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J.P. Magué & B. Ménard

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[1]  arXiv:1610.06174 [pdf, other]
Title: M32 Analogs? A Population of Massive Ultra Compact Dwarf Galaxies in intermediate redshift CLASH Clusters
Comments: Intended to be a letter. 4 figures, 1 table. Comments much appreciated
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report the discovery of relatively massive, M32-like Ultra Compact Dwarf (UCD) galaxy candidates in $0.2<z<0.6$ massive galaxy clusters imaged by the CLASH survey. Examining the nearly unresolved objects in the survey, we identify a sample of compact objects concentrated around the brightest cluster galaxies with colors similar to cluster red sequence galaxies. Their colors and magnitudes suggest stellar masses around $10^9 \mathrm{M_{\odot}}$. More than half of these galaxies have half-light radii smaller than 200pc, falling into the category of massive Ultra Compact Dwarfs (UCD), with properties similar to M32. The properties are consistent with a tidal stripping origin, but we can not rule out the possibility that they are early-formed compact objects trapped in massive dark matter halos. The 17 CLASH clusters studied in this work on average contain 2.7 of these objects in the their central 0.3 Mpc and 0.6 in their central 50 kpc. Our study demonstrates the possibility of statistically characterizing UCDs with a large set of uniform imaging survey data.

[2]  arXiv:1610.06175 [pdf, other]
Title: HI4PI: A full-sky HI survey based on EBHIS and GASS
Comments: 14 pages, 8 figures, A&A in press, corresponding authors: B. Winkel and P. M. W. Kalberla
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Measurement of the Galactic neutral atomic hydrogen (HI) column density, NHI, and brightness temperatures, Tb, is of high scientific value for a broad range of astrophysical disciplines. In the past two decades, one of the most-used legacy HI datasets has been the Leiden/Argentine/Bonn Survey (LAB). We release the HI 4$\pi$ survey (HI4PI), an all-sky database of Galactic HI, which supersedes the LAB survey. The HI4PI survey is based on data from the recently completed first coverage of the Effelsberg-Bonn HI Survey (EBHIS) and from the third revision of the Galactic All-Sky Survey (GASS). EBHIS and GASS share similar angular resolution and match well in sensitivity. Combined, they are ideally suited to be a successor to LAB. The new HI4PI survey outperforms the LAB in angular resolution (16.2', FWHM) and sensitivity (RMS: 43 mK). Moreover, it has full spatial sampling and thus overcomes a major drawback of LAB, which severely undersamples the sky. We publish all-sky column density maps of the neutral atomic hydrogen in the Milky Way, along with full spectroscopic data, in several map projections including HEALPix.

[3]  arXiv:1610.06176 [pdf, other]
Title: On the linearity of tracer bias around voids
Comments: 13 pages, 8 figures, MNRAS submitted
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The large-scale structure of the universe can only be observed directly via luminous tracers of the underlying distribution of dark matter. However, the clustering statistics of tracers are biased and depend on various properties of the tracers themselves, such as their host-halo mass and formation and assembly history. On very large scales, where density fluctuations are within the linear regime, this tracer bias results in a constant offset in the clustering amplitude, which is known as linear bias. Towards smaller non-linear scales, this is no longer the case and tracer bias becomes a complicated function of scale and time. We focus on tracer bias centered on cosmic voids, depressions of the density field that spatially dominate the universe. We consider three different types of tracers: galaxies, galaxy clusters and AGNs, extracted from the hydrodynamical simulation suite Magneticum Pathfinder. In contrast to common clustering statistics that focus on the auto-correlation of tracers, we find that void-tracer cross-correlations are successfully described by a linear bias-relation within voids. The tracer-density profile of voids can thus be related to their matter-density profile by a single number. We show that this number coincides with the linear tracer bias extracted from the large-scale auto-correlation function and expectations from theory, if sufficiently large voids are considered. For smaller voids we observe a shift towards higher values. This has important consequences on cosmological parameter inference from large-scale structure, as the problem of unknown tracer bias is alleviated up to a constant number. The smallest scales in existing datasets become accessible to simpler models, providing modes of the density field that have been disregarded so far, but may help to further reduce statistical errors and to constrain cosmology on smaller scales.

[4]  arXiv:1610.06180 [pdf, other]
Title: Hubble Tarantula Treasury Project V. The star cluster Hodge 301: the old face of 30 Doradus
Comments: accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Based on color-magnitude diagrams (CMDs) from the Hubble Space Telescope Hubble Tarantula Treasury Project (HTTP) survey, we present the star formation history (SFH) of Hodge~301, the oldest star cluster in the Tarantula Nebula. The HTTP photometry extends faint enough to reach, for the first time, the cluster pre-main sequence (PMS) turn-on, where the PMS joins the main sequence. Using the location of this feature, along with synthetic CMDs generated with the latest PARSEC models, we find that Hodge~301 is older than previously thought, with an age between 26.5 and 31.5 Myr. From this age, we also estimate that between 38 and 61 supernovae Type-II exploded in the region. The same age is derived from the main sequence turn-off, whereas the age derived from the post-main sequence stars is younger and between 20 and 25 Myr. Other relevant parameters are a total stellar mass of $\approx 8800\,\pm 800$M$_{\odot}$ and average reddening E(B$-$V) $\approx 0.22-0.24$ mag, with a differential reddening $\delta$E(B$-$V)$\approx 0.04$ mag.

[5]  arXiv:1610.06182 [pdf, other]
Title: Bayesian analysis of spatial-dependent cosmic-ray propagation: astrophysical background of antiprotons and positrons
Comments: 17 pages, 14 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

The AMS-02 experiment has reported a new measurement of the antiproton/proton ratio in Galactic cosmic rays (CRs). In the energy range $E\sim\,$60-450 GeV, this ratio is found to be remarkably constant. Using recent data on CR proton, helium, carbon, 10Be/9Be, and B/C ratio, we have performed a global Bayesian analysis based on a Markov-Chain Monte-Carlo sampling algorithm under a "two halo model" of CR propagation. In this model, CRs are allowed to experience a different type of diffusion when they propagate in the region close of the Galactic disk. We found that the vertical extent of this region is about 900 pc above and below the disk, and the corresponding diffusion coefficient scales with energy as $D\sim\,E^{0.15}$, describing well the observations on primary CR spectra, secondary/primary ratios and anisotropy. Under this model we have carried out improved calculations of antiparticle spectra arising from secondary CR production and their corresponding uncertainties. We made use of Monte-Carlo generators and accelerator data to assess the antiproton production cross-sections and their uncertainties. While the positron excess requires the contribution of additional unknown sources, we found that the new AMS-02 antiproton data are consistent, within the estimated uncertainties, with our calculations based on secondary production.

[6]  arXiv:1610.06183 [pdf, ps, other]
Title: La Fin du MOND? Λ CDM is Fully Consistent with SPARC Acceleration Law
Comments: 5 pages, 3 figures, submitted to ApJ Letters
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Recent analysis (McGaugh et al. 2016) of the SPARC galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves, and the acceleration due to the baryonic components of the disc. It has been suggested that this relation may be evidence for new physics, beyond {\Lambda}CDM . In this letter we show that the 18 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star forming, rotationally supported discs were simulated with a WMAP3 {\Lambda}CDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration law is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.

[7]  arXiv:1610.06184 [pdf, other]
Title: A new asteroseismic diagnostic for internal rotation in $γ$ Doradus stars
Comments: 17 pages, 14 figures, 4 tables, accepted for publication on MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

With four years of nearly-continuous photometry from Kepler, we are finally in a good position to apply asteroseismology to $\gamma$ Doradus stars. In particular several analyses have demonstrated the possibility to detect non-uniform period spacings, which have been predicted to be directly related to rotation. In the present work, we define a new seismic diagnostic for rotation in $\gamma$ Doradus stars that are too rapidly rotating to present rotational splittings. Based on the non uniformity of their period spacings, we define the observable $\Sigma$ as the slope of the period spacing when plotted as a function of period. We provide a one-to-one relation between this observable $\Sigma$ and the internal rotation, which applies widely in the instability strip of $\gamma$ Doradus stars. We apply the diagnostic to a handful of stars observed by Kepler. Thanks to g-modes in $\gamma$ Doradus stars, we are now able to determine the internal rotation of stars on the lower main sequence, which is still not possible for Sun-like stars.

[8]  arXiv:1610.06185 [pdf, other]
Title: The radii and limb darkenings of Alpha Centauri A and B - Interferometric measurements with VLTI/PIONIER
Comments: 15 pages, 9 figures, in press for Astronomy & Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The photospheric radius is one of the fundamental parameters governing the radiative equilibrium of a star. We report new observations of the nearest solar-type stars Alpha Centauri A (G2V) and B (K1V) with the VLTI/PIONIER optical interferometer. The combination of four configurations of the VLTI enable us to measure simultaneously the limb darkened angular diameter thetaLD and the limb darkening parameters of the two solar-type stars in the near-infrared H band (lambda = 1.65 microns). We obtain photospheric angular diameters of thetaLD(A) = 8.502 +/- 0.038 mas (0.43%) and thetaLD(B) = 5.999 +/- 0.025 mas (0.42%), through the adjustment of a power law limb darkening model. We find H band power law exponents of alpha(A) = 0.1404 +/- 0.0050 (3.6%) and alpha(B) = 0.1545 +/- 0.0044 (2.8%), which closely bracket the observed solar value (alpha_sun = 0.15027). Combined with the parallax pi = 747.17 +/- 0.61 mas recently determined, we derive linear radii of RA = 1.2234 +/- 0.0053 Rsun (0.43%) and RB = 0.8632 +/- 0.0037 Rsun (0.43%). The power law exponents that we derive for the two stars indicate a significantly weaker limb darkening than predicted by both 1D and 3D stellar atmosphere models. As this discrepancy is also observed on near-infrared limb darkening profile of the Sun, an improvement of the calibration of stellar atmosphere models is clearly needed. The reported PIONIER visibility measurements of Alpha Cen A and B provide a robust basis to validate the future evolutions of these models.

[9]  arXiv:1610.06187 [pdf, other]
Title: Testing universality of cosmic-ray acceleration with proton/helium data from AMS and Voyager-1
Comments: 11 pages, 5 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The AMS experiment has recently measured the proton and helium spectra in cosmic rays (CRs) in the GeV-TeV energy region. The two spectra are found to progressively harden at rigidity $R = pc/Z >\,$200 GV, while the p/He ratio is found to fall off steadily as $p/He\sim\,R^{-0.08}$. The p/He decrease is often interpreted in terms of particle-dependent acceleration, which is in contrast with the universal nature of DSA mechanisms. A different explanation is that the p-He anomaly reflects a flux transition between two components: a sub-TeV flux component (L) provided by hydrogen-rich supernova remnants with soft acceleration spectra, and a multi-TeV component (G) injected by younger sources with amplified magnetic fields and hard spectra. In this scenario the universality of particle acceleration is not violated because both sources provide composition-blind injection spectra. The present work is aimed at testing this model using the low-energy CR flux which is expected to be L-dominated. However, at $E\sim\,$0.5-10 GeV, the fluxes are affected by energy losses and solar modulation for which a proper modeling is required. To set the properties of the L-source, I have used the Voyager-1 data collected in the interstellar space. To compare my calculations with the AMS data, I have performed a determination of the force-field modulation parameter using neutron monitor measurements. I will show that the recent $p-He$ data reported by AMS and Voyager-1 are in good agreement with the predictions of such a scenario, supporting the hypothesis that CRs are injected in the Galaxy by universal, composition-blind accelerators. At energies below $\sim\,$0.5 GeV/n, however, the model is found to underpredict the data collected by PAMELA from 2006 to 2010. This discrepancy is found to increase with increasing solar activity, reflecting an expected breakdown of the force-field approximation.

[10]  arXiv:1610.06189 [pdf, ps, other]
Title: MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II
Authors: Stacy S. McGaugh
Comments: 5 pages, no figures. Submitted to ApJ Letters
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Crater II is an unusual object among the dwarf satellite galaxies of the Local Group in that it has a very large size for its small luminosity. This provides a strong test of MOND, as Crater II should be in the deep MOND regime ($g_{in} \approx 34\;\mathrm{km}^2\,\mathrm{s}^{-2}\,\mathrm{kpc}^{-1} \ll a_0 = 3700\;\mathrm{km}^2\,\mathrm{s}^{-2}\,\mathrm{kpc}^{-1}$). Despite its great distance ($\approx 120$ kpc) from the Milky Way, the external field of the host ($g_{ex} \approx 282\; \mathrm{km}^2\,\mathrm{s}^{-2}\,\mathrm{kpc}^{-1}$) comfortably exceeds the internal field. Consequently, Crater II should be subject to the external field effect, a feature unique to MOND. This leads to the prediction of a very low velocity dispersion: $\sigma_{efe} = 2.1^{+0.9}_{-0.6}\;\mathrm{km}\,\mathrm{s}^{-1}$.

[11]  arXiv:1610.06190 [pdf, other]
Title: Simulations of the Fe K-alpha Energy Spectra from Gravitationally Microlensed Quasars
Authors: Henric Krawczynski (Washington University in Saint Louis), George Chartas (College of Charleston)
Comments: 13 pages, 14 figures, submitted to Phys. Rev. D
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Chartas et al. (2012, 2016a,b) reported the discovery of multiple and energy variable peaks of the Fe K-alpha emission from the gravitationally lensed quasar RX J1131-1231. The authors explain the observations by the microlensing (produced by the stars of the lensing galaxy) of the emission from different regions of the accretion disk with different Doppler and gravitational frequency shifts. In this paper, we combine detailed simulations of the Fe K-alpha emission of the accretion disk in the Kerr spacetime of the black hole with calculations of the effect of gravitational microlensing on the observed energy spectra. The simulations give multiply peaked energy spectra similar to the observed ones. We explore the dependence of the spectral characteristics on black hole spin, accretion disk inclination, corona height, and microlensing amplification factor, and show that the measurements can be used to constrain these parameters. The detailed simulations described in this paper confirm the earlier constraints on the inclination of QSO RX J1131-1231, and allow us to constrain the height of the quasar lamppost corona above the black hole to be smaller than 30 gravitational radii. More detailed modeling of the spectral peak energy and energy difference distributions should make it possible to use the data to improve constraints on the accretion disk inclination, the corona height, and the black hole spin.

[12]  arXiv:1610.06192 [pdf, other]
Title: Initial conditions for inflation
Comments: 9 pages, 1 figure
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

A novel proposal is presented, which manages to overcome the initial conditions problem of inflation with a plateau. An earlier period of proto-inflation, beginning at Planck scale, accounts for the Universe expansion and arranges the required initial conditions for inflation on the plateu to commence. We show that, if proto-inflation is power-law, it does not suffer from any eternal inflationary stage. A simple model realisation is constructed in the context of $\alpha$-attractors, which can both generate the inflationary plateau and the exponential slopes around it, necessary for the two inflation stages. Our mechanism allows to assume chaotic initial conditions at the Planck scale for proto-inflation, it is generic and it is shown to work without fine-tunings.

[13]  arXiv:1610.06196 [pdf, ps, other]
Title: Structure of radiation dominated gravitoturbulent quasar discs
Comments: Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Self-gravitating accretion discs in a gravitoturbulent state, including radiation and gas pressures, are studied using a set of new analytical solutions. While the Toomre parameter of the disc remains close to its critical value for the onset of gravitational instability, the dimensionless stress parameter is uniquely determined from the thermal energy reservoir of the disc and its cooling rate. Our solutions are applicable to the accretion discs with dynamically important radiation pressure like in the quasars discs. We show that physical quantities of a gravitoturbulent disc in the presence of radiation are significantly modified compared to solutions with only gas pressure. We show that the dimensionless stress parameter is an increasing function of the radial distance so that its steepness strongly depends on the accretion rate. In a disc without radiation its slope is 4.5, however, we show that in the presence of radiation, it varies between 2 and 4.5 depending on the accretion rate and the central mass. As for the surface density, we find a shallower profile with an exponent -2 in a disc with sub-Eddington accretion rate compared to a similar disc, but without radiation, where its surface density slope is -3 independent of the accretion rate. We then investigate gravitational stability of the disc when the stress parameter reaches to its critical value. In order to self-consistently determine the fragmentation boundary, however, it is shown that the critical value of the stress parameter is a power-law function of the ratio of gas pressure and the total pressure and its exponent is around 1.7. We also estimate the maximum mass of the central black hole using our analytical solutions.

[14]  arXiv:1610.06206 [pdf, ps, other]
Title: HERUS: A CO Atlas from SPIRE Spectroscopy of local ULIRGs
Comments: MNRAS, accepted
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the Herschel SPIRE Fourier Transform Spectroscopy (FTS) atlas for a complete flux limited sample of local Ultra-Luminous Infra-Red Galaxies as part of the HERschel ULIRG Survey (HERUS). The data reduction is described in detail and was optimized for faint FTS sources with particular care being taken with the subtraction of the background which dominates the continuum shape of the spectra. Special treatment in the data reduction has been given to any observation suffering from artefacts in the data caused by anomalous instrumental effects to improve the final spectra. Complete spectra are shown covering $200 - 671\mu$m with photometry in the SPIRE bands at 250$\mu$m, 350$\mu$m and 500$\mu$m. The spectra include near complete CO ladders for over half of our sample, as well as fine structure lines from [CI] 370 $\mu$m, [CI] 609 $\mu$m, and [NII] 205 $\mu$m. We also detect H$_{2}$O lines in several objects. We construct CO Spectral Line Energy Distributions (SLEDs) for the sample, and compare their slopes with the far-infrared colours and luminosities. We show that the CO SLEDs of ULIRGs can be broadly grouped into three classes based on their excitation. We find that the mid-J (5$<$J$<$8) lines are better correlated with the total far-infrared luminosity, suggesting that the warm gas component is closely linked to recent star-formation. The higher J transitions do not linearly correlate with the far-infrared luminosity, consistent with them originating in hotter, denser gas unconnected to the current star-formation. {\bf We conclude that in most cases more than one temperature components are required to model the CO SLEDs.}

[15]  arXiv:1610.06215 [pdf, other]
Title: Density-dependent clustering: I. Pulling back the curtains on motions of the BAO peak
Comments: Submitted to MNRAS, 8 pages, 5 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The most common statistic used to analyze large-scale structure surveys is the correlation function, or power spectrum. Here, we show how `slicing' the correlation function on local density brings sensitivity to interesting non-Gaussian features in the large-scale structure, such as the expansion or contraction of baryon acoustic oscillations (BAO) according to the local density. The sliced correlation function measures the large-scale flows that smear out the BAO, instead of just correcting them as reconstruction algorithms do. Thus, we expect the sliced correlation function to be useful in constraining the growth factor, and modified gravity theories that involve the local density. We find that the full run of the BAO peak location with density is best revealed when slicing on a $\sim$40 Mpc/$h$ filtered density. But slicing on a $\sim100$ Mpc/$h$ filtered density may be most useful in distinguishing between underdense and overdense regions, whose BAO peaks are shifted by a substantial $\sim$5 Mpc/$h$ at $z=0$. We also introduce `curtain plots' showing how local densities drive particle motions toward or away from each other over the course of an $N$-body simulation.

[16]  arXiv:1610.06216 [pdf, other]
Title: A Versatile Technique to Enable sub-milli-Kelvin Instrument Stability for Precise Radial Velocity Measurements: Tests with the Habitable-zone Planet Finder
Comments: Accepted for publication in ApJ. 16 pages, 10 figures. For a publicly available SolidWorks model of the HPF ECS, see this https URL
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP)

Insufficient instrument thermo-mechanical stability is one of the many roadblocks for achieving 10cm/s Doppler radial velocity (RV) precision, the precision needed to detect Earth-twins orbiting Solar-type stars. Highly temperature and pressure stabilized spectrographs allow us to better calibrate out instrumental drifts, thereby helping in distinguishing instrumental noise from astrophysical stellar signals. We present the design and performance of the Environmental Control System (ECS) for the Habitable-zone Planet Finder (HPF), a high-resolution (R=50,000) fiber-fed near infrared (NIR) spectrograph for the 10m Hobby Eberly Telescope at McDonald Observatory. HPF will operate at 180K, driven by the choice of an H2RG NIR detector array with a 1.7micron cutoff. This ECS has demonstrated 0.6mK RMS stability over 15 days at both 180K and 300K, and maintained high quality vacuum (<$10^{-7}$Torr) over months, during long-term stability tests conducted without a planned passive thermal enclosure surrounding the vacuum chamber. This control scheme is versatile and can be applied as a blueprint to stabilize future NIR and optical high precision Doppler instruments over a wide temperature range from ~77K to elevated room temperatures. A similar ECS is being implemented to stabilize NEID, the NASA/NSF NN-EXPLORE spectrograph for the 3.5m WIYN telescope at Kitt Peak, operating at 300K. A full SolidWorks 3D-CAD model and a comprehensive parts list of the HPF ECS are included with this manuscript to facilitate the adaptation of this versatile environmental control scheme in the broader astronomical community.

[17]  arXiv:1610.06223 [pdf, ps, other]
Title: Constraints on the Early Terrestrial Surface UV Environment Relevant to Prebiotic Chemistry
Comments: Accepted to Astrobiology. Preprint format; 3 tables, 29 figures, 95 pages)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The UV environment is a key boundary condition for the origin of life. However, considerable uncertainty exists as to planetary conditions and hence surface UV at abiogenesis. Here, we present two-stream multi-layer clear-sky calculations of the UV surface radiance on Earth at 3.9 Ga to constrain the UV surface fluence as a function of albedo, solar zenith angle (SZA), and atmospheric composition. Variation in albedo and latitude (through SZA) can affect maximum photoreaction rates by a factor of >10.4; for the same atmosphere, photoreactions can proceed an order of magnitude faster at the equator of a snowball Earth than at the poles of a warmer world. Surface conditions are important considerations when computing prebiotic UV fluences. For climatically reasonable levels of CO2, fluence shortward of 189 nm is screened out, meaning that prebiotic chemistry is robustly shielded from variations in UV fluence due to solar flares or variability. Strong shielding from CO2 also means that the UV surface fluence is insensitive to plausible levels of CH4, O2, and O3. At scattering wavelengths, UV fluence drops off comparatively slowly with increasing CO2 levels. However, if SO2 and/or H2S can build up to the 1-100 ppm level as hypothesized by some workers, then they can dramatically suppress surface fluence and hence prebiotic photoprocesses. H2O is a robust UV shield for <198 nm. This means that regardless of the levels of other atmospheric gases, fluence <198 nm is only available for cold, dry atmospheres, meaning sources with emission <198 nm (e.g. ArF eximer lasers) can only be used in simulations of cold environments with low abundance of volcanogenic gases. On the other hand, fluence at 254 nm is unshielded by H2O and is available across a broad range of CO2 columns, meaning that mercury lamps are suitable for initial studies regardless of the uncertainty in primordial H2O and CO2 levels.

[18]  arXiv:1610.06234 [pdf, other]
Title: Gamma-Ray Emission from Supernova Remnants and Surrounding Molecular Clouds
Authors: Stefano Gabici (APC)
Comments: Invited talk at GAMMA2016. 12 pages, 7 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Galactic cosmic rays are believed to be accelerated at supernova remnant shocks. Gamma-ray observations of both supernova remnants and associated molecular clouds have been used in several occasions to test (so far quite successfully) this popular hypothesis. Despite that, a conclusive solution to the problem of cosmic ray origin is still missing, and further observational and theoretical efforts are needed. In this paper, the current status of these investigations is briefly reviewed.

[19]  arXiv:1610.06243 [pdf, other]
Title: Detection of faint broad emission lines in type 2 AGN: I. Near infrared observations and spectral fitting
Comments: MNRAS in press; published on MNRAS Advance Access, issue September 16, 2016
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present medium resolution near infrared spectroscopic observations of 41 obscured and intermediate class AGN (type 2, 1.9 and 1.8; AGN2) with redshift $z \lesssim$0.1, selected from the Swift/BAT 70-month catalogue. The observations have been carried out in the framework of a systematic study of the AGN2 near infrared spectral properties and have been executed using ISAAC/VLT, X-shooter/VLT and LUCI/LBT, reaching an average S/N ratio of $\sim$30 per resolution element. For those objects observed with X-shooter we also obtained simultaneous optical and UV spectroscopy. We have identified a component from the broad line region in 13 out of 41 AGN2, with FWHM ${\rm > 800 }$ km/s. We have verified that the detection of the broad line region components does not significantly depend on selection effects due to the quality of the spectra, the X-ray or near infrared fluxes, the orientation angle of the host galaxy or the hydrogen column density measured in the X-ray band. The average broad line region components found in AGN2 has a significantly (a factor 2) smaller FWHM if compared with a control sample of type 1 AGN.

[20]  arXiv:1610.06277 [pdf, other]
Title: The near-surface methane humidity on Titan
Comments: Accepted for publication in Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We retrieve vertical and meridional variations of methane mole fraction in Titan's lower troposphere by re-analyzing near-infrared ground-based observations from 17 July 2014 UT (Adamkovics et al., 2016). We generate synthetic spectra using atmospheric methane profiles that do not contain supersaturation or discontinuities to fit the observations, and thereby retrieve minimum saturation altitudes and corresponding specific humidities in the boundary layer. We relate these in turn to surface-level relative humidities using independent surface temperature measurements. We also compare our results with general circulation model simulations to interpret and constrain the relationship between humidities and surface liquids. The results show that Titan's lower troposphere is undersaturated at latitudes south of 60N, consistent with a dry surface there, but increases in humidity toward the north pole indicate appreciable surface liquid coverage. While our observations are consistent with considerably more liquid methane existing at the north pole than is present in observed lakes, a degeneracy between low-level methane and haze leads to substantial uncertainty in determining the extent of the source region.

[21]  arXiv:1610.06285 [pdf, other]
Title: Top Argelander Stars: Pedagogy & Prize
Authors: S. R. Kulkarni
Comments: 9 pages, 1 figure, 3 tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Stellar astronomy, fueled by massive capital investments, advances in numerical modeling and theory, is resurgent and arguably is on the verge of a magnificent renaissance. Powerful time domain optical surveys, both on ground and in space, are producing data on variable stars on an unprecedented industrial scale. Those with deep knowledge of variable stars will stand to benefit from this resurgence. Notwithstanding these developments, in some astronomical communities, classical stellar astronomy has been in the doldrums. I offer a modest proposal to establish a basic level of familiarity with variable stellar phenomenology and an attractive scheme to make research in variable star astronomy visible, alluring and fashionable.

[22]  arXiv:1610.06313 [pdf, other]
Title: William Herschel Telescope site characterization using the MOAO pathfinder CANARY on-sky data
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Canary is the Multi-Object Adaptive Optics (MOAO) pathfinder for the future MOAO-assisted Integral-Field Units (IFU) proposed for Extremely Large Telescopes (ELT). The MOAO concept relies on tomographically reconstructing the turbulence using multiple measurements along different lines of sight. Tomography requires the knowledge of the statistical turbulence parameters, commonly recovered from the system telemetry using a dedicated profiling technique. For demonstration purposes with the MOAO pathfinder Canary , this identification is performed thanks to the Learn & Apply (L&A) algorithm, that consists in model- fitting the covariance matrix of WFS measurements dependent on relevant parameters: $C_n^2(h)$ profile, outer scale profile and system mis-registration. We explore an upgrade of this algorithm, the Learn 3 Steps (L3S) approach, that allows one to dissociate the identification of the altitude layers from the ground in order to mitigate the lack of convergence of the required empirical covariance matrices therefore reducing the required length of data time-series for reaching a given accuracy. For nominal observation conditions, the L3S can reach the same level of tomographic error in using five times less data frames than the L&A approach. The L3S technique has been applied over a large amount of Canary data to characterize the turbu- lence above the William Herschel Telescope (WHT). These data have been acquired the 13th, 15th, 16th, 17th and 18th September 2013 and we find 0.67"/8.9m/3.07m/s of total seeing/outer scale/wind-speed, with 0.552"/9.2m/2.89m/s below 1.5 km and 0.263"/10.3m/5.22m/s between 1.5 and 20 km. We have also de- termined the high altitude layers above 20 km, missed by the tomographic reconstruction on Canary , have a median seeing of 0.187" and have occurred 16% of observation time.

[23]  arXiv:1610.06318 [pdf, other]
Title: Submillimeter polarization observation of the protoplanetary disk around HD 142527
Comments: 8 pages, 3 figures, accepted for publication in ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We present the polarization observations toward the circumstellar disk around HD 142527 by using Atacama Large Millimeter/submillimeter Array (ALMA) at the frequency of 343 GHz. The beam size is $0.51 " \times 0.44 "$, which corresponds to the spatial resolution of $\sim$ 71 $\times$ 62 AU. The polarized intensity displays a ring-like structure with a peak located on the east side with a polarization fraction of $P= 3.26 \pm 0.02$ %, which is different from the peak of the continuum emission from the northeast region. The polarized intensity is significantly weaker at the peak of the continuum where $P= 0.220 \pm 0.010$ %. The polarization vectors are in the radial direction in the main ring of the polarized intensity, while there are two regions outside at the northwest and northeast areas where the vectors are in the azimuthal direction. If the polarization vectors represent the magnetic field morphology, the polarization vectors indicate the toroidal magnetic field configuration on the main ring and the poloidal fields outside. On the other hand, the flip of the polarization vectors is predicted by the self-scattering of thermal dust emission due to the change of the direction of thermal radiation flux. Therefore, we conclude that self-scattering of thermal dust emission plays a major role in producing polarization at millimeter wavelengths in this protoplanetary disk. Also, this puts a constraint on the maximum grain size to be approximately 150 ${\rm \mu m}$ if we assume compact spherical dust grains.

[24]  arXiv:1610.06333 [pdf, ps, other]
Title: Suzaku Observations of Spectral Variations of the Ultra Luminous X-ray Source Holmberg IX X-1
Comments: 10 pages, 6 figures, accepted for publication in PASJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Observations of the Ultra Luminous X-ray source (ULX) Holmberg IX X-1 were carried out with Suzaku twice, once on 2012 April 13 and then on 2012 October 24, with exposures of 180 ks and 217 ks, respectively. The source showed a hard power-law shape spectrum with a mild cutoff at $\sim 8$ keV, which is typical of ULXs when they are relatively dim. On both occasions, the 0.6-11 keV spectrum was explained successfully in terms a cool ($\sim 0.2$ keV) multi-color disk blackbody emission model and a thermal Comptonization emission produced by an electron cloud with a relatively low temperature and high optical depth, assuming that a large fraction of the disk-blackbody photons are Comptonized whereas the rest is observed directly. The 0.5-10 keV luminosity was $1.2\times10^{40}$ erg s$^{-1}$ in April, and $\sim 14\%$ higher in October. This brightening was accompanied by spectral softening in $\ge 2$ keV, with little changes in the $\le 2$ keV spectral shape. This behavior can be understood if the accretion disk remains unchanged, while the electron cloud covers a variable fraction of the disk. The absorbing column density was consistent with the galactic line-of sight value, and did not vary by more than $1.6\times 10^{21}$ cm$^{-2}$. Together with the featureless spectra, these properties may not be reconciled easily with the super-critical accretion scenario of this source.

[25]  arXiv:1610.06339 [pdf, other]
Title: Combined Nucleosynthetic Yields of Multiple First Stars
Comments: 3 pages, 2 figures, NIC 2016 Conference Proceedings
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Modern numerical simulations of the formation of the first stars predict that the first stars formed in multiples. In those cases, the chemical yields of multiple supernova explosions may have contributed to the formation of a next generation star. We match the chemical abundances of the oldest observed stars in the universe to a database of theoretical supernova models, to show that it is likely that the first stars formed from the ashes of two or more progenitors.

[26]  arXiv:1610.06351 [pdf, other]
Title: Structural Transition in the NGC 6251 Jet: An Interplay with the Supermassive Black Hole and Its Host Galaxy
Comments: 12 pages, accepted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The structure of the NGC 6251 jet at the milliarcsecond scale is investigated using the images taken with the European VLBI Network and the Very Long Baseline Array. We detect a structural transition of the jet from a parabolic to a conical shape at a distance of (1-2) x 10^5 times the Schwarzschild radius from the central engine, which is close to the sphere of gravitational influence (SGI) of the supermassive black hole (SMBH). We also examine the jet pressure profiles with the synchrotron minimum energy assumption to discuss the physical origin of the structural transition. The NGC 6251 jet, together with the M 87 jet, suggests a fundamental process of the structural transition in active galactic nuclei (AGN) jets. The collimated AGN jets are characterized by their external galactic medium, showing that AGN jets interplay with the SMBH and its host galaxy.

[27]  arXiv:1610.06372 [pdf, other]
Title: The influence of dust grain porosity on the analysis of debris disc observations
Comments: accepted by MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Debris discs are often modelled assuming compact dust grains, but more and more evidence for the presence of porous grains is found. We aim at quantifying the systematic errors introduced when modelling debris discs composed of porous dust with a disc model assuming spherical, compact grains. We calculate the optical dust properties derived via the fast, but simple effective medium theory. The theoretical lower boundary of the size distribution -- the so-called 'blowout size' -- is compared in the cases of compact and porous grains. Finally, we simulate observations of hypothetical debris discs with different porosities and feed them into a fitting procedure using only compact grains. The deviations of the results for compact grains from the original model based on porous grains are analysed. We find that the blowout size increases with increasing grain porosity up to a factor of two. An analytical approximation function for the blowout size as a function of porosity and stellar luminosity is derived. The analysis of the geometrical disc set-up, when constrained by radial profiles, are barely affected by the porosity. However, the determined minimum grain size and the slope of the grain size distribution derived using compact grains are significantly overestimated. Thus, the unexpectedly high ratio of minimum grain size to blowout size found by previous studies using compact grains can be partially described by dust grain porosity, although the effect is not strong enough to completely explain the trend.

[28]  arXiv:1610.06375 [pdf, ps, other]
Title: NIHAO XII: galactic uniformity in a $Λ$CDM universe
Authors: Aaron A. Dutton (NYUAD), Aura Obreja (NYUAD), Liang Wang (ICRAR, PMO), Thales A. Gutcke (MPIA), Tobias Buck (MPIA), Silviu M. Udrescu (NYUAD), Jonas Frings (MPIA), Gregory S. Stinson (MPIA), Xi Kang (PMO), Andrea V. Macciò (NYUAD, MPIA)
Comments: 14 pages, 10 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We use a sample of 83 high-resolution cosmological zoom-in simulations and a semi-analytic model to study the stocasticity of galaxy formation in haloes ranging from dwarf ($M_{200} \sim 10^{10} M_{\odot}$) to Milky Way ($M_{200}\sim 10^{12}M_{\odot}$) masses. Our simulated galaxies reproduce the observed inefficiency of galaxy formation as expressed through the stellar, gas and baryonic Tully-Fisher (TF) relations. The scatter in our simulated TF relations is very small, and velocity dependent. For HI velocities in the range ($70 < V < 220$ km/s), the scatter is just 0.08 to 0.14 dex, consistent with the observed intrinsic scatter. At low velocities ($20 < V < 70$ km/s), the simulated scatter is 0.20-0.25 dex, which could be tested with future observations. The scatter in the stellar mass vs dark halo velocity relation is constant for $30 < V < 200$ km/s, and smaller ($\simeq 0.17$ dex) when using the maximum circular velocity of the dark matter only simulation, $V_{max}^{DMO}$, compared to the virial velocity ($V_{200}$ or $V_{200}^{DMO}$). The scatter in stellar mass is correlated with halo concentration, and is minimized when using a circular velocity at a fixed fraction of the virial radius $\simeq 0.4 R_{200}$ or with $V_{\alpha}=V_{200}^{DMO} (V_{max}^{DMO}/V_{200}^{DMO})^\alpha$ with $\alpha\simeq 0.7$, consistent with constraints from halo clustering. This uniformity in galaxy formation efficiency we see in our hydrodynamical simulations and a semi-analytic model proves the simplicity and self-regulating nature of galaxy formation in a $\Lambda$CDM universe.

[29]  arXiv:1610.06380 [pdf, ps, other]
Title: R-modes and neutron star recycling scenario
Comments: 14 pages, 3 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)

To put new constraints on the r-mode instability window, we analyse formation of millisecond pulsars (MSPs) within the recycling scenario, making use of three sets of observations: (a) X-ray observations of neutron stars (NSs) in low-mass X-ray binaries; (b) timing of millisecond pulsars (MSPs); and (c) X-ray and UV observations of MSPs. As shown in previous works, r-mode dissipation by shear viscosity is not sufficient to explain observational set (a), and enhanced r-mode dissipation at internal temperatures $T^\infty\sim 10^8$ K is required to stabilize the observed NSs. Here we argue, that models with enhanced bulk viscosity can hardly lead to a self-consistent explanation of observational set (a) due to strong neutrino emission, which is typical for these models (unrealistically powerful energy source is required to keep NSs at the observed temperatures). We also demonstrate that the observational set (b) requires enhanced r-mode dissipation at low temperatures, $T^\infty\sim(1-2)\times 10^7$ K. Observational set (c) allows us to set an upper limit on the red-shifted internal temperatures of MSPs, $T^\infty<2\times 10^7$ K (assuming a canonical NS with the accreted crust). Recycling scenario can produce MSPs at these temperatures only if r-mode instability is suppressed in the whole MSP spin frequency range ($\nu\lesssim 750$ Hz) at temperatures $2\times 10^7\lesssim T^\infty\lesssim 3 \times 10^7$ K, providing thus a new constraint on the r-mode instability window. These observational constraints are analysed in more details in application to the resonance uplift scenario of Gusakov et al. [Phys. Rev. Lett., 112 (2014), 151101].

[30]  arXiv:1610.06396 [pdf, ps, other]
Title: Photometric properties of intermediate redshift Type Ia Supernovae observed by SDSS-II Supernova Survey
Comments: 21 pages, 15 figures, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We have analyzed multi-band light curves of 328 intermediate redshift (0.05 <= z < 0.24) type Ia supernovae (SNe Ia) observed by the Sloan Digital Sky Survey-II Supernova Survey (SDSS-II SN Survey). The multi-band light curves were parameterized by using the Multi-band Stretch Method, which can simply parameterize light curve shapes and peak brightness without dust extinction models. We found that most of the SNe Ia which appeared in red host galaxies (u - r > 2.5) don't have a broad light curve width and the SNe Ia which appeared in blue host galaxies (u - r < 2.0) have a variety of light curve widths. The Kolmogorov-Smirnov test shows that the colour distribution of SNe Ia appeared in red / blue host galaxies is different (significance level of 99.9%). We also investigate the extinction law of host galaxy dust. As a result, we find the value of Rv derived from SNe Ia with medium light curve width is consistent with the standard Galactic value. On the other hand, the value of Rv derived from SNe Ia that appeared in red host galaxies becomes significantly smaller. These results indicate that there may be two types of SNe Ia with different intrinsic colours, and they are obscured by host galaxy dust with two different properties.

[31]  arXiv:1610.06397 [pdf, other]
Title: Luminescence of water or ice as a new detection method for magnetic monopoles
Authors: Anna Obertacke Pollmann (for the IceCube Collaboration)
Comments: Proceedings of the 5th International Conference on New Frontiers in Physics (ICNFP '16), to be submitted to EPJ web conf
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Detectors (physics.ins-det)

Cosmic ray detectors use air as a radiator for luminescence. In water and ice, Cherenkov light is the dominant light producing mechanism when the particle's velocity exceeds the Cherenkov threshold, approximately three quarters of the speed of light in vacuum. Luminescence is produced by highly ionizing particles passing through matter due to the electronic excitation of the surrounding molecules. The observables of luminescence, such as the wavelength spectrum and decay times, are highly dependent on the properties of the medium, in particular, temperature and purity. The results for the light yield of luminescence of previous measurements vary by two orders of magnitude. It will be shown that even for the lowest measured light yield, luminescence is an important signature of highly ionizing particles below the Cherenkov threshold. These could be magnetic monopoles or other massive and highly ionizing exotic particles. With the highest observed efficiencies, luminescence may even contribute significantly to the light output of standard model particles such as the PeV IceCube neutrinos. We present analysis techniques to use luminescence in neutrino telescopes and discuss experimental setups to measure the light yield of luminescence for the particular conditions in neutrino detectors.

[32]  arXiv:1610.06407 [pdf, other]
Title: The perihelion activity of comet 67P/Churyumov-Gerasimenko as seen by robotic telescopes
Comments: To appear in special issue of MNRAS "The ESLAB 50 Symposium - spacecraft at comets from 1P/Halley to 67P/Churyumov-Gerasimenko"
Journal-ref: MNRAS 462, S138 (2016)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Around the time of its perihelion passage the observability of 67P/Churyumov-Gerasimenko from Earth was limited to very short windows each morning from any given site, due to the low solar elongation of the comet. The peak in the comet's activity was therefore difficult to observe with conventionally scheduled telescopes, but was possible where service/queue scheduled mode was possible, and with robotic telescopes. We describe the robotic observations that allowed us to measure the total activity of the comet around perihelion, via photometry (dust) and spectroscopy (gas), and compare these results with the measurements at this time by Rosetta's instruments. The peak of activity occurred approximately two weeks after perihelion. The total brightness (dust) largely followed the predictions from Snodgrass et al. 2013, with no significant change in total activity levels from previous apparitions. The CN gas production rate matched previous orbits near perihelion, but appeared to be relatively low later in the year.

[33]  arXiv:1610.06412 [pdf, ps, other]
Title: NuSTAR observations of the Dwarf Nova GK Persei in 2015: comparison between outburst and quiescent phases
Comments: 6 pages, 3 figures, "20th European White Dwarf Workshop" conference proceedings, submitted
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report on NuSTAR observations of the Intermediate Polar GK Persei which also behaves as a Dwarf Nova. It exhibited a Dwarf Nova outburst in 2015 March-April. The object was observed in 3-79 keV X-rays with NuSTAR, once at the outburst peak, and again in 2015 September during quiescence. The 5-50 keV flux during the outburst was 26 times higher than that during the quiescence. With a multi-temperature emission model and a reflection model, we derived the post-shock temperature as 19.2 +/- 0.7 keV in the outburst, and 38.5 +4.1/-3.6 keV in the quiescence. This temperature difference is considered to reflect changes in the radius at which the accreting matter, forming an accretion disk, is captured by the magnetosphere of the white dwarf (WD). Assuming that this radius scales as the power of -2/7 of the mass accretion rate, and utilizing the two temperature measurements, as well as the standard mass-radius relation of WDs, we determined the WD mass in GK Persei as 0.90 +/- 0.06 solar masses. The magnetic field is estimated as 4*10^5 G.

[34]  arXiv:1610.06424 [pdf]
Title: The contrivance of Neptune
Authors: Davor Krajnovic
Comments: A somewhat expanded version of the article published in A&G (October 2016). It differs in two additional text boxes pertaining to the Titius-Bode rule and the naming of the planet, and a correction to the table with pre-discovery sightings of Neptune. 17 pages, two figures and six explanatory boxes. Numeration of figures, tables and boxes is different from the published version
Journal-ref: Astronomy & Geophysics 2016 57 (5): 5.28-5.34
Subjects: History and Philosophy of Physics (physics.hist-ph); Earth and Planetary Astrophysics (astro-ph.EP); Physics and Society (physics.soc-ph)

Celebrating 170th anniversary of the discovery of Neptune, I review the story of the discovery that startled the world. The story is an interplay of scientific triumph and human weakness and an example of how science works in a socio-political context.

[35]  arXiv:1610.06428 [pdf, ps, other]
Title: The rotation of brown dwarfs
Authors: Aleks Scholz (University of St Andrews)
Comments: 4 pages, 2 figures, Perspective article for the Star Formation Newsletter no. 276, December 2015 (this http URL)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

One of the characteristic features of low-mass stars is their propensity to shed large amounts of angular momentum throughout their evolution. This distinguishs them from brown dwarfs which remain fast rotators over timescales of gigayears. Brown dwarfs with rotation periods longer than a couple of days have only been found in star forming regions and young clusters. This is a useful constraint on the mass dependency of mechanisms for angular momentum regular in stars. Rotational braking by disks and winds become highly inefficient in the substellar regime. In this short review I discuss the observational evidence for the fast rotation in brown dwarfs, the implications, and the link to the spin-mass relation in planets.

[36]  arXiv:1610.06460 [pdf, other]
Title: On the detectability of solar-like oscillations with the NASA TESS mission
Comments: Submitted to EPJ Web of Conferences, to appear in the Proceedings of the joint TASC2/KASC9 workshop - SPACEINN & HELAS8 conference; 5 pages, 4 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The upcoming NASA TESS mission will perform an all-sky survey for planets transiting bright nearby stars. In addition, its excellent photometric precision will enable asteroseismology of solar-type and red-giant stars. We apply a newly developed detection test along a sequence of stellar evolutionary tracks in order to predict the detectability of solar-like oscillations with TESS.

[37]  arXiv:1610.06463 [pdf, other]
Title: Tracing water vapor and ice during dust growth
Comments: Accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The processes that govern the evolution of dust and water (in the form of vapor or ice) in protoplanetary disks are intimately connected. We have developed a model that simulates dust coagulation, dust dynamics (settling, turbulent mixing), vapor diffusion, and condensation/sublimation of volatiles onto grains in a vertical column of a protoplanetary disk. We employ the model to study how dust growth and dynamics influence the vertical distribution of water vapor and water ice in the region just outside the radial snowline. Our main finding is that coagulation (boosted by the enhanced stickiness of icy grains) and the ensuing vertical settling of solids results in water vapor being depleted, but not totally removed, from the region above the snowline on a timescale commensurate with the vertical turbulent mixing timescale. Depending on the strength of the turbulence and the temperature, the depletion can reach factors of up to ${\sim}50$ in the disk atmosphere. In our isothermal column, this vapor depletion results in the vertical snowline moving closer to the midplane (by up to 2 gas scale heights) and the gas-phase C/O ratio above the vertical snowline increasing. Our findings illustrate the importance of dynamical effects and the need for understanding coevolutionary dynamics of gas and solids in planet-forming environments.

[38]  arXiv:1610.06480 [pdf, other]
Title: The Gaia-ESO Survey: calibration strategy
Authors: E. Pancino (INAF - OAA), the Gaia-ESO Survey collaboration
Comments: 17 pages, 18 figures, accepted by A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

The Gaia-ESO survey (GES) is now in its fifth and last year of observations, and has already produced tens of thousands of high-quality spectra of stars in all Milky Way components. This paper presents the strategy behind the selection of astrophysical calibration targets, ensuring that all GES results on radial velocities, atmospheric parameters, and chemical abundance ratios will be both internally consistent and easily comparable with other literature results, especially from other large spectroscopic surveys and from Gaia. The calibration of GES is particularly delicate because of: (i) the large space of parameters covered by its targets, ranging from dwarfs to giants, from O to M stars, and with a large range of metallicities, as well as including fast rotators, emission line objects, stars affected by veiling and so on; (ii) the variety of observing setups, with different wavelength ranges and resolution; and (iii) the choice of analyzing the data with many different state-of-the art methods, each stronger in a different region of the parameter space, which ensures a better understanding of systematic uncertainties. An overview of the GES calibration and homogenization strategy is also given, along with some examples of the usage and results of calibrators in GES iDR4 - the fourth internal GES data release, that will form the basis of the next GES public data release. The agreement between GES iDR4 recommended values and reference values for the calibrating objects are very satisfactory. The average offsets and spreads are generally compatible with the GES measurement errors, which in iDR4 data already meet the requirements set by the main GES scientific goals.

[39]  arXiv:1610.06481 [pdf, other]
Title: Science with the space-based interferometer LISA. IV: Probing inflation with gravitational waves
Comments: 53 pages, 18 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

We investigate the potential for the LISA space-based interferometer to detect the stochastic gravitational wave background produced from different mechanisms during inflation. Focusing on well-motivated scenarios, we study the resulting contributions from particle production during inflation, inflationary spectator fields with varying speed of sound, effective field theories of inflation with specific patterns of symmetry breaking and models leading to the formation of primordial black holes. The projected sensitivities of LISA are used in a model-independent way for various detector designs and configurations. We demonstrate that LISA is able to probe these well-motivated inflationary scenarios beyond the irreducible vacuum tensor modes expected from any inflationary background.

[40]  arXiv:1610.06491 [pdf, other]
Title: Spheroidal and ellipsoidal harmonic expansions of the gravitational potential of small Solar System bodies. Case study: Comet 67P/Churyumov-Gerasimenko
Comments: published in JGR Planets
Journal-ref: J. Geophys. Res. Planets, 121, 497-515 (2016)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Gravitational features are a fundamental source of information to learn more about the interior structure and composition of planets, moons, asteroids and comets. Gravitational field modeling typically approximates the target body with a sphere, leading to a representation in spherical harmonics. However, small celestial bodies are often irregular in shape, and hence poorly approximated by a sphere. A much better suited geometrical fit is achieved by a tri-axial ellipsoid. This is also mirrored in the fact that the associated harmonic expansion (ellipsoidal harmonics) shows a significantly better convergence behavior as opposed to spherical harmonics. Unfortunately, complex mathematics and numerical problems (arithmetic overflow) so far severely limited the applicability of ellipsoidal harmonics. In this paper, we present a method that allows expanding ellipsoidal harmonics to a considerably higher degree compared to existing techniques. We apply this novel approach to model the gravitational field of comet 67P, the final target of the Rosetta mission. The comparison of results based on the ellipsoidal parameterization with those based on the spheroidal and spherical approximations reveals that the latter is clearly inferior; the spheroidal solution, on the other hand, is virtually just as accurate as the ellipsoidal one. Finally, in order to generalize our findings, we assess the gravitational field modeling performance for some 400 small bodies in the solar system. From this investigation we generally conclude that the spheroidal representation is an attractive alternative to the complex ellipsoidal parameterization on the one hand, and the inadequate spherical representation on the other hand.

[41]  arXiv:1610.06522 [pdf, other]
Title: The canonical Luminous Blue Variable AG Car and its neighbor Hen 3-519 are much closer than previously assumed
Authors: Nathan Smith (1), Keivan G. Stassun (2,3) ((1) University of Arizona, (2) Vanderbilt University, (3) Fisk University)
Comments: 14 pages, 2 figures, 1 table. Submitted to AAS journals
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The strong mass loss of Luminous Blue Variables (LBVs) is thought to play a critical role in the evolution of massive stars, but the physics of their instability and their place in the evolutionary sequence remains uncertain and debated. A key to understanding their peculiar instability is their high observed luminosity, which for Galactic LBVs often depends on an uncertain distance estimate. Here we report direct distances and space motions of four canonical Milky Way LBVs---AG Car, HR Car, HD 168607, and (the LBV candidate) Hen 3-519---whose parallaxes and proper motions have been provided by the Gaia first data release. Whereas the distances of HR Car and HD 168607 are consistent with those previously adopted in the literature within the uncertainty, we find that the distances to Hen 3-519 and AG Car, both at $\sim$2 kpc, are much closer than the 6--8 kpc distances previously assumed. For Hen 3-519, this moves the star far from the locus of LBVs on the HR Diagram. AG Car has been considered a defining example of a classical LBV, but its lower luminosity also moves it off the S~Dor instability strip. The lower luminosities allow AG Car and Hen 3-519 to have passed through a previous red supergiant phase, they lower the mass estimates for their shell nebulae, and imply that binary evolution is needed to account for their peculiar properties. These lower luminosities and initial masses for LBVs may also have important implications for understanding LBVs as potential supernova progenitors. Improved distances from next year's Gaia data release, which will include additional LBVs, may alter our traditional view of LBVs.

[42]  arXiv:1610.06559 [pdf, other]
Title: Prospects for Cosmological Collider Physics
Comments: 19 pages, 12 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

It is generally expected that heavy fields are present during inflation, which can leave their imprint in late-time cosmological observables. The main signature of these fields is a small amount of distinctly shaped non-Gaussianity, which if detected, would provide a wealth of information about the particle spectrum of the inflationary Universe. Here we investigate to what extent these signatures can be detected or constrained using futuristic 21-cm surveys. We construct model-independent templates that extract the squeezed-limit behavior of the bispectrum, and examine their overlap with standard inflationary shapes and secondary non-Gaussianities. We then use these templates to forecast detection thresholds for different masses and couplings using a 3D reconstruction of modes during the dark ages ($z\sim 30-100$). We consider interactions of several broad classes of models and quantify their detectability as a function of the baseline of a dark ages interferometer. Our analysis shows that there exists the tantalizing possibility of discovering new particles with different masses and interactions with future 21-cm surveys.

[43]  arXiv:1610.06561 [pdf, ps, other]
Title: Detecting the Elusive Blazar Counter-Jets
Comments: 13 pages, 15 figures, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Detection of blazar pc scale counter-jets is difficult, but it can provide invaluable insight into the relativistic effects, radiative processes and the complex mechanisms of jet production, collimation and accelation in blazars. We build on recent populations models (optimized using the MOJAVE apparent velocity and redshift distributions) in order to derive the distribution of jet-to-counter-jet ratios and the flux densities of the counter-jet at different frequencies, in an effort to set minimum sensitivity limits required for existing and future telescope arrays in order to detect these elusive counter-jets. We find that: for the BL Lacs $5\%$ of their counter-jets have a flux-density higher than 100mJy, $15\%$ are higher than 10 mJy, and $32\%$ have higher flux-density than 1 mJy, whereas for the FSRQs $8\%$ have a flux-density higher than 10mJy, $17\%$ are higher than 1 mJy, and $32\%$ are higher than 0.1 mJy (at 15 GHz). Future telescopes like the SKA and newly operating like e-MERLIN and JVLA may detect up to $99\%$ of the BL Lac and $77\%$ of the FSRQ counter-jets. Sources with both low apparent velocity and a low Doppler factor make prime candidates for counter-jet detection. Combining our findings with literature values we have identified five such counter-jet detection candidates. Finally, we discuss possible effects beyond relativistic deboosting that may complicate the detection of counter-jets and that need to be accounted for in the interpretation of detections.