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J.P. Magué & B. Ménard



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[1]  arXiv:1501.05643 [pdf, other]
Title: Stacking of SKA data: comparing uv-plane and image-plane stacking
Comments: Accepted for publication in the SKA Science Book 'Advancing Astrophysics with the Square Kilometre Array', to appear in 2015
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

Stacking as a tool for studying objects that are not individually detected is becoming popular even for radio interferometric data, and will be widely used in the SKA era. Stacking is typically done using imaged data rather than directly using the visibilities (the uv-data). We have investigated and developed a novel algorithm to do stacking using the uv-data. We have performed exten- sive simulations comparing to image-stacking, and summarize the results of these simulations. Furthermore, we disuss the implications in light of the vast data volume produced by the SKA. Having access to the uv-stacked data provides a great advantage, as it allows the possibility to properly analyse the result with respect to calibration artifacts as well as source properties such as size. For SKA the main challenge lies in archiving the uv-data. For purposes of robust stacking analysis, it would be strongly desirable to either keep the calibrated uv-data at least in an aver- age form, or implement a stacking queue where stacking positions could be provided prior to the observations and the uv-stacking is done almost in real time.

[2]  arXiv:1501.05645 [pdf, other]
Title: Spiral Disk Instability Can Drive Thermonuclear Explosions in Binary White Dwarf Mergers
Comments: Accepted to ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Thermonuclear, or Type Ia supernovae (SNe Ia), originate from the explosion of carbon-oxygen white dwarfs, and serve as standardizable cosmological candles. However, despite their importance, the nature of the progenitor systems which give rise to SNe Ia has not been hitherto elucidated. Observational evidence favors the double-degenerate channel, in which merging white dwarf binaries lead to SNe Ia. Furthermore, significant discrepancies exist between observations and theory, and to date, there has been no self-consistent merger model which yields a SNe Ia. Here we show that a spiral mode instability in the accretion disk formed during a binary white dwarf merger leads to a detonation on a dynamical timescale. This mechanism sheds light on how white dwarf mergers may frequently yield SNe Ia.

[3]  arXiv:1501.05646 [pdf, other]
Title: Spatially extended and high-velocity dispersion molecular component in spiral galaxies: single-dish vs. interferometric observations
Comments: 12 pages, 5 figures, Accepted to AJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Recent studies of the molecular medium in nearby galaxies have provided mounting evidence that the molecular gas can exist in two phases: one that is clumpy and organized as molecular clouds and another one that is more diffuse. This last component has a higher velocity dispersion than the clumpy one. In order to investigate these two molecular components further, we compare the fluxes and line widths of CO in NGC 4736 and NGC 5055, two nearby spiral galaxies for which high-quality interferometric as well as single-dish data sets are available. Our analysis leads to two main results: 1) Employing three different methods, we determine the flux recovery of the interferometer as compared to the single-dish to be within a range of 35-74% for NGC4736 and 81-92% for NGC5055, and 2) when focusing on high (SNR>5) lines of sight, the single-dish line widths are larger by ~(40+-20)% than the ones derived from interferometric data; which is in agreement with stacking all lines of sight. These results point to a molecular gas component that is distributed over spatial scales larger than 30"(~1kpc), and is therefore filtered out by the interferometer. The available observations do not allow us to distinguish between a truly diffuse gas morphology and a uniform distribution of small clouds that are separated by less than the synthesized beam size (~3" or ~100pc), as they would both be invisible for the interferometer. This high velocity dispersion component has a dispersion similar to what is found in the atomic medium, as traced through observations of the HI line.

[4]  arXiv:1501.05648 [pdf, other]
Title: Gamma-ray lines from SN2014J
Comments: 12 pages, 15 figures, 10th INTEGRAL Workshop: "A Synergistic View of the High Energy Sky" - Integral2014, 15-19 September 2014, Annapolis, MD, USA
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

On 21 January 2014, SN2014J was discovered in M82 and found to be the closest type Ia supernova (SN Ia) in the last four decades. INTEGRAL observed SN2014J from the end of January until late June for a total exposure time of about 7 Ms. SNe Ia light curves are understood to be powered by the radioactive decay of iron peak elements of which $^{56}$Ni is dominantly synthesized during the thermonuclear disruption of a CO white dwarf (WD). The measurement of $\gamma$-ray lines from the decay chain $^{56}$Ni$\rightarrow$$^{56}$Co$\rightarrow$$^{56}$Fe provides unique information about the explosion in supernovae. Canonical models assume $^{56}$Ni buried deeply in the supernova cloud, absorbing most of the early $\gamma$-rays, and only the consecutive decay of $^{56}$Co should become directly observable through the overlaying material several weeks after the explosion when the supernova envelope dilutes as it expands. Surprisingly, with the spectrometer on INTEGRAL, SPI, we detected $^{56}$Ni $\gamma$-ray lines at 158 and 812 keV at early times with flux levels corresponding to roughly 10% of the total expected amount of $^{56}$Ni, and at relatively small velocities. This implies some mechanism to create a major amout of $^{56}$Ni at the outskirts, and at the same time to break the spherical symmetry of the supernova. One plausible explanation would be a belt accreted from a He companion star, exploding, and triggering the explosion of the white dwarf. The full set of observations of SN2014J show $^{56}$Co $\gamma$-ray lines at 847 and 1238 keV, and we determine for the first time a SN Ia $\gamma$-ray light curve. The irregular appearance of these $\gamma$-ray lines allows deeper insights about the explosion morphology from its temporal evolution and provides additional evidence for an asymmetric explosion, from our high-resolution spectroscopy and comparisons with recent models.

[5]  arXiv:1501.05649 [pdf, ps, other]
Title: Galaxy formation in the Planck cosmology III: star-formation histories and post-processing magnitude reconstruction
Comments: Submitted to MNRAS; SFHs available on Millennium database this http URL
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We adapt the L-Galaxies semi-analytic model to follow the star-formation histories (SFH) of galaxies -- by which we mean a record of the formation time and metallicities of the stars that are present in each galaxy at a given time. We use these to construct stellar spectra in post-processing, which offers large efficiency savings and allows user-defined spectral bands and dust models to be applied to data stored in the Millennium data repository.
We contrast model SFHs from the Millennium Simulation with observed ones from the VESPA algorithm as applied to the SDSS-7 catalogue. The overall agreement is good, with both simulated and SDSS galaxies showing a steeper SFH with increased stellar mass. The SFHs of blue and red galaxies, however, show poor agreement between data and simulations, which may indicate that the termination of star formation is too abrupt in the models.
The mean star-formation rate (SFR) of model galaxies is well-defined and is accurately modelled by a double power law at all redshifts: SFR proportional to 1/(x^{-1.39}+x^{1.33}), where x=(T-t)/3.0 Gyr, t is the age of the stars and T is the loopback time to the onset of galaxy formation; above a redshift of unity, this is well approximated by a gamma function: SFR proportional to x^{1.5}e^{-x}, where x=(T-t)/2.0 Gyr. Individual galaxies, however, show a wide dispersion about this mean. When split by mass, the SFR peaks earlier for high-mass galaxies than for lower-mass ones, and we interpret this downsizing as a mass-dependence in the evolution of the quenched fraction: the SFHs of star-forming galaxies show only a weak mass dependence.

[6]  arXiv:1501.05650 [pdf, ps, other]
Title: The effect of dark matter resolution on the collapse of baryons in high redshift numerical simulations
Comments: 15 pages. Submitted to MNRAS. Comments welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We examine the impact of dark matter particle resolution on the formation of a baryonic core in high resolution adaptive mesh refinement simulations. We test the effect that both particle smoothing and particle splitting have on the hydrodynamic properties of a collapsing halo at high redshift (z > 20). Furthermore, we vary the background field intensity, with energy below the Lyman limit (< 13.6 eV), as may be relevant for the case of metal-free star formation and super-massive black hole seed formation. We find that using particle splitting methods greatly increases our particle resolution without introducing any numerical noise and allows us to achieve converged results over a wide range of external background fields. Furthermore, we find that for lower values of the background field a lower dark matter particle mass is required. We use the characteristic Jeans length of the gas to define the core of a collapsing halo, $\rm{R_{core} \lesssim 1\ pc}$ for T $\lesssim 8000$ K, and number density, $\rm{n \sim 1 \times 10^6\ cm^{-3}}$. We find that in order to produce converged results which are not affected by dark matter particles requires that the relationship ${M_{\rm{core}} / M_{\rm{DM}}} > 100.0$ be satisfied, where ${M_{\rm{core}}}$ is the enclosed baryon mass within the core and $M_{\rm{DM}}$ is the minimum dark matter particle mass. This ratio should provide a very useful starting point for conducting convergence tests before any production run simulations. We find that dark matter particle smoothing is a useful adjunct to already highly resolved simulations.

[7]  arXiv:1501.05651 [pdf]
Title: A spin-down clock for cool stars from observations of a 2.5-billion-year-old cluster
Comments: 24 pages, 12 figures, 1 table, published in Nature January 2015
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The ages of the most common stars - low-mass (cool) stars like the Sun, and smaller - are difficult to derive because traditional dating methods use stellar properties that either change little as the stars age or are hard to measure. The rotation rates of all cool stars decrease substantially with time as the stars steadily lose their angular momenta. If properly calibrated, rotation therefore can act as a reliable determinant of their ages based on the method of gyrochronology. To calibrate gyrochronology, the relationship between rotation period and age must be determined for cool stars of different masses, which is best accomplished with rotation period measurements for stars in clusters with well-known ages. Hitherto, such measurements have been possible only in clusters with ages of less than about one billion years, and gyrochronology ages for older stars have been inferred from model predictions. Here we report rotation period measurements for 30 cool stars in the 2.5-billion-year-old cluster NGC 6819. The periods reveal a well-defined relationship between rotation period and stellar mass at the cluster age, suggesting that ages with a precision of order 10 per cent can be derived for large numbers of cool Galactic field stars.

[8]  arXiv:1501.05652 [pdf, other]
Title: Modeling giant extrasolar ring systems in eclipse and the case of J1407b: sculpting by exomoons?
Comments: 13 pages, 6 figures, 3 tables. Accepted for publication in ApJ. Data and computer code for model at: this http URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

The light curve of 1SWASP J140747.93-394542.6, a $\sim$16 Myr old star in the Sco-Cen OB association, underwent a complex series of deep eclipses that lasted 56 days, centered on April 2007. This light curve is interpreted as the transit of a giant ring system that is filling up a fraction of the Hill sphere of an unseen secondary companion, J1407b. We fit the light curve with a model of an azimuthally symmetric ring system, including spatial scales down to the temporal limit set by the star's diameter and relative velocity. The best ring model has 37 rings and extends out to a radius of 0.6 AU (90 million km), and the rings have an estimated total mass on the order of $100 M_{Moon}$. The ring system has one clearly defined gap at 0.4 AU (61 million km), which we hypothesize is being cleared out by a $< 0.8 M_{\oplus}$ exosatellite orbiting around J1407b. This eclipse and model implies that we are seeing a circumplanetary disk undergoing a dynamic transition to an exosatellite-sculpted ring structure and is one of the first seen outside our Solar system.

[9]  arXiv:1501.05655 [pdf, ps, other]
Title: Towards simulating star formation in turbulent high-z galaxies with mechanical supernova feedback
Comments: 22 pages, 18 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Feedback from supernovae is essential to understanding the self-regulation of star formation in galaxies. However, the efficacy of the process in a cosmological context remains unclear due to excessive radiative losses during the shock propagation. To better understand the impact of SN explosions on the evolution of galaxies, we perform a suite of high-resolution (12 pc), zoom-in cosmological simulations of a Milky Way-like galaxy at z=3 with adaptive mesh refinement. We find that SN explosions can efficiently regulate star formation, leading to the stellar mass and metallicity consistent with the observed mass-metallicity relation and stellar mass-halo mass relation at z~3. This is achieved by making three important changes to the classical feedback scheme: i) the different phases of SN blast waves are modelled directly by injecting radial momentum expected at each stage, ii) the realistic time delay of SNe, commencing at as early as 3 Myr, is required to disperse very dense gas before a runaway collapse sets in at the galaxy centre via mergers of gas clumps, and iii) a non-uniform density distribution of the ISM is taken into account below the computational grid scale for the cell in which SN explodes. The last condition is motivated by the fact that our simulations still do not resolve the detailed structure of a turbulent ISM in which the fast outflows can propagate along low-density channels. The simulated galaxy with the SN feedback model shows strong outflows, which carry approximately ten times larger mass than star formation rate, as well as smoothly rising circular velocity. Other feedback models that do not meet the three conditions form too many stars, producing a peaked rotation curve. Our results suggest that understanding the structure of the turbulent ISM may be crucial to assess the role of SN and other feedback processes in galaxy formation theory. [abridged]

[10]  arXiv:1501.05657 [pdf, ps, other]
Title: Constraining globular cluster formation through studies of young massive clusters - V. ALMA observations of clusters in the Antennae
Comments: 9 pages, 2 figures, accepted by MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Some formation scenarios that have been put forward to explain multiple populations within Globular Clusters (GCs) require that the young massive cluster have large reservoirs of cold gas within them, which is necessary to form future generations of stars. In this paper we use deep observations taken with Atacama Large Millimeter/sub-millimeter Array (ALMA) to assess the amount of molecular gas within 3 young (50-200 Myr) massive (~10^6 Msun) clusters in the Antennae galaxies. No significant CO(3--2) emission was found associated with any of the three clusters. We place upper limits for the molecular gas within these clusters of ~1x10^5 Msun (or <9 % of the current stellar mass). We briefly review different scenarios that propose multiple episodes of star formation and discuss some of their assumptions and implications. Our results are in tension with the predictions of GC formation scenarios that expect large reservoirs of cool gas within young massive clusters at these ages.

[11]  arXiv:1501.05659 [pdf, ps, other]
Title: Formation of Super-Earth Mass Planets at 125-250 AU from a Solar-type Star
Comments: 43 pages of text, 24 figures, submitted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We investigate pathways for the formation of icy super-Earth mass planets orbiting at 125-250 AU around a 1 solar mass star. An extensive suite of coagulation calculations demonstrates that swarms of 1 cm to 10 m planetesimals can form super-Earth mass planets on time scales of 1-3 Gyr. Collisional damping of 0.01-100 cm particles during oligarchic growth is a highlight of these simulations. In some situations, damping initiates a second runaway growth phase where 100-3000 km protoplanets grow to super-Earth sizes. Our results establish the initial conditions and physical processes required for in situ formation of super-Earth planets at large distances from the host star. For nearby dusty disks in HD 107146, HD 202628, and HD 207129, ongoing super-Earth formation at 80-150 AU could produce gaps and other structures in the debris. In the solar system, forming a putative planet X at a < 300 AU (a > 1000 AU) requires a modest (very massive) protosolar nebula.

[12]  arXiv:1501.05666 [pdf, ps, other]
Title: Testing Sunyaev-Zel'dovich measurements of the hot gas content of dark matter haloes using synthetic skies
Comments: 15 pages, 10 figures, submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

[Abridged] A large fraction of the baryons in the Universe are `missing' and believed to reside in the form of warm-hot gas in and around the dark matter haloes of massive galaxies and galaxy groups and clusters. The thermal Sunyaev-Zel'dovich (tSZ) effect offers a means of probing this component directly. The Planck collaboration recently performed a tSZ stacking analysis of a large sample of `locally brightest galaxies' (LBGs) selected from the Sloan Digital Sky Survey DR7 and, surprisingly, inferred an approximately self-similar relation between the tSZ flux and halo mass from massive clusters down to individual galaxies. At face value, this implies that galaxies, groups and clusters have the same hot gas mass fractions, a result which is in apparent conflict with X-ray observations. Here, we test the robustness of the inferred trend using synthetic maps of the tSZ effect sky generated from cosmological hydrodynamical simulations. We analyse these maps using the same tools and assumptions applied in the Planck LBG study. We show that, while the detection of the tSZ signal itself appears to be reliable and the estimate of the `total' flux is reasonably robust, the inferred flux originating from within $r_{500}$ is highly sensitive to the assumed pressure distribution of the gas. Using as a guide our most realistic simulations that invoke AGN feedback and reproduce a wide variety of properties of groups and clusters, we estimate that the derived tSZ flux within $r_{500}$ is biased high by up to to an order of magnitude for haloes with masses $M_{500}\lesssim10^{13}$ M$_{\odot}$. Moreover, we show that the AGN simulations are fully consistent with the total tSZ flux-mass relation observed with Planck, whereas a self-similar model is ruled out. Finally, we present a new mass-dependent spatial template which can be used for deriving more accurate estimates of the tSZ flux within $r_{500}$.

[13]  arXiv:1501.05685 [pdf, other]
Title: Exoplanetary Geophysics -- An Emerging Discipline
Comments: Review chapter to appear in Treatise on Geophysics, 2nd Edition
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Thousands of extrasolar planets have been discovered, and it is clear that the galactic planetary census draws on a diversity greatly exceeding that exhibited by the solar system's planets. We review significant landmarks in the chronology of extrasolar planet detection, and we give an overview of the varied observational techniques that are brought to bear. We then discuss the properties of the currently known distribution, using the mass-period diagram as a guide to delineating hot Jupiters, eccentric giant planets, and a third, highly populous, category that we term "ungiants", planets having masses less than 30 Earth masses and orbital periods less than 100 days. We then move to a discussion of the bulk compositions of the extrasolar planets. We discuss the long-standing problem of radius anomalies among giant planets, as well as issues posed by the unexpectedly large range in sizes observed for planets with masses somewhat greater than Earth's. We discuss the use of transit observations to probe the atmospheres of extrasolar planets; various measurements taken during primary transit, secondary eclipse, and through the full orbital period, can give clues to the atmospheric compositions, structures, and meteorologies. The extrasolar planet catalog, along with the details of our solar system and observations of star-forming regions and protoplanetary disks, provide a backdrop for a discussion of planet formation in which we review the elements of the favored pictures for how the terrestrial and giant planets were assembled. We conclude by listing several research questions that are relevant to the next ten years and beyond.

[14]  arXiv:1501.05689 [pdf, other]
Title: A case study for a tidal interaction between dwarf galaxies in UGC 6741
Comments: 8 pages, Accepted for publication in AJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a case study of the tidal interaction between low mass, star-forming, galaxies initially found exploring the Sloan Digital Sky Survey (SDSS) images and further analyzed with SDSS spectroscopy and UV GALEX photometry. With a luminosity of M$_{r}$ = $-$17.7 mag and exhibiting a prominent tidal filament, UGC 6741 appears as a scale down version of massive gas--rich interacting systems and mergers.The stellar disk of the smaller companion, UGC 6741_B, which is three times less massive, has likely been already destroyed. Both galaxies, which are connected by a 15 kpc long stellar bridge, have a similar oxygen abundance of 12+log(O/H)$\sim$8.3. Several knots of star-forming regions are identified along the bridge, some with masses exceeding $\sim$10$^{7}$ M$_{\sun}$. The most compact of them, which are unresolved, may evolve into globular clusters or Ultra Compact Dwarf galaxies (UCDs). This would be the first time progenitors of such objects are detected in mergers involving dwarf galaxies. UGC 6741 has currently the color and star formation properties of Blue Compact Dwarf galaxies (BCDs). However the analysis of its surface photometry suggests that the galaxy lies within the scaling relations defined by early-type dwarf galaxies (dEs). Thus UGC 6741 appears as a promising system to study the possible transformation of BCDs into dEs, through possibly a merger episode. The frequency of such dwarf-dwarf mergers should now be explored.

[15]  arXiv:1501.05690 [pdf, other]
Title: Photoionization Heating of Nova Ejecta by the Post-Outburst Supersoft Source
Comments: 8 pages, 6 figures. Submitted to the Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The expanding ejecta from a classical nova remains hot enough ($\sim10^{4}\, {\rm K}$) to be detected in thermal radio emission for up to years after the cessation of mass loss triggered by a thermonuclear instability on the underlying white dwarf (WD). Nebular spectroscopy of nova remnants confirms the hot temperatures observed in radio observations. During this same period, the unstable thermonuclear burning transitions to a prolonged period of stable burning of the remnant hydrogen-rich envelope, causing the WD to become, temporarily, a super-soft X-ray source. We show that photoionization heating of the expanding ejecta by the hot WD maintains the observed nearly constant temperature of $(1-4)\times10^4\mathrm{~K}$ for up to a year before an eventual decline in temperature due to either the cessation of the supersoft phase or the onset of a predominantly adiabatic expansion. We simulate the expanding ejecta using a one-zone model as well as the Cloudy spectral synthesis code, both incorporating the time-dependent WD effective temperatures for a range of masses from $0.60\ M_{\odot}$ to $1.10\ M_{\odot}$. We show that the duration of the nearly isothermal phase depends most strongly on the velocity and mass of the ejecta and that the ejecta temperature depends on the WD's effective temperature, and hence its mass.

[16]  arXiv:1501.05694 [pdf, other]
Title: ALMA Multi-line Imaging of the Nearby Starburst Galaxy NGC 253
Authors: David S. Meier (1,2,3), Fabian Walter (4,2), Alberto D. Bolatto (5), Adam K. Leroy (4), Jürgen Ott (2), Erik Rosolowsky (7), Sylvain Veilleux (8,5), Steven R. Warren (5), Axel Weiss (9), Martin A. Zwaan (10), Laura K. Zschaechner (4) ((1) New Mexico Institute of Mining and Technology, (2) National Radio Astronomy Observatory, Socorro, NM, (3) Adjunct Astronomer, National Radio Astronomy Observatory, (4) Max-Planck Institut für Astronomie, (5) University of Maryland, College Park, Department of Astronomy and Joint Space-Science Institute, (6) National Radio Astronomy Observatory, Charlottesville, VA, (7) University of Alberta, (8) University of Maryland, College Park, (9) Max Planck Institut für Radioastronomie, (10) European Southern Observatory)
Comments: 20 pages, 10 figures, accepted to the Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present spatially resolved ($\sim$50 pc) imaging of molecular gas species in the central kiloparsec of the nearby starburst galaxy NGC 253, based on observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA). A total of 50 molecular lines are detected over a 13 GHz bandwidth imaged in the 3 mm band. Unambiguous identifications are assigned for 27 lines. Based on the measured high CO/C$^{17}$O isotopic line ratio ($\gtrsim$350), we show that $^{12}$CO(1-0) has moderate optical depths. A comparison of the HCN and HCO$^{+}$ with their $^{13}$C-substituted isotopologues shows that the HCN(1-0) and HCO$^{+}$(1-0) lines have optical depths at least comparable to CO(1-0). H$^{13}$CN/H$^{13}$CO$^{+}$ (and H$^{13}$CN/HN$^{13}$C) line ratios provide tighter constraints on dense gas properties in this starburst. SiO has elevated abundances across the nucleus. HNCO has the most distinctive morphology of all the bright lines, with its global luminosity dominated by the outer parts of the central region. The dramatic variation seen in the HNCO/SiO line ratio suggests that some of the chemical signatures of shocked gas are being erased in the presence of dominating central radiation fields (traced by C$_{2}$H and CN). High density molecular gas tracers (including HCN, HCO$^+$, and CN) are detected at the base of the molecular outflow. We also detect hydrogen $\beta$ recombination lines that, like their $\alpha$ counterparts, show compact, centrally peaked morphologies, distinct from the molecular gas tracers. A number of sulfur based species are mapped (CS, SO, NS, C$_{2}$S, H$_{2}$CS and CH$_{3}$SH) and have morphologies similar to SiO.

[17]  arXiv:1501.05706 [pdf, ps, other]
Title: Absorption features in the emission line profiles of transition region explosive events
Comments: 11 pages, 5 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Transition region explosive events (EEs) are characterized by transient enhancement in the red and/or blue wings of transition region line profiles, and they are usually interpreted as signatures of magnetic reconnection in the transition region. We report an observation of an EE with the Interface Region Imaging Spectrograph (IRIS) in an emerging active region. The EE occurs in a region with mixed-polarity magnetic fields. During the EE, the radiance profiles of Si\,{\sc iv} and C\,{\sc ii} lines become greatly enhanced in both the red and blue wings. The wing enhancement clearly extends to more than 300~km\,s^{-1}. We have identified many narrow absorption features in the profiles of these transition region lines. Some of these absorption features can be identified as lines of Ni\,{\sc ii} and Fe\,{\sc ii}, which are formed in the upper chromosphere and usually shown as emission lines. The electron density of the Si\,{\sc iv} source region is estimated to be roughly 10^{11}--10^{12} cm^{-3}. These results suggest that reconnection in the middle chromosphere heats the plasma locally to transition region temperatures. Moreover, we have observed obvious self-absorption features in the Si\,{\sc iv} 1393.755 \AA\ and 1402.77 \AA\ lines during an EE for the first time. The self-absorption appears to be associated with an overlying loop in the emerging active region. We demonstrate that these narrow absorption features could not be observed with previous poor-resolution spectrometers.

[18]  arXiv:1501.05712 [pdf, other]
Title: The Local-time variations of Lunar Prospector epithermal-neutron data
Authors: L.F.A. Teodoro (BAER/NASA Ames), D.J. Lawrence (JHU/APL), V.E. Eke (Durham University), R.E. Elphic (NASA Ames), W.C. Feldman (PSI), S. Maurice (CESR), M.A. Siegler (PSI), D.A. Paige (UCLA)
Comments: 8 pages, 7 figures and 3 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We assess local-time variations of epithermal-neutron count rates measured by the Lunar Prospector Neutron Spectrometer. We investigate the nature of these variations and find no evidence to support the idea that such variations are caused by diurnal variations of hydrogen concentration across the lunar surface. Rather we find an anticorrelation between instrumental temperature and epithermal-neutron count rate. We have also found that the measured counts are dependent on the temperatures of the top decimeters of the lunar subsurface as constrained by the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment temperature measurements. Finally, we have made the first measurement of the effective leakage depth for epithermal-neutrons of ~20 cm.

[19]  arXiv:1501.05721 [pdf, ps, other]
Title: A Study of Mid-Infrared Sources that Dramatically Brightened
Comments: 35 pages, 13 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present results of near-infrared photometric and spectroscopic observations of mid-infrared (MIR) sources that dramatically brightened. Using IRAS, AKARI, and WISE point source catalogs, we found that 4 sources (IRAS 19574+491, V2494 Cyg, IRAS 22343+7501, and V583 Cas) significantly brightened at MIR wavelengths over the 20-30 years of difference in observing times. Little is known about these sources except V2494 Cyg, which is considered a FU Orionis star. Our observation clearly resolves IRAS 22343+7501 into 4 stars (2MASS J22352345+7517076, 2MASS J22352442+7517037, [RD95] C, and 2MASS J22352497+7517113) and first JHKs photometric data for all 4 sources are obtained. Two of these stars (2MASS J22352442+7517037 and 2MASS J22352497+7517113) are known as T Tau stars. Our spectroscopic observation reveals that IRAS 19574+9441 is an M-type evolved star and V583 Cas is a carbon star. 2MASS J22352345+7517076 is probably a YSO, judging from our observation that it has featureless near-infrared (NIR) spectrum and also showed dramatic brightening in NIR (about 4 magnitudes in Ks-band). The possible reasons for dramatic brightening in MIR are discussed in this paper.

[20]  arXiv:1501.05723 [pdf, other]
Title: The High Time and Frequency Resolution Capabilities of the Murchison Widefield Array
Comments: 9 pages, 6 figures, 1 table. Accepted for publication in PASA
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The science cases for incorporating high time resolution capabilities into modern radio telescopes are as numerous as they are compelling. Science targets range from exotic sources such as pulsars, to our Sun, to recently detected possible extragalactic bursts of radio emission, the so-called fast radio bursts (FRBs). Originally conceived purely as an imaging telescope, the initial design of the Murchison Widefield Array (MWA) did not include the ability to access high time and frequency resolution voltage data. However, the flexibility of the MWA's software correlator allowed an off-the-shelf solution for adding this capability. This paper describes the system that records the 100 micro-second and 10 kHz resolution voltage data from the MWA. Example science applications, where this capability is critical, are presented, as well as accompanying commissioning results from this mode to demonstrate verification.

[21]  arXiv:1501.05727 [pdf, ps, other]
Title: Inertial-Acoustic Oscillations of Black-Hole Accretion Discs with Large-Scale Poloidal Magnetic Fields
Authors: Cong Yu, Dong Lai
Comments: 7 pages, 4 figures, submitted to MNRAS. arXiv admin note: substantial text overlap with arXiv:1212.1219
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We study the effect of large-scale magnetic fields on the non-axisymmetric inertial-acoustic modes (also called p-modes) trapped in the innermost regions of accretion discs around black holes (BHs). These global modes could provide an explanation for the high-frequency quasi-periodic oscillations (HFQPOs) observed in BH X-ray binaries. There may be observational evidence for the presence of such large-scale magnetic fields in the disks since episodic jets are observed in the same spectral state when HFQPOs are detected. We find that a large-scale poloidal magnetic field can enhance the corotational instability and increase the growth rate of the purely hydrodynamic overstable p-modes. In addition, we show that the frequencies of these overstable p-modes could be further reduced by such magnetic fields, making them agree better with observations.

[22]  arXiv:1501.05736 [pdf, other]
Title: Optical technologies for the observation of low Earth orbit objects
Comments: 8 pages, 5 figures, Proc. of IAC 2014 (Toronto)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Space Physics (physics.space-ph)

In order to avoid collisions with space debris, the near Earth orbit must be continuously scanned by either ground- or spaced-based facilities. For the low Earth orbit, radar telescopes are the workhorse for this task, especially due to their continuous availability. However, optical observation methods can deliver complementary information, especially towards high accuracy measurements. Passive-optical observations are inexpensive and can yield very precise information about the apparent position of the object in the sky via comparison with background stars. However, the object's distance from the observer is not readily accessible, which constitutes a major drawback of this approach for the precise calculation of the orbital elements. Two experimental methods have been devised to overcome this problem: Using two observatories a few kilometres apart, strictly simultaneous observations of the same object yield an accurate, instantaneous 3D position determination through measurement of the parallax. If only one observatory is available, a pulsed laser can be used in addition to the passive-optical channel to measure the distance to the object, in a similar fashion as used by the satellite laser ranging community. However, compared to conventional laser ranging, a stronger laser and more elaborate tracking algorithms are necessary. The two approaches can also be combined by illuminating the object with a pulsed laser from one observatory and measuring the return times at both observatories. These techniques are explored by German Aerospace Center in Stuttgart using its orbital debris research observatory, in cooperation with the Satellite Laser Ranging station in Graz and the Geodetic Observatory in Wettzell. This contribution will present some of the results and plans for further measurement campaigns.

[23]  arXiv:1501.05754 [pdf, other]
Title: Radiation-hydrodynamical simulations of massive star formation using Monte Carlo radiative transfer: I. Algorithms and numerical methods
Authors: Tim J. Harries
Comments: 12 pages, 15 figures. Accepted by MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a set of new numerical methods that are relevant to calculating radiation pressure terms in hydrodynamics calculations, with a particular focus on massive star formation. The radiation force is determined from a Monte Carlo estimator and enables a complete treatment of the detailed microphysics, including polychromatic radiation and anisotropic scattering, in both the free-streaming and optically-thick limits. Since the new method is computationally demanding we have developed two new methods that speed up the algorithm. The first is a photon packet splitting algorithm that enables efficient treatment of the Monte Carlo process in very optically thick regions. The second is a parallelisation method that distributes the Monte Carlo workload over many instances of the hydrodynamic domain, resulting in excellent scaling of the radiation step. We also describe the implementation of a sink particle method that enables us to follow the accretion onto, and the growth of, the protostars. We detail the results of extensive testing and benchmarking of the new algorithms.

[24]  arXiv:1501.05784 [pdf, ps, other]
Title: The Cosmic Battery in Astrophysical Accretion Disks
Comments: 11 pages, 5 figures, submitted to the Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The aberrated radiation pressure at the inner edge of the accretion disk around an astrophysical black hole imparts a relative azimuthal velocity on the electrons with respect to the ions which gives rise to a ring electric current that generates large scale poloidal magnetic field loops. This is the Cosmic Battery established by Contopoulos and Kazanas in 1998. In the present work we perform realistic numerical simulations of this important astrophysical mechanism in advection-dominated accretion flows-ADAF. We confirm the original prediction that the inner parts of the loops are continuously advected toward the central black hole and contribute to the growth of the large scale magnetic field, whereas the outer parts of the loops are continuously diffusing outward through the turbulent accretion flow. This process of inward advection of the axial field and outward diffusion of the return field proceeds all the way to equipartition, thus generating astrophysically significant magnetic fields on astrophysically relevant timescales. We confirm that there exists a critical value of the magnetic Prandtl number between unity and 10 in the outer disk above which the Cosmic Battery mechanism is suppressed.

[25]  arXiv:1501.05786 [pdf, other]
Title: Constraints on hybrid metric-Palatini models from background evolution
Comments: 10 pages, 4 figures and 1 table. Submitted to PRD. arXiv admin note: text overlap with arXiv:1402.4458
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

In this work, we introduce two models of the hybrid metric-Palatini theory of gravitation. We explore their background evolution, showing explicitly that one recovers standard General Relativity with an effective Cosmological Constant at late times. This happens because the Palatini Ricci scalar evolves towards and asymptotically settles at the minimum of its effective potential during cosmological evolution. We then use a combination of cosmic microwave background, Supernovae and baryonic accoustic oscillations background data to constrain the models' free parameters. For one model in particular, we are able to constrain the deviation from the gravitational constant $G$ one can have at early times.

[26]  arXiv:1501.05791 [pdf, ps, other]
Title: Forming chondrules in impact splashes. I. Radiative cooling model
Journal-ref: 2014, The Astrophysical Journal, 794, 91
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The formation of chondrules is one of the oldest unsolved mysteries in meteoritics and planet formation. Recently an old idea has been revived: the idea that chondrules form as a result of collisions between planetesimals in which the ejected molten material forms small droplets which solidify to become chondrules. Pre-melting of the planetesimals by radioactive decay of 26Al would help producing sprays of melt even at relatively low impact velocity. In this paper we study the radiative cooling of a ballistically expanding spherical cloud of chondrule droplets ejected from the impact site. We present results from a numerical radiative transfer models as well as analytic approximate solutions. We find that the temperature after the start of the expansion of the cloud remains constant for a time t_cool and then drops with time t approximately as T ~ T_0[(3/5)t/t_cool+ 2/5]^(-5/3) for t>t_cool. The time at which this temperature drop starts t_cool depends via an analytical formula on the mass of the cloud, the expansion velocity and the size of the chondrule. During the early isothermal expansion phase the density is still so high that we expect the vapor of volatile elements to saturate so that no large volatile losses are expected.

[27]  arXiv:1501.05805 [pdf, ps, other]
Title: Oxygen abundances in G- and F-type stars from HARPS
Comments: Manuscript accepted for publication on A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present a detailed and uniform study of oxygen abundance from two different oxygen lines at 6158$\AA$ and 6300$\AA$ in a large sample of solar-type stars. The results are used to check the behaviour of these spectral lines as oxygen abundance indicators and to study the evolution of oxygen in thick and thin disk populations of the Galaxy. Equivalent width measurements were carried out for the [OI]~6158$\AA$ and OI~6300$\AA$ lines. LTE abundances were obtained from these two lines in 610 and 535 stars, respectively. We were able to measure oxygen abundance from both indicators in 447 stars, enabling us, for the first time, to compare them in a uniform way. Careful error analysis has been performed. We found that oxygen abundances derived from the 6158$\AA$ and 6300$\AA$ lines agree to within 0.1dex in 58\% of the stars in our sample, and this result improves for higher signal-to-noise values. We confirm an oxygen enhancement in stars of the thick disk, as has also been seen for other $\alpha$-elements. The new oxygen abundances confirm previous findings for a progressive linear rise in the oxygen-to-iron ratio with a slope equal to 0.78 from solar metallicity to [Fe/H]$\sim$-1. However, the slope we measured is steeper than the one found in previous studies based on the oxygen triplet. Below [Fe/H]=$-$0.6 our stars show [O/Fe] ratios as high as $\sim$0.8, which can be interpreted as evidence for oxygen overproduction in the Galactic thick disk. These high oxygen abundances do not pose a problem to chemodynamical models since there is a range of parameters that can accommodate our results.

[28]  arXiv:1501.05822 [pdf, other]
Title: The GRAVITY instrument software / High-level software
Comments: 8 pages, 7 figures, published in Proc. SPIE 9146, Optical and Infrared Interferometry IV, 91462B
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

GRAVITY is the four-beam, near- infrared, AO-assisted, fringe tracking, astrometric and imaging instrument for the Very Large Telescope Interferometer (VLTI). It is requiring the development of one of the most complex instrument software systems ever built for an ESO instrument. Apart from its many interfaces and interdependencies, one of the most challenging aspects is the overall performance and stability of this complex system. The three infrared detectors and the fast reflective memory network (RMN) recorder contribute a total data rate of up to 20 MiB/s accumulating to a maximum of 250 GiB of data per night. The detectors, the two instrument Local Control Units (LCUs) as well as the five LCUs running applications under TAC (Tools for Advanced Control) architecture, are interconnected with fast Ethernet, RMN fibers and dedicated fiber connections as well as signals for the time synchronization. Here we give a simplified overview of all subsystems of GRAVITY and their interfaces and discuss two examples of high-level applications during observations: the acquisition procedure and the gathering and merging of data to the final FITS file.

[29]  arXiv:1501.05823 [pdf, other]
Title: Dynamic temperature selection for parallel-tempering in Markov chain Monte Carlo simulations
Comments: 15 pages, 15 figures, submitted to MNRAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Modern problems in astronomical Bayesian inference require efficient methods for sampling from complex, high-dimensional, often multi-modal probability distributions. Most popular methods, such as Markov chain Monte Carlo sampling, perform poorly on strongly multi-modal probability distributions, rarely jumping between modes or settling on just one mode without finding others. Parallel tempering addresses this problem by sampling simultaneously with separate Markov chains from tempered versions of the target distribution with reduced contrast levels. Gaps between modes can be traversed at higher temperatures, while individual modes can be efficiently explored at lower temperatures. In this paper, we investigate how one might choose the ladder of temperatures to achieve lower autocorrelation time for the sampler (and therefore more efficient sampling). In particular, we present a simple, easily-implemented algorithm for dynamically adapting the temperature configuration of a sampler while sampling in order to maximise its efficiency. This algorithm dynamically adjusts the temperature spacing to achieve a uniform rate of exchanges between neighbouring temperatures. We compare the algorithm to conventional geometric temperature configurations on a number of test distributions, and report efficiency gains by a factor of 1.2--2.5 over a well-chosen geometric temperature configuration and by a factor of 1.5--5 over a poorly chosen configuration. On all of these test distributions a sampler using the dynamical adaptations to achieve uniform acceptance ratios between neighbouring chains outperforms one that does not.

[30]  arXiv:1501.05825 [pdf, ps, other]
Title: From the atmosphere to the circumstellar environment in cool evolved stars
Comments: To appear in the Book of the VLTI School 2013, held 9-21 Sep 2013 Barcelonnette (France), "What the highest angular resolution can bring to stellar astrophysics?", Ed. Millour, Chiavassa, Bigot, Chesneau, Meilland, Stee, EAS Publications Series (2015)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We discuss and illustrate contributions that optical interferometry has made on our current understanding of cool evolved stars. We include red giant branch (RGB) stars, asymptotic giant branch (AGB) stars, and red supergiants (RSGs). Studies using optical interferometry from visual to mid-infrared wavelengths have greatly increased our knowledge of their atmospheres, extended molecular shells, dust formation, and winds. These processes and the morphology of the circumstellar environment are important for the further evolution of these stars toward planetary nebulae (PNe) and core-collapse supernovae (SNe), and for the return of material to the interstellar medium.

[31]  arXiv:1501.05846 [pdf, ps, other]
Title: X-ray Evidence for a Pole-Dominated Corona on AB Dor
Comments: To appear in the Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

A fine analysis of spectral line widths and Doppler shifts employing Fourier transform and cross-correlation techniques has been applied to Chandra HETG spectra obtained in 1999 October of the rapidly rotating young star AB Doradus in order to investigate its coronal topology. The observation lasted 52.3ks, covering 1.2 rotation periods. The X-ray light curve obtained from integrating the dispersed signal revealed a moderate intensity flare midway through the exposure in which the count rate increased sharply by about 50% and subsequently decayed over the next 10ks. We find no significant Doppler shifts in the spectra or modulation of the light curve that could be attributed to rotation of dominant coronal structures at this epoch. Individual spectral line widths are statistically consistent with thermal broadening and formally require no rotational broadening, while the $1\sigma$ limit to rotational broadening corresponds to a compact corona restricted to latitudes $>57\deg$. Fourier analysis suggests a small amount of rotational broadening is present consistent with a corona restricted largely to the poles, and excludes models with surface rotational broadening or greater. These results present direct spectroscopic evidence that the dominant coronal activity on rapidly-rotating active stars is associated with the dark polar spots commonly seen in photospheric Doppler images, and support models in which these spots are of mixed magnetic polarity that forms closed loops.

[32]  arXiv:1501.05864 [pdf, other]
Title: A separate universe view of the asymmetric sky
Comments: 17 pages, 2 figures
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 provide a unified description of the hemispherical asymmetry in the cosmic microwave background generated by the mechanism proposed by Erickcek, Kamionkowski, and Carroll, using a delta N formalism that consistently accounts for the asymmetry-generating mode throughout. We derive a general form for the power spectrum which explicitly exhibits the broken translational invariance. This can be directly compared to cosmic microwave background observables, including the observed quadrupole and fNL values, automatically incorporating the Grishchuk--Zel'dovich effect. Our calculation unifies and extends previous calculations in the literature, in particular giving the full dependence of observables on the phase of our location in the super-horizon mode that generates the asymmetry. We demonstrate how the apparently different results obtained by previous authors arise as different limiting cases. We confirm the existence of non-linear contributions to the microwave background quadrupole from the super-horizon mode identified by Erickcek et al. and further explored by Kanno et al., and show that those contributions are always significant in parameter regimes capable of explaining the observed asymmetry. We indicate example parameter values capable of explaining the observed power asymmetry without violating other observational bounds.

[33]  arXiv:1501.05866 [pdf, ps, other]
Title: Revisiting Spitzer transit observations with Independent Component Analysis: new results for the GJ436 system
Comments: accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We analyzed four Spitzer/IRAC observations at 3.6 and 4.5 {\mu}m of the primary transit of the exoplanet GJ436b, by using blind source separation techniques. These observations are important to investigate the atmospheric composition of the planet GJ436b. Previous analyses claimed strong inter-epoch variations of the transit parameters due to stellar variability, casting doubts on the possibility to extract conclusively an atmospheric signal; those analyses also reported discrepant results, hence the necessity of this reanalysis. The method we used has been proposed in Morello et al. (2014) to analyze 3.6 {\mu}m transit light-curves of the hot Jupiter HD189733b; it performes an Independent Component Analysis (ICA) on a set of pixel-light-curves, i.e. time series read by individual pixels, from the same photometric observation. Our method only assumes the independence of instrumental and astrophysical signals, and therefore guarantees a higher degree of objectivity compared to parametric detrending techniques published in the literature. The datasets we analyzed in this paper represent a more challenging test compared to the previous ones. Contrary to previous results reported in the literature, our results (1) do not support any detectable inter-epoch variations of orbital and stellar parameters, (2) are photometrically stable at the level 10e-4 in the IR, and (3) the transit depth measurements at the two wavelengths are consistent within 1{\sigma}. We also (4) detect a possible transit duration variation (TDV) of 80 s (2 {\sigma} significance level), that has not been pointed out in the literature, and (5) confirm no transit timing variations (TTVs) >30 s.

[34]  arXiv:1501.05883 [pdf]
Title: Correlated Strontium and Barium Isotopic Compositions of Acid-Cleaned Single Silicon Carbides from Murchison
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We present strontium, barium, carbon, and silicon isotopic compositions of 61 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing both strontium and barium contamination. For the first time, by using correlated $^{88}Sr$/$^{86}Sr$ and $^{138}Ba$/$^{136}Ba$ ratios in mainstream SiC grains, we are able to resolve the effect of $^{13}C$ concentration from that of $^{13}C$-pocket mass on s-process nucleosynthesis, which points towards the existence of large $^{13}C$-pockets with low $^{13}C$ concentration in AGB stars. The presence of such large $^{13}$R-pockets with a variety of relatively low $^{13}C$ concentrations seems to require multiple mixing processes in parent AGB stars of mainstream SiC grains.

[35]  arXiv:1501.05897 [pdf, ps, other]
Title: A search for H$α$ emission in high-metallicity damped Lyman-$α$ systems at $z \sim 2.4$
Authors: Wei-Hao Wang (1,2), Nissim Kanekar (3), J. Xavier Prochaska (4) ((1) Academia Sinica Institute of Astronomy and Astrophysics, Taiwan, (2) Canada-France-Hawaii Telescope, USA, (3) National Centre for Radio Astrophysics, India, (4) UCO/Lick Observatory, USA)
Comments: 8 pages, 3 figures; accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report on a sensitive search for redshifted H$\alpha$ line-emission from three high-metallicity damped Ly$\alpha$ absorbers (DLAs) at $z \approx 2.4$ with the Near-infrared Integral Field Spectrometer (NIFS) on the Gemini-North telescope, assisted by the ALTtitude conjugate Adaptive optics for the InfraRed (ALTAIR) system with a laser guide star. Within the NIFS field-of-view, $\approx 3.22" \times 2.92"$ corresponding to $\approx 25$ kpc $ \times 23$ kpc at $z=2.4$, we detect no statistically significant line-emission at the expected redshifted H$\alpha$ wavelengths. The measured root-mean-square noise fluctuations in $0.4"$ apertures are $1-3\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$. Our analysis of simulated, compact, line-emitting sources yields stringent limits on the star-formation rates (SFRs) of the three DLAs, $< 2.2$~M$_{\odot}$ yr$^{-1}$ ($3\sigma$) for two absorbers, and $< 11$~M$_{\odot}$ yr$^{-1}$ ($3\sigma$) for the third, at all impact parameters within $\approx 12.5$~kpc to the quasar sightline at the DLA redshift. For the third absorber, the SFR limit is $< 4.4$~M$_\odot$ yr$^{-1}$ for locations away from the quasar sightline. These results demonstrate the potential of adaptive optics-assisted, integral field unit searches for galaxies associated with high-$z$ DLAs.

[36]  arXiv:1501.05911 [pdf, other]
Title: Possible ring material around centaur (2060) Chiron
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We propose that several short duration events observed in past stellar occultations by Chiron were produced by rings material. From a reanalysis of the stellar occultation data in the literature we determined two possible orientations of the pole of Chiron's rings, with ecliptic coordinates l=(352+/-10) deg, b=(37+/-10) deg or l=(144+/-10) deg, b=(24+/-10) deg . The mean radius of the rings is (324 +/- 10) km. One can use the rotational lightcurve amplitude of Chiron at different epochs to distinguish between the two solutions for the pole. Both imply lower lightcurve amplitude in 2013 than in 1988, when the rotational lightcurve was first determined. We derived Chiron's rotational lightcurve in 2013 from observations at the 1.23-m CAHA telescope and indeed its amplitude is smaller than in 1988. We also present a rotational lightcurve in 2000 from images taken at CASLEO 2.15-m telescope that is consistent with our predictions. Out of the two poles the l=(144+/-10) deg, b=(24+/-10) deg solution provides a better match to a compilation of rotational lightcurve amplitudes from the literature and those presented here. We also show that using this preferred pole, Chiron's long term brightness variations are compatible with a simple model that incorporates the changing brightness of the rings as the tilt angle with respect to the Earth changes with time. Also, the variability of the water ice band in Chiron's spectra in the literature can be explained to a large degree by an icy ring system whose tilt angle changes with time and whose composition includes water ice, analogously to the case of Chariklo. We present several possible formation scenarios for the rings from qualitative points of view and speculate on the reasons why rings might be common in centaurs. We speculate on whether the known bimodal color distribution of centaurs could be due to presence of rings and lack of them.

[37]  arXiv:1501.05913 [pdf, ps, other]
Title: Cosmic Axion Bose-Einstein Condensation
Comments: 18 pages. This is a chapter for a book entitled "Universal Themes of Bose-Einstein Condensation", to be published by Cambridge University Press, edited by David Snoke, Nikolaos Proukakis and Peter Littlewood
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

QCD axions are a well-motivated candidate for cold dark matter. Cold axions are produced in the early universe by vacuum realignment, axion string decay and axion domain wall decay. We show that cold axions thermalize via their gravitational self-interactions, and form a Bose-Einstein condensate. As a result, axion dark matter behaves differently from the other proposed forms of dark matter. The differences are observable.

[38]  arXiv:1501.05914 [pdf]
Title: Solar irradiance changes and photobiological effects at Earth's surface following astrophysical ionizing radiation events
Authors: Brian C. Thomas (Washburn Univ.), Patrick J. Neale (SERC), Brock R. Snyder II (Washburn Univ.)
Comments: In press at Astrobiology
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); High Energy Astrophysical Phenomena (astro-ph.HE); Populations and Evolution (q-bio.PE)

Astrophysical ionizing radiation events have been recognized as a potential threat to life on Earth, primarily through depletion of stratospheric ozone and subsequent increase in surface-level solar ultraviolet radiation. Simulations of the atmospheric effects of a variety of events (such as supernovae, gamma-ray bursts, and solar proton events) have been previously published, along with estimates of biological damage at Earth's surface. In this work, we employed the TUV radiative transfer model to expand and improve calculations of surface-level irradiance and biological impacts following an ionizing radiation event. We considered changes in surface-level UVB, UVA, and photosynthetically active radiation (visible light) for clear-sky conditions and fixed aerosol parameter values. We also considered a wide range of biological effects on organisms ranging from humans to phytoplankton. We found that past work overestimated UVB irradiance, but that relative estimates for increase in exposure to DNA damaging radiation are still similar to our improved calculations. We also found that the intensity of biologically damaging radiation varies widely with organism and specific impact considered; these results have implications for biosphere-level damage following astrophysical ionizing radiation events. When considering changes in surface-level visible light irradiance, we found that, contrary to previous assumptions, a decrease in irradiance is only present for a short time in very limited geographical areas; instead we found a net increase for most of the modeled time-space region. This result has implications for proposed climate changes associated with ionizing radiation events.

[39]  arXiv:1501.05925 [pdf, ps, other]
Title: Discovery And Characterization of Wide Binary Systems With a Very Low Mass Component
Comments: 18 pages, 6 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We report the discovery of 14 low-mass binary systems containing mid-M to mid-L dwarf companions with separations larger than 250 AU. We also report the independent discovery of 9 other systems with similar characteristics that were recently discovered in other studies. We have identified these systems by searching for common proper motion sources in the vicinity of known high proper motion stars, based on a cross-correlation of wide area near-infrared surveys (2MASS, SDSS, and SIMP). An astrometric follow-up, for common proper motion confirmation, was made with SIMON and/or CPAPIR at the OMM 1.6 m and CTIO 1.5 m telescopes for all the candidates identified. A spectroscopic follow-up was also made with GMOS or GNIRS at Gemini to determine the spectral types of 11 of our newly identified companions and 10 of our primaries. Statistical arguments are provided to show that all of the systems we report here are very likely to be physical binaries. One of the new systems reported features a brown dwarf companion: LSPM J1259+1001 (M5) has an L4.5 (2M1259+1001) companion at about 340 AU. This brown dwarf was previously unknown. Seven other systems have a companion of spectral type L0-L1 at a separation in the 250-7500 AU range. Our sample includes 14 systems with a mass ratio below 0.3.