- ID:
- ivo://CDS.VizieR/J/ApJS/254/11
- Title:
- The Spitzer Kepler Survey (SpiKeS) catalog
- Short Name:
- J/ApJS/254/11
- Date:
- 17 Jan 2022 00:38:57
- Publisher:
- CDS
- Description:
- The ~200000 targets monitored for photometric variability during the Kepler prime mission include the best-studied group of stars in the sky, due both to the extensive time history provided by Kepler and to the substantial amount of ancillary data provided by other investigators or compiled by the Kepler team. To complement this wealth of data, we surveyed the entire Kepler field using the 3.6 and 4.5{mu}m bands of the Warm Spitzer Space Telescope, obtaining photometry in both bands for almost 170000 objects. We demonstrate relative photometric precision ranging from better than ~1.5% for the brighter stars down to slightly greater than ~2% for the faintest stars monitored by Kepler. We describe the data collection and analysis phases of this work and identify several stars with large infrared excess, although none that is also known to be the host of an exoplanetary system.
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- ID:
- ivo://CDS.VizieR/J/ApJ/708/1076
- Title:
- The WHIQII survey: compact blue galaxies
- Short Name:
- J/ApJ/708/1076
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of the WIYN High Image Quality Indiana-Irvine (WHIQII) survey, we present 123 spectra of faint emission-line galaxies, selected to focus on intermediate redshift (0.4<~z<~0.8) galaxies with blue colors that appear physically compact on the sky. The sample includes 15 true Luminous Compact Blue Galaxies (LCBGs) and an additional 27 slightly less extreme emission-line systems. These galaxies represent a highly evolving class that may play an important role in the decline of star formation since z~1, but their exact nature and evolutionary pathways remain a mystery. Here, we use emission lines to determine metallicities and ionization parameters, constraining their intrinsic properties and state of star formation. Some LCBG metallicities are consistent with a "bursting dwarf" scenario, while a substantial fraction of others are not, further confirming that LCBGs are a highly heterogeneous population but are broadly consistent with the intermediate redshift field. In agreement with previous studies, we observe overall evolution in the luminosity-metallicity relation at intermediate redshift. Our sample, and particularly the LCBGs, occupies a region in the empirical R_23_-O_32_ plane that differs from luminous local galaxies and is more consistent with dwarf irregulars at the present epoch, suggesting that cosmic "downsizing" is observable in even the most fundamental parameters that describe star formation.
- ID:
- ivo://CDS.VizieR/J/A+A/525/A90
- Title:
- Thick disc vertical properties
- Short Name:
- J/A+A/525/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work investigates the properties (metallicity and kinematics) and interfaces of the Galactic thick disc as a function of height above the Galactic plane. The main aim is to study the thick disc in a place where it is the main component of the sample. We take advantage of former astrometric work in two fields of several square degrees in which accurate proper motions were measured down to V-magnitudes of 18.5 in two directions, one near the north galactic pole and the other at a galactic latitude of 46{deg} and galactic longitude near 0{deg}. Spectroscopic observations have been acquired in these two fields for a total of about 400 stars down to magnitude 18.0, at spectral resolutions of 3.5 to 6.25{AA}. The spectra have been analysed with the code ETOILE, comparing the target stellar spectra with a grid of 1400 reference stellar spectra. This comparison allowed us to derive the parameters effective temperature, gravity, [Fe/H] and absolute magnitude for each target star.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/156
- Title:
- Ti and Fe lines in red supergiants
- Short Name:
- J/ApJ/751/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed non-LTE (NLTE) calculations for red supergiant (RSG) stars are presented to investigate the influence of NLTE on the formation of atomic iron and titanium lines in the J band. With their enormous brightness at J band RSG stars are ideal probes of cosmic abundances. Recent LTE studies have found that metallicities accurate to 0.15 dex can be determined from medium-resolution spectroscopy of individual RSGs in galaxies as distant as 10 Mpc. The NLTE results obtained in this investigation support these findings. NLTE abundance corrections for iron are smaller than 0.05 dex for effective temperatures between 3400 K and 4200 K and 0.1 dex at 4400 K. For titanium the NLTE abundance corrections vary smoothly between -0.4 dex and +0.2 dex as a function of effective temperature. For both elements, the corrections also depend on stellar gravity and metallicity. The physical reasons behind the NLTE corrections and the consequences for extragalactic J-band abundance studies are discussed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/404/1321
- Title:
- TiII in Milky way and Magellanic clouds
- Short Name:
- J/MNRAS/404/1321
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss several sets of TiII absorption-line data, which probe a variety of interstellar environments in our Galaxy and in the Magellanic Clouds. Comparisons of high-resolution [full width at half-maximum (FWHM)~1.3-1.5km/s] TiII spectra of Galactic targets with corresponding high-resolution spectra of NaI, KI and CaII reveal both similarities and differences in the detailed structure of the absorption-line profiles - reflecting component-to-component differences in the ionization and depletion behaviour of those species. Moderate-resolution (FWHM~3.4-4.5km/s) spectra of more heavily reddened Galactic stars provide more extensive information on the titanium depletion in colder, denser clouds - where more than 99.9 per cent of the Ti may be in the dust phase. Moderate-resolution (FWHM~4.5-8.7km/s) spectra of stars in the Magellanic Clouds suggest that the titanium depletion is generally much less severe in the Large and Small Magellanic Clouds than in our Galaxy [for a given N(Htot), E(B-V), or molecular fraction f(H2)]- providing additional evidence for differences in depletion patterns in those two lower-metallicity galaxies. We briefly discuss possible implications of these results for the interpretation of gas-phase abundances in quasi-stellar object absorption-line systems and of variations in the D/H ratio in the local Galactic interstellar medium.
- ID:
- ivo://CDS.VizieR/J/ApJS/228/11
- Title:
- Time-dependent cooling in photoionized plasma
- Short Name:
- J/ApJS/228/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I explore the thermal evolution and ionization states in gas cooling from an initially hot state in the presence of external photoionizing radiation. I compute the equilibrium and nonequilibrium cooling efficiencies, heating rates, and ion fractions for low-density gas cooling while exposed to the ionizing metagalactic background radiation at various redshifts (z=0-3), for a range of temperatures (10^8^-10^4^K), densities (10^-7^-10^3^cm^-3^), and metallicities (10^-3^-2 times solar). The results indicate the existence of a threshold ionization parameter, above which the cooling efficiencies are very close to those in photoionization equilibrium (so that departures from equilibrium may be neglected), and below which the cooling efficiencies resemble those in collisional time-dependent gas cooling with no external radiation (and are thus independent of density).
- ID:
- ivo://CDS.VizieR/J/A+A/641/A116
- Title:
- Titan middle atmosphere thermal field
- Short Name:
- J/A+A/641/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the seasonal evolution of Titan's thermal field and distributions of haze, C_2_H_2_, C_2_H_4_, C_2_H_6_, CH_3_C_2_H, C_3_H_8_, C_4_H_2_, C_6_H_6_, HCN, and HC_3_N from March 2015 (Ls=66{deg}) to September 2017 (Ls=93{deg}) (i.e., from the last third of northern spring to early summer). We analyzed thermal emission of Titan's atmosphere acquired by the Cassini Composite Infrared Spectrometer (CIRS) with limb and nadir geometry to retrieve the stratospheric and mesospheric temperature and mixing ratios pole-to-pole meridional cross sections from 5mbar to 50ubar (120-650km). The southern stratopause varied in a complex way and showed a global temperature increase from 2015 to 2017 at high-southern latitudes. Stratospheric southern polar temperatures, which were observed to be as low as 120K in early 2015 due to the polar night, showed a 30K increase (at 0.5mbar) from March 2015 to May 2017 due to adiabatic heating in the subsiding branch of the global overturning circulation. All photochemical compounds were enriched at the south pole by this subsidence. Polar cross sections of these enhanced species, which are good tracers of the global dynamics, highlighted changes in the structure of the southern polar vortex. These high enhancements combined with the unusually low temperatures (<120K) of the deep stratosphere resulted in condensation at the south pole between 0.1 and 0.03mbar (240-280km) of HCN, HC_3_N, C_6_H_6_ and possibly C4H2 in March 2015 (Ls=66{deg}). These molecules were observed to condense deeper with increasing distance from the south pole. At high-northern latitudes, stratospheric enrichments remaining from the winter were observed below 300km between 2015 and May 2017 (Ls=90{deg}) for all chemical compounds and up to September 2017 (Ls=93{deg}) for C_2_H_2_, C_2_H_4_, CH_3_C_2_H, C_3_H_8_, and C_4_H_2_. In September 2017, these local enhancements were less pronounced than earlier for C_2_H_2_, C_4_H_2_, CH_3_C_2_H, HC_3_N, and HCN, and were no longer observed for C_2_H_6_ and C_6_H_6_, which suggests a change in the northern polar dynamics near the summer solstice. These enhancements observed during the entire spring may be due to confinement of this enriched air by a small remaining winter circulation cell that persisted in the low stratosphere up to the northern summer solstice, according to predictions of the Institut Pierre Simon Laplace Titan Global Climate Model (IPSL Titan GCM). In the mesosphere we derived a depleted layer in C_2_H_2_, HCN, and C_2_H_6_ from the north pole to mid-southern latitudes, while C_4_H_2_, C_3_H_4_, C_2_H_4_, and HC_3_N seem to have been enriched in the same region. In the deep stratosphere, all molecules except C_2_H_4_ were depleted due to their condensation sink located deeper than 5mbar outside the southern polar vortex. HCN, C_4_H_2_, and CH_3_C_2_H volume mixing ratio (VMR) cross section contours showed steep slopes near the mid-latitudes or close to the equator, which can be explained by upwelling air in this region. Upwelling is also supported by the cross section of the C_2_H_4_ (the only molecule not condensing among those studied here) volume mixing ratio observed in the northern hemisphere. We derived the zonal wind velocity up to mesospheric levels from the retrieved thermal field. We show that zonal winds were faster and more confined around the south pole in 2015 (Ls=67-72{deg}) than later. In 2016, the polar zonal wind speed decreased while the fastest winds had migrated toward low-southern latitudes.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A194
- Title:
- Titans metal-poor reference stars. I.
- Short Name:
- J/A+A/650/A194
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Several large stellar spectroscopic surveys are producing overwhelming amounts of data that can be used for determining stellar atmospheric parameters and chemical abundances. Nonetheless, the accuracy achieved in the derived astrophysical parameters is still insufficient, mainly because of the paucity of adequate calibrators, particularly in the metal-poor regime ([Fe/H]<=-1.0). Our aim is to increase the number of metal-poor stellar calibrators that have accurate parameters. Here, we introduce the Titans metal-poor reference stars: a sample of 41 dwarf and subgiant stars with accurate, but model-dependent, parameters. Effective temperatures (Teff) were derived by fitting observed H{alpha} profiles with synthetic lines computed using three dimensional (3D) hydrodynamic model atmospheres that take into account departures from the local thermodynamic equilibrium (non-LTE effects). Surface gravities (logg) were computed using evolutionary tracks and parallaxes from Gaia early-data release 3. The same methods recover the Teff values of the Gaia benchmark stars, which are mostly based on interferometric measurements, with a 1{sigma} dispersion of 50K. We assume this to be the accuracy of the H{alpha} profiles computed from 3D non-LTE models for metal-poor dwarfs and subgiants, although this is likely an upper-bound estimate dominated by the uncertainty of the standard Teff values. We achieved an internal precision typically between 30-40K, these errors dominated by instrumental effects. The final total uncertainty for the Teff values of the Titans are thus estimated to be of the order of 1%. The typical error for logg is 0.04dex. In addition, we identified a few members of Gaia-Enceladus, of Sequoia, and of the Helmi stream in our sample. These stars can pave the way for the accurate chemical characterization of these Galactic substructures. Using the Titans as reference, large stellar surveys will be able to improve the internal calibration of their astrophysical parameters. Ultimately, this sample will help users of data from Gaia and large surveys in reaching their goal of redefining our understanding of stars, stellar systems, and the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A79
- Title:
- TO stars metallicity estimate
- Short Name:
- J/A+A/651/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal of the Turn-Off Primordial Stars survey (TOPoS) project is to find and analyse turn-off (TO) stars of extremely low metallicity. To select the targets for spectroscopic follow-up at high spectral resolution, we relied on low-resolution spectra from the Sloan Digital Sky Survey (SDSS). In this paper, we use the metallicity estimates we obtained from our analysis of the SDSS spectra to construct the metallicity distribution function (MDF) of the Milky Way, with special emphasis on its metal-weak tail. The goal is to provide the underlying distribution out of which the TOPoS sample was extracted. We made use of SDSS photometry, Gaia photometry, and distance estimates derived from the Gaia parallaxes to derive a metallicity estimate for a large sample of over 24 million TO stars. This sample was used to derive the metallicity bias of the sample for which SDSS spectra are available. We determined that the spectroscopic sample is strongly biased in favour of metal-poor stars, as intended. A comparison with the unbiased photometric sample allows us to correct for the selection bias. We selected a sub-sample of stars with reliable parallaxes for which we combined the SDSS radial velocities with Gaia proper motions and parallaxes to compute actions and orbital parameters in the Galactic potential. This allowed us to characterise the stars dynamically, and in particular to select a sub-sample that belongs to the Gaia-Sausage-Enceladus (GSE) accretion event. We are thus also able to provide the MDF of GSE. The metal-weak tail derived in our study is very similar to that derived in the H3 survey and in the Hamburg/ESO Survey. This allows us to average the three MDFs and provide an error bar for each metallicity bin. Inasmuch as the GSE structure is representative of the progenitor galaxy that collided with the Milky Way, that galaxy appears to be strongly deficient in metal-poor stars compared to the Milky Way, suggesting that the metal-weak tail of the latter has been largely formed by accretion of low-mass galaxies rather than massive galaxies, such as the GSE progenitor.
- ID:
- ivo://CDS.VizieR/J/A+A/609/A53
- Title:
- Tracing stars of MW dwarf galaxies: Sextans
- Short Name:
- J/A+A/609/A53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep and very spatially extended CTIO/DECam g and r photometric catalogue of point-sources (reaching out to ~2 magnitudes below the oldest main-sequence turn-off and covering ~20deg^2^) around the Sextans dwarf spheroidal galaxy, together with another catalogue of literature spectroscopic measurements (Walker et al., 2009, Cat. J/AJ/137/3100 and Battaglia et al., 2011, Cat. J/MNRAS/411/1013) with updated membership probabilities.
