entire sample of long GRBs, we do not find evidence for a lag-luminosity correlation, rather the lag-luminosity plane appears filled on the left hand side, thus suggesting that the lag-luminosity correlation could be a boundary. Short GRBs are consistent with the long ones in the lag-luminosity plane.

[39]  arXiv:1410.5225 [pdf, ps, other]
Title: Multicolour photometry of pulsating stars in the Galactic Bulge fields
Comments: 2 pages, 1 figure. Accepted for publication in the proceedings of IAU Symposium 301
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a study of photometric properties of very crowded stellar fields toward the Galactic Bulge. We performed a search for pulsating stars among thousands of variable stars from the OGLE-II survey supplementing the variability study with photometric measurements in four Johnson-Cousins $UBVI_{\rm C}$ passbands. Using these data, we analysed the properties of objects located at different distances and, whenever possible, classified them.

[40]  arXiv:1410.5228 [pdf, ps, other]
Title: Understanding the spin-down rate changes of PSR B0919+06
Comments: 10 pages, 12 Figures, Accepted by MNRAS on 10 October 2014
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We study the spin-down properties of PSR B0919+06 based on almost 30 years of radio observations. We confirm that the time derivative of the rotational frequency $\dot \nu$ is modulated quasi-periodically and show that it exhibits a repeating double-peaked structure throughout the entire observation span. We model the $\dot \nu$ variation of the pulsar assuming two spin-down rates with sudden switches between them in time. Our results show that the double-peak structure in $\dot \nu$ has a repetition time of about 630 days until MJD 52000 (April 2001) and 550 days since then. During this cycle, the pulsar spin varies from the lower spin-down rate to the upper spin-down rate twice with different amounts of time spent in each state, resulting in a further quasi-stable secondary modulation of the two-state switching. This particular spin-down state switching is broadly consistent with free precession of the pulsar, however, a strong evidence linked with this mechanism is not clearly established. We also confirm that the pulsar occasionally emits groups of pulses which appear early in pulse phase, so-called "flares", and these events significantly contribute to the pulse profile shape. We find the $\dot \nu$ modulation and the pulse shape variations are correlated throughout the observations. However, the flare-state is not entirely responsible for this correlation. In addition to the flare-state, we detect flare-like events from the pulsar in single pulse observations. During these events, the shift in pulse phase is small compared to that of the main flare-state and clearly visible only in single pulse observations.

[41]  arXiv:1410.5229 [pdf, other]
Title: Lower mass normalization of the stellar initial mass function for dense massive early-type galaxies at z ~ 1.4
Comments: 9 pages, 4 figures, accepted for pubblication on A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

This paper aims at understanding if the normalization of the stellar initial mass function (IMF) of massive early-type galaxies (ETGs) varies with cosmic time and/or with mean stellar mass density Sigma (M*/2\pi Re^2). For this purpose we have collected a sample of 18 dense (Sigma>2500 M_sun/pc^2) ETGs at 1.2<z<1.6 with available velocity dispersion sigma_e. We have constrained their mass-normalization by comparing their true stellar masses (M_true) derived through virial theorem, hence IMF independent, with those inferred through the fit of the photometry assuming a reference IMF (M_ref). Adopting the virial estimator as proxy of the true stellar mass, we have assumed for these ETGs zero dark matter (DM). However, dynamical models and numerical simulations of galaxy evolution have shown that the DM fraction within Re in dense high-z ETGs is negligible. We have considered the possible bias of virial theorem in recovering the total masses and have shown that for dense ETGs the virial masses are in agreement with those derived through more sophisticated dynamical models. The variation of the parameter $\Gamma$ = M_true/M_ref with sigma_e shows that, on average, dense ETGs at <z> = 1.4 follow the same IMF-sigma_e trend of typical local ETGs, but with a lower mass-normalization. Nonetheless, once the IMF-sigma_e trend we have found for high-z dense ETGs is compared with that of local ETGs with similar Sigma and sigma_e, they turn out to be consistent. The similarity between the IMF-sigma_e trends of dense high-z and low-z ETGs over 9 Gyr of evolution and their lower mass-normalization with respect to the mean value of local ETGs suggest that, independently on formation redshift, the physical conditions characterizing the formation of a dense spheroid lead to a mass spectrum of new formed stars with an higher ratio of high- to low-mass stars with respect to the IMF of normal local ETGs.

[42]  arXiv:1410.5236 [pdf, ps, other]
Title: The reflection of two past outbursts of Sagittarius A* observed by Chandra during the last decade
Authors: Maïca Clavel (1,2), R. Terrier (1), A. Goldwurm (1,2), M. R. Morris (3), G. Ponti (4), S. Soldi (1), G. Trap (1,2) ((1) APC - Paris, (2) CEA - Saclay, (3) UCLA, (4) MPE - Garching)
Comments: 4 pages, 2 figures, Proceeding of the IAU Symposium 303 "The Galactic Center: Feeding and Feedback in a Normal Galactic Nucleus"
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The supermassive black hole at the Galactic center, Sagittarius A*, has experienced periods of higher activity in the past. The reflection of these past outbursts is observed in the molecular material surrounding the black hole but reconstructing its precise lightcurve is difficult since the distribution of the clouds along the line of sight is poorly constrained. Using Chandra high-resolution data collected from 1999 to 2011 we studied both the 6.4 keV and the 4-8 keV emission of the region located between Sgr A* and the Radio Arc, characterizing its variations down to 15" angular scale and 1-year time scale. The emission from the molecular clouds in the region varies significantly, showing either a 2-year peaked emission or 10-year linear variations. This is the first time that such fast variations are measured. Based on the cloud parameters, we conclude that these two behaviors are likely due to two distinct past outbursts of Sgr A* during which its luminosity rose to at least 10^39 erg/s.

[43]  arXiv:1410.5248 [pdf, other]
Title: SOPHIE velocimetry of Kepler transit candidates. XIV. KOI-189 B and KOI-686 B: two very low-mass stars in long-period orbits
Authors: R. F. Díaz (1,2), G. Montagnier (3,4), J. Leconte (5), A. S. Bonomo (6), M. Deleuil (2), J. M. Almenara (2), S. C. C. Barros (2), F. Bouchy (3,4), G. Bruno (2), C. Damiani (2), G. Hébrard (3,4), C. Moutou (2,7), A. Santerne (2,8,9) ((1) Observatoire Astronomique de l'Université de Genéve, Switzerland, (2) Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille), Marseille, France, (3) Institut d'Astrophysique de Paris, Paris, France, (4) Observatoire de Haute-Provence, Saint-Michel-l'Observatoire, France, (5) Canadian Institute for Theoretical Astrophysics, Toronto, Canada, (6) INAF - Osservatorio Astrofisico di Torino, Pino Torinese, Italy, (7) Canada France Hawaii Telescope Corporation, Kamuela, USA, (8) Centro de Astrofísica, Universidade do Porto, Porto, Portugal, (9) Instituto de Astrofísica e Ciências do Espaco, Porto, Portugal)
Comments: Accepted for publication in Astronomy and Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

We present the radial-velocity follow-up of two Kepler planetary transiting candidates (KOI-189 and KOI-686) carried out with the SOPHIE spectrograph at the Observatoire de Haute Provence. These data promptly discard these objects as viable planet candidates and show that the transiting objects are in the regime of very low-mass stars, where a strong discrepancy between observations and models persists for the mass and radius parameters. By combining the SOPHIE spectra with the Kepler light curve and photometric measurements found in the literature, we obtain a full characterization of the transiting companions, their orbits, and their host stars. The two companions are in significantly eccentric orbits with relatively long periods (30 days and 52.5 days), which makes them suitable objects for a comparison with theoretical models, since the effects invoked to understand the discrepancy with observations are weaker for these orbital distances. KOI-189 B has a mass M = 0.0745 +/- 0.0033 Msun and a radius R = 0.1025 +/- 0.0024 Rsun. The density of KOI-189 B is significantly lower than expected from theoretical models for a system of its age. We explore possible explanations for this difference. KOI-189 B is the smallest hydrogen-burning star with such a precise determination of its fundamental parameters. KOI-686 B is larger and more massive (M = 0.0915 +/- 0.0043 Msun; R = 0.1201 +/- 0.0033 Rsun), and its position in the mass-radius diagram agrees well with theoretical expectations.

[44]  arXiv:1410.5251 [pdf, ps, other]
Title: Calibration and in orbit performance of the reflection grating spectrometer onboard XMM-Newton
Comments: Accepted for publication in Astronomy and Astrophysics, Astronomical instrumentation section
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Context: XMM-Newton was launched on 10 December 1999 and has been operational since early 2000. One of the instruments onboard XMM-Newton is the reflection grating spectrometer (RGS). Two identical RGS instruments are available, with each RGS combining a reflection grating assembly (RGA) and a camera with CCDs to record the spectra. Aims: We describe the calibration and in-orbit performance of the RGS instrument. By combining the preflight calibration with appropriate inflight calibration data including the changes in detector performance over time, we aim at profound knowledge about the accuracy in the calibration. This will be crucial for any correct scientific interpretation of spectral features for a wide variety of objects. Methods: Ground calibrations alone are not able to fully characterize the instrument. Dedicated inflight measurements and constant monitoring are essential for a full understanding of the instrument and the variations of the instrument response over time. Physical models of the instrument are tuned to agree with calibration measurements and are the basis from which the actual instrument response can be interpolated over the full parameter space. Results: Uncertainties in the instrument response have been reduced to < 10% for the effective area and < 6 mA for the wavelength scale (in the range from 8 A to 34 A. The remaining systematic uncertainty in the detection of weak absorption features has been estimated to be 1.5%. Conclusions: Based on a large set of inflight calibration data and comparison with other instruments onboard XMM-Newton, the calibration accuracy of the RGS instrument has been improved considerably over the preflight calibrations.

[45]  arXiv:1410.5255 [pdf, ps, other]
Title: Comparison of Atmospheric Parameters Determined from Spectroscopy and Photometry for DA White Dwarfs in the Sloan Digital Sky Survey
Comments: 52 pages, 25 figures, accepted for publication in the Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a comparative analysis of atmospheric parameters obtained with the so-called photometric and spectroscopic techniques. Photometric and spectroscopic data for 1360 DA white dwarfs from the Sloan Digital Sky Survey (SDSS) are used, as well as spectroscopic data from the Villanova White Dwarf Catalog. We first test the calibration of the ugriz photometric system by using model atmosphere fits to observed data. Our photometric analysis indicates that the ugriz photometry appears well calibrated when the SDSS to AB_95 zeropoint corrections are applied. The spectroscopic analysis of the same data set reveals that the so-called high-log g problem can be solved by applying published correction functions that take into account 3D hydrodynamical effects. However, a comparison between the SDSS and the White Dwarf Catalog spectra also suggests that the SDSS spectra still suffer from a small calibration problem. We then compare the atmospheric parameters obtained from both fitting techniques and show that the photometric temperatures are systematically lower than those obtained from spectroscopic data. This systematic offset may be linked to the hydrogen line profiles used in the model atmospheres. We finally present the results of an analysis aimed at measuring surface gravities using photometric data only.

[46]  arXiv:1410.5262 [pdf, ps, other]
Title: Gravitational redshift of galaxies in clusters from SDSS and BOSS
Comments: 6 pages, 2 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The gravitational redshift effect allows one to directly probe the gravitational potential in clusters of galaxies. As such, it provides a fundamental test of general relativity (GR), and may help to constrain alternative theories of gravity. Following up on Wojtak, Hansen & Hjorth (2011), we present a new measurement. We take advantage of new data from the tenth data release of SDSS and BOSS, covering a range of redshift between 0.05 and 0.6. After selection, our dataset includes 60k galaxies, matched to 12k clusters, with an average cluster mass of $10^{14} M_{\odot}$. The analysis is focused on optimizing the selection method of clusters and of galaxies, taking into account possible systematic biases. We compare the light originating from the brightest cluster galaxies (BCGs), to that of galaxies at the outskirts of clusters. We find that BCGs have an average relative redshift of 11 km/s, with a standard deviation of +7 and -5 km/s. The result is consistent with the measurement of Wojtak et al. and is in good agreement with the predictions from GR. Considering the current systematic uncertainties, we can not distinguish between the baseline GR effect and the recently proposed kinematic modifications.

[47]  arXiv:1410.5266 [pdf, other]
Title: Spiral Arms as Cosmic Ray Source Distributions
Comments: 50 pages, 13 figures, accepted for publication in Astroparticle Physics
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

There is evidence that the distribution of suspected cosmic ray sources are associated with the spiral arm structure of galaxies. It is yet not clearly understood what effect such a cosmic ray source distribution has on the particle transport in our Galaxy. We use the PICARD code to perform high-resolution 3D simulations of electrons and protons in galactic propagation scenarios that include four-arm and two-arm logarithmic spiral cosmic ray source distributions with and without a central bar structure as well as the spiral arm configuration of the NE2001 model for the distribution of free electrons in the Milky Way. Results of these simulation are compared to an axisymmetric radial source distribution. Also, effects on the cosmic ray flux and spectra due to different positions of the Earth relative to the spiral structure are studied. We find that high energy electrons are strongly confined to their sources and the obtained spectra largely depend on the Earth's position relative to the spiral arms. Similar finding have been obtained for low energy protons and electrons albeit at smaller magnitude. We find that even fractional contributions of a spiral arm component to the total cosmic ray source distribution influences the spectra on the Earth. This is apparent when compared to an axisymmetric radial source distribution as well as with respect to the Earth's position relative to the spiral arm structure. We demonstrate that the presence of a Galactic bar manifests itself as an overall excess of low energy electrons at the Earth. Using a spiral arm geometry as a cosmic ray source distributions offers a genuine new quality of modelling and is used to explain features in cosmic ray spectra at the Earth that are else-wise attributed to other propagation effects. We show that realistic cosmic ray propagation scenarios have to acknowledge non-axisymmetric source distributions.[Abbreviated]

[48]  arXiv:1410.5277 [pdf, ps, other]
Title: Cosmological evolution in a two-brane warped geometry model
Comments: 11 pages, Latex style, 4 eps figures and 1 table
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)

We study an effective 4-dimensional scalar-tensor field theory, originated from an underlying brane-bulk warped geometry, to explore the scenario of inflation. It is shown that the inflaton potential naturally emerges from the radion energy-momentum tensor which in turn results into an inflationary model of the Universe on the visible brane that is consistent with the recent results from the Planck's experiment. The dynamics of modulus stabilization from the inflaton rolling condition is demonstrated. The implications of our results in the context of recent BICEP2 results are also discussed.

[49]  arXiv:1410.5279 [pdf, ps, other]
Title: First Investigation of the Combined Impact of Ionizing Radiation and Momentum Winds from a Massive Star on a Self-Gravitating Core
Comments: Accepted for publication in ApJ (12 pages, 15 figures)
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Massive stars shape the surrounding ISM by emitting ionizing photons and ejecting material through stellar winds. To study the impact of the momentum from the wind of a massive star on the surrounding neutral or ionized material, we implemented a new HEALPix-based momentum conserving wind scheme in the Smoothed Particle Hydrodynamics (SPH) code SEREN. A qualitative study of the impact of the feedback from an O7.5-like star on a self gravitating sphere shows that, on its own, the transfer of momentum from a wind onto cold surrounding gas has both a compressing and dispersing effect. It mostly affects gas at low and intermediate densities. When combined with a stellar source's ionizing UV radiation, we find the momentum driven wind to have little direct effect on the gas. We conclude that, during a massive star's main sequence, the UV ionizing radiation is the main feedback mechanism shaping and compressing the cold gas. Overall, the wind's effects on the dense gas dynamics and on the triggering of star formation are very modest. The structures formed in the ionization-only simulation and in the combined feedback simulation are remarkably similar. However, in the combined feedback case, different SPH particles end up being compressed. This indicates that the microphysics of gas mixing differ between the two feedback simulations and that the winds can contribute to the localized redistribution and reshuffling of gas.

[50]  arXiv:1410.5285 [pdf, ps, other]
Title: Self-shadowing Effects of Slim Accretion Disks in Active Galactic Nuclei: Diverse Appearance of the Broad-line Region
Authors: J.-M. Wang (IHEP and NAOC), J. Qiu (IHEP), P. Du (IHEP), L. C. Ho (PKU)
Comments: emulatapj style, 15 pages, 6 figures, in press
Journal-ref: The Astrophysical Journal, 2014
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

Supermassive black holes in active galactic nuclei (AGNs) undergo a wide range of accretion rates, which lead to diversity of appearance. We consider the effects of anisotropic radiation from accretion disks on the broad-line region (BLR), from the Shakura-Sunyaev regime to slim disks with super-Eddington accretion rates. The geometrically thick funnel of the inner region of slim disks produces strong self-shadowing effects that lead to very strong anisotropy of the radiation field. We demonstrate that the degree of anisotropy of the radiation fields grows with increasing accretion rate. As a result of this anisotropy, BLR clouds receive different spectral energy distributions depending on their location relative to the disk, resulting in diverse observational appearance of the BLR. We show that the self-shadowing of the inner parts of the disk naturally produces two dynamically distinct regions of the BLR, depending on accretion rate. These two regions manifest themselves as kinematically distinct components of the broad H$\beta$ line profile with different line widths and fluxes, which jointly account for the Lorentzian profile generally observed in narrow-line Seyfert 1 galaxies. In the time domain, these two components are expected reverberate with different time lags with respect to the varying ionizing continuum, depending on the accretion rate and the viewing angle of the observer. The diverse appearance of the BLR due to the anisotropic ionizing energy source can be tested by reverberation mapping of H$\beta$ and other broad emission lines (e.g., \feii), providing a new tool to diagnose the structure and dynamics of the BLR. Other observational consequences of our model are also explored.

[51]  arXiv:1410.5310 [pdf, ps, other]
Title: Low-temperature spectroscopy of the $^{12}$C$_2$H$_2$ ($\upsilon_1 +\upsilon_3$) band in a helium buffer gas
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Buffer gas cooling with a $^4$He gas is used to perform laser-absorption spectroscopy of the $^{12}$C$_2$H$_2$ ($\nu_1+\nu_3$) band at cryogenic temperatures. Doppler thermometry is first carried out to extract translational temperatures from the recorded spectra. Then, rotational temperatures down to 20 K are retrieved by fitting the Boltzmann distribution to the relative intensities of several ro-vibrational lines. The underlying helium-acetylene collisional physics, relevant for modeling planetary atmospheres, is also addressed. In particular, the diffusion time of $^{12}$C$_2$H$_2$ in the buffer cell is measured against the $^4$He flux at two separate translational temperatures; the observed behavior is then compared with that predicted by a Monte Carlo simulation, thus providing an estimate for the respective total elastic cross sections: $\sigma_{el}(100\ {\rm K})=(4\pm1)\cdot 10^{-20}$ m$^{2}$ and $\sigma_{el}(25\ {\rm K})=(7\pm2)\cdot 10^{-20}$ m$^{2}$.

[52]  arXiv:1410.5320 [pdf, other]
Title: Understanding tidal dissipation in gaseous giant planets : the respective contributions of their core and envelope
Comments: 4 pages, 3 figures, SF2A 2014 proceedings
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Tidal dissipation in planetary interiors is one of the key physical mechanisms that drive the evolution of star-planet and planet-moon systems. New constraints are now obtained both in the Solar and exoplanetary systems. Tidal dissipation in planets is intrinsically related to their internal structure. In particular, fluid and solid layers behave differently under tidal forcing. Therefore, their respective dissipation reservoirs have to be compared. In this work, we compute separately the contributions of the potential dense rocky/icy core and of the convective fluid envelope of gaseous giant planets, as a function of core size and mass. We then compare the associated dissipation reservoirs, by evaluating the frequency-average of the imaginary part of the Love numbers $k^2_2$ in each region. We demonstrate that in general both mechanisms must be taken into account.

[53]  arXiv:1410.5323 [pdf, other]
Title: Cosmic ray propagation with CRPropa 3
Comments: 16th International workshop on Advanced Computing and Analysis Techniques in physics research (ACAT 2014) proceedings, 6 pages, 6 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)

Solving the question of the origin of ultra-high energy cosmic rays (UHECRs) requires the development of detailed simulation tools in order to interpret the experimental data and draw conclusions on the UHECR universe. CRPropa is a public Monte Carlo code for the galactic and extragalactic propagation of cosmic ray nuclei above $\sim 10^{17}$ eV, as well as their photon and neutrino secondaries. In this contribution the new algorithms and features of CRPropa 3, the next major release, are presented. CRPropa 3 introduces time-dependent scenarios to include cosmic evolution in the presence of cosmic ray deflections in magnetic fields. The usage of high resolution magnetic fields is facilitated by shared memory parallelism, modulated fields and fields with heterogeneous resolution. Galactic propagation is enabled through the implementation of galactic magnetic field models, as well as an efficient forward propagation technique through transformation matrices. To make use of the large Python ecosystem in astrophysics CRPropa 3 can be steered and extended in Python.

[54]  arXiv:1410.5325 [pdf, other]
Title: Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA
Comments: Submitted to ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We report the first spectroscopic detection of ethyl cyanide (C$_2$H$_5$CN) in Titan's atmosphere, obtained using spectrally and spatially resolved observations of multiple emission lines with the Atacama Large Millimeter/submillimeter array (ALMA). The presence of C$_2$H$_5$CN in Titan's ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C$_2$H$_5$CNH$^+$. Here we report the detection of 27 rotational lines from C$_2$H$_5$CN (in 19 separate emission features detected at $>3\sigma$ confidence), in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from HC$_3$N, CH$_3$CN and CH$_3$CCH were also obtained. In contrast to HC$_3$N, CH$_3$CN and CH$_3$CCH, which peak in Titan's northern (spring) hemisphere, the emission from C$_2$H$_5$CN is found to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly different chemistry for this species, consistent with a relatively short chemical lifetime for C$_2$H$_5$CN. Radiative transfer models show that most of the C$_2$H$_5$CN is concentrated at altitudes 300-600 km, suggesting production predominantly in the mesosphere and above. Vertical column densities are found to be in the range (2-5)$\times10^{14}$ cm$^{-2}$.

[55]  arXiv:1410.5333 [pdf, ps, other]
Title: On the characterization of transiting exoplanets and magnetic spots with optical interferometry
Comments: 10 pages + 1 appendix, 7 figures. Accepted for publication in Astronomy & Astrophysics
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

Stellar activity causes difficulties in the characterization of transiting exoplanets. Studies have been performed to quantify its impact on infrared interferometry, but not in the visible domain, which however allows reaching better angular resolution and is also the one mostly used for spectroscopic and photometric measurements.
We use a textbook case to make a complete analysis of the impact of an exoplanet and a spot on interferometric observables and relate it to current instruments capabilities, taking into account realistic achievable precisions.
We have built a numerical code called COMETS using analytical formulae to perform a simple comparison of exoplanets and spots' signals. We explore instrumental specificities needed to detect them, like the baseline length required, the accuracy and SNR. We also discuss the impact of exoplanets and spot's parameters on squared visibility and phase.
We find that the main improvement to bring is the sensitivity of instruments. The accuracy on squared visibilities has to be improved by a factor 10 to detect an exoplanet of 0.1 mas, leading to $<0.5%$ precision, along with phase measurements of ~$5^{\deg}$ accuracy beyond the first null of visibility. For a 0.05 mas exoplanet, accuracies of ~$0.1%$ and ~$1^{\deg}$ from the first null are required on squared visibilities and phases, respectively. Magnetic spots can mimic these signals, leading to false exoplanet characterization. Phases measurements from the 3rd lobe is needed to disentangle between a spot and an exoplanet if they have the same radius.
Increasing interferometers sensitivity, more objects will become common between interferometric targets and photometric ones. Furthermore, new missions like PLATO, CHEOPS or TESS will provide bright exoplanets host stars. Measurements will thus overlap and provide a better characterization of stellar activity and exoplanets.

[56]  arXiv:1410.5336 [pdf, other]
Title: How accurate are stellar ages based on stellar models ? I. The impact of stellar models uncertainties
Comments: 83 pages, 46 figures, contribution to the proceedings of the 13rd Evry Schatzman School on Stellar Astrophysics, "The Ages of Stars", Roscoff 2013, EAS Publications Series, eds. Y. Lebreton, D. Valls-Gabaud, C. Charbonnel
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Among the various methods used to age-date stars, methods based on stellar model predictions are widely used, for nearly all kind of stars in large ranges of masses, chemical compositions and evolutionary stages. The precision and accuracy on the age determination depend on both the precision and number of observational constraints, and on our ability to correctly describe the stellar interior and evolution. The imperfect input physics of stellar models as well as the uncertainties on the initial chemical composition of stars are responsible for uncertainties in the age determination. We present an overview of the calculation of stellar models and discuss the impact on age of their numerous inputs.

[57]  arXiv:1410.5337 [pdf, other]
Title: How accurate are stellar ages based on stellar models? II. The impact of asteroseismology
Comments: 49 pages, 20 figures, contribution to the proceedings of the 13rd Evry Schatzman School on Stellar Astrophysics, "The Ages of Stars", Roscoff 2013, EAS Publications Series, eds. Y. Lebreton, D. Valls-Gabaud, C. Charbonnel
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Accurate and precise stellar ages are best determined for stars which are strongly observationally constrained, that is which are intrinsically oscillating. We review here the seismic diagnostics which are sensitive to stellar ages and provide some illustrating examples of seismically age-dated stars.

[58]  arXiv:1410.5354 [pdf, ps, other]
Title: Discriminant analysis of solar bright points and faculae II. Contrast and morphology analysis
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Taken at a high spatial resolution of 0.1 arcsec, Bright Points (BPs) are found to coexist with faculae in images and the latter are often resolved as adjacent striations. Understanding the properties of these different features is fundamental to carrying out proxy magnetometry. To shed light on the relationship between BPs and faculae, we studied them separately after the application of a classification method, developed and described in a previous paper) on active region images at various heliocentric angles. In this Paper, we explore different aspects of the photometric properties of BPs and faculae, namely their G-band contrast profiles, their peak contrast in G-band and continuum, as well as morphological parameters. We find that: (1) the width of the contrast profiles of the classified BPs and faculae are consistent with studies of disk center BPs at and limb faculae, which indirectly confirms the validity of our classification, (2) the profiles of limb faculae are limbward skewed on average, while near disk center they exhibit both centerward and limbward skewnesses due to the distribution of orientations of the faculae, (3) the relation between the peak contrasts of BPs and faculae and their apparent area discloses a trend reminiscent of magnetogram studies. The skewness of facular profiles provides a novel constraint for 3D MHD models of faculae. As suggested by the asymmetry and orientation of their contrast profiles, faculae near disk center could be induced by inclined fields, while apparent BPs near the limb seem to be in fact small faculae misidentified. The apparent area of BPs and faculae could be possibly exploited for proxy magnetometry.

[59]  arXiv:1410.5363 [pdf, ps, other]
Title: Close stellar binary systems by grazing envelope evolution
Authors: Noam Soker (Technion, Israel)
Comments: Submitted as a Letter
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

I suggest a spiral-in process by which a stellar companion graze the envelope of a giant star while both the orbital separation and the giant radius shrink simultaneously, and a close binary system is formed. The binary system might be viewed as evolving in a constant state of `just entering a common envelope (CE) phase'. In cases where this process takes place it can be an alternative to the CE evolution where the secondary star is immerses in the giant's envelope. The grazing envelope evolution (GEE) is made possible only if the companion manages to accreted mass at a high rate and launch jets that remove the outskirts of the giant envelope, hence preventing the formation of a CE . The high accretion rate is made possible by the accretion disk that launches jets that efficiently carry the excess angular momentum and energy from the accreted mass. Mass loss through the second Lagrangian point can carry additional angular momentum and envelope mass. The GEE lasts for tens to hundreds of years. The high accretion rate with peaks lasting months to years might lead to a bright object termed intermediate luminosity optical transient (ILOT; Red Novae; Red Transients). A bipolar nebula and/or equatorial ring are formed around the binary remnant.

[60]  arXiv:1410.5367 [pdf, other]
Title: Constraints on Very High Energy Emission from GRB 130427A
Comments: 22 pages, 4 figures, 1 table
Journal-ref: Astrophysical Journal Letters, 795, 2014, L3
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Prompt emission from the very fluent and nearby (z=0.34) gamma-ray burst GRB 130427A was detected by several orbiting telescopes and by ground-based, wide-field-of-view optical transient monitors. Apart from the intensity and proximity of this GRB, it is exceptional due to the extremely long-lived high-energy (100 MeV to 100 GeV) gamma-ray emission, which was detected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope for ~70 ks after the initial burst. The persistent, hard-spectrum, high-energy emission suggests that the highest-energy gamma rays may have been produced via synchrotron self-Compton processes though there is also evidence that the high-energy emission may instead be an extension of the synchrotron spectrum. VERITAS, a ground-based imaging atmospheric Cherenkov telescope array, began follow-up observations of GRB 130427A ~71 ks (~20 hr) after the onset of the burst. The GRB was not detected with VERITAS; however, the high elevation of the observations, coupled with the low redshift of the GRB, make VERITAS a very sensitive probe of the emission from GRB 130427A for E > 100 GeV. The non-detection and consequent upper limit derived place constraints on the synchrotron self-Compton model of high-energy gamma-ray emission from this burst.

[61]  arXiv:1410.5380 [pdf, other]
Title: A self-consistent and time-dependent hybrid blazar emission model - Properties and application
Comments: 9 pages, 7 figures
Journal-ref: Astronomy and Astrophysics, 09 October 2014
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

A time-dependent emission model for blazar jets, taking acceleration due to Fermi-I and Fermi-II processes for electrons and protons as well as all relevant radiative processes self-consistently into account, is presented. The presence of highly relativistic protons within the jet extends the simple synchrotron self-Compton case not only in the very high energy radiation of blazars, but also in the X-ray regime, introducing non-linear behaviour in the emitting region of the model by photon-meson production and emerging electron positron pair cascades. We are able to investigate the variability patterns of blazars in terms of our model in all energy bands, thus narrowing down the parameters used. The blazar 1 ES 1011+496 serves as an example of how this model is applied to high frequency peaked BL Lac Objects in the presence of non-thermal protons within the jet. Typical multiband patterns are derived, which are experimentally accessible.

[62]  arXiv:1410.5383 [pdf, ps, other]
Title: Resonance capture at arbitrary inclination
Comments: 16 pages. Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Resonance capture is studied numerically in the three-body problem for arbitrary inclinations. Massless particles are set to drift from outside the 1:5 resonance with a Jupiter-mass planet thereby encountering the web of the planet's diverse mean motion resonances. Randomly constructed samples explore parameter space for inclinations from 0 to 180 deg with 5deg increments totalling nearly 6x10^5 numerical simulations. Thirty resonances internal and external to the planet's location are monitored. We find that retrograde resonances are unexpectedly more efficient at capture than prograde resonances and that resonance order is not necessarily a good indicator of capture efficiency at arbitrary inclination. Capture probability drops significantly at moderate sample eccentricity for initial inclinations in the range [10deg,110deg]. Orbit inversion is possible for initially circular orbits with inclinations in the range [60deg,130deg]. Capture in the 1:1 coorbital resonance occurs with great likelihood at large retrograde inclinations. The planet's orbital eccentricity, if larger than 0.1, reduces the capture probabilities through the action of the eccentric Kozai-Lidov mechanism. A capture asymmetry appears between inner and outer resonances as prograde orbits are preferentially trapped in inner resonances. The relative capture efficiency of retrograde resonance suggests that the dynamical lifetimes of Damocloids and Centaurs on retrograde orbits must be significantly larger than those on prograde orbits implying that the recently identified asteroids in retrograde resonance, 2006 BZ8, 2008 SO218, 2009 QY6 and 1999 LE31(Morais and Namouni, 2013, MNRAS 436, L30) may be among the oldest small bodies that wander between the outer giant planets.

[63]  arXiv:1410.5395 [pdf, other]
Title: Trends in Dwarf Early-Type Kinematics with Cluster-centric Radius Driven By Tidal Stirring
Authors: A. J. Benson (1), E. Toloba (1 and 2), L. Mayer (3 and 4), J. D. Simon (1), P. Guhathakurta (2) ((1) Observatories of the Carnegie Institution for Science, (2) UCO/Lick Observatory, University of California, (3) Institute for Astronomy, ETH Zurich, (4) Institute for Theoretical Physics, University of Zurich)
Comments: 5 pages, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We model the dynamics of dwarf early-type galaxies in the Virgo cluster when subject to a variety of environmental processes. We focus on how these processes imprint trends in dynamical state (rotational vs. pressure support as measured by the $\lambda^*_{\rm Re/2}$ statistic) with projected distance from the cluster center, and compare these results to observational estimates. We find a large scatter in the gradient of $\lambda^*_{\rm Re/2}$ with projected radius. A statistical analysis shows that models with no environmental effects produce gradients as steep as those observed in none of the 100 cluster realizations we consider, while in a model incorporating tidal stirring by the cluster potential 34% of realizations produce gradients as steep as that observed. Our results suggest that tidal stirring may be the cause of the observed radial dependence of dwarf early-type dynamics in galaxy clusters.

[64]  arXiv:1410.5408 [pdf, other]
Title: New insights on Saturn's formation from its nitrogen isotopic composition
Comments: Accepted for publication in Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The recent derivation of a lower limit for the $^{14}$N/$^{15}$N ratio in Saturn's ammonia, which is found to be consistent with the Jovian value, prompted us to revise models of Saturn's formation using as constraints the supersolar abundances of heavy elements measured in its atmosphere. Here we find that it is possible to account for both Saturn's chemical and isotopic compositions if one assumes the formation of its building blocks at $\sim$45 K in the protosolar nebula, provided that the O abundance was $\sim$2.6 times protosolar in its feeding zone. To do so, we used a statistical thermodynamic model to investigate the composition of the clathrate phase that formed during the cooling of the protosolar nebula and from which the building blocks of Saturn were agglomerated. We find that Saturn's O/H is at least $\sim$34.9 times protosolar and that the corresponding mass of heavy elements ($\sim$43.1 \Mearth) is within the range predicted by semi-convective interior models.