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[1]  arXiv:1412.6097 [pdf, ps, other]
Title: Scientific Return of Coronagraphic Exoplanet Imaging and Spectroscopy Using WFIRST
Authors: Adam Burrows
Comments: A study outlining the scientific case for a high-contrast coronagraph on WFIRST in support of its exoplanet campaign, performed on behalf of the WFIRST/AFTA Science Definition Team and the Exo-S and Exo-C Science and Technology Definition Teams
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

In this study, we explore and review the scientific potential for exoplanet characterization by a high-contrast optical coronagraph on WFIRST/AFTA. We suggest that the heterogeneity in albedo spectra and planet/star flux ratios as a function of orbital distance, planet mass, and composition expected for the giant exoplanets at separations from their primaries accessible to WFIRST will provide unique constraints on giant planet atmospheres, evolution, aerosol and cloud properties, and general theory. Such exoplanets are not merely extrapolations of Jupiter and Saturn, but are likely to occupy a rich continuum of varied behaviors. Each in themselves and jointly, optical spectra, photometry, and polarization measurements of a diverse population of giant exoplanets in the solar neighborhood has the potential to reveal a multitude of fundamental features of their gas-giant chemistry, atmospheres, and formation. Such a campaign will enrich our understanding of this class of planets beyond what is possible with even a detailed exploration of the giants in our own solar system, and will compliment ongoing studies of exoplanets in the infrared and on close-in orbits inaccessible to coronagraphy.

[2]  arXiv:1412.6099 [pdf, other]
Title: Distinguishing Dark Matter from Unresolved Point Sources in the Inner Galaxy with Photon Statistics
Comments: 27 pages, 8 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

Data from the Fermi Large Area Telescope suggests that there is an extended excess of GeV gamma-ray photons in the Inner Galaxy. Identifying potential astrophysical sources that contribute to this excess is an important step in verifying whether the signal originates from annihilating dark matter. In this paper, we focus on the potential contribution of unresolved point sources, such as millisecond pulsars (MSPs). We propose that the statistics of the photons---in particular, the flux probability distribution function (PDF) of the photon counts below the point-source detection threshold---can potentially distinguish between the dark-matter and point-source interpretations. We calculate the flux PDF via the method of generating functions for these two models of the excess. Working in the framework of Bayesian model comparison, we then demonstrate that the flux PDF can potentially provide evidence for an unresolved MSP-like point-source population.

[3]  arXiv:1412.6100 [pdf, ps, other]
Title: Stable Umbral Chromospheric Structures
Comments: Accepted to Astronomy and Astrophysics. Online material (Fig3.mov and Fig4.mov) will be available at A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Aims. To understand the morphology of the chromosphere in sunspot umbra. We investigate if the horizontal structures observed in the spectral core of the Ca II H line are ephemeral visuals caused by the shock dynamics of more stable structures, and examine their relationship with observables in the H-alpha line. Methods. Filtergrams in the core of the Ca II H and H-alpha lines as observed with the Swedish 1-m Solar Telescope are employed. We utilise a technique that creates composite images and tracks the flash propagation horizontally. Results. We find 0"15 wide horizontal structures, in all of the three target sunspots, for every flash where the seeing was moderate to good. Discrete dark structures are identified that are stable for at least two umbral flashes, as well as systems of structures that live for up to 24 minutes. We find cases of extremely extended structures with similar stability, with one such structure showing an extent of 5". Some of these structures have a correspondence in H-alpha but we were unable to find a one to one correspondence for every occurrence. If the dark streaks are formed at the same heights as umbral flashes then there are systems of structures with strong departures from the vertical for all three analysed sunspots. Conclusions. Long-lived Ca II H filamentary horizontal structures are a common and likely ever-present feature in the umbra of sunspots. If the magnetic field in the chromosphere of the umbra is indeed aligned with the structures, then the present theoretical understanding of the typical umbra needs to be revisited.

[4]  arXiv:1412.6101 [pdf, ps, other]
Title: Direct Spectrum of the Benchmark T dwarf HD 19467 B
Comments: Accepted to ApJ Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R~30 observations obtained simultaneously across the $JH$ bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5+/-1 dwarf with effective temperature Teff=$978^{+20}_{-43}$ K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.

[5]  arXiv:1412.6104 [pdf, other]
Title: Chiral Imprint of a Cosmic Gauge Field on Primordial Gravitational Waves
Comments: 5 pages, 6 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

A cosmological gauge field with isotropic stress-energy introduces parity violation into the behavior of gravitational waves. We show that a primordial spectrum of inflationary gravitational waves develops a preferred handedness, left- or right-circularly polarized, depending on the abundance and coupling of the gauge field during the radiation era. A modest abundance of the gauge field would induce parity-violating correlations of the cosmic microwave background temperature and polarization patterns that could be detected by current and future experiments.

[6]  arXiv:1412.6105 [pdf, ps, other]
Title: The early phases of galaxy clusters formation in IR: coupling hydrodynamical simulations with GRASIL3D
Comments: 12 pages, 10 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We compute and study the infrared and sub-mm properties of high redshift (z>1) simulated clusters and proto-clusters, by coupling the results of a large set of hydro-dynamical zoom-in simulations including active galactic nuclei (AGN) feedback (Ragone-Figueroa et al. 2013), with the recently developed radiative transfer code GRASIL3D (Dominguez-Tenreiro et al. 2014), which accounts for the effect of dust reprocessing in an arbitrary geometry, and we customized for the present purpose. While this field is in its infancy from the observational point of view, a rapid development is expected in the near future, thanks to observations performed in the far IR and sub-mm bands. Notably, we find that in this spectral regime our prediction are little affected by the assumption required by this post-processing, and the emission is mostly powered by star formation rather than accretion onto super massive black hole (SMBH). The comparison with the little observational information available so far, highlights that the simulated cluster regions never attain the impressive star formation rates suggested by these observations. This problem becomes more intriguing taking into account that the brightest cluster galaxies (BCGs) in the same simulations turns out to be too massive (Ragone-Figueroa et al. 2013). It seems that the interplay between the feedback schemes and the starformation model should be revised, possibly incorporating a positive feedback mode.

[7]  arXiv:1412.6109 [pdf, other]
Title: Kepler Flares III: Stellar Activity on GJ 1245 A and B
Comments: 15 pages, 10 figures, 2 tables. Accepted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present the flare occurrence rates and starspot evolution for GJ 1245 A and B, two active M5 stars, based on nine months of Kepler short cadence observations, and four years of nearly continuous long cadence observations. The A component is separated from the B component by 7 arcseconds, and the stars are not resolved in the Kepler pipeline processing due to Kepler's large plate scale of 4 arcseconds/pixel. Analyzing the target pixel data, we have generated separate light curves for components A and B using the PyKE pixel response function modeling procedures, and note the effects of CCD saturation and non-linear response to high energy flares. In our sample, GJ 1245A and B exhibit an average of 3.0 and 2.6 flares per day, respectively. We introduce a new metric, $L_{fl}/L_{\mathrm{Kp}}$, to compare the flare rates between stars, and discuss this in the context of GJ 1245 A and B. Both stars exhibit starspot features that evolve on long time scales, with the slower rotating B component showing evidence of differential rotation. Intriguingly, the angular separation between the A and B component photocenters decreases during the four years of observations in a manner consistent with a shift in the position of the A photocenter due to the orbit of its unseen M8 companion (GJ 1245C), which is $\sim$94% less bright. Among the most detailed photometric studies of fully convective M dwarfs in a multiple system, these results provide an important constraint on stellar age-rotation-activity models.

[8]  arXiv:1412.6110 [pdf, ps, other]
Title: Constraints on Radial Migration in Spiral Galaxies I. Analytic Criterion for Capture at Corotation
Comments: 21 pages, 10 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Near the corotation resonance of a transient spiral arm, stellar orbital angular momenta may be changed without inducing significant kinematic heating, resulting in what has come to be known as radial migration. When radial migration is very efficient, a large fraction of disk stars experiences significant, permanent changes to their individual orbital angular momenta over the lifetime of the disk, having strong implications for the evolution of disk galaxies. The first step for a star in a spiral disk to migrate radially is to be captured in a "trapped" orbit, associated with the corotation resonance of the spiral pattern. An analytic criterion for determining whether or not a star is in a trapped orbit has previously been derived only for stars with zero random orbital energy in the presence of a spiral with fixed properties. In this first paper in a series, we derive an analytic criterion appropriate for a star that is on an orbit of finite random orbital energy. Our new criterion demonstrates that whether or not a star is in a "trapped" orbit primarily depends on the star's orbital angular momentum. This criterion could be a powerful tool in the interpretation of the results of N-body simulations. In future papers of this series, we apply our criterion to explore the physical parameters important to determining the efficiency of radial migration and its potential importance to disk evolution.

[9]  arXiv:1412.6114 [pdf, other]
Title: An Origami Approximation to the Cosmic Web
Authors: Mark C. Neyrinck (JHU)
Comments: 6 pages, 5 figures. Proceedings of IAU Symposium 308 "The Zeldovich Universe: Genesis and Growth of the Cosmic Web", 23-28 June 2014, Tallinn, Estonia. Interactive tetrahedral-collapse model at this http URL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The powerful Lagrangian view of structure formation was essentially introduced to cosmology by Zel'dovich. In the current cosmological paradigm, a dark-matter-sheet 3D manifold, inhabiting 6D position-velocity phase space, was flat (with vanishing velocity) at the big bang. Afterward, gravity stretched and bunched the sheet together in different places, forming a cosmic web when projected to the position coordinates. Here, I explain some properties of an origami approximation, in which the sheet does not stretch or contract (an assumption that is false in general), but is allowed to fold. Even without stretching, the sheet can form an idealized cosmic web, with convex polyhedral voids separated by straight walls and filaments, joined by convex polyhedral nodes. The nodes form in 'polygonal' or 'polyhedral' collapse, somewhat like spherical/ellipsoidal collapse, except incorporating simultaneous filament and wall formation. The origami approximation allows phase-space geometries of nodes, filaments, and walls to be more easily understood, and may aid in understanding spin correlations between nearby galaxies. This contribution explores kinematic origami-approximation models giving velocity fields for the first time.

[10]  arXiv:1412.6117 [pdf, other]
Title: Simultaneous Linear and Circular Optical Polarimetry of Asteroid (4) Vesta
Authors: Sloane J. Wiktorowicz (1), Larissa A. Nofi (1 and 2) ((1) University of California, Santa Cruz, (2) Institute for Astronomy, University of Hawaii)
Comments: Accepted for publication to ApJ Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

From a single, 3.8-hour observation of asteroid (4) Vesta at $13.7^\circ$ phase angle with the POLISH2 polarimeter at the Lick Observatory Shane 3-m telescope, we confirm rotational modulation of linear polarization in $B$ and $V$ bands. We measure the peak-to-peak modulation in degree of linear polarization to be $\Delta P = (294 \pm 35) \times 10^{-6}$ (ppm) and time-averaged $\Delta P / P = 0.0577 \pm 0.0069$. After rotating the plane of linear polarization to the scattering plane, asteroidal rotational modulation is detected with $12 \sigma$ confidence and observed solely in Stokes $Q/I$. POLISH2 simultaneously measures Stokes $I$, $Q$, $U$ (linear polarization), and $V$ (circular polarization), but we detect no significant circular polarization with a $1 \sigma$ upper limit of 140 ppm in $B$ band. Circular polarization is expected to arise from multiple scattering of sunlight by rough surfaces, and it has previously been detected in nearly all other classes of Solar System bodies save asteroids. Subsequent observations may be compared with surface albedo maps from the Dawn Mission, which may allow identification of compositional variation across the asteroidal surface. These results demonstrate the high accuracy achieved by POLISH2 at the Lick 3-m telescope, which is designed to directly detect scattered light from spatially unresolvable exoplanets.

[11]  arXiv:1412.6119 [pdf, other]
Title: Dark Matter-induced Collapse of Neutron Stars: A Possible Link Between Fast Radio Bursts and the Missing Pulsar Problem
Comments: Submitted to MNRAS Letters. Comments welcome
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Fast radio bursts (FRBs) are an emerging class of short and bright radio transients whose sources remain enigmatic. Within the galactic center, the non-detection of pulsars within the inner $\sim \!10\,{\rm pc}$ has created a missing pulsar problem that has intensified with time. With all reserve, we advance the notion that the two problems could be linked by a common solution: the collapse of neutron stars (NS) due to capture and sedimentation of dark matter (DM) within their cores. Bramante \& Linden (2014), Phys.\ Rev.\ Lett.~19, 191301 showed that certain DM properties allow for rapid NS collapse within the high DM density environments near galactic centers while permitting NS survival elsewhere. Each DM-induced collapse could generate an FRB as the NS magnetosphere is suddenly expelled. This scenario could explain several features of FRBs: their short time scales, large energies, locally produced scattering tails, and high event rates. Our scenario predicts that FRBs are localized to galactic centers, and that our own galactic center harbors a large population of NS-mass ($M\sim1.4 M_\odot$) black holes. The DM-induced collapse scenario is intrinsically unlikely because it can only occur in a small region of allowable DM parameter space. However, if observed to occur, it would place tight constraints on DM properties.

[12]  arXiv:1412.6120 [pdf, ps, other]
Title: Characterization of the Most Luminous Star in M33: A Super Symbiotic Binary
Comments: 17 pages, 2 figures, submitted to ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We present the first spectrum of the most luminous infrared star in M33, and use it to demonstrate that the object is almost certainly a binary composed of a massive O star and a dust-enshrouded Red Hypergiant. This is the most luminous symbiotic binary ever discovered. Its radial velocity is an excellent match to that of the hydrogen gas in the disk of M33, supporting our interpretation that it is a very young and massive binary star.

[13]  arXiv:1412.6121 [pdf, other]
Title: The Chandra Deep Group Survey -- cool core evolution in groups and clusters of galaxies
Comments: Accepted by MNRAS, 24 pages, 11 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

We report the results of a study which assembles deep observations with the ACIS-I instrument on the Chandra Observatory to study the evolution in the core properties of a sample of galaxy groups and clusters out to redshifts $z\approx 1.3$. A search for extended objects within these fields yields a total of 62 systems for which redshifts are available, and we added a further 24 non-X-ray-selected clusters, to investigate the impact of selection effects and improve our statistics at high redshift. Six different estimators of cool core strength are applied to these data: the entropy (K) and cooling time ($t_{cool}$) within the cluster core, the cooling time as a fraction of the age of the Universe ($t_{cool}/t_{Uni}$), and three estimators based on the cuspiness of the X-ray surface brightness profile. A variety of statistical tests are used to quantify evolutionary trends in these cool core indicators. In agreement with some previous studies, we find that there is significant evolution in $t_{cool}/t_{Uni}$, but little evolution in $t_{cool}$, suggesting that gas is accumulating within the core, but that the cooling time deep in the core is controlled by AGN feedback. We show that this result extends down to the group regime and appears to be robust against a variety of selection biases (detection bias, archival biases and biases due to the presence of central X-ray AGN) which we consider.

[14]  arXiv:1412.6152 [pdf, other]
Title: Polyspectra searches for sharp oscillatory features in cosmic microwave sky data
Comments: 25 pages, 23 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We undertake a thorough search for signatures of sharp oscillatory features in the WMAP9 power spectrum and bispectrum as well as in the Planck power spectrum. For the first time, we carry out searches in both the power spectrum and bispectrum simultaneously, employing well-defined look-elsewhere statistics to assess significances in a rigorous manner. Developing efficient methods to scan power spectrum likelihoods for oscillatory features, we present results for the phenomenological bare sine and cosine modulations, allowing validation against existing Planck Likelihood surveys, as well as templates that include the correct sharp feature scaling. In particular, we study degeneracies between feature and cosmological parameters. For frequencies beyond the scale set by the acoustic peaks, the dependencies are realised through uninteresting adjustments of the comoving distance to last scattering. Hence, it is sufficient to keep cosmological parameters fixed and employ fast Gaussian approximations to the likelihood as a function of the feature model amplitude. In cases where results can be compared to the literature, our method shows excellent agreement. We supplement results from the Planck Likelihood with an analysis based on the Planck SMICA component separation map that, working on the assumption that the component separation algorithm is reliable, allows for the inclusion of a larger sky fraction. In principle, this allows us to place the most stringent constraints to date on the amplitudes of feature models in the temperature power spectrum. Invoking the WMAP bispectrum, we perform a combined power spectrum and bispectrum survey. We use and slightly generalise statistics developed in previous work to reliably judge the significance of large feature model amplitude estimates. We conclude that our results are entirely consistent with a featureless realisation of a Gaussian CMB.

[15]  arXiv:1412.6158 [pdf, other]
Title: Field topologies in ideal and near ideal magnetohydrodynamics and vortex dynamics
Authors: B. C. Low
Comments: Review article, 20 pages, 2 figures, 158 references. see this http URL
Journal-ref: Science China - Physics, Mechanics and Astronomy 2015 Vol. 58 No. 1: 015201
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Magnetic field topology frozen in ideal magnetohydrodynamics (MHD) and its breakage in near ideal MHD are reviewed in two parts. The first part gives a physically complete description of the frozen in field topology, taking magnetic flux conservation as fundamental and treating four topics, Eulerian and Lagrangian descriptions of MHD, Chandrasekhar-Kendall and Euler-potential field representations, magnetic helicity, and inviscid vortex dynamics in comparison to ideal MHD. A corollary clarifies the challenge of achieving a high degree of the frozen in condition in numerical MHD. The second part treats field topology breakage centered on the Parker Magnetostatic Theorem on a general incompatibility of a continuous magnetic field with the dual demand of force free equilibrium and an arbitrarily prescribed, 3D field topology. Preserving field topology as a global constraint readily results in formation of tangential magnetic discontinuities, i.e., electric current sheets of zero thickness. A similar incompatibility is present in the steady, force and thermal balance of a heated radiating fluid subject to an anisotropic thermal flux conducted strictly along the frozen in magnetic field in the low beta limit. In a weakly resistive fluid the thinning of current sheets by these incompatibilities inevitably results in sheet dissipation, resistive heating and topological changes in the field despite the small resistivity. Faraday induction drives but also macroscopically limits this mode of energy dissipation, storing free energy in self organized, ideal MHD structures. This property of MHD turbulence captured by the Taylor hypothesis is reviewed in relation to the Sun's corona, calling for a basic quantitative description of the breakdown of flux conservation in the low resistivity limit. A cylindrical, initial boundary value problem provides specificity in the review.

[16]  arXiv:1412.6178 [pdf, ps, other]
Title: Multi-filter transit observations of WASP-39b and WASP-43b with three San Pedro Mártir telescopes
Comments: 13 pages, 7 figures, accepted in PASP, scheduled for the February 1, 2015 issue
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Three optical telescopes located at the San Pedro M\'artir National Observatory were used for the first time to obtain multi-filter defocused photometry of the transiting extrasolar planets WASP-39b and WASP-43b. We observed WASP-39b with the 2.12m telescope in the U filter for the first time, and additional observations were carried out in the R and I filters using the 0.84m telescope. WASP-43b was observed in VRI with the same instrument, and in the i filter with the robotic 1.50m telescope. We reduced the data using different pipelines and performed aperture photometry with the help of custom routines, in order to obtain the light curves. The fit of the light curves (1.5--2.5mmag rms), and of the period analysis, allowed a revision of the orbital and physical parameters, revealing for WASP-39b a period ($4.0552947 \pm 9.65 \times 10^{-7}$ days) which is $3.084 \pm 0.774$ seconds larger than previously reported. Moreover, we find for WASP-43b a planet/star radius ($0.1738 \pm 0.0033$) which is $0.01637 \pm 0.00371$ larger in the i filter with respect to previous works, and that should be confirmed with additional observations. Finally, we confirm no evidence of constant period variations in WASP-43b.

[17]  arXiv:1412.6189 [pdf, ps, other]
Title: Dust in the Torus of the AGN Unified Model
Authors: Rachel E. Mason
Comments: Submitted to Planetary & Space Science
Subjects: Astrophysics of Galaxies (astro-ph.GA)

These proceedings are based on an invited review talk at the 7th Meeting on Cosmic Dust. The scope of the meeting was broad, covering dust-related topics in areas from comets to debris disks and high-redshift galaxies. This is therefore intended to be an accessible, introductory overview of the dusty torus of the AGN unified model, aimed at summarizing our current understanding of the torus and with some emphasis on the solid-state spectral features observed.

[18]  arXiv:1412.6203 [pdf, ps, other]
Title: Spiral Density Waves in M81. II. Hydrodynamic Simulations for Gas Response to Stellar Spiral Density Waves
Comments: 20 pages, 10 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Gas response to the underlying stellar spirals is explored for M81 using unmagnetized hydrodynamic simulations. Constrained within the uncertainty of observations, 18 simulations are carried out to study the effects of selfgravity and to cover the parameter space comprising three different sound speeds and three different arm strengths. The results are confronted with those data observed at wavelengths of 8 $\mu$m and 21 cm. In the outer disk, the ring-like structure observed in 8 $\mu$m image is consistent with the response of cold neutral medium with an effective sound speed 7 km s$^{-1}$, while for the inner disk, the presence of spiral shocks can be understood as a result of 4:1 resonances associated with the warm neutral medium with an effective sound speed 19 km s$^{-1}$. Simulations with single effective sound speed alone cannot simultaneously explain the structures in the outer and inner disks. This justifies the coexistence of cold and warm neutral media in M81. The anomalously high streaming motions observed in the northeast arm and the outward shifted turning points in the iso-velocity contours seen along the southwest arm are interpreted as signatures of interactions with companion galaxies. The level of simulated streaming motions narrows down the uncertainty of observed arm strength toward larger amplitudes.

[19]  arXiv:1412.6227 [pdf, other]
Title: Modeling the Initial Conditions of Interacting Galaxy Pairs Using Identikit
Comments: 18 pages, 13 figures, 3 Tables, Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We develop and test an automated technique to model the dynamics of interacting galaxy pairs. We use Identikit (Barnes & Hibbard 2009; Barnes 2011) as a tool for modeling and matching the morphology and kinematics of the interacting pairs of equal-mass galaxies. In order to reduce the effect of subjective human judgement, we automate the selection of phase-space regions used to match simulations to data, and we explore how selection of these regions affects the random uncertainties of parameters in the best-fit model. In this work, we used an independent set of GADGET SPH simulations as input data, to determine the systematic bias in the measured encounter parameters based on the known initial conditions of these simulations. We tested both cold gas and young stellar components in the GADGET simulations to explore the effect of choosing HI vs. H$\alpha$ as the line of sight velocity tracer. We found that we can group the results into tests with good, fair, and poor convergence based on the distribution of parameters of models close to the best-fit model. For tests with good and fair convergence, we rule out large fractions of parameter space and recovered merger stage, eccentricity, viewing angle, and pericentric distance within 2$\sigma$ of the correct value. All of tests on gaseous component of prograde systems have either good or fair convergence. Retrograde systems and most of tests on young stars do not converge and may require constraints from regions other than the tidal tails and bridges.

[20]  arXiv:1412.6230 [pdf, other]
Title: Using the Inclinations of Kepler Systems to Prioritize New Titius-Bode-Based Exoplanet Predictions
Comments: 19 pages, 5 figures. Submitted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We analyze a sample of multiple-exoplanet systems which contain at least 3 transiting planets detected by the Kepler mission ("Kepler multiples"). We use a generalized Titius-Bode relation to predict the periods of 228 additional planets in 151 of these Kepler multiples. These Titius-Bode-based predictions suggest that there are, on average, ~2 planets in the habitable zone of each star. We estimate the inclination of the invariable plane for each system and prioritize our planet predictions by their geometric probability to transit. We highlight a short list of 77 predicted planets in 40 systems with a high geometric probability to transit, resulting in an expected detection rate of ~15%, ~3 times higher than the detection rate of our previous Titius-Bode-based predictions.

[21]  arXiv:1412.6233 [pdf, ps, other]
Title: Summary of the 2014 IACHEC Meeting
Authors: David Burrows (1), Fabio Gastaldello (2), Catherine E.Grant (3), Matteo Guainazzi (4), Kristin Madsen (5), Eric Miller (3), Jukka Nevalainen (6), Paul P.Plucinsky (7), Steve Sembay (8) ((1) Pennsylvania University, (2) INAF - IASF Milano, (3) MIT Kavli Institute for Astrophysics and Space Research, (4) European Space Astronomy Centre of ESA, (5) Space Radiation Lab., California Institute of Technology, (6) University of Tartu, (7) Harvard-Smithsonian Centre for Astrophysics, (8) Department of Physics and Astronomy, University of Leicester)
Comments: International Astronomical Consortium for High-Energy Calibration, IACHEC: this http URL
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present the main results of the 9th meeting of the International Astronomical Consortium for High Energy Calibration (IACHEC), held in Warrenton (Virginia) in May 2014. Over 50 scientists directly involved in the calibration of operational and future high-energy missions gathered during 3.5 days to discuss the status of the X-ray payloads inter-calibration, as well as possible ways to improve it. Sect.2 of this Report summarises our current understanding of the energy-dependent inter-calibration status.

[22]  arXiv:1412.6240 [pdf, other]
Title: IceCube Neutrino Events from Fermi Bubbles
Comments: 7pages, 6 figures. To appear in the proceedings of the 59th annual conference of the South African Institute of Physics, 7-11 July 2014
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The IceCube Neutrino Observatory announced thirty-seven candidate events observed with deposited energies above $\sim$ 30 TeV with three-year dataset, more than expected from atmospheric backgrounds. We discuss the detectability of the Fermi Bubbles (FB) by IceCube and show that up to 6 -- 7 of the 37 events could originate from the FB. If the observed gamma rays from the FB are created due to baryonic mechanism, high-energy ($>$ GeV) neutrinos should be emitted as a counterpart. These neutrinos should be detectable as shower- or track-like events at a Km$^3$ neutrino detector. For a hard primary cosmic-ray proton spectrum, $E^{-2.1}$, and cutoff energy at or above 10 PeV, the FB flux substantially exceeds the atmospheric backgrounds. For a steeper spectrum, $E^{-2.3}$, and/or lower cutoff energy, detection with high significance will require a longer running time.

[23]  arXiv:1412.6256 [pdf, other]
Title: Modeling Complex Organic Molecules in dense regions: Eley-Rideal and complex induced reaction
Comments: 14 pages, 12 figures, 8 tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Recent observations have revealed the existence of Complex Organic Molecules (COMs) in cold dense cores and prestellar cores. The presence of these molecules in such cold conditions is not well understood and remains a matter of debate since the previously proposed "warm- up" scenario cannot explain these observations. In this article, we study the effect of Eley- Rideal and complex induced reaction mechanisms of gas-phase carbon atoms with the main ice components of dust grains on the formation of COMs in cold and dense regions. Based on recent experiments we use a low value for the chemical desorption efficiency (which was previously invoked to explain the observed COM abundances). We show that our introduced mechanisms are efficient enough to produce a large amount of complex organic molecules in the gas-phase at temperatures as low as 10K.

[24]  arXiv:1412.6278 [pdf, other]
Title: The role of magnetic field for quiescence-outburst models in CVs
Authors: S. De Bianchi (1 and 2), V. F. Braga (3), S. Gaudenzi (1) ((1) Dept. of Physics, Universitá degli Studi di Roma La Sapienza, Rome, Italy, (2) École Normale Supérieure, CNRS-UMR, Paris, France, (3) Dept. of Physics, Universitá degli Studi di Roma Tor Vergata, Rome, Italy)
Comments: 5 pages, 2 figures, CTU Proceedings, Acta Polytechnica (accepted)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

In this paper we present the elementary assumptions of our research on the role of the magnetic field in modelling the quiescence-outbursts cycle in Cataclysmic Variables (CVs). The behaviour of the magnetic field is crucial not only to integrate the disk instability model (Osaki 1974), but also to determine the cause and effect nexus among parameters affecting the behavior of complex systems. On the ground of our interpretation of the results emerging from the literature, we suggest that in models describing DNe outbursts, such as the disk instability model, the secondary instability model (Bath 1973) and the thermonuclear runaway model (Mitrofanov 1978), the role of the magnetic field is at least twofold. On the one hand, it activates a specific dynamic pathway for the accreting matter by channelling it. On the other hand, it could be indirectly responsible for switching a particular outburst modality. In order to represent these two roles of the magnetic field, we need to integrate the disk instability model by looking at the global behaviour of the system under analysis. Stochastic resonance in dynamo models, we believe, is a suitable candidate for accomplishing this task. We shall present the MHD model including this mechanism elsewhere.

[25]  arXiv:1412.6304 [pdf, other]
Title: Precise time-series photometry for the Kepler-2.0 mission
Comments: 15 pages, 12 figures, accepted for publication in MNRAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The recently approved NASA K2 mission has the potential to multiply by an order of magnitude the number of short-period transiting planets found by Kepler around bright and low-mass stars, and to revolutionise our understanding of stellar variability in open clusters. However, the data processing is made more challenging by the reduced pointing accuracy of the satellite, which has only two functioning reaction wheels. We present a new method to extract precise light curves from K2 data, combining list-driven, soft-edged aperture photometry with a star-by-star correction of systematic effects associated with the drift in the roll-angle of the satellite about its boresight. The systematics are modelled simultaneously with the stars' intrinsic variability using a semi-parametric Gaussian process model. We test this method on a week of data collected during an engineering test in January 2014, perform checks to verify that our method does not alter intrinsic variability signals, and compute the precision as a function of magnitude on long-cadence (30-min) and planetary transit (2.5-hour) timescales. In both cases, we reach photometric precisions close to the precision reached during the nominal Kepler mission for stars fainter than 12th magnitude, and between 40 and 80 parts per million for brighter stars. These results confirm the bright prospects for planet detection and characterisation, asteroseismology and stellar variability studies with K2. Finally, we perform a basic transit search on the light curves, detecting 2 bona fide transit-like events, 7 detached eclipsing binaries and 13 classical variables.

[26]  arXiv:1412.6315 [pdf, ps, other]
Title: On the environments of type Ia supernovae within host galaxies
Comments: Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present constraints on supernovae type Ia (SNe~Ia) progenitors through an analysis of the environments found at the explosion sites of 102 events within star-forming host galaxies. H-alpha and GALEX near-UV images are used to trace on-going and recent star formation (SF), while broad band B, R, J, K imaging is also analysed. Using pixel statistics we find that SNe~Ia show the lowest degree of association with H-alpha emission of all supernova types. It is also found that they do not trace near-UV emission. As the latter traces SF on timescales less than 100 Myr, this rules out any extreme 'prompt' delay-times as the dominant progenitor channel of SNe~Ia. SNe~Ia best trace the B-band light distribution of their host galaxies. This implies that the population within star-forming galaxies is dominated by relatively young progenitors. Splitting SNe by their (B-V) colours at maximum light, 'redder' events show a higher degree of association to HII regions and are found more centrally within hosts. We discuss possible explanations of this result in terms of line of sight extinction and progenitor effects. No evidence for correlations between SN stretch and environment properties is observed.

[27]  arXiv:1412.6337 [pdf, other]
Title: Diffuse radio emission in the complex merging galaxy cluster Abell 2069
Comments: 6 pages, 3 figures, accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Galaxy clusters with signs for a recent merger show in many cases extended diffuse radio features. This emission originates from relativistic electrons which suffer synchrotron losses due to the intra-cluster magnetic field. The mechanisms of the particle acceleration and the properties of the magnetic field are still poorly understood. We search for diffuse radio emission in galaxy clusters. Here, we study the complex galaxy cluster Abell 2069, for which X-ray observations indicate a recent merger. We investigate the cluster's radio continuum emission by deep Westerbork Synthesis Radio Telescope (WSRT) observations at 346 MHz and a Giant Metrewave Radio Telescope (GMRT) observation at 322 MHz. We find an extended diffuse radio feature roughly coinciding with the main component of the cluster. We classify this emission as a radio halo and estimate its lower limit flux density to 25 +/- 9 mJy. Moreover, we find a second extended diffuse source located at the cluster's companion and estimate its flux density to 15 +/- 2 mJy. We speculate that this is a small halo or a mini-halo. If true, this cluster is the first example of a double-halo in a single galaxy cluster.

[28]  arXiv:1412.6363 [pdf, ps, other]
Title: Multiwaveband photometry of the irradiated brown dwarf WD0137-349B
Comments: 9 pages, 9 figures, 5 tables. Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

WD0137-349 is a white dwarf-brown dwarf binary system in a 116 minute orbit. We present radial velocity observations and multiwaveband photometry from V, R and I in the optical, to J, H and Ks in the near-IR and [3.6], [4.5], [5.8] and [8.0] microns in the mid-IR. The photometry and lightcurves show variability in all wavebands, with the amplitude peaking at [4.5] microns, where the system is also brightest. Fluxes and brightness temperatures were computed for the heated and unheated atmosphere of the brown dwarf (WD0137-349B) using synthetic spectra of the white dwarf using model atmosphere simulations. We show that the flux from the brown dwarf dayside is brighter than expected in the Ks and [4.5] micron bands when compared to models of irradiated brown dwarfs with full energy circulation and suggest this over-luminosity may be attributed to H2 fluorescence or H3+ being generated in the atmosphere by the UV irradiation.

[29]  arXiv:1412.6367 [pdf, other]
Title: PyFAI: a Python library for high performance azimuthal integration on GPU
Comments: Part of the Proceedings of the 7th European Conference on Python in Science (EuroSciPy 2014), Pierre de Buyl and Nelle Varoquaux editors, (2014)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Distributed, Parallel, and Cluster Computing (cs.DC); Mathematical Software (cs.MS)

The pyFAI package has been designed to reduce X-ray diffraction images into powder diffraction curves to be further processed by scientists. This contribution describes how to convert an image into a radial profile using the Numpy package, how the process was accelerated using Cython. The algorithm was parallelised, needing a complete re-design to benefit from massively parallel devices like graphical processing units or accelerators like the Intel Xeon Phi using the PyOpenCL library.

[30]  arXiv:1412.6379 [pdf, ps, other]
Title: Why Galaxies Care about AGB Stars: Setting the Stage
Authors: Alvio Renzini
Comments: 6 Pages, 1 figure. Opeming talk at the III Conference on "Why Galaxies Care About AGB Stars", Vienna, July 28-August 1, 2014
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In this introduction to the Third Congress of Vienna on AGB stars I first try to highlight why it is so hard to cope with the AGB evolutionary phase. This phase is indeed dominated by three main physical processes concerning bulk motions of matter inside/around stars, namely envelope convection, mixing and mass loss. They are inextricably interlaced with each other in a circular sequence of reactions and counter-reactions which has so far undermined our attempts at calibrating such processes one independent of the other. The second part of this introduction is focused on Globular Clusters, illustrating how they came to be a {\it new frontier} for the AGB evolution and a new opportunity to understand it.

[31]  arXiv:1412.6390 [pdf, other]
Title: The PAC2MAN mission: a new tool to understand and predict solar energetic events
Comments: Accepted for publication in the Journal of Space Weather and Space Climate (SWSC)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

An accurate forecast of flare and CME initiation requires precise measurements of the magnetic energy build up and release in the active regions of the solar atmosphere. We designed a new space weather mission that performs such measurements using new optical instruments based on the Hanle and Zeeman effects. The mission consists of two satellites, one orbiting the L1 Lagrangian point (Spacecraft Earth, SCE) and the second in heliocentric orbit at 1AU trailing the Earth by 80$^\circ$ (Spacecraft 80, SC80). Optical instruments measure the vector magnetic field in multiple layers of the solar atmosphere. The orbits of the spacecraft allow for a continuous imaging of nearly 73\% of the total solar surface. In-situ plasma instruments detect solar wind conditions at 1AU and ahead of our planet. Earth directed CMEs can be tracked using the stereoscopic view of the spacecraft and the strategic placement of the SC80 satellite. Forecasting of geoeffective space weather events is possible thanks to an accurate surveillance of the magnetic energy build up in the Sun, an optical tracking through the interplanetary space, and in-situ measurements of the near-Earth environment.

[32]  arXiv:1412.6409 [pdf, other]
Title: Radio Jets in Young Stellar Objects with the SKA
Comments: 8 pages, 3 figures, to be published in proceedings of "Advancing Astrophysics with the Square Kilometre Array", PoS(AASKA14)121
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Jets are ubiquitous in the star-forming process since accretion is intimately associated with outflow. Weak free-free continuum emission in the centimeter domain is associated with these jets.
Observations in the cm range are most useful to trace the base of the ionized jets, close to the YSO and its accretion disk, where jets are accelerated and collimated. Optical or near-IR images are obscured by the high extinction present. Radio recombination lines in jets (in combination with proper motions) should provide their 3D kinematics. SKA will be crucial to perform this kind of observations.
Thermal radio jets are associated with both low and high mass protostars. The ionizing mechanism appears to be related to shocks in the associated outflows, as suggested by the observed correlation between the centimeter luminosity and the outflow momentum rate. From this correlation and that with the bolometric luminosity of the driving star it will be possible to discriminate with SKA between unresolved HII regions and jets, and to infer physical properties of the embedded objects.
Some jets show indications of non-thermal emission (negative spectral indices) in their lobes. Linearly polarized synchrotron emission has been found in the lobes of the jet of HH 80-81, allowing us to measure the direction and intensity of the magnetic field, a clue ingredient in determining the jet collimation and ejection mechanisms. As only a fraction of the emission is polarized, very sensitive observations such as those that will be feasible with SKA are required to perform these studies in other objects.
Jets are common in many kinds of astrophysical scenarios. Characterizing YSO radio jets, whose physical conditions can be reliably determined from their thermal emission, would be also useful in understanding acceleration and collimation mechanisms in all kinds of astrophysical jets.

[33]  arXiv:1412.6416 [pdf, other]
Title: Seasonal Evolution of Saturn's Polar Temperatures and Composition
Comments: Preprint of article accepted for publication in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The seasonal evolution of Saturn's polar atmospheric temperatures and hydrocarbon composition is derived from a decade of Cassini Composite Infrared Spectrometer (CIRS) 7-16 $\mu$m thermal infrared spectroscopy. We construct a near-continuous record of atmospheric variability poleward of 60$^\circ$ from northern winter/southern summer (2004, $L_s=293^\circ$) through the equinox (2009, $L_s=0^\circ$) to northern spring/southern autumn (2014, $L_s=56^\circ$). The hot tropospheric polar cyclones and the hexagonal shape of the north polar belt are both persistent features throughout the decade of observations. The hexagon vertices rotated westward by $\approx30^\circ$ longitude between March 2007 and April 2013, confirming that they are not stationary in the Voyager-defined System III longitude system as previously thought. The extended region of south polar stratospheric emission has cooled dramatically poleward of the sharp temperature gradient near 75$^\circ$S, coinciding with a depletion in the abundances of acetylene and ethane, and suggestive of stratospheric upwelling with vertical wind speeds of $w\approx+0.1$ mm/s. This is mirrored by a general warming of the northern polar stratosphere and an enhancement in acetylene and ethane abundances that appears to be most intense poleward of 75$^\circ$N, suggesting subsidence at $w\approx-0.15$ mm/s. However, the sharp gradient in stratospheric emission expected to form near 75$^\circ$N by northern summer solstice (2017, $L_s=90^\circ$) has not yet been observed, so we continue to await the development of a northern summer stratospheric vortex. North polar minima in tropospheric and stratospheric temperatures were detected in 2008-2010 (lagging one season, or 6-8 years, behind winter solstice); south polar maxima appear to have occurred before the start of the Cassini observations (1-2 years after summer solstice). [Abridged]

[34]  arXiv:1412.6424 [pdf, other]
Title: Atmospheric Lepton Fluxes
Comments: 8 pages, 6 figures, for Proceedings of ISVHECRI 2014
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

This review of atmospheric muons and neutrinos emphasizes the high energy range relevant for backgrounds to high-energy neutrinos of astrophysical origin. After a brief historical introduction, the main distinguishing features of atmospheric $\nu_\mu$ and $\nu_e$ are discussed, along with the implications of the muon charge ratio for the $\nu_\mu/\bar{\nu}_\mu$ ratio. Methods to account for effects of the knee in the primary cosmic-ray spectrum and the energy-dependence of hadronic interactions on the neutrino fluxes are discussed and illustrated in the context of recent results from IceCube. A simple numerical/analytic method is proposed for systematic investigation of uncertainties in neutrino fluxes arising from uncertainties in the primary cosmic-ray spectrum/composition and hadronic interactions.

[35]  arXiv:1412.6425 [pdf, ps, other]
Title: IGR J17480-2446: a new class of accreting binaries?
Comments: 5 pages, 2 figures. Astronomy and Astrophysics, to appear
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

The recent discovery of long-period, low magnetic field pulsars in low-mass X-ray binaries (LMXBs) represents a challenge for the standard evolutionary scenario. These pulsars have a magnetic field strength comparable to that of millisecond pulsars ($\sim 10^8 - 10^9$ G), but their period is at least an order of magnitude longer. We discuss the origin of this new class of pulsars within the standard picture of LMXBs formation and apply our results to the case of IGR J17480-2446. The magnetothermal evolution of the binary system is studied numerically by taking into account the effect of different accretion rates during the Roche-lobe overflow in the framework of the minimal cooling scenario. We show that, in addition to standard millisecond pulsars, long-period low magnetic field pulsars should also be expected as a possible outcome of the binary evolution, depending on the strength of the accretion rate during the Roche-lobe overflow. In particular, we argue that IGR J17480-2446 belongs to this new class of objects.

[36]  arXiv:1412.6427 [pdf, other]
Title: Detecting the cosmological neutrino background
Comments: 4 pages 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

Three relativistic particles in addition to the photon are detected in the cosmic microwave background (CMB). In the standard model of cosmology, these are interpreted as the three neutrino species. However, at the time of CMB-decoupling, neutrinos are not only relativistic particles but they are also freestreaming. Here, we investigate, whether the CMB is sensitive to this defining feature of neutrinos, or whether the CMB-data allow to replace neutrinos with a relativistic gas. We show that free streaming particles are highly preferred over a relativistic perfect gas with $\Delta\chi^2\simeq 250$. We also study the possibility to replace the neutrinos by a viscous gas and find that a relativistic viscous gas with the standard values $c_{\rm eff}^2=c_{\rm vis}^2=1/3$ cannot provide a good fit to present CMB data. It has $\Delta \chi^2=52$ with respect to free streaming neutrinos. Even if we allow for arbitrary $c_{\rm eff}^2$ and $c_{\rm vis}^2$, the best fit still has $\Delta\chi^2=22$, which shows that also this possibility is highly disfavoured.

[37]  arXiv:1412.6444 [pdf, other]
Title: A Raspberry Pi-Based Attitude Sensor
Comments: Journal of Astronomical Instrumentation, Volume 03, Issue 02, November 2014
Journal-ref: A. G. Sreejith et al, J. Astron. Instrum. 03, 1440006 (2014) [10 pages]
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We have developed a lightweight low-cost attitude sensor, based on a Raspberry Pi, built with readily available commercial components. It can be used in experiments where weight and power are constrained, such as in high- altitude lightweight balloon flights. This attitude sensor will be used as a major building block in a closed-loop control system with driver motors to stabilize and point cameras and telescopes for astronomical observations from a balloon-borne payload.

[38]  arXiv:1412.6445 [pdf, other]
Title: The Gould Belt Very Large Array Survey IV: The Taurus-Auriga complex
Comments: 43 pages, 6 figures, accepted in The Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a multi-epoch radio study of the Taurus-Auriga star-forming complex made with the Karl G. Jansky Very Large Array at frequencies of 4.5 GHz and 7.5 GHz. We detect a total of 610 sources, 59 of which are related to young stellar objects and 18 to field stars. The properties of 56\% of the young stars are compatible with non-thermal radio emission. We also show that the radio emission of more evolved young stellar objects tends to be more non-thermal in origin and, in general, that their radio properties are compatible with those found in other star forming regions. By comparing our results with previously reported X-ray observations, we notice that young stellar objects in Taurus-Auriga follow a G\"{u}del-Benz relation with $\kappa$=0.03, as we previously suggested for other regions of star formation. In general, young stellar objects in Taurus-Auriga and in all the previous studied regions seem to follow this relation with a dispersion of $\sim1$ dex. Finally, we propose that most of the remaining sources are related with extragalactic objects but provide a list of 46 unidentified radio sources whose radio properties are compatible with a YSO nature.

[39]  arXiv:1412.6457 [pdf, other]
Title: Design and Performance of the X-ray polarimeter X-Calibur
Comments: 53 pages, 32 figures, accepted by the Journal of Astronomical Instrumentation
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems, micro-quasars, active galactic nuclei, neutron stars, and gamma-ray bursts. We designed, built and tested a X-ray polarimeter, X-Calibur, to be used in the focal plane of the balloon-borne InFOCuS grazing incidence X-ray telescope. X-Calibur combines a low-Z scatterer with a CZT detector assembly to measure the polarization of 20-80keV X-rays making use of the fact that polarized photons scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of ~80%. The X-Calibur detector assembly is completed, tested, and fully calibrated. The response to a polarized X-ray beam was measured successfully at the Cornell High Energy Synchrotron Source. This paper describes the design, calibration and performance of the X-Calibur polarimeter. In principle, a similar space-borne scattering polarimeter could operate over the broader 2-100keV energy band.

[40]  arXiv:1412.6470 [pdf, other]
Title: Mopra CO Observations of the Bubble HII Region RCW120
Comments: 35 pages, 14 figures. Accepted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We use the Mopra radio telescope to test for expansion of the molecular gas associated with the bubble HII region RCW120. A ring, or bubble, morphology is common for Galactic HII regions, but the three-dimensional geometry of such objects is still unclear. Detected near- and far-side expansion of the associated molecular material would be consistent with a three-dimensional spherical object. We map the $J = 1\rightarrow 0$ transitions of $^{12}$CO, $^{13}$CO, C$^{18}$O, and C$^{17}$O, and detect emission from all isotopologues. We do not detect the $0_0\rightarrow 1_{-1} E$ masing lines of CH$_3$OH at 108.8939 GHz. The strongest CO emission is from the photodissociation region (PDR), and there is a deficit of emission toward the bubble interior. We find no evidence for expansion of the molecular material associated with RCW120 and therefore can make no claims about its geometry. The lack of detected expansion is roughly in agreement with models for the time-evolution of an HII region like RCW120, and is consistent with an expansion speed of $< 1.5\, {\rm km\, s^{-1}}$. Single-position CO spectra show signatures of expansion, which underscores the importance of mapped spectra for such work. Dust temperature enhancements outside the PDR of RCW120 coincide with a deficit of emission in CO, confirming that these temperature enhancements are due to holes in the RCW120 PDR. H$\alpha$ emission shows that RCW120 is leaking $\sim5\%$ of the ionizing photons into the interstellar medium (ISM) through PDR holes at the locations of the temperature enhancements. H-alpha emission also shows a diffuse "halo" from leaked photons not associated with discrete holes in the PDR. Overall $25\pm10\%$ of all ionizing photons are leaking into the nearby ISM.

[41]  arXiv:1412.6481 [pdf, ps, other]
Title: Tomography of Galactic star-forming regions and spiral arms with the Square Kilometer Array
Authors: Laurent Loinard (CRyA-UNAM), Mark Thompson (University of Hertfordshire), Melvin Hoare (Leeds University), Huib Jan van Langevelde (JIVE/Sterrewacht Leiden), Simon Ellingsen (University of Tasmania), Andreas Brunthaler (MPIfR Bonn), Jan Forbrich (University of Vienna), Kazi L.J. Rygl (ESA-ESTEC Noordwijk), Luis F. Rodriguez (CRyA-UNAM), Amy J. Mioduszewski (NRAO Socorro), Rosa M. Torres-Lopez (U. Guadalajara), Sergio A. Dzib (MPIfR Bonn), Gisela N. Ortiz-Leon (CRyA-UNAM), Tyler L. Bourke (SKA Organisation), James A. Green (SKA Organisation)
Comments: To appear in the Proceedings Advancing Astrophysics with the SKA (AASKA14)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Very Long Baseline Interferometry (VLBI) at radio wavelengths can provide astrometry accurate to 10 micro-arcseconds or better (i.e. better than the target GAIA accuracy) without being limited by dust obscuration. This means that unlike GAIA, VLBI can be applied to star-forming regions independently of their internal and line-of-sight extinction. Low-mass young stellar objects (particularly T Tauri stars) are often non-thermal compact radio emitters, ideal for astrometric VLBI radio continuum experiments. Existing observations for nearby regions (e.g. Taurus, Ophiuchus, or Orion) demonstrate that VLBI astrometry of such active T Tauri stars enables the reconstruction of both the regions' 3D structure (through parallax measurements) and their internal kinematics (through proper motions, combined with radial velocities). The extraordinary sensitivity of the SKA telescope will enable similar "tomographic mappings" to be extended to regions located several kpc from Earth, in particular to nearby spiral arm segments. This will have important implications for Galactic science, galactic dynamics and spiral structure theories.

[42]  arXiv:1412.6483 [pdf, other]
Title: Temperature diagnostics of the solar atmosphere using SunPy
Comments: Part of the Proceedings of the 7th European Conference on Python in Science (EuroSciPy 2014), Pierre de Buyl and Nelle Varoquaux editors, (2014)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Computational Engineering, Finance, and Science (cs.CE)

The solar atmosphere is a hot (about 1MK), magnetised plasma of great interest to physicists. There have been many previous studies of the temperature of the Sun's atmosphere (Plowman2012, Wit2012, Hannah2012, Aschwanden2013, etc.). Almost all of these studies use the SolarSoft software package written in the commercial Interactive Data Language (IDL), which has been the standard language for solar physics. The SunPy project aims to provide an open-source library for solar physics. This work presents (to the authors' knowledge) the first study of its type to use SunPy rather than SolarSoft. This work uses SunPy to process multi-wavelength solar observations made by the Atmospheric Imaging Assembly (AIA) instrument aboard the Solar Dynamics Observatory (SDO) and produce temperature maps of the Sun's atmosphere. The method uses SunPy's utilities for querying databases of solar events, downloading solar image data, storing and processing images as spatially aware Map objects, and tracking solar features as the Sun rotates. An essential consideration in developing this software is computational efficiency due to the large amount of data collected by AIA/SDO, and in anticipating new solar missions which will result in even larger sets of data. An overview of the method and implementation is given, along with tests involving synthetic data and examples of results using real data for various regions in the Sun's atmosphere.

[43]  arXiv:1412.6489 [pdf, other]
Title: MHD Effects on Pulsed YSO Jets. I. 2.5-D Simulations
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

In this paper we explore the dynamics of radiative axisymmetric MHD jets at high resolution using AMR methods. The goal of the study is to determine both the dynamics and emission properties of such jets. To that end we have implemented microphysics enabling us to produce synthetic maps of H$\alpha$ and [S II]. The jets are pulsed either sinusoidally or randomly via a time-dependent ejection velocity which leads to a complicated structure of internal shocks and rarefactions as has been seen in previous simulations. The high resolution of our simulations allows us to explore in great detail the effect of pinch forces (due to the jet's toroidal magnetic field) within the "working surfaces" where pulses interact. We map the strong H$\alpha$ emission marking shock fronts and the strong [S II] emission inside cooling regions behind shocks as observed with high-resolution images of jets. We find that pinch forces in the stronger field cases produce additional emission regions along the axis as compared with purely hydrodynamic runs. These simulations are a first step to understanding the full 3-D emission properties of radiative MHD jets.

[44]  arXiv:1412.6492 [pdf, ps, other]
Title: Pan-chromatic observations of the remarkable nova LMC 2012
Comments: 18 figures, 6 tables (one online only containing all the photometry)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present the results of an intensive multiwavelength campaign on nova LMC 2012. This nova evolved very rapidly in all observed wavelengths. The time to fall two magnitudes in the V band was only 2 days. In X-rays the super soft phase began 13$\pm$5 days after discovery and ended around day 50 after discovery. During the super soft phase, the \Swift/XRT and \Chandra\ spectra were consistent with the underlying white dwarf being very hot, $\sim$ 1 MK, and luminous, $\sim$ 10$^{38}$ erg s$^{-1}$. The UV, optical, and near-IR photometry showed a periodic variation after the initial and rapid fading had ended. Timing analysis revealed a consistent 19.24$\pm$0.03 hr period in all UV, optical, and near-IR bands with amplitudes of $\sim$ 0.3 magnitudes which we associate with the orbital period of the central binary. No periods were detected in the corresponding X-ray data sets. A moderately high inclination system, $i$ = 60$\pm$10$^{\arcdeg}$, was inferred from the early optical emission lines. The {\it HST}/STIS UV spectra were highly unusual with only the \ion{N}{5} (1240\AA) line present and superposed on a blue continuum. The lack of emission lines and the observed UV and optical continua from four epochs can be fit with a low mass ejection event, $\sim$ 10$^{-6}$ M$_{\odot}$, from a hot and massive white dwarf near the Chandrasekhar limit. The white dwarf, in turn, significantly illuminated its subgiant companion which provided the bulk of the observed UV/optical continuum emission at the later dates. The inferred extreme white dwarf characteristics and low mass ejection event favor nova LMC 2012 being a recurrent nova of the U Sco subclass.

[45]  arXiv:1412.6495 [pdf, other]
Title: Numerical Simulations of Mach Stem Formation via Intersecting Bow Shocks
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Hubble Space Telescope observations show bright knots of H$\alpha$ emission within outflowing young stellar jets. Velocity variations in the flow create secondary bow shocks that may intersect and lead to enhanced emission. When the bow shocks intersect at or above a certain critical angle, a planar shock called a Mach stem is formed. These shocks could produce brighter H$\alpha$ emission since the incoming flow to the Mach stem is parallel to the shock normal. In this paper we report first results of a study using 2-D numerical simulations designed to explore Mach stem formation at the intersection of bow shocks formed by hypersonic "bullets" or "clumps". Our 2-D simulations show how the bow shock shapes and intersection angles change as the adiabatic index $\gamma$ changes. We show that the formation or lack of a Mach stem in our simulations is consistent with the steady-state Mach stem formation theory. Our ultimate goal, which is part of an ongoing research effort, is to characterize the physical and observational consequences of bow shock intersections including the formation of Mach stems.

[46]  arXiv:1412.6501 [pdf, other]
Title: Confirmation of a Star Formation Bias in Type Ia Supernova Distances and its Effect on Measurement of the Hubble Constant
Comments: 3 Figures ; Submitted to ApJ: Oct.~30, 2014 -- Accepted: Dec.~17, 2014
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Previously we used the Nearby Supernova Factory sample to show that SNe~Ia having locally star-forming environments are dimmer than SNe~Ia having locally passive environments.Here we use the \constitution\ sample together with host galaxy data from \GALEX\ to independently confirm that result. The effect is seen using both the SALT2 and MLCS2k2 lightcurve fitting and standardization methods, with brightness differences of $0.094 \pm 0.037\ \mathrm{mag}$ for SALT2 and $0.155 \pm 0.041\ \mathrm{mag}$ for MLCS2k2 with $R_V=2.5$. When combined with our previous measurement the effect is $0.094 \pm 0.025\ \mathrm{mag}$ for SALT2. If the ratio of these local SN~Ia environments changes with redshift or sample selection, this can lead to a bias in cosmological measurements. We explore this issue further, using as an example the direct measurement of $H_0$. \GALEX{} observations show that the SNe~Ia having standardized absolute magnitudes calibrated via the Cepheid period--luminosity relation using {\textit{HST}} originate in predominately star-forming environments, whereas only ~50% of the Hubble-flow comparison sample have locally star-forming environments. As a consequence, the $H_0$ measurement using SNe~Ia is currently overestimated. Correcting for this bias, we find a value of $H_0^{corr}=70.6\pm 2.6\ \mathrm{km\ s^{-1}\ Mpc^{-1}}$ when using the LMC distance, Milky Way parallaxes and the NGC~4258 megamaser as the Cepheid zeropoint, and $68.8\pm 3.3\ \mathrm{km\ s^{-1}\ Mpc^{-1}}$ when only using NGC~4258. Our correction brings the direct measurement of $H_0$ within $\sim 1\,\sigma$ of recent indirect measurements based on the CMB power spectrum.

[47]  arXiv:1412.6510 [pdf, other]
Title: Search for Prompt Neutrino Emission from Gamma-Ray Bursts with IceCube
Comments: 14 pages, 3 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present constraints derived from a search of four years of IceCube data for a prompt neutrino flux from gamma-ray bursts (GRBs). A single low-significance neutrino was found in coincidence with one of the 506 observed bursts, consistent with the expectation from atmospheric backgrounds. Although GRBs have been proposed as candidate sources for ultra-high energy cosmic rays, our limits on the neutrino flux disfavor much of the parameter space for the latest models. We also find that no more than $\sim1\%$ of the recently observed astrophysical neutrino flux consists of prompt emission from GRBs that are potentially observable by existing satellites.

[48]  arXiv:1412.6511 [pdf, other]
Title: Discordant optical and X-ray classification of AGN
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: Astrophysics of Galaxies (astro-ph.GA)

To provide insight into the apparent mismatch between the optical and X-ray absorption properties observed in 10-30 % of Active Galactic Nuclei (AGN), we have conducted a detailed study of two X-ray unabsorbed AGN with a type-2 optical spectroscopic classification. In addition to high quality X-ray spectroscopic observations, that we used to determine both the AGN luminosities and absorption, we have a VLT/XSHOOTER UV-to-near-IR high resolution spectrum for each object, that we used to determine the AGN intrinsic emision corrected for both contamination from the AGN hosts and extinction. Our analysis has revealed that the apparent mismatch is provoked by galaxy dilution. We dilution of two AGN with extreme properties: one of them has an intrinsically very high Balmer decrement while the other lies in a galaxy more massive than expected.

[49]  arXiv:1412.6512 [pdf, other]
Title: Revealing the Physics and Evolution of Galaxies and Galaxy Clusters with SKA Continuum Surveys
Authors: I. Prandoni, N. Seymour (Continuum Science SKA Working Group)
Comments: to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the SKA' PoS(AASKA14)067. Overview chapter of the collection of 'Continuum Science' chapters
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Astrophysics of Galaxies (astro-ph.GA)

In this chapter we provide an overview of the science enabled by radio continuum surveys in the SKA era, focusing on galaxy/galaxy cluster physics and evolution studies, and other relevant continuum science in the >2020 scientific framework. We outline a number of 'reference' radio-continuum surveys for SKA1 that can address such topics, and comprehensively discuss the most critical science requirements that we have identified. We highlight what should be achieved by SKA1, to guarantee a major leap forwards with respect to the pre-SKA era, considering the science advances expected in the coming years with existing and upcoming telescopes (JVLA, LOFAR, eMERLIN, and the three SKA precursors: MWA, ASKAP and MeerKAT). In this exercise we take in due account also the other waveband facilities coming online at the same time (e.g. Euclid, LSST, etc.), which tackle overlapping scientific goals, but in a different manner. In this respect particular attention has been payed to ensure that the proposed reference surveys are able to exploit the existing synergies with such facilities, so as to generate strong involvement from all astronomical communities, and leave a lasting legacy value. It is clear that a certain degree of freedom is allowed to some of the observational parameters. We believe it is very important to best fine-tune such parameters taking into proper account existing commensalities with SKA1 surveys addressing other science areas (HI galaxy science, magnetism, cosmology).

[50]  arXiv:1412.6518 [pdf, other]
Title: Code dependencies of pre-supernova evolution and nucleosynthesis in massive stars: Evolution to the end of core helium burning
Authors: Samuel Jones (UVic), Raphael Hirschi (Keele), Marco Pignatari (Basel), Alexander Heger (Monash), Cyril Georgy (Keele), Nobuya Nishimura (Keele), Chris Fryer (LANL), Falk Herwig (UVic)
Comments: 17 pages, 10 figures, 7 tables; accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Massive stars are key sources of radiative, kinetic, and chemical feedback in the universe. Grids of massive star models computed by different groups each using their own codes, input physics choices and numerical approximations, however, lead to inconsistent results for the same stars. We use three of these 1D codes---GENEC, KEPLER and MESA---to compute non-rotating stellar models of $15~\mathrm{M}_\odot$, $20~\mathrm{M}_\odot$, and $25~\mathrm{M}_\odot$ and compare their nucleosynthesis. We follow the evolution from the main sequence until the end of core helium burning. The GENEC and KEPLER models hold physics assumptions used in large grids of published models. The MESA code was set up to use convective core overshooting such that the CO core masses are consistent with those obtained by GENEC. For all models, full nucleosynthesis is computed using the NuGrid post-processing tool MPPNP.
We find that the surface abundances predicted by the models are in reasonable agreement. In the helium core, the standard deviation of the elemental overproduction factors for Fe to Mo is less than $30\,\%$---smaller than the impact of the present nuclear physics uncertainties. For our three initial masses, the three stellar evolution codes yield consistent results. Differences in key properties of the models, e.g., helium and CO core masses and the time spent as a red supergiant, are traced back to the treatment of convection and, to a lesser extent, mass loss. The mixing processes in stars remain the key uncertainty in stellar modelling. Better constrained prescriptions are thus necessary to improve the predictive power of stellar evolution models.

[51]  arXiv:1412.6524 [pdf, ps, other]
Title: Dark Matter Particles in the Galactic Halo
Authors: R. Bernabei (Dip. di Fisica, Univ. Roma Tor Vergata and INFN-Tor Vergata, Rome, Italy)
Comments: To appear in the Proceedings of the 17th Bled workshop "What comes beyond the standard models"
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Physics - Experiment (hep-ex); Instrumentation and Detectors (physics.ins-det)

The DAMA/LIBRA-phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton $\times$ yr, corresponding to 14 annual cycles) give evidence at 9.3 $\sigma$ C.L. for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radio-pure NaI(Tl) target. Results and comparisons will be shortly addressed as well as perspectives of the presently running DAMA/LIBRA-phase2. Finally, some arguments arisen in the discussion section of this workshop are mentioned in the Appendix.