- ID:
- ivo://CDS.VizieR/J/ApJ/762/25
- Title:
- The most metal-poor stars in HES and SDSS. I.
- Short Name:
- J/ApJ/762/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of 34 stars in the Hamburg/ESO Survey (HES) for metal-poor stars and the Sloan Digital Sky Survey (SDSS) that have [Fe/H]<~-3.0. Their median and minimum abundances are [Fe/H]=-3.1 and -4.1, respectively, while 10 stars have [Fe/H]<-3.5. High-resolution, high signal-to-noise spectroscopic data --equivalent widths and radial velocities-- are presented for these stars, together with an additional four objects previously reported or currently being investigated elsewhere. We have determined the atmospheric parameters, effective temperature (T_eff_), and surface gravity (logg), which are critical in the determination of the chemical abundances and the evolutionary status of these stars. Three techniques were used to derive these parameters. Spectrophotometric fits to model atmosphere fluxes were used to derive T_eff_, logg, and an estimate of E(B-V); H{alpha}, H{beta}, and H{gamma} profile fitting to model atmosphere results provided the second determination of T_eff_and logg; and finally, we used an empirical T_eff_-calibrated H{delta} index, for the third, independent T_eff_determination. The three values of T_eff_ are in good agreement, although the profile fitting may yield systematically cooler T_eff_values, by ~100K. This collective data set will be analyzed in future papers in the present series to utilize the most metal-poor stars as probes of conditions in the early universe.
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- ID:
- ivo://CDS.VizieR/J/ApJ/841/84
- Title:
- Theoretical framework for RR Lyrae. II. MIR data
- Short Name:
- J/ApJ/841/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new theoretical period-luminosity-metallicity (PLZ) relations for RR Lyrae stars (RRLs) at Spitzer and WISE wavelengths. The PLZ relations were derived using nonlinear, time-dependent convective hydrodynamical models for a broad range of metal abundances (Z=0.0001-0.0198). In deriving the light curves, we tested two sets of atmospheric models and found no significant difference between the resulting mean magnitudes. We also compare our theoretical relations to empirical relations derived from RRLs in both the field and in the globular cluster M4. Our theoretical PLZ relations were combined with multi-wavelength observations to simultaneously fit the distance modulus, {mu}0, and extinction, A_V_, of both the individual Galactic RRL and of the cluster M4. The results for the Galactic RRL are consistent with trigonometric parallax measurements from Gaia's first data release. For M4, we find a distance modulus of {mu}0=11.257+/-0.035mag with A_V_=1.45+/-0.12mag, which is consistent with measurements from other distance indicators. This analysis has shown that, when considering a sample covering a range of iron abundances, the metallicity spread introduces a dispersion in the PL relation on the order of 0.13mag. However, if this metallicity component is accounted for in a PLZ relation, the dispersion is reduced to ~0.02mag at mid-infrared wavelengths.
423. The PASTEL catalogue
- ID:
- ivo://CDS.VizieR/B/pastel
- Title:
- The PASTEL catalogue
- Short Name:
- B/pastel
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- PASTEL is a bibliographical catalogue compiling determinations of stellar atmospheric parameters. It provides (Teff, logg, [Fe/H]) determinations obtained from detailed analyses of high resolution, high signal to noise spectra, carried out with the help of model atmospheres. It also provides effective temperatures Teff from various methods. PASTEL is regularly updated. The catalogue supersedes the two previous versions of the [Fe/H] catalogue (Cayrel de Strobel et al., 1997 [Cat. III/200], 2001 [Cat. III/221]). PASTEL is regularly updated.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A94
- Title:
- The role of the host star's metallicity
- Short Name:
- J/A+A/624/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most of our current understanding of the planet formation mechanism is based on the planet metallicity correlation derived mostly from solar-type stars harbouring gas-giant planets. To achieve a more extensive grasp on the substellar formation process, we aim to analyse in terms of their metallicity a diverse sample of stars (in terms of mass and spectral type) covering the whole range of possible outcomes of the planet formation process (from planetesimals to brown dwarfs and low-mass binaries). Our methodology is based on the use of high-precision stellar parameters derived by our own group in previous works from high-resolution spectra by using the iron ionisation and equilibrium conditions. All values were derived in an homogeneous way, except for the M dwarfs where a methodology based on the use of pseudo equivalent widths of spectral features was used. Our results show that as the mass of the substellar companion increases the metallicity of the host star tends to lower values. The same trend is maintained when analysing stars with low-mass stellar companions and a tendency towards a wide range of host star's metallicity is found for systems with low-mass planets. We also confirm that more massive planets tend to orbit around more massive stars. The core-accretion formation mechanism for planet formation achieves its maximum efficiency for planets with masses in the range 0.2 and 2M_{Jup}_. Substellar objects with higher masses have higher probabilities of being formed as stars. Low-mass planets and planetesimals might be formed by core-accretion even around low-metallicity stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/784/170
- Title:
- The SEGUE K giant survey. II. Distances of 6036 stars
- Short Name:
- J/ApJ/784/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an online catalog of distance determinations for 6036 K giants, most of which are members of the Milky Way's stellar halo. Their medium-resolution spectra from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration are used to derive metallicities and rough gravity estimates, along with radial velocities. Distance moduli are derived from a comparison of each star's apparent magnitude with the absolute magnitude of empirically calibrated color-luminosity fiducials, at the observed (g-r)_0_ color and spectroscopic [Fe/H]. We employ a probabilistic approach that makes it straightforward to properly propagate the errors in metallicities, magnitudes, and colors into distance uncertainties. We also fold in prior information about the giant-branch luminosity function and the different metallicity distributions of the SEGUE K-giant targeting sub-categories. We show that the metallicity prior plays a small role in the distance estimates, but that neglecting the luminosity prior could lead to a systematic distance modulus bias of up to 0.25mag, compared to the case of using the luminosity prior. We find a median distance precision of 16%, with distance estimates most precise for the least metal-poor stars near the tip of the red giant branch. The precision and accuracy of our distance estimates are validated with observations of globular and open clusters. The stars in our catalog are up to 125kpc from the Galactic center, with 283 stars beyond 50kpc, forming the largest available spectroscopic sample of distant tracers in the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/80
- Title:
- The SEGUE K giant survey. III. Galactic halo
- Short Name:
- J/ApJ/816/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's Sloan Extension for Galactic Understanding and Exploration (SEGUE) project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (~33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.
- 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.
- 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.
