- ID:
- ivo://CDS.VizieR/J/ApJ/838/90
- Title:
- Abundance analysis of 9 very metal-poor stars
- Short Name:
- J/ApJ/838/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a differential line-by-line chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main-sequence (MS) halo stars, near [Fe/H]=-2dex. Our abundances range from -2.66<=[Fe/H]<=-1.40dex with conservative uncertainties of 0.07dex. We find an average [{alpha}/Fe]=0.34+/-0.09dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with Hubble Space Telescope parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this difference, it is not supported by current effective temperature studies and would create large uncertainties in the abundance determinations. Both 1D and <3D> hydrodynamical models combined with separate 1D non-LTE effects do not yet account for the atmospheres of real metal-poor MS stars, but a fully 3D non-LTE treatment may be able to explain the ionization imbalance found in this work.
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- ID:
- ivo://CDS.VizieR/J/AJ/157/234
- Title:
- ACRONYM. III. Candidate young low-mass stars
- Short Name:
- J/AJ/157/234
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young, low-mass stars in the solar neighborhood are vital for completing the mass function for nearby, young coeval groups, establishing a more complete census for evolutionary studies, and providing targets for direct-imaging exoplanet and/or disk studies. We present properties derived from high-resolution optical spectra for 336 candidate young nearby, low-mass stars. These include measurements of radial velocities and age diagnostics such as H{alpha} and Li {lambda}6707 equivalent widths. Combining our radial velocities with astrometry from Gaia DR2 (Cat. I/345), we provide full 3D kinematics for the entire sample. We combine the measured spectroscopic youth information with additional age diagnostics (e.g., X-ray and UV fluxes, color-magnitude diagram positions) and kinematics to evaluate potential membership in nearby, young moving groups and associations. We identify 77 objects in our sample as bona fide members of 10 different moving groups, 14 of which are completely new members or have had their group membership reassigned. We also reject 44 previously proposed candidate moving group members. Furthermore, we have newly identified or confirmed the youth of numerous additional stars that do not belong to any currently known group and find 69 comoving systems using Gaia DR2 astrometry. We also find evidence that the Carina association is younger than previously thought, with an age similar to the {beta} Pictoris moving group (~22 Myr).
- ID:
- ivo://CDS.VizieR/J/ApJ/870/9
- Title:
- Ages & masses for GPS1 WD-MS binary systems
- Short Name:
- J/ApJ/870/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observational tests of stellar and Galactic chemical evolution call for the joint knowledge of a star's physical parameters, detailed element abundances, and precise age. For cool main-sequence (MS) stars the abundances of many elements can be measured from spectroscopy, but ages are very hard to determine. The situation is different if the MS star has a white dwarf (WD) companion and a known distance, as the age of such a binary system can then be determined precisely from the photometric properties of the cooling WD. As a pilot study for obtaining precise age determinations of field MS stars, we identify nearly 100 candidates for such wide binary systems: a faint WD whose Gaia-PS1-SDSS (GPS1) proper motion (Tian+ 2017, I/343) matches that of a brighter MS star in Gaia/TGAS (Gaia Collaboration 2016, I/337) with a good parallax ({sigma}_{rho}_/{rho}=<0.05). We model the WD's multi-band photometry with the BASE-9 code using this precise distance (assumed to be common for the pair) and infer ages for each binary system. The resulting age estimates are precise to =<10% (=<20%) for 42 (67) MS-WD systems. Our analysis more than doubles the number of MS-WD systems with precise distances known to date, and it boosts the number of such systems with precise age determination by an order of magnitude. With the advent of the Gaia DR2 (Gaia Collaboration, 2018, I/345) data, this approach will be applicable to a far larger sample, providing ages for many MS stars (that can yield detailed abundances for over 20 elements), especially in the age range of 2-8Gyr, where there are only few known star clusters.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/58
- Title:
- Ages of field stars from white dwarf comp. in Gaia
- Short Name:
- J/ApJS/253/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze 4050 wide binary star systems involving a white dwarf (WD) and usually a main-sequence (MS) star, drawn from the large sample assembled by Tian+ (2020, J/ApJS/246/4). Using the modeling code BASE-9, we determine the system's ages, the WD progenitors' zero-age MS masses, the extinction values (AV), and the distance moduli. Discarding the cases with poor age convergences, we obtain ages for 3551 WDs, with a median age precision of {sigma}{tau}/{tau}=20%, and system ages typically in the range of 1-6Gyr. We validated these ages against the very few known clusters and through cross validation of 236 WD-WD binaries. Under the assumption that the components are coeval in a binary system, this provides precise age constraints on the usually low-mass MS companions, mostly inaccessible by any other means.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/77
- Title:
- A library of high-S/N optical spectra of FGKM stars
- Short Name:
- J/ApJ/836/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution (R~60000), high signal-to-noise ratio (S/N~150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types ~M5-F1 (T_eff_~3000-7000K, R_*_~0.1-16R_{Sun}_). We also present "Empirical SpecMatch" (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100K in effective temperature (T_eff_), 15% in stellar radius (R_*_), and 0.09dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars ~K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70K in T_eff_, 10% in R_*_, and 0.12dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.
- ID:
- ivo://CDS.VizieR/I/280B
- Title:
- All-Sky Compiled Catalogue of 2.5 million stars
- Short Name:
- I/280B
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The All-Sky Compiled Catalogue of 2501313 stars (ASCC-2.5) with the limiting magnitude V=12-14 is a result of a merging of star lists from present day large high-precision catalogues from space (Hipparcos- Tycho family catalogues: Hipparcos main catalogue including Multiple System Annex [I/239], Tycho-1 [I/239], Tycho-2 [I/259], ACT-RC [I/246], TRC [I/250]) and ground-based (PPM-N [I/146], PPM-S [I/193], PPM-add [I/208], CMC11 [I/256]) observations and reduction to standard systems of corresponding stellar data. The data from the Tycho-2 Spectral Type Catalog [III/231], and the 2MASS All-Sky Catalog of Point Sources [II/246] are added. The basic stellar data presented in the ASCC-2.5 are the equatorial coordinates (J2000, epoch 1991.25), proper motions in the Hipparcos system, B and/or V stellar magnitudes in the Johnson system. Additionally, for some stars we give trigonometric parallaxes, spectral classes in the MK or HD system, multiplicity and variability flags, Hipparcos, Tycho-2, HD, DM designations. Equatorial coordinates and their standard errors were taken from the source catalogues in accordance with the priority: Hipparcos [I/239/hip_main], Tycho-2 [I/259], Tycho-1 [I/239/tyc_main], CMC11 [I/256], PPM [I/146,I/193,I/208]. Proper motions from the source catalogues were compared with Hipparcos data.The compiled proper motions in the Hipparcos system and their standard errors were computed as the weighted means. The weights were set in accordance with the proper motion errors listed for individual stars in the source catalogues. Trigonometric parallaxes are taken from the Hipparcos and Tycho-1 catalogues. Stellar B, V magnitudes were determined on the basis of the ground- based photometric data taken from CMC11, Hipparcos, as well as space BT, VT from Tycho-1, Tycho-2. Magnitudes from the PPM catalogue were used if no other photometric data were available. Tycho data were transformed to the Johnson system via: V = VT - 0.09 (B-V)T + dV, (B-V) = 0.850 (B-V)T + d(B-V), i.e. using the recommendations from the Introduction to the Tycho catalogue and including additional corrections dV and d(B-V). These additional corrections were determined by comparison with ground-based data in the Johnson system. These corrections depend non-linearly on colour and reach 0.02 and 0.04 mag, respectively. Infrared stellar magnitudes J, H, K_s_ and their errors were copied from the 2MASS catalogue. Spectral classes in the MK or HD systems were taken from Hipparcos, CMC11, PPM, and Tycho-2 Spectral Type catalogues. Multiplicity and variability flags were taken from Tycho-1, Tycho-2, Hipparcos, CMC11, and PPM catalogues. The 1st version of the ASCC-2.5 contained some errors in the zones -1 to +1 degree which have been corrected (see details in the "History" section below). The 2nd version included a new file (ccadd.dat) containing the previously missing stars (including components of multiple systems). Note that the ASCC numbers did not change between the two versions, but additional numbers (2600001 to 2603318) were assigned. In the present 3rd version of the ASCC-2.5 the stars from file ccadd.dat are inserted in the basic files in accordance with their coordinates. Stars in the ASCC-2.5 are divided into 30 files ordered by declination (North and South polar caps and 28 bands of 5 degrees width), then sorted in order of right ascension within each file.
- ID:
- ivo://CDS.VizieR/J/AJ/156/94
- Title:
- APOGEE and Gaia DR2 analysis of IC 166
- Short Name:
- J/AJ/156/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IC 166 is an intermediate-age open cluster (OC) (~1 Gyr) that lies in the transition zone of the metallicity gradient in the outer disk. Its location, combined with our very limited knowledge of its salient features, make it an interesting object of study. We present the first high-resolution spectroscopic and precise kinematical analysis of IC 166, which lies in the outer disk with R_GC_~12.7 kpc. High-resolution H-band spectra were analyzed using observations from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment survey. We made use of the Brussels Automatic Stellar Parameter code to provide chemical abundances based on a line-by-line approach for up to eight chemical elements (Mg, Si, Ca, Ti, Al, K, Mn, and Fe). The {alpha}-element (Mg, Si, Ca, and whenever available Ti) abundances, and their trends with Fe abundances have been analyzed for a total of 13 high-likelihood cluster members. No significant abundance scatter was found in any of the chemical species studied. Combining the positional, heliocentric distance, and kinematic information, we derive, for the first time, the probable orbit of IC 166 within a Galactic model including a rotating boxy bar, and found that it is likely that IC 166 formed in the Galactic disk, supporting its nature as an unremarkable Galactic OC with an orbit bound to the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/MNRAS/460/3179
- Title:
- APOGEE stars distance and extinction
- Short Name:
- J/MNRAS/460/3179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a Bayesian technology, we derived distances and extinctions for over 100000 red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey by taking into account spectroscopic constraints from the APOGEE stellar parameters and photometric constraints from Two Micron All-Sky Survey, as well as a prior knowledge on the Milky Way. Derived distances are compared with those from four other independent methods, the Hipparcos parallaxes, star clusters, APOGEE red clump stars, and asteroseismic distances from APOKASC and Stromgren survey for Asteroseismology and Galactic Archaeology catalogues. These comparisons covers four orders of magnitude in the distance scale from 0.02 to 20kpc. The results show that our distances agree very well with those from other methods: the mean relative difference between our Bayesian distances and those derived from other methods ranges from -4.2 per cent to +3.6 per cent, and the dispersion ranges from 15 per cent to 25 per cent. The extinctions towards all stars are also derived and compared with those from several other independent methods: the Rayleigh-Jeans Colour Excess (RJCE) method, Gonzalez's 2D extinction map, as well as 3D extinction maps and models. The comparisons reveal that, overall, estimated extinctions agree very well, but RJCE tends to overestimate extinctions for cool stars and objects with low logg.
- ID:
- ivo://CDS.VizieR/J/AJ/156/84
- Title:
- APOGEE-2 survey of Orion Complex. II.
- Short Name:
- J/AJ/156/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of spectroscopic and astrometric data from APOGEE-2 and Gaia DR2 (Cat. I/345) to identify structures toward the Orion Complex. By applying a hierarchical clustering algorithm to the six-dimensional stellar data, we identify spatially and/or kinematically distinct groups of young stellar objects with ages ranging from 1 to 12 Myr. We also investigate the star-forming history within the Orion Complex and identify peculiar subclusters. With this method we reconstruct the older populations in the regions that are currently largely devoid of molecular gas, such as Orion C (which includes the {sigma} Ori cluster) and Orion D (the population that traces Ori OB1a, OB1b, and Orion X). We report on the distances, kinematics, and ages of the groups within the Complex. The Orion D group is in the process of expanding. On the other hand, Orion B is still in the process of contraction. In {lambda} Ori the proper motions are consistent with a radial expansion due to an explosion from a supernova; the traceback age from the expansion exceeds the age of the youngest stars formed near the outer edges of the region, and their formation would have been triggered when they were halfway from the cluster center to their current positions. We also present a comparison between the parallax and proper-motion solutions obtained by Gaia DR2 and those obtained toward star-forming regions by the Very Long Baseline Array.
- ID:
- ivo://CDS.VizieR/J/AJ/128/463
- Title:
- A preliminary 20pc census from the NLTT catalogue
- Short Name:
- J/AJ/128/463
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Continuing our census of late-type dwarfs in the solar neighborhood, we present BVRI photometry and optical spectroscopy of 800 mid-type M dwarfs drawn from the NLTT proper-motion catalog. The targets are taken both from our own cross-referencing of the NLTT Catalogue and the 2MASS Second Incremental Data Release, and from the revised NLTT compiled recently by Salim & Gould (Cat. <J/ApJ/582/1011>). All are identified as nearby-star candidates based on their location in the (m_r_, m_r_-K_s_) diagram. Three hundred stars discussed here have previous astrometric, photometric, or spectroscopic observations. We present new BVRI photometry for 101 stars, together with low-resolution spectroscopy of a further 400 dwarfs.
