53 articles on Sunday, November 18


arXiv:1811.06542v1 [pdf, other]
Active Galaxy Science in the LSST Deep-Drilling Fields: Footprints, Cadence Requirements, and Total-Depth Requirements
Comments: 22 pages, white paper on LSST cadence optimization, comments welcome

This white paper specifies the footprints, cadence requirements, and total-depth requirements needed to allow the most-successful AGN studies in the four currently selected LSST Deep-Drilling Fields (DDFs): ELAIS-S1, XMM-LSS, CDF-S, and COSMOS. The information provided on cadence and total-depth requirements will also likely be applicable to enabling effective AGN science in any additional DDFs that are chosen.


arXiv:1811.06543v1 [pdf, other]
The Orbital Parameters of the Eclipsing High-Mass X-ray Binary Pulsar IGR J16493-4348 from Pulsar Timing
Comments: 21 pages, 13 figures, 9 tables, Accepted for publication in ApJ on 2018 November 9

IGR J16493-4348 is an eclipsing supergiant high-mass X-ray binary (sgHMXB), where accretion onto the compact object occurs via the radially outflowing stellar wind of its early B-type companion. We present an analysis of the system's X-ray variability and periodic modulation using pointed observations (2.5-25 keV) and Galactic bulge scans (2-10 keV) from the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA), along with Swift Burst Alert Telescope (BAT) 70-month snapshot (14-195 keV) and transient monitor (15-50 keV) observations. The orbital eclipse profiles in the PCA bulge scans and BAT light curves are modeled using asymmetric and symmetric step and ramp functions. We obtain an improved orbital period measurement of 6.7828 $\pm$ 0.0004 days from an observed minus calculated (O-C) analysis of mid-eclipse times derived from the BAT transient monitor and PCA scan data. No evidence is found for the presence of a strong photoionization or accretion wake. We refine the superorbital period to 20.067 $\pm$ 0.009 days from the discrete Fourier transform (DFT) of the BAT transient monitor light curve. A pulse period of 1093.1036 $\pm$ 0.0004 s is measured from a pulsar timing analysis using pointed PCA observations spanning $\sim$1.4 binary orbits. We present pulse times of arrival (ToAs), circular and eccentric timing models, and calculations of the system's Keplerian binary orbital parameters. We derive an X-ray mass function of $f_{x}(M)$ $=$ 13.2$^{+2.4}_{-2.5}$ $M_{\odot}$ and find a spectral type of B0.5 Ia for the supergiant companion through constraints on the mass and radius of the donor. Measurements of the eclipse half-angle and additional parameters describing the system geometry are provided.


arXiv:1811.06544v1 [pdf, other]
Kinematic links and the co-evolution of MHD winds, jets, and inner disks from a high-resolution optical [OI] survey
Comments: Accepted for publication on ApJ

We present a survey of optical [OI] emission at 6300 \AA\ toward 65 TTauri stars at the spectral resolution of $\sim7$ km/s. Past work identified a highly blueshifted velocity component (HVC) tracing microjets, and a less blueshifted low-velocity-component (LVC) attributed to winds. We focus here on the LVC kinematics to investigate links between winds, jets, accretion, and disk dispersal. We track the behavior of four types of LVC components: a broad and narrow component ("BC" and "NC") in LVCs that are decomposed into two Gaussians, which typically have an HVC, and the single-Gaussian LVC profiles separated into those that have an HVC ("SCJ") and those that do not ("SC"). LVC centroid velocities and line widths correlate with HVC equivalent width and accretion luminosity, suggesting that LVC/winds and HVC/jets are kinematically linked and connected to accretion. The deprojected HVC velocity correlates with accretion luminosity, showing that faster jets come with higher accretion. BC and NC kinematics correlate and their blueshifts are maximum at $\sim 35^{\circ}$, suggesting a conical wind geometry with this semi-opening angle. Only SCs include $n_{13-31}$ up to $\sim3$ and their properties correlate with this infrared index, showing that [OI] emission recedes to larger radii as the inner dust is depleted, tracing less dense/hot gas and a decrease in wind velocity. All together, these findings support a scenario where optically thick, accreting inner disks launch radially-extended MHD disk winds that feed jets, and where inner disk winds recede to larger radii and jets disappear in concert with dust depletion.


arXiv:1811.06545v1 [pdf, other]
Early-type galaxy density profiles from IllustrisTNG: I. Galaxy correlations and the impact of baryons
Comments: 23 pages, 18 figures, 8 tables. Submitted to MNRAS

We explore the isothermal total matter radial density profiles in early-type galaxies (ETGs) selected from the IllustrisTNG simulation. For a sample of 514 ETGs in the stellar mass range of $10^{10.7}\mathrm{M}_{\odot} \leqslant M_{\ast} \leqslant 10^{11.9}\mathrm{M}_{\odot}$ at $z = 0$, the total power-law slope has a mean of $\langle\gamma^{\prime}\rangle = 2.003 \pm 0.008$ and a standard deviation of $\sigma_{\gamma^{\prime}} = 0.175$ over the radial range from 0.4 to 4 times the stellar half mass radius. Several correlations between $\gamma^{\prime}$ and galactic properties including stellar mass, effective radius, stellar surface density, central velocity dispersion, central dark matter fraction and in-situ-formed stellar mass ratio are compared to observations and other simulations, revealing that IllustrisTNG reproduce correlation trends qualitatively, and $\gamma^{\prime}$ is almost constant with redshift below $z = 2$. The power-law density profile of the ETG dark matter halos is steeper in the full physics (FP) run than their counterparts in the dark matter only (DMO) run. The dark matter inner slopes of the best-fit generalized NFW profile are much steeper than the standard NFW profile and they are anti-correlated (constant) with the halo mass in the FP (DMO) run. The dark matter inner slope is also anti-correlated with the halo concentration parameter $c_{200}$ in both runs. Comparison of the mass-weighted slope/central dark matter fraction correlation, $\gamma_{\mathrm{mw}}^{\prime}-f_{\mathrm{DM}}$, with models and observations indicates contraction of the IllustrisTNG dark matter halos, especially in lower-mass systems.


arXiv:1811.06547v1 [pdf, other]
Three regimes of CO emission in galaxy mergers
Comments: A&A accepted, 6 pages, 5 figures

The conversion factor $\alpha_{\rm CO}$ from the observable CO(1-0) luminosity to the mass of molecular gas is known to vary between isolated galaxies and some mergers, but the underlying reasons are not clearly understood. Thus, the value(s) of $\alpha_{\rm CO}$ to be adopted remain highly uncertain. To provide better constraints, we apply the large velocity gradient method to a series of hydrodynamical simulations of galaxies and derive the evolution of $\alpha_{\rm CO}$. We report significant variations of $\alpha_{\rm CO}$, and identify three distinct regimes: disk galaxies, starbursts and post-burst phases. We show that estimating the star formation rate over 20 Myr smooths out some of these differences, but still maintains a distinction between disks and starbursts. We find a tighter correlation of $\alpha_{\rm CO}$ with the gas depletion time than with star formation rate, yet with deviations induced by the transitions to and from the starburst episodes. We conclude that $\alpha_{\rm CO}$ fluctuates because of both the feedback energy and the velocity dispersion. Identifying the phase of an interaction by classical means (e.g. morphology, luminosity) could then help selecting the relevant conversion factor to be used and get more accurate estimates of the molecular masses of galaxies.


arXiv:1811.06548v1 [pdf, other]
HST/WFC3 grism observations of $z~\mathtt{\sim}~1$ clusters: The cluster vs. field stellar mass-size relation and evidence for size growth of quiescent galaxies from minor mergers
Comments: 23 pages, 13 figures, submitted to MNRAS

Minor mergers are thought to be responsible for the size growth of quiescent field galaxies with decreasing redshift. We test this hypothesis using the cluster environment as a laboratory. Satellite galaxies in clusters move at high velocities, making mergers between them rare. The stellar mass-size relation in ten clusters and in the field is measured and compared at $z~\mathtt{\sim}~1$. Our cluster sample contains 344 spectroscopically-confirmed cluster members with Gemini/GMOS and 182 confirmed with HST WFC3 G141 grism spectroscopy. On average, quiescent and star-forming cluster galaxies are smaller than their field counterparts by ($0.08\pm0.04$) dex and ($0.07\pm0.01$) dex respectively. These size offsets are consistent with the average sizes of quiescent and star-forming field galaxies between $1.2\leqslant z\leqslant1.5$, implying the cluster environment has inhibited size growth between this period and $z~\mathtt{\sim}~1$. The negligible differences measured between the $z~\mathtt{\sim}~0$ field and cluster quiescent mass-size relations in other work imply that the average size of quiescent cluster galaxies must rise with decreasing redshift. Using a toy model, we show this is possible if $\mathtt{\sim}40\%$ of the most compact cluster galaxies merge with their brightest cluster galaxies (BCGs) and $\mathtt{\sim}60\%$ are tidally destroyed into the intra-cluster light (ICL) between $0\leqslant z\leqslant1$. This is in agreement with the observed stellar mass growth of BCGs between $0\leqslant z\leqslant1$ and the observed ICL stellar mass fraction at $z~\mathtt{\sim}~0$. Our results support minor mergers as the cause for the size growth in quiescent field galaxies, with cluster-specific processes responsible for the similarity between the field and cluster quiescent mass-size relations at low redshift.


arXiv:1811.06549v1 [pdf, other]
The MUSE-Wide Survey: Survey Description and First Data Release
Comments: 25 pages 15+1 figures. Submitted to A&A. Comments welcome

We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the CANDELS/GOODS-S and CANDELS/COSMOS regions. Each MUSE-Wide pointing has a depth of 1 hour and hence targets more extreme and more luminous objects over 10 times the area of the MUSE-Deep fields (Bacon et al. 2017). The legacy value of MUSE-Wide lies in providing "spectroscopy of everything" without photometric pre-selection. We describe the data reduction, post-processing and PSF characterization of the first 44 CANDELS/GOODS-S MUSE-Wide pointings released with this publication. Using a 3D matched filtering approach we detected 1,602 emission line sources, including 479 Lyman-$\alpha$ (Lya) emitting galaxies with redshifts $2.9 \lesssim z \lesssim 6.3$. We cross-match the emission line sources to existing photometric catalogs, finding almost complete agreement in redshifts and stellar masses for our low redshift (z < 1.5) emitters. At high redshift, we only find ~55% matches to photometric catalogs. We encounter a higher outlier rate and a systematic offset of $\Delta$z$\simeq$0.2 when comparing our MUSE redshifts with photometric redshifts. Cross-matching the emission line sources with X-ray catalogs from the Chandra Deep Field South, we find 127 matches, including 10 objects with no prior spectroscopic identification. Stacking X-ray images centered on our Lya emitters yielded no signal; the Lya population is not dominated by even low luminosity AGN. A total of 9,205 photometrically selected objects from the CANDELS survey lie in the MUSE-Wide footprint, which we provide optimally extracted 1D spectra of. We are able to determine the spectroscopic redshift of 98% of 772 photometrically selected galaxies brighter than 24th F775W magnitude. All the data in the first data release - datacubes, catalogs, extracted spectra, maps - are available on the website https://musewide.aip.de. [abridged]


arXiv:1811.06550v1 [pdf, other]
Predicted Yield of Transits of Known Radial Velocity Exoplanets from the TESS Primary and Extended Missions
Comments: Accepted for publication in PASP. 6 figures, 1 table. Supplementary data included in source files

Radial velocity (RV) surveys have detected hundreds of exoplanets through their gravitational interactions with their host stars. Some will be transiting, but most lack sufficient follow-up observations to confidently detect (or rule out) transits. We use published stellar, orbital, and planetary parameters to estimate the transit probabilities for nearly all exoplanets that have been discovered via the RV method. From these probabilities, we predict that $25.5^{+0.7}_{-0.7}$ of the known RV exoplanets should transit their host stars. This prediction is more than double the amount of RV exoplanets that are currently known to transit. The Transiting Exoplanet Survey Satellite (TESS) presents a valuable opportunity to explore the transiting nature of many of the known RV exoplanet systems. Based on the anticipated pointing of TESS during its two-year primary mission, we identify the known RV exoplanets that it will observe and predict that $11.7^{+0.3}_{-0.3}$ of them will have transits detected by TESS. However, we only expect the discovery of transits for $\sim$3 of these exoplanets to be novel (i.e., not previously known). We predict that the TESS photometry will yield dispositive null results for the transits of $\sim$125 RV exoplanets. This will represent a substantial increase in the effort to refine ephemerides of known RV exoplanets. We demonstrate that these results are robust to changes in the ecliptic longitudes of future TESS observing sectors. Finally, we consider how several potential TESS extended mission scenarios affect the number of transiting RV exoplanets we expect TESS to observe.


arXiv:1811.06552v1 [pdf, other]
The binary black hole explorer: on-the-fly visualizations of precessing binary black holes
Comments: Visualizations available at https://vijayvarma392.github.io/binaryBHexp

Binary black hole mergers are of great interest to the astrophysics community, not least because of their promise to test general relativity in the highly dynamic, strong field regime. Detections of gravitational waves from these sources by LIGO and Virgo have garnered widespread media and public attention. Among these sources, precessing systems (with misaligned black-hole spin/orbital angular momentum) are of particular interest because of the rich dynamics they offer. However, these systems are, in turn, more complex compared to nonprecessing systems, making them harder to model or develop intuition about. Visualizations of numerical simulations of precessing systems provide a means to understand and gain insights about these systems. However, since these simulations are very expensive, they can only be performed at a small number of points in parameter space. We present binaryBHexp, a tool that makes use of surrogate models of numerical simulations to generate on-the-fly interactive visualizations of precessing binary black holes. These visualizations can be generated in a few seconds, and at any point in the 7-dimensional parameter space of the underlying surrogate models. With illustrative examples, we demonstrate how this tool can be used to learn about precessing binary black hole systems.


arXiv:1811.06554v1 [pdf, other]
Dark matter-baryon scaling relations from Einasto halo fits to SPARC galaxy rotation curves
Comments: 27 pages, 10 figures, submitted -- comments welcome

Dark matter-baryon scaling relations in galaxies are important in order to constrain galaxy formation models. Here, we provide a modern quantitative assessment of those relations, by modelling the rotation curves of galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database with the Einasto dark halo model. Our analysis is complementary to the analysis of Chemin et al. (2011) and the recent one of Li et al. (2018). In particular, we focus here on the comparison between the original SPARC parameters, with constant mass-to-light ratios for bulges and disks, and the parameters for which galaxies follow the tightest radial acceleration relation (RAR). We show that fits are improved in the second case, and that the pure halo scaling relations also become tighter. We report that the density at the radius where the slope is $-2$ is strongly anticorrelated to this radius, and to the Einasto index. The latter is close to unity for a large number of galaxies, indicative of large cores. In terms of dark matter-baryon scalings, we focus on relations between the core properties and the extent of the baryonic component, which are relevant to the cusp-core transformation process. We report a positive correlation between the core size of halos with small Einasto index and the stellar disk scale-length, as well as between the averaged dark matter density within 2 kpc and the baryon-induced rotational velocity at that radius. This finding is related to the consequence of the RAR on the diversity of rotation curve shapes, quantified by the rotational velocity at 2 kpc. While a tight RAR slightly decreases the observed diversity compared to the original SPARC parameters, the diversity of baryon-induced accelerations at 2 kpc is sufficient to induce a large diversity, incompatible with current hydrodynamical simulations of galaxy formation, while maintaining a tight RAR.


arXiv:1811.06556v1 [pdf, other]
Biases in inferring dark matter profiles from dynamical and lensing measurements
Comments: 13 pages, 8 figures, submitted for MNRAS publication Nov 15th 2018

The degeneracy between disc and halo contributions in spiral galaxy rotation curves makes it difficult to obtain a full understanding of the distribution of baryons and dark matter in disc galaxies like our own Milky Way. Using mock data, we study how constraints on dark matter profiles obtained from kinematics, strong lensing, or a combination of the two are affected by assumptions about the halo model. We compare four different models: spherical isothermal and Navarro-Frenk-White halos, along with spherical and elliptical Burkert halos. For both kinematics and lensing we find examples where different models fit the data well but give enclosed masses that are inconsistent with the true (i.e., input) values. This is especially notable when the input and fit models differ in having cored or cuspy profiles (such as fitting an NFW model when the underlying dark matter distribution follows a different profile). We find that mass biases are more pronounced with lensing than with kinematics, and using both methods can help reduce the bias and provide stronger constraints on the dark matter distributions.


arXiv:1811.06559v1 [pdf, other]
Luminous and Variable Stars in NGC 2403 and M81
Comments: To appear in the Astronomical Journal

We present the results of spectroscopy and multi-wavelength photometry of luminous and variable star candidates in the nearby spiral galaxies NGC 2403 and M81. We discuss specific classes of stars, the Luminous Blue Variables (LBVs), B[e] supergiants (sgB[e]), and the high luminosity yellow hypergiants. We identify two new LBV candidates, and three sgB[e] stars in M81. We also find that some stars previously considered LBV candidates are actually field stars. The confirmed and candidate LBVs and sgB[e] stars together with the other confirmed members are shown on the HR Diagrams for their respective galaxies. We also present the HR Diagrams for the two "SN impostors", V37 (SN2002kg) and V12(SN1954J) in NGC 2403 and the stars in their immediate environments.


arXiv:1811.06561v1 [pdf, other]
Radius Inflation at Low Rossby Number in the Hyades Cluster
Comments: 14 Pages, 11 Figures, 2 Tables

Radius inflation continues to be explored as a peculiar occurrence among magnetically active, low-mass stars. Recently Somers et. al. 2017 showed that radius inflation among low-mass stars in the young open cluster M45 (Pleiades Cluster) is correlated to the rotation rate; faster rotators are more inflated. Here we extend that work to a sample of 68 stars of the older open cluster Melotte 25 (Hyades Cluster). We employ spectral energy distribution fitting to derive bolometric flux. With spectroscopically defined Teff, and Gaia DR2 distances we calculate stellar radii using the Stefan-Boltzmann equation. We find numerous stars that exhibit significant (3--4$\sigma$) radius inflation relative to a nominal cluster isochrone. We compare these results to that of the younger Pleiades and consider radius inflation as a function of open cluster evolution. We find that unlike the Pleiades, there is not a statistically significant correlation between radius inflation and stellar rotation period. However, we do find that most inflated stars have (rapid) rotational Rossby numbers of 0.1--0.2, such that the correlation of radius inflation with Rossby number is statistically significant with 99.98% confidence. Our results imply that magnetic activity within the convective layers of low-mass stars preferentially drives radius inflation.


arXiv:1811.06565v1 [pdf, other]
Fast-to-Alfvén mode conversion mediated by Hall current. II Application to the solar atmosphere
Comments: No comment found

Coupling between fast magneto-acoustic and Alfv\'en waves can be observe in fully ionized plasmas mediated by stratification and 3D geometrical effects. In Paper I, Cally & Khomenko (2015) have shown that in a weakly ionized plasma, such as the solar photosphere and chromosphere, the Hall current introduces a new coupling mechanism. The present study extends the results from Paper I to the case of warm plasma. We report on numerical experiments where mode transformation is studied using quasi-realistic stratification in thermodynamic parameters resembling the solar atmosphere. This redresses the limitation of the cold plasma approximation assumed in Paper I, in particular allowing the complete process of coupling between fast and slow magneto-acoustic modes and subsequent coupling of the fast mode to the Alfv\'en mode through the Hall current. Our results confirm the efficacy of the mechanism proposed in Paper I for the solar case. We observe that the efficiency of the transformation is a sensitive function of the angle between the wave propagation direction and the magnetic field, and of the wave frequency. The efficiency increases when the field direction and the wave direction are aligned for increasing wave frequencies. After scaling our results to typical solar values, the maximum amplitude of the transformed Alfv\'en waves, for a frequency of 1 Hz, corresponds to an energy flux (measured above the height of peak Hall coupling) of $\sim10^3$ $\rm W\,m^{-2}$, based on an amplitude of 500 $\rm m\,s^{-1}$ at $\beta=1$, which is sufficient to play a major role in both quiet and active region coronal heating.


arXiv:1811.06574v1 [pdf, other]
In Situ Formation of Icy Moons of Uranus and Neptune
Comments: In press at ApJL

Satellites of giant planets thought to form in gaseous circumplanetary disks (CPDs) during the late planet-formation phase, but it was unknown so far whether smaller mass planets, such as the ice giants could form such disks, thus moons there. We combined radiative hydrodynamical simulations with satellite population synthesis to investigate the question in the case of Uranus and Neptune. For both ice giants we found that a gaseous CPD is created at the end of their formation. The population synthesis confirmed that Uranian-like, icy, prograde satellite-system could form in these CPDs within a couple of $10^5$ years. This means that Neptune could have a Uranian-like moon-system originally that was wiped away by the capture of Triton. Furthermore, the current moons of Uranus can be reproduced by our model without the need for planet-planet impact to create a debris disk for the moons to grow. These results highlight that even ice giants -- that among the most common mass-category of exoplanets -- can also form satellites, opening a way to a potentially much larger population of exomoons than previously thought.


arXiv:1811.06576v1 [pdf, other]
Intermediate-Mass Black Hole Feedback in Dwarf Galaxies: a View from Cosmological Simulations
Comments: 4 pages, Proceedings of Talk presented at the IAU Symposium 342 - "Perseus in Sicily: from black hole to cluster outskirts", held at Noto (Sicily, Italy), 2018 May 13-18

Black holes are usually observed to be of stellar-mass or supermassive. By natural extension, there should be a population of Intermediate-Mass Black Holes (IMBHs: with mass between $100$ to $10^6 M_{\odot}$) in the Universe; which has started to been observed. An exciting claim has been made recently by Silk (2017): that early feedback by IMBHs in gas-rich dwarf galaxies at $z=5-8$, can potentially solve multiple dwarf galaxy problems within the $\Lambda$-cold-dark-matter cosmology. We are performing Cosmological Hydrodynamical Simulations of $(2 Mpc)^3$ volumes, starting from $z=100$, to test the case for IMBHs in Dwarf Galaxies. Black holes of mass $1000 M_{\odot}$ are seeded inside halos when they reach a mass of $10^7 M_{\odot}$. The black holes grow by accretion of gas from their surroundings and by merger with other black holes, and consequently eject feedback energy. We analyze the simulation output in post-processing to study the growth of the first IMBHs, and their impact on star-formation. Our conclusions, based on numerical simulation results, support the phenomenological ideas made by Silk (2017). IMBHs at the centers of dwarf galaxies can be a strong source of feedback to quench star-formation and generate outflows. At the same time, these IMBHs form the missing link between stellar-mass and supermassive BHs.


arXiv:1811.06577v1 [pdf, other]
Global Correlations Between the Radio Continuum, Infrared and CO Emission in Dwarf Galaxies
Comments: accepted for publication in MNRAS

Correlations between the radio continuum, infrared and CO emission are known to exist for several types of galaxies and across several orders of magnitude. However, the low-mass, low-luminosity and low-metallicity regime of these correlations is not well known. A sample of metal-rich and metal-poor dwarf galaxies from the literature has been assembled to explore this extreme regime. The results demonstrate that the properties of dwarf galaxies are not simple extensions of those of more massive galaxies; the different correlations reflect different star-forming conditions and different coupling between the star formation and the various quantities. It is found that dwarfs show increasingly weaker CO and infrared emission for their luminosity, as expected for galaxies with a low dust content, slower reaction rates, and a hard ionizing radiation field. In the higher-luminosity dwarf regime (L_1.4GHz > 10^27 W, where L_1.4GHz ~ 10^29 W for a Milky Way star formation rate of ~1 M_sun yr^-1), the total and non-thermal radio continuum emission appear to adequately trace the star formation rate. A breakdown of the dependence of the (Halpha-based) thermal, non-thermal, and, hence, total radio continuum emission on star formation rate occurs below L_1.4GHz ~ 10^27 W, resulting in a steepening or downturn of the relations at extreme low luminosity. Below L_FIR ~ 10^36 W ~ 3 x 10^9 L_sun, the infrared emission ceases to adequately trace the star formation rate. A lack of a correlation between the magnetic field strength and the star formation rate in low star formation rate dwarfs suggests a breakdown of the equipartition assumption. As extremely metal-poor dwarfs mostly populate the low star formation rate and low luminosity regime, they stand out in their infrared, radio continuum and CO properties.


arXiv:1811.06578v1 [pdf, other]
Polymer amide as a carrier of 15N in Allende and Acfer 086 meteorites
Comments: 15 pages, 3 tables, 6 figures

Polymers of amino acids have been found in Allende and Acfer 086, with extra-terrestrial origin evidenced by isotopically enhanced satellite peaks in the 800-1200 Dalton mass range. The present work employs focused ion beam milling of micron scale powder to generate negative ion spectra containing CN ions at masses 26 and 27 for 15N determination. Respectively, for CN ions, Allende and Acfer 086 show delta 15N = 410 +/- 220 per mil and 1,015 +/- 220 per mil in the powder samples. We measure an exact 1:2 ratio of C2 to CN negative ions that is consistent with ion beam fragmentation of a polymer amide -CCN- backbone into diatomic fragments. It is inferred that polymer amide comprises a large part of the 15N bearing organic material in this CV3 meteorite class.


arXiv:1811.06581v1 [pdf, other]
HR 62: A New Evolved Chemically Peculiar Late-B Star?
Comments: 4 pages, 4 figures, accepted proceeding of the Radiative Signatures from the Cosmos: A Meeting in Honor of Ivan Hubeny, October 23-26, 2018, Paris, France

The spectrum of the evolved B8 III giant HR 62 exhibits weak He-lines and strong Mn and P lines. HR 62 therefore resembles both a HgMn star (CP3) and a He-weak PGa star (CP4). This study is a companion project to a high resolution survey of slowly rotationg late-B type stars aiming at finding new chemically peculiar stars. We have analysed the spectra of HR 62 (B8 III) and the dwarf comparison star HR 677 (B8 V) to derive their chemical abundances. Both stars have similar effective temperatures (12500 K) and projected rotational velocities ($\sim$25 km s$^{-1}$). The medium resolution ($R$ $\sim$14000) spectra covering the wavelength range of 4380-7350 \AA{} of HR 62 and HR 677 have been obtained with the \'{e}chelle spectrograph attached to the 40 cm telescope in Ankara University Kreiken Observatory (AUKR), Turkey. We have used SYNSPEC49/SYNPLOT written by I. Hubeny and T. Lanz to compute grids of synthetic spectra and derive elemental abundances by modeling selected unblended lines. We find that HR 62 exhibits underabundance of Si and remarkable overabundance of P and Mn with respect to the Sun. In contrast, HR 677 does not have abundances departing by more than $\pm$ 0.25 dex from solar abundances. A mass of 5.4 $M_\odot$ and an age of 90 Myr have been estimated for HR 62. We discuss the origin of the chemical peculiarities of HR 62 and its status as a CP star. The effective temperature of the star (12500 K) agrees well with those of HgMn (CP3) stars. Furthermore, the main sequence end of its evolutionary track also intersects the domain of He-weak CP4 stars. Hence these first results suggest that HR 62 may be a transition object between the CP4 to CP3 subgroup. However, a more detailed analysis of higher resolution spectra at shorter wavelengths (< 4380 \AA{}) is necessary to clearly address the nature of this interesting object.


arXiv:1811.06594v1 [pdf, other]
Searching for the Origin of Flares in M dwarfs
Comments: No comment found

We present an overview of K2 short cadence observations for 34 M dwarfs observed in Campaigns 1 - 9 which have spectral types between M0 - L1. All of the stars in our sample showed flares with the most energetic reaching $3\times10^{34}$ ergs. As previous studies have found, we find rapidly rotating stars tend to show more flares, with evidence for a decline in activity in stars with rotation periods longer than approximately 10 days. We determined the rotational phase of each flare and performed a simple statistical test on our sample to determine whether the phase distribution of the flares is random or if there is a preference for phase. We find, with the exception of one star which is in a known binary system, that none show a preference for the rotational phase of the flares. This is unexpected and all stars in our sample show flares at all rotational phases, suggesting these flares are not all originating from one dominant starspot on the surface of the stars. We outline three scenarios which could explain the lack of a correlation between the number of flares and the stellar rotation phase. In addition we also highlight preliminary observations of DP Cnc, observed in campaigns 16 and 18, and is one of the stars in our extended sample from K2 Campaigns 10 -18 which are still to be examined.


arXiv:1811.06597v1 [pdf, other]
The Binary Fraction of Stars in Dwarf Galaxies: the Cases of Draco and Ursa Minor
Comments: 23 pages, 14 figures, 8 tables. Published in AJ

Measuring the frequency of binary stars in dwarf spheroidal galaxies (dSphs) requires data taken over long time intervals. We combine radial velocity measurements from five literature sources taken over the course of ~30 years to yield the largest multi-epoch kinematic sample for stars in the dSphs Draco and Ursa Minor. With this data set, we are able to implement an improved version of the Bayesian technique described in Spencer et al. (2017b) to evaluate the binary fraction of red giant stars in these dwarf galaxies. Assuming Duquennoy & Mayor (1991) period and mass ratio distributions, the binary fractions in Draco and Ursa Minor are $0.50^{+0.04}_{-0.06}$ and $0.78^{+0.09}_{-0.08}$, respectively. We find that a normal mass ratio distribution is preferred over a flat distribution, and that log-normal period distributions centered on long periods ($\mu_{\log P}>3.5$) are preferred over distributions centered on short ones. We reanalyzed the binary fractions in Leo II, Carina, Fornax, Sculptor, and Sextans, and find that there is <1% chance that binary fraction is a constant quantity across all seven dwarfs, unless the period distribution varies greatly. This indicates that the binary populations in Milky Way dSphs are not identical in regard to their binary fractions, period distributions, or both. We consider many different properties of the dwarfs (e.g. mass, radius, luminosity, etc.) and find that binary fraction might be larger in dwarfs that formed their stars quickly and/or have high velocity dispersions.


arXiv:1811.06602v1 [pdf, other]
Star formation in outer rings of S0 galaxies. I. NGC 6534 and MCG 11-22-015
Comments: 5 pages, 6 figures, accepted into the Astronomy and Astrophysics

Though S0 galaxies are usually thought to be 'red and dead', they often demonstrate star formation organized in ring structures. We try to clarify the nature of this phenomenon and its difference from star formation in spiral galaxies. Two early-type galaxies with outer rings, NGC 6534 and MCG 11-22-015, are selected to be studied. The ionized gas is excited by young stars in the ring of NGC 6534 and partly by shocks -- in MCG 11-22-015. The oxygen abundances in the HII regions of the rings are close to solar. We estimate the star formation rates (SFR) in the two outer rings of the galaxies by using several SFR indicators derived from narrow-band photometry in the H-alpha emission line and archival GALEX ultraviolet images of the galaxies. The derived SFRs allow to qualitatively restore star formation histories (SFH) in the rings: in NGC 6534 the SFH is flat during the last 100-200 Myr, and in MCG 11-22-015 the star formation has started only a few Myr ago. We suggest that the rings in NGC 6534 and MCG 11-22-015 have different natures: the former is a resonant one supplied with gas perhaps through tidal effects, and the latter has been produced by a satellite accretion. Recent outer gas accretion is implied in both cases.


arXiv:1811.06638v1 [pdf, other]
Overshooting in the core helium burning stage of a $30M_{\odot}$ star using the $k$-$ω$ model
Comments: accepted for publication by ApJ

Overshooting and semiconvection are among the most uncertainties in the evolution of massive stars. Complete mixing over a certain distance beyond the convective boundary (Stothers \& Chin 1985) and an exponentially decaying diffusion outside the convection zone (Herwig 2000) are commonly adopted for the overshoot mixing. Recently, Li (2012, 2017) developed the $k$-$\omega$ model, which can be used in both convection zones and overshooting regions. We incorporated it in calculations of $30M_{\odot}$ stellar models. We find that in the main sequence stage, models with the $k$-$\omega$ model are almost identical to models with complete mixing in the overshooting region beyond the convective core, and the overshooting in the $k$-$\omega$ model is equivalent to an overshooting distance of about $0.15H_P$. In the post main sequence stage, we find that the overshooting below the bottom of the intermediate convection zone beyond the hydrogen-burning shell can significantly restrict the size of the hydrogen-depleted core, and can penetrate effectively into the hydrogen-burning shell. These two effects are crucial for the evolution of the core helium burning stage. During the core helium burning stage, we find that the overshooting model based on the $k$-$\omega$ model results in a similar complete mixing region but a much wider partial mixing region than the overshooting model based on Herwig (2000). In particular, the overshooting distance in the core helium burning stage may be significantly smaller than that in the main sequence phase for massive stars.


arXiv:1811.06644v1 [pdf, other]
SITELLE: An Imaging Fourier Transform Spectrometer for the Canada-France-Hawaii Telescope
Comments: 19 pages, 22 figures, submitted to MNRAS

We present an overview of SITELLE, an Imaging Fourier Transform Spectrometer (iFTS) available at the 3.6-meter Canada-France-Hawaii Telescope. SITELLE is a Michelson-type interferometer able to reconstruct the spectrum of every light source within its 11' field of view in filter-selected bands of the visible (350 to 900 nm). The spectral resolution can be adjusted up to R = 10 000 and the spatial resolution is seeing-limited and sampled at 0.32 arcsec per pixel. We describe the design of the instrument as well as the data reduction and analysis process. To illustrate SITELLE's capabilities, we present some of the data obtained during and since the August 2015 commissioning run. In particular, we demonstrate its ability to separate the components of the [OII] $\lambda\lambda$ 3726,29 doublet in Orion and to reach R = 9500 around H-alpha; to detect diffuse emission at a level of 4 x 10e-17 erg/cm2/s/arcsec2; to obtain integrated spectra of stellar absorption lines in galaxies despite the well-known multiplex disadvantage of the iFTS; and to detect emission-line galaxies at different redshifts.


arXiv:1811.06659v1 [pdf, other]
Calibrating Interstellar Abundances using SNR Radiative Shocks
Comments: Accepted for publication in AJ, 16 pp, 10 figs

Using integral field data we extract the optical spectra of shocked interstellar clouds in Kepler's supernova remnant located in the inner regions of our Galaxy, as well as in the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), NGC6822 and IC 1613. Using self-consistent shock modelling, we make a new determination of the chemical composition of the interstellar medium (ISM) in N, O, Ne, S, Cl and Ar in these galaxies and obtain accurate estimates of the fraction of refractory grains destroyed in the shock. By comparing our derived abundances with those obtained in recent works using observations of B stars, F supergiant stars and HII regions, we provide a new calibration for abundance scaling in the range $7.9 \lesssim 12+\log {\mathrm {O/H}} \lesssim 9.1$.


arXiv:1811.06674v1 [pdf, other]
A Deeply Buried Narrow-Line Seyfert 1 Nucleus Uncovered in Scattered Light
Comments: 9 pages, 6 figures, ApJ Accepted

We present spectropolarimetric and spectrophotometric observations of the peculiar active galactic nucleus (AGN) SDSS J120300.19+162443.7 (hereafter J1203+1624) at $z=0.1656$. Its optical total flux spectra clearly show broad emission lines (BELs) in H$\alpha$ and H$\beta$. After removal of narrow emission lines (NELs), the full width at half maximum of the lorentzian BEL is $FWHM_{\rm BEL} \approx 1,270$~\kms, fulfilling the conventional definition of a narrow line Seyfert 1 (NLS1) galaxy. However, its NELs are unprecedentedly strong when compared to type 1AGNs. This, together with its large MIR excess ($g-W_4 = 13.172$ mag), implies that the observer and the narrow emission line region (NELR) might see a different ionization continuum. Our optical spectropolarimetry confirms its type 2 nature by detecting a polarized blue continuum and Balmer BELs ($FWHM_{\rm Polarized~BEL} \approx 1,183$~\kms), with a high polarization degree of $> 20$% in the blue wing. The mass and Eddington rate of the central black hole is estimated based on both transmitted and scattered AGN radiation, which is $M_{\bullet} < 2.9 \times 10^7 M_\odot$ and $L_{\rm bol}/L_{\rm Edd} > 1.5$. Severe extinction of the AGN emission also enables a clear view of the compact host galaxy. Discovery of J1203+1624 suggests that NLS1 follows AGN unfication scheme, studying of its analogs could blaze a new trail for exploring the connection between black hole growth and star formation in the host galaxy. Interesting features of J1203+1624 like the peculiar NELs, inflowing scattering clouds within sublimation radius are worth detailed follow-ups in the future.


arXiv:1811.06675v1 [pdf, other]
Does misalignment between magnetic field and angular momentum enhance or suppress circumstellar disk formation?
Comments: 21 pages, 12 figures, accepted by ApJ, published as an open access article and can be downloaded from https://doi.org/10.3847/1538-4357/aae4dc

The effect of misalignment between the magnetic field $\magB$ and the angular momentum $\Jang$ of molecular cloud cores on the angular momentum evolution during the gravitational collapse is investigated by ideal and non-ideal MHD simulations. For the non-ideal effect, we consider the ohmic and ambipolar diffusion. Previous studies that considered the misalignment reported qualitatively contradicting results. Magnetic braking was reported as being either strengthened or weakened by misalignment in different studies. We conducted simulations of cloud-core collapse by varying the stability parameter $\alpha$ (the ratio of the thermal to gravitational energy of the core) with and without including magnetic diffusion The non-ideal MHD simulations show the central angular momentum of the core with $\theta=0^\circ$ ($\Jang \parallel \magB$) being always greater than that with $\theta=90^\circ$ ($\Jang \perp \magB$), independently of $\alpha$, meaning that circumstellar disks form more easily form in a core with $\theta=0^\circ$. The ideal MHD simulations, in contrast, show the the central angular momentum of the core with $\theta=90^\circ$ being greater than with $\theta=0^\circ$ for small $\alpha$, and is smaller for large $\alpha$. Inspection of the angular momentum evolution of the fluid elements reveals three mechanisms contributing to the evolution of the angular momentum: (i) magnetic braking in the isothermal collapse phase, (ii) selective accretion of the rapidly (for $\theta=90^\circ$ ) or slowly (for $\theta=0^\circ$) rotating fluid elements to the central region, and (iii) magnetic braking in the first-core and the disk. The difference between the ideal and non-ideal simulations arises from the different efficiencies of (iii).


arXiv:1811.06691v1 [pdf, other]
CCD astrometric observations of 2017 VR12,Camillo and Midas
Comments: No comment found

We have observed three near-Earth objects(NEOs), 2017VR12, Camillo, and Midas during the year 2018. The observations were made by the 1-m telescope of Yunnan Observatory over 2 nights. Their precise astrometric positions are derived from 989 CCD observations. The theoretical positions of asteroids are retrieved from the Jet Propulsion Laboratory (JPL) Horizons System and Institut de M\'{e}canique C\'{e}leste et de Calcul des \'{E}ph\'{e}m\'{e}rides (IMCCE). The positions of three asteroids are measured with respect to the stars in Gaia DR2 star catalogue. For 2017 VR12, the mean (O-C) of right ascension and declination are -0.090$^{''}$ and -0.623$^{''}$ based on the ephemeris of published JPL, but the mean (O-C) are 3.122$^{''}$ and -0.636$^{''}$ based on the ephemeris of published IMCCE. The great difference in declination could be explained by several factors. (1)The degenerated CCD images caused by the high apparent motion speed of the object leads to the reduction of positioning accuracy. (2)The poor timing system may bring the system error, especially in the high speed direction. (3)The asteroid may be perturbed by the earth when it approaches the earth too closely. The astrometric results show that the centroid centring method can reduce the dispersion of the non-Gaussian images compared with the PSF model method. For Camillo and Midas, the astrometric results are consistent based on two ephemerides. High-precision timing system, some astronomical effects and geometric distortion of CCD images should be carefully considered in the future works.


arXiv:1811.06696v1 [pdf, other]
A deep survey for symbiotic stars in the Magellanic Clouds - 1. Methodology and first discoveries in the SMC
Comments: 10 pages, 9 figures, submitted to ApJ, comments welcome

We have initiated a survey aimed at locating a nearly complete sample of classical symbiotic stars (SySt) in the Magellanic Clouds. Such a sample is nearly impossible to obtain in the Milky Way, and is essential to constrain the formation, evolution and demise of these strongly interacting, evolved binary stars. We have imaged both Clouds in Halpha and He II 4686 narrow-band filters deeply enough to detect all known symbiotic stars. While He II 4686 is not present in all SySt, our method should yield a high success rate because the mimics of SySt are not as likely as true symbiotics to show this emission line. We demonstrate the viability of our method through the discovery and characterization of three new SySt in the Small Magellanic Cloud: 2MASS J00411657-7233253, 2MASS J01104404-7208464 and 2MASS J01113745-7159023. Enigmatic variability was observed in 2MASS J01113745-7159023, where changes in the amplitude of its quasi-periodic variability may suggest an enhanced mass transfer rate during a periastron passage on an elliptical orbit. 2MASS J01104404-7208464 is an ellipsoidal variable with an orbital period of 403d.


arXiv:1811.06726v1 [pdf, other]
Gravitational-Wave Emission from Binary Black Holes Formed in Open Clusters
Comments: 7 pages, 6 figures, submitted to MNRAS

In order to investigate the formation rate of binary black holes (BBHs) in stellar clusters with a mass comparable to open clusters, we performed a series of direct $N$-body simulations of open clusters with a mass of $2.5\times10^3$ (Model A) and $10^4 M_{\odot}$ (Model B). Since such low-mass clusters would have been more populous than globular clusters when they were born, low-mass clusters are also candidates as the origin of BBHs which are the source of the gravitational waves. In model A, most of BBHs merged within 10 Gyr formed via dynamically formed main-sequence binary stars and stable and unstable mass transfer between them since open clusters collapse within the main-sequence life-time of massive stars. These binaries, therefore, have little eccentricities. The fraction of such binaries among all merging BBHs increases as the cluster mass decrease due to the shorter relaxation time. In our simulations, $4.0\times10^{-5}$ and $1.7\times10^{-5}$ BBHs per solar mass merged within 10 Gyr for models A and B, respectively. These values correspond to $\sim$ 20-50% of the number of mergers per solar mass originated from globular clusters with a mass of $10^5$-$10^6M_{\odot}$. Thus, the contribution of BBHs originated from open clusters is not negligible. The estimated mergers rate density in the local universe is about 0.3 yr$^{-1}$ Gpc$^{-3}$ assuming a cluster mass function with a power of $-$2.


arXiv:1811.06727v1 [pdf, other]
A photoionization model grid for novae: estimation of physical parameters
Comments: Accepted for publication in MNRAS. 10 pages, 10 figures

We present here a method to estimate physical parameters of novae systems using an extensive grid of photoionization models for novae. We use the photoionization code CLOUDY to construct grid of models covering a wide range of different parameters, e.g. total hydrogen density ($n_H$), source temperature ($T_{BB}$) and luminosity ($L$), inner radius ($R_{in}$) and thickness of ejecta ($\Delta R$), keeping other elements at solar metallicity. In this way, a total of 1792 models have been generated. From the model generated spectra which cover a wide wavelength region from ultra-violet to infrared, we calculate ratios of hydrogen and helium emission lines fluxes which are generally strong in novae spectra. We show that physical parameters associated with novae system could be estimated by comparing these line ratios with those obtained from observed spectra. We elaborate the idea with examples and estimate the parameter values in case of few other novae. The results of the grid model are available online.


arXiv:1811.06745v1 [pdf, other]
Analysis of the duration--hardness ratio plane of gamma-ray bursts using skewed distributions
Comments: 15 pages; accepted in ApJ

The two widely accepted classes of gamma-ray bursts (GRBs), short and long, are with confidence ascribed to mergers of compact objects and collapse of massive stars, respectively. A third, intermediate/soft class, remains putative. Its existence was claimed based on univariate and bivariate analyses of GRB observables modeled with Gaussian distributions. This, however, may not be the appropriate approach, as it has been already shown that the univariate distributions of durations are better described by mixtures of two skewed components rather than three Gaussian ones. This paper investigates whether data in the duration--hardness ratio plane is better modeled by mixtures of skewed bivariate distributions than by normal ones. The archival data set of the Compton Gamma-Ray Observatory/BATSE and Fermi/GBM data from the most recent catalogue release are examined. The preferred model is chosen based on two information criteria, Akaike ($AIC$) and Bayesian ($BIC$). It is found that the best description is given by a two-component mixture of skewed Student-$t$ distributions, which outperforms any other model considered. This implies that the distribution of the studied parameters is intrinsically skewed, introducing spurious Gaussian components, and hence the third class is unlikely to be a real phenomenon. Its existence, based on statistical inference, is therefore rejected as unnecessary to explain the observations.


arXiv:1811.06764v1 [pdf, other]
The reconfinement of AGN jets
Comments: Submitted to Computational Astrophysics and Cosmology

In this paper we study the reconfinement of initially freely-expanding unmagnetised relativistic jets by the pressure of non-uniform external gas using numerical approach. The results are compared with the simple semi-analytic model proposed by Komissarov & Falle (1997). In particular, we explore the reconfinement in power-law atmospheres and in the King atmosphere, which describes the X-ray coronas of giant elliptic galaxies. The results show significant deviations from the KF model, which systematically underestimates the reconfinement scale. For the power-law atmospheres the disagreement increases with the power index k, exceeding two orders of magnitude for k=1.5. For the King model, strong deviations are found on the outskirts of the atmosphere, where the distribution approaches a power law. However for jets reconfined inside the core, the reconfinement scale is increased only by the factor of two. When the King model is modified by adding a central cusp, this has little impact on the jets which are reconfined outside of the cusp region but inside the cusp the reconfinement scale significantly reduces.


arXiv:1811.06769v1 [pdf, other]
X-ray spectral characterization of the young Cygnus OB2 population
Comments: 28 pages, 16 figures, accepted for publication in ApJS as part of the special issue on the Chandra Cygnus OB2 Legacy Survey

We analyze the X-ray spectra of the $\sim$8000 sources detected in the Cygnus OB2 Chandra Legacy Survey (Drake et al., this issue), with the goals of characterizing the coronal plasma of the young low-mass stars in the region and estimating their intrinsic X-ray luminosities. We adopt two different strategies for X-ray sources for which more or less than 20 photons were detected. For the brighter sample we fit the spectra with absorbed isothermal models. In order to limit uncertainties, for most of the fainter Cygnus OB2 members in this sample, we constrain the spectral parameters to characteristic ranges defined from the brightest stars. For X-ray sources with $<$20 net photons we adopt a conversion factor from detected photon flux to intrinsic flux. This was defined, building on the results for the previous sample, as a function of the 20% quantile of the detected photon energy distributions, which we prove to also correlate well with extinction. We then use the X-ray extinction from the spectral fits to constrain the ratio between optical and X-ray extinction toward Cygnus OB2, finding it consistent with standard "Galactic"' values, when properly accounting for systematics. Finally we exploit the large number of sources to constrain the average coronal abundances of several elements, through two different ensemble analyses of the X-ray spectra of low-mass Cygnus OB2 members. We find the pattern of abundances to be largely consistent with that derived for the young stellar coronae in the Orion Nebula Cluster.


arXiv:1811.06778v1 [pdf, other]
The Formation of Compact Elliptical Galaxies in The Vicinity of A Massive Galaxy: The Role of Ram-pressure Confinement
Comments: 13 pages, 11 figures. Submitted to ApJ. Comments are welcome

Compact ellipticals (cEs) are outliers from the scaling relations of early-type galaxies, particularly the mass-metallicity relation which is an important outcome of feedback. The formation of such low-mass, but metal-rich and compact, objects is a long-standing puzzle. Using a pair of high-resolution N-body+gas simulations, we investigate the evolution of a gas-rich low-mass galaxy on a highly radial orbit around a massive host galaxy. As the infalling low-mass galaxy passes through the host's corona at supersonic speeds, its diffuse gas outskirts are stripped by ram pressure, as expected. However, the compactness increases rapidly because of bursty star formation in the gas tidally driven to the centre. The metal-rich gas produced by supernovae and stellar winds is confined by the ram pressure from the surrounding environment, leading to subsequent generations of stars being more metal-rich. After the gas is depleted, tidal interactions enhance the metallicity further via the stripping of weakly-bound, old and metal-poor stars, while the size of the satellite is changed only modestly. The outcome is a metal-rich cE that is consistent with observations. These results argue that classical cEs are neither the stripped remnants of much more massive galaxies nor the merger remnants of normal dwarfs. We present observable predictions that can be used to test our model.


arXiv:1811.06781v1 [pdf, other]
Concerning the occurrence of bow shocks around high-mass X-ray binaries
Comments: 15 pages, 12 figures, accepted for publication in Astronomy and Astrophysics

We investigate the occurrence of stellar bow shocks around high-mass X-ray binaries (HMXBs) in the Galaxy. We seek to conduct a survey of HMXBs in the mid-infrared to search for the presence of bow shocks around these objects. Telescopes operating in the mid-infrared, such as the Spitzer Space Telescope or Wide-field Infrared Survey Explorer (WISE), are potent tools for searching for the stellar bow shocks. We used the available archival data from these telescopes to search for bow shock candidates around the confirmed and candidate HMXBs in the Galaxy. We detected extended mid-infrared structures around several surveyed confirmed and candidate HMXBs. Two of these structures, associated with Vela X-1 and 4U 1907+09, are genuine bow shocks that have been studied previously. However, there are no new unambiguous bow shocks among the rest of the objects. The paucity of bow shocks around HMXBs suggests that the majority of these systems still reside within hot, low-density bubbles around their parent star clusters or associations. This also implies that the dynamical ejection of massive binaries is apparently less efficient than the ejections caused by the supernova explosions inside a binary.


arXiv:1811.06792v1 [pdf, other]
The code PEGASE.3 for distant RadioGalaxies with JWST
Comments: 2 pages, 3 figures, IAU2018 Proceedings (FM3 session)

The physical link of the star formation-AGN activities is analyzed from multiwavelength energy distributions of distant radiogalaxies (RG) with the help of two models: the new evolutionary code PEGASE.3 with dust predictions and the Siebenmorgen's AGN model, with the aim to to disentangle the farIR dust emissions from respectively interstellar medium and torus of RGs. Best-fits of the HST-Spitzer-Herschel (UV-to-IR) observations of the 3CR RGs with libraries of hybrid SED templates identify three components (AGN, old galaxy and young starburst) tracing the relation of starburst-AGN luminosities. To confirm this relation at higher resolutions, the JWST/NIRCam, MIRI and NIRspec instruments are needed, SED libraries and evolving colors of galaxy hosts adapted to the JWST instruments are in preparation with PEGASE.3.


arXiv:1811.06814v1 [pdf, other]
A simple approach to CO cooling in molecular clouds
Comments: 8 pages, 1 figure,

CO plays an important role in interstellar molecular clouds, both as a coolant, and as a diagnostic molecule. However, a proper evaluation of the cooling rate due to CO requires a determination of the populations of many levels, the spontaneous and stimulated radiative de-excitation rates between these levels, and the transfer of the emitted multi-line radiation; additionally, this must be done for three isotopologues. It would be useful to have a simple analytic formulation that avoided these complications; this could then be used in situations where CO plays an important role as a coolant, but the details of this role are not the main concern. We derive such a formulation here, by first considering the two asymptotic forms that obtain in the limits of (a) low volume-density and optical depth, and (b) high volume-density and optical depth. These forms are then combined in such a way as to fit the detailed numerical results from Goldsmith \& Langer (1978), which cover low temperatures, and a range of physical conditions where the interplay of thermal and sub-thermal excitation, optical-depth effects, and the contributions from rare isotopologues, are all important. The fit is obtained using the Metropolis-Hastings method, and reproduces the results of GL78 well. It is a purely local and analytic function of state --- specifically a function of the density, $\rho$, isothermal sound speed, $a$, CO abundance, $X_{_{\rm CO}}$, and velocity divergence, $\nabla\cdot{\boldsymbol\upsilon}$. As an application, we consider the cooling layer following a slow steady non-magnetic planar J-shock. We show that, if the post-shock cooling is dominated by CO and its isotopologues, the thickness of the post-shock cooling layer is very small and approximately independent of the pre-shock velocity, $\upsilon_o$, or pre-shock isothermal sound speed, $a_o$.


arXiv:1811.06818v1 [pdf, other]
The Environments of Luminous Radio - WISE Selected Infrared Galaxies
Comments: 17 pages, 16 figures, 2 tables

We have observed the environments of a population of 33 heavily dust obscured, ultra-luminous, high-redshift galaxies, selected using WISE and NVSS at $z>$1.3 with the Infra-Red Array Camera on the $Spitzer$ Space Telescope over $\rm5.12\,'\times5.12\,'$ fields. Colour selections are used to quantify any potential overdensities of companion galaxies in these fields. We find no significant excess of galaxies with the standard colour selection for IRAC colours of $\rm[3.6]-[4.5]>-0.1$ consistent with galaxies at $z>$1.3 across the whole fields with respect to wide-area $Spitzer$ comparison fields, but there is a $\rm>2\sigma$ statistical excess within $\rm0.25\,'$ of the central radio-WISE galaxy. Using a colour selection of $\rm[3.6]-[4.5]>0.4$, 0.5 magnitudes redder than the standard method of selecting galaxies at $z>$1.3, we find a significant overdensity, in which $\rm76\%$ ($\rm33\%$) of the 33 fields have a surface density greater than the $\rm3\sigma$ ($\rm5\sigma$) level. There is a statistical excess of these redder galaxies within $\rm0.5\,'$, rising to a central peak $\rm\sim2$--4 times the average density. This implies that these galaxies are statistically linked to the radio-WISE selected galaxy, indicating similar structures to those traced by red galaxies around radio-loud AGN.


arXiv:1811.06828v1 [pdf, other]
Bipolar H{\sc ii} regions produced by cloud/cloud collisions
Comments: 17 pages, 6 figures

We suggest that Bipolar H{\sc ii} Regions may be the aftermath of collisions between clouds. Such a collision will produce a shock-compressed layer, and a star cluster can then condense out of the dense gas near the centre of the layer. If the clouds are sufficiently massive, the star cluster is likely to contain at least one massive star, which emits ionising radiation, and excites an H{\sc ii} region, which then expands, sweeping up the surrounding neutral gas. Once most of the matter in the clouds has accreted onto the layer, expansion of the H{\sc ii} Region meets little resistance in directions perpendicular to the mid-plane of the layer, and so it expands rapidly to produce two lobes of ionised gas, one on each side of the layer. Conversely, in directions parallel to the mid-plane of the layer, expansion of the H{\sc ii} Region stalls due to the ram-pressure of the gas that continues to fall towards the star cluster from the outer parts of the layer; a ring of dense neutral gas builds up around the waist of the Bipolar H{\sc ii} Region, and may spawn a second generation of star formation. In this paper we present a dimensionless model for the flow of ionised gas in a Bipolar H{\sc ii} Region created according to the above scenario, and predict the characteristics of the resulting freefree continuum and recombination-line emission. This dimensionless model can be scaled to the physical parameters of any particular system. Our intention is that these predictions will be useful in testing the scenario outlined above, and thereby providing indirect support for the role of cloud/cloud collisions in triggering star formation.


arXiv:1811.06833v1 [pdf, other]
Brown Dwarf Formation: Theory
Comments: 22 pages, 1 figure

We rehearse the physical and theoretical considerations that define the nature of Brown Dwarfs, in particular the maximum mass for a Brown Dwarf (set by the Hydrogen-Burning Limit) and the minimum mass for a Brown Dwarf (set by the Opacity Limit). We then review the range of mechanisms that have been invoked to explain the formation of Brown Dwarfs and their statistical properties. These include turbulent fragmentation, fragmentation of filaments and discs, dynamical ejection of stellar embryos, and photoerosion. The primary contenders would seem to be turbulent fragmentation and disc fragmentation, and the observations needed to evaluate their relative importance may soon be available.


arXiv:1811.06844v1 [pdf, other]
Paleo-detectors: Searching for Dark Matter with Ancient Minerals
Comments: 22 pages, 7 figures, 1 table

Recently, we proposed paleo-detectors as a method for the direct detection of Weakly Interacting Massive Particle (WIMP) dark matter. In paleo-detectors, one would search for the persistent traces left by dark matter-nucleon interactions in ancient minerals. Thanks to the large integration time of paleo-detectors, relatively small target masses suffice to obtain exposures, i.e. the product of integration time and target mass, much larger than what is feasible in the conventional direct detection approach. Here, we discuss the paleo-detector proposal in detail, in particular, a range of background sources. For low-mass WIMPs with masses $m_\chi\lesssim10\,$GeV, the largest contribution to the background budget comes from nuclear recoils induced by coherent scattering of solar neutrinos. For heavier WIMPs, the largest background source is nuclear recoils induced by fast neutrons created by heavy radioactive contaminants, particularly $^{238}$U; neutrons can arise in spontaneous fission or from $\alpha$-particles created in $^{238}$U decays. We also discuss the challenges of mineral optimization, specifically the determination of readily available minerals from rocks in deep boreholes which are able to record persistent damage from nuclear recoils. In order to suppress backgrounds induced by radioactive contaminants, we propose to use minerals found in marine evaporites or in ultra-basic rocks. We estimate the sensitivity of paleo-detectors to spin-independent and spin-dependent WIMP-nucleus interactions. In all interaction cases considered here, the sensitivity to low-mass WIMPs with masses $m_\chi\lesssim10\,$GeV extends to WIMP-nucleon cross sections many orders of magnitude smaller than current upper limits. For heavier WIMPs with masses $m_\chi\gtrsim30\,$GeV cross sections a factor of a few to $\sim100$ smaller than current upper limits can be probed by paleo-detectors. [Abridged]


arXiv:1811.06880v1 [pdf, other]
Imaging the disc rim and a moving close-in companion candidate in the pre-transitional disc of V1247 Orionis
Comments: 17 pages, 14 figures

V1247 Orionis harbours a pre-transitional disc with a partially cleared gap. Earlier interferometric and polarimetric observations revealed strong asymmetries both in the gap region and in the outer disc. The presence of a companion was inferred to explain these asymmetric structures and the ongoing disc clearing. Using an extensive set of multi-wavelength and multi-epoch observations we aimed to identify the origin of the previously detected asymmetries. We have observed V1247 Ori at three epochs spanning $\sim678$ days using sparse aperture masking interferometry with Keck/NIRC2 and VLT/NACO. In addition, we search for signs of accretion through VLT/SPHERE-ZIMPOL spectral differential imaging in H$\alpha$ and R-band continuum. Our SMA sub-millimetre interferometry in 880 $\mu$m continuum and in the CO(3-2) line allows us to constrain the orientation and direction of rotation of the outer disc. We find the L'-band emission to be dominated by static features which trace forward-scattered dust emission from the inner edge of the outer disc located to the north-east. In H- and K-band, we see evidence for a companion candidate that moved systematically by 45$^{\circ}$ within the first $\sim$345 days. The separation of the companion candidate is not well constrained, but the observed position angle change is consistent with Keplerian motion of a body located on a 6 au orbit. From the SMA CO moment map, the location of the disc rim, and the detected orbital motion, we deduced the three-dimensional orientation of the disc. We see no indication of accretion in H$\alpha$ and set upper limits for an accreting companion. The measured contrast of the companion candidate in H and K is consistent with an actively accreting protoplanet. Hence, we identify V1247 Ori as a unique laboratory for studying companion-disc interactions and disc clearing.


arXiv:1811.06886v1 [pdf, other]
Numerical Study of Statistical Properties of the Galactic Center Distance Estimate from the Geometry of Spiral Arm Segments
Comments: 27 pages, 12 figures, 6 tables. Published in Astronomy Letters (AL)

The influence of various factors on the statistical properties of the Galactic center distance ($R_0$) estimate obtained by solving the general problem of determining the geometric parameters of a Galactic spiral arm from its segment with the inclusion of the distance to the spiral pole, i.e., $R_0$, in the set of parameters has been studied by the Monte Carlo method. Our numerical simulations have been performed for the model segments representing the Perseus and Scutum arms based on masers in high-mass star forming regions. We show that the uncertainty in the present-day parallax measurements for these objects systematically decreases (!) with increasing heliocentric distance, while the relative uncertainty in the parallaxes is approximately constant. This lucky circumstance increases by a factor of 1.4-1.7 the accuracy of estimating $R_0$ from the arm segment traced by masers. Our numerical experiments provide evidence for the consistency of the $R_0$ estimate from the spiral-segment geometry. The significant biases of the estimate detected only for the Scutum arm are caused mainly by the random parallax errors, the small angular extent of the segment, and the small number of objects representing it. The dispersion of the $R_0$ estimate depends most strongly on the angular extent of the segment and the parallax uncertainty if the latter, on average, does not depend on the distance. When the data on 3-8 segments are processed simultaneously, the predicted standard error of the final estimate is $\sigma_{R_0} \simeq 0.5$-$0.3$ kpc, respectively. The accuracy can be improved by increasing the extent of the identified segments and the number of objects belonging to them. A more complex variant of the method taking into account the measuring and natural dispersions of objects relative to the arm center line will avoid the biases of the parameter estimates.


arXiv:1811.06906v1 [pdf, other]
The loss of large amplitude pulsations at the end of AGB evolution
Comments: 2 pages, no figures, to appear in IAUS 343, Why Galaxies Care about AGB Stars, F. Kerschbaum, M. Groenewegen \& H. Olofsson, eds

Since 2013 we are performing with the Nancay Radio Telescope (NRT) a monitoring program of >100 Galactic disk OH/IR stars, having bright 1612-MHz OH maser emission. The variations of the maser emission are used to probe the underlying stellar variability. We wish to understand how the large-amplitude variations are lost during the AGB - post-AGB transition. The fading out of pulsations with steadily declining amplitudes seems to be a viable process.


arXiv:1811.06908v1 [pdf, other]
The dependence of the X-ray AGN clustering on the properties of the host galaxy
Comments: MNRAS accepted, 15 pages, 13 figures, 9 Tables

We study the clustering dependence of X-ray AGN and normal galaxies on the stellar mass (M$_\star$), star-formation rate (SFR) and specific star-formation rate (sSFR) of the (host) galaxy. Towards this end, we use 407 X-ray AGN from the XMM-XXL survey ($\sim$ 25 deg$^2$ in the North) and $\sim45,000$ galaxies in the VIPERS field (W1: $\sim$16 deg$^2$). We match the AGN and galaxy samples to have the same M$_\star$, SFR and redshift distributions. Based on our results, the two populations live in DMHs with similar mass ($\log M / (M_{\odot} \, h^{-1})\approx 12.8$) and have similar dependence on the galaxy properties. Specifically, our measurements show a positive dependence of the AGN and galaxy clustering on M$_\star$ and a negative dependence on SFR and sSFR. We also find that the X-ray clustering is independent of the location of the host galaxy above or below the star-forming main sequence.


arXiv:1811.06911v1 [pdf, other]
Reverberation Reveals the Truncated Disc in the Hard State of GX 339-4
Comments: 16 pages; submitted to MNRAS

The nature and geometry of the hard state in black hole binaries is controversial. The broadband continuum spectrum and fast variability properties can be explained in a model where the inner disc evaporates into a geometrically thick, hot flow. However these models are challenged by the persistent detection of an extremely broad iron line, which requires that the disc extends down to the last stable orbit of a high spin black hole. This line width can be considerably reduced if the Comptonisation continuum is multi-component rather than single temperature, but such models are highly degenerate. Here we show a specific model of a radially stratified continuum coupled to a model of propagating fluctuations, fit to some of the best hard state data from GX 339-4. This full spectral-timing model can fit the time averaged spectrum, the power spectra in different energy bands, and the frequency dependent lags between these bands. For the first time we also include disc reverberation and show that this same spectral-timing successfully predicts the lag-energy spectra on all timescales. This gives a more robust method to determine the inner radius of the disc, which is of order $20~R_g$, i.e. significantly truncated. This opens up the way to use the fast variability spectral-timing data to trace the source geometry of black hole binaries in all states.


arXiv:1811.06925v1 [pdf, other]
HATS-70b: A 13 Mjup brown dwarf transiting an A star
Comments: Accepted for publication in AJ

We report the discovery of HATS-70b, a transiting brown dwarf at the deuterium burning limit. HATS-70b has a mass of Mp=12.9 +1.8/-1.6 Mjup and a radius of Rp=1.384 +0.079/-0.074 Rjup, residing in a close-in orbit with a period of 1.89 days. The host star is a M*=1.78 +/- 0.12 Msun A star rotating at vsini=40.61 +0.32/-0.35 km/s, enabling us to characterize the spectroscopic transit of the brown dwarf via Doppler tomography. We find that HATS-70b, like other massive planets and brown dwarfs previously sampled, orbits in a low projected-obliquity orbit with lambda=8.9 +5.6/-4.5 deg. The low obliquities of these systems is surprising given all brown dwarf and massive planets with obliquities measured orbit stars hotter than the Kraft break. This trend is tentatively inconsistent with dynamically chaotic migration for systems with massive companions, though the stronger tidal influence of these companions makes it difficult to draw conclusions on the primordial obliquity distribution of this population. We also introduce a modeling scheme for planets around rapidly rotating stars, accounting for the influence of gravity darkening on the derived stellar and planetary parameters.


arXiv:1811.06926v1 [pdf, other]
New changing look case in NGC 1566
Comments: 7 pages, 5 figures

We present a study of optical, UV and X-ray light-curves of the nearby changing look active galactic nucleus in the galaxy NGC 1566 obtained with the Neil Gehrels Swift Observatory and the MASTER Global Robotic Network over the period 2007 - 2018. We also report on our optical spectroscopy at the South African Astronomical Observatory with the 1.9-m telescope on the night 2-3 August 2018. A substantial increase of X-ray flux by 1.5 orders of magnitude was observed following the brightening in the UV and optical bands during the last year. After a maximum was reached at the beginning of July 2018 the fluxes in all bands decreased with some fluctuations. The amplitude of the flux variability is strongest in the X-ray band and decreases with increasing wavelength. Low resolution spectra reveal a dramatic strengthening of the broad emission as well as high ionisation [FeX]6374 A lines. These lines were not detected so strongly in the past published spectra. The change in the type of the optical spectrum was accompanied by a significant change in the X-ray spectrum. All these facts confirm NGC 1566 to be a changing look Seyfert galaxy.


arXiv:1811.06932v1 [pdf, other]
Observational constraints on dynamical dark energy with pivoting redshift
Comments: 19 pages, 10 tables, 11 figures; comments are welcome!

We investigate the generalized Chevallier-Polarski-Linder (CPL) parametrization, which contains the pivoting redshift $z_p$ as an extra free parameter. We use various data combinations from cosmic microwave background (CMB), baryon acoustic oscillations (BAO), redshift space distortion (RSD), weak lensing (WL), joint light curve analysis (JLA), cosmic chronometers (CC), and we include a Gaussian prior on the Hubble constant value, in order to extract the observational constraints on various quantities. For the case of free $z_p$ we find that for all data combinations it always remains unconstrained, and there is a degeneracy with the current value of the dark energy equation of state $w_0$. For the case where $z_p$ is fixed to specific values, and for the full data combination, we find that with increasing $z_p$ the mean value of $w_0$ slowly moves into the phantom regime, however the cosmological constant is always allowed within 1$\sigma$ confidence-level. However, the significant effect is that with increasing $z_p$ the correlations between $w_0$ and $w_a$ change from negative to positive, with the case $z_p =0.35$ corresponding to no correlation. This feature indeed justifies why a non-zero pivoting redshift should be taken into account.


arXiv:1811.06938v1 [pdf, other]
How to Constrain Your M dwarf II: the mass-luminosity-metallicity relation from 0.075 to 0.70$M_\odot$
Comments: Accepted to AAS Journals. Comments welcome. Full tables available at https://github.com/awmann/masses_paper and code for computing mass posteriors at https://github.com/awmann/M_-M_K-

The mass-luminosity relation for late-type stars has long been a critical tool for estimating stellar masses. However, there is growing need for both a higher-precision relation and a better understanding of systematic effects (e.g., metallicity). Here we present an empirical relationship between Mks and mass spanning $0.075M_\odot<M<0.70M_\odot$. The relation is derived from 62 nearby binaries, whose orbits we determine using a combination of Keck/NIRC2 imaging, archival adaptive optics data, and literature astrometry. From their orbital parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use these total masses, in combination with resolved Ks magnitudes and system parallaxes, to calibrate the mass-Mks relation. The result can be used to determine masses of single stars with a precision of 2-3%, which we confirm by a comparison to dynamical masses from the literature. The precision is limited by scatter around the best-fit relation beyond mass uncertainties, perhaps driven by intrinsic variation in the mass-Mks relation or underestimated measurement errors. We find the effect of [Fe/H] on the mass-Mks relation is likely negligible for metallicities in the Solar neighborhood (0.0+/-2.2% change in mass per dex change in [Fe/H]). This weak effect is consistent with predictions from the Dartmouth Stellar Evolution Database, but inconsistent with those from MESA Isochrones and Stellar Tracks. A sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in extreme populations (e.g., in the Galactic Halo or thick disk).


arXiv:1811.06957v1 [pdf, other]
Milky Way globular clusters in gamma-rays: analyzing the dynamical formation of millisecond pulsars
Comments: Submitted to MNRAS. 17 pages, 6 figures, 3 tables

Globular clusters (GCs) are evolved stellar systems containing entire populations of millisecond pulsars (MSPs), which are efficient gamma-ray emitters. Observations of this emission can be used as a powerful tool to explore the dynamical processes leading to binary system formation in GCs. In this work, 9 years of Fermi Large Area Telescope data were used to investigate the gamma-ray emission from all GCs in the Milky Way. 23 clusters were found as gamma-ray bright, with 2 of them never having been reported before. It was also found that magnetic braking probably has a smaller impact on the formation rate of binary systems in metal-rich GCs than previously suggested, while large values for two-body encounter rate and intermediate values for encounter rate per binary seem to be a necessary condition. No extended emission was found even for clusters whose optical extent is 0.5deg. The possibility of extrapolating these results to ultra-compact dwarf galaxies is discussed, as these systems are believed to be the intermediate case between GCs and dwarf galaxies.


arXiv:1811.06971v1 [pdf, other]
GRRMHD Simulations of Tidal Disruption Event Accretion Disks around Supermassive Black Holes: Jet Formation, Spectra, and Detectability
Comments: 31 pages, 28 figures

We report results from general relativistic radiation MHD (GRRMHD) simulations of a super-Eddington black hole (BH) accretion disk formed as a result of a tidal disruption event (TDE). We consider the fiducial case of a solar mass star on a mildly penetrating orbit disrupted by a supermassive BH of mass $10^6 \, M_\odot$, and consider the epoch of peak fall back rate. We post-process the simulation data to compute viewing angle dependent spectra. We perform a parameter study of the dynamics of the accretion disk as a function of BH spin and magnetic flux, and compute model spectra as a function of the viewing angle of the observer. We also consider detection limits based on the model spectra. We find that an accretion disk with a relatively weak magnetic field around the BH (so-called SANE regime of accretion) does not launch a relativistic jet, whether or not the BH is rotating. Such models reasonably reproduce several observational properties of non-jetted TDEs. The same is also true for a non-rotating BH with a strong magnetic field (MAD regime). One of our simulations has a rapidly rotating BH (spin parameter 0.9) as well as a MAD accretion disk. This model launches a powerful relativistic jet, which is powered by the BH spin energy. It reproduces the high energy emission and jet structure of the jetted TDE Swift J1644+57 surprisingly well. Jetted TDEs may thus correspond to the subset of TDE systems that have both a rapidly spinning BH and MAD accretion.