- ID:
- ivo://CDS.VizieR/J/AJ/161/100
- Title:
- Ages and alpha-abundances of population in K2
- Short Name:
- J/AJ/161/100
- Date:
- 19 Jan 2022 13:30:38
- Publisher:
- CDS
- Description:
- We explore the relationships between the chemistry, ages, and locations of stars in the Galaxy using asteroseismic data from the K2 mission and spectroscopic data from the Apache Point Galactic Evolution Experiment survey. Previous studies have used giant stars in the Kepler field to map the relationship between the chemical composition and the ages of stars at the solar circle. Consistent with prior work, we find that stars with high [{alpha}/Fe] have distinct, older ages in comparison to stars with low [{alpha}/Fe]. We provide age estimates for red giant branch (RGB) stars in the Kepler field, which support and build upon previous age estimates by taking into account the effect of {alpha}-enrichment on opacity. Including this effect for [{alpha}/Fe]-rich stars results in up to 10% older ages for low- mass stars relative to corrected solar mixture calculations. This is a significant effect that Galactic archeology studies should take into account. Looking beyond the Kepler field, we estimate ages for 735 RGB stars from the K2 mission, mapping age trends as a function of the line of sight. We find that the age distributions for low- and high-[{alpha}/Fe] stars converge with increasing distance from the Galactic plane, in agreement with suggestions from earlier work. We find that K2 stars with high [{alpha}/Fe] appear to be younger than their counterparts in the Kepler field, overlapping more significantly with a similarly aged low-[{alpha}/Fe] population. This observation may suggest that star formation or radial migration proceeds unevenly in the Galaxy.
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- ID:
- ivo://CDS.VizieR/J/other/NewA/19.1
- Title:
- Ages and masses of NGC1893 PMS stars
- Short Name:
- J/other/NewA/19.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we continued our efforts to understand the star formation scenario in and around the young cluster NGC 1893. We used a sample of the young stellar sources (YSOs) identified on the basis of multiwavelength data (optical, near-infrared (NIR), mid-infrared (MIR) and X-ray) to study the nature of YSOs associated with the region. The identified YSOs show an age spread of ~5Myr. The YSOs located near the nebulae at the periphery of the cluster are relatively younger in comparison to those located within the cluster region. The present results are in accordance with those obtained by us in previous studies. Other main results from the present study are: 1) the fraction of disk bearing stars increases towards the periphery of the cluster; 2) there is an evidence supporting the notion that the mechanisms for disk dispersal operate less efficiently for low-mass stars; 3) the sample of Class II sources is found to be relatively older in comparison to that of Class III sources. A comparison of various properties of YSOs in the NGC 1893 region with those in the Tr 37/ IC 1396 region is also discussed.
- 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/ApJ/889/157
- Title:
- Ages of FGK stars considering C and O abundances
- Short Name:
- J/ApJ/889/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise stellar ages of stars are necessary to study the evolution of the Milky Way. The age determination is significantly affected by C and O abundances of stars due to their contribution to the overall metallicity and opacity. On the basis of C and O abundances derived from high-resolution observations, we determine the ages of 148 FGK-type dwarfs in the solar neighborhood by considering C and O enhancements individually. Our results show that using C and O enhancements individually could affect the age determination of the high-{alpha} population, especially for stars with [O/{alpha}]>0.2dex, making them about 1Gyr younger compared to the results using traditional {alpha}-enhanced models. This results in a steeper slope in the age-[{alpha}/Fe] relation for the high-{alpha} population (changes from 0.0339+/-0.0075 to 0.0436+/-0.0086), indicating a higher formation rate. We find no tight relation between age and [{alpha}/Fe] or [O/Fe] in the high-{alpha} populations. The distribution of space velocity for young {alpha}-rich stars shows that they are more likely characterized to the low-{alpha} populations.
- 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/868/32
- Title:
- A large moving group within the LCC association
- Short Name:
- J/ApJ/868/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Scorpius-Centaurus is the nearest OB association, and its hundreds of members are divided into subgroups, including the Lower Centaurus Crux (LCC). Here we study the dynamics of the LCC area. We report the revelation of a large moving group containing more than 1800 intermediate- and low-mass young stellar objects and brown dwarfs that escaped identification until Gaia DR2 allowed a kinematic and photometric selection to be performed. We investigate the stellar and substellar content of this moving group using the Gaia DR2 astrometric and photometric measurements. The median distance of the members is 114.5pc, and 80% lie between 102 and 135pc from the Sun. Our new members cover a mass range of 0.02-5M_{sun}_ and add up to a total mass of about 700M_{sun}_. The present-day mass function follows a log-normal law with m_c_=0.22M_{sun}_ and {sigma}=0.64. We find more than 200 brown dwarfs in our sample. The star formation rate had its maximum of 8x10^-5^M_{sun}_/yr about 9Myr ago. We grouped the new members into four denser subgroups, which have increasing age from 7 to 10Myr, surrounded by "free-floating" young stars with mixed ages. Our isochronal ages, now based on accurate parallaxes, are compatible with several earlier studies of the region. The whole complex is presently expanding, and the expansion started between 8 and 10Myr ago. Two hundred members show infrared excess compatible with circumstellar disks from full to debris disks. This discovery provides a large sample of nearby young stellar and substellar objects for disk and exoplanet studies.
- 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/J/ApJ/826/16
- Title:
- ALMA and GeMS observations of the OMC1 region
- Short Name:
- J/ApJ/826/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ALMA observations of the Orion Nebula that cover the OMC1 outflow region. Our focus in this paper is on compact emission from protoplanetary disks. We mosaicked a field containing ~600 near-IR-identified young stars, around which we can search for sub-millimeter emission tracing dusty disks. Approximately 100 sources are known proplyds identified with the Hubble Space Telescope. We detect continuum emission at 1mm wavelengths toward ~20% of the proplyd sample, and ~8% of the larger sample of near-IR objects. The noise in our maps allows 4{sigma} detection of objects brighter than ~1.5mJy, corresponding to protoplanetary disk masses larger than 1.5M_J_ (using standard assumptions about dust opacities and gas-to-dust ratios). None of these disks are detected in contemporaneous CO(2-1) or C^18^O(2-1) observations, suggesting that the gas-to-dust ratios may be substantially smaller than the canonical value of 100. Furthermore, since dust grains may already be sequestered in large bodies in Orion Nebula cluster (ONC) disks, the inferred masses of disk solids may be underestimated. Our results suggest that the distribution of disk masses in this region is compatible with the detection rate of massive planets around M dwarfs, which are the dominant stellar constituent in the ONC.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/125
- Title:
- ALMA 887{mu}m obs. of ChaI star-forming region
- Short Name:
- J/ApJ/831/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887{mu}m survey of the disk population around objects from ~2 to 0.03M_{sun}_ in the nearby ~2Myr old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887{mu}m flux densities into dust disk masses, hereafter M_dust_. We find that the M_dust_-M_*_ relation is steeper than linear and of the form M_dust_{propto}(M_*_)^1.3-1.9^, where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1-3 Myr old regions of Taurus, Lupus, and Chamaeleon I share the same M_dust_-M_*_ relation, while the 10 Myr old Upper Sco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/895/126
- Title:
- ALMA observation of 152 1-11Myr aged stars
- Short Name:
- J/ApJ/895/126
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We utilize ALMA archival data to estimate the dust disk size of 152 protoplanetary disks in Lupus (1-3Myr), Chamaeleon I (2-3Myr), and Upper-Sco (5-11Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust disk radii were estimated, as here, through fitting radial profile models to visibility data. We use these 199 homogeneously derived disk sizes to identify empirical disk-disk and disk-host property relations as well as to search for evolutionary trends. In agreement with previous studies, we find that dust disk sizes and millimeter luminosities are correlated, but show for the first time that the relationship is not universal between regions. We find that disks in the 2-3Myr old ChaI are not smaller than disks in other regions of similar age, and confirm the Barenfeld et al. finding that the 5-10Myr USco disks are smaller than disks belonging to younger regions. Finally, we find that the outer edge of the solar system, as defined by the Kuiper Belt, is consistent with a population of dust disk sizes which have not experienced significant truncation.
