- ID:
- ivo://CDS.VizieR/J/A+A/537/A120
- Title:
- Rotational velocities of A-type stars. IV.
- Short Name:
- J/A+A/537/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In previous works of this series, we have shown that late B- and early A-type stars have genuine bimodal distributions of rotational velocities and that late A-type stars lack slow rotators. The distributions of the surface angular velocity ratio Omega/Omega_crit_ (Omega_crit_ is the critical angular velocity) have peculiar shapes according to spectral type groups, which can be caused by evolutionary properties. We aim to review the properties of these rotational velocity distributions in some detail as a function of stellar mass and age. We have gathered vsini for a sample of 2014 B6- to F2-type stars. We have determined the masses and ages for these objects with stellar evolution models. The (Teff,logL/L_{sun}_)-parameters were determined from the uvby-beta photometry and the HIPPARCOS parallaxes.
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- ID:
- ivo://CDS.VizieR/J/A+A/597/A30
- Title:
- Seismology and spectroscopy of CoRoGEE red giants
- Short Name:
- J/A+A/597/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the CoRoGEE dataset -- obtained from CoRoT lightcurves for 606 red giant stars in two fields of the Galactic disc which have been co-observed for an ancillary project of the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The CoRoGEE stars cover a large radial range of the Milky Way's disc (5kpc<RGal<14kpc) and thus provide a valuable dataset for Galactic Archaeology studies. We have used the Bayesian parameter estimation code PARAM to calculate distances, extinctions, masses, and ages for these stars in a homogeneous analysis, resulting in relative statistical uncertainties of 2% in distance, 4% in radius, ~9% in mass and ~25% in age. We also assess systematic age uncertainties due to different input physics and mass loss.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/46
- Title:
- SHARDS: GOODS-N spectrophotometry survey
- Short Name:
- J/ApJ/762/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Survey for High-z Absorption Red and Dead Sources (SHARDS), an ESO/GTC Large Program carried out using the OSIRIS instrument on the 10.4m Gran Telescopio Canarias (GTC). SHARDS is an ultra-deep optical spectro-photometric survey of the GOODS-N field covering 130arcmin2 at wavelengths between 500 and 950nm with 24 contiguous medium-band filters (providing a spectral resolution R~50). The data reach an AB magnitude of 26.5 (at least at a 3{sigma} level) with sub-arcsec seeing in all bands. SHARDS' main goal is to obtain accurate physical properties of intermediate- and high-z galaxies using well-sampled optical spectral energy distributions (SEDs) with sufficient spectral resolution to measure absorption and emission features, whose analysis will provide reliable stellar population and active galactic nucleus (AGN) parameters. Among the different populations of high-z galaxies, SHARDS' principal targets are massive quiescent galaxies at z>1, whose existence is one of the major challenges facing current hierarchical models of galaxy formation. In this paper, we outline the observational strategy and include a detailed discussion of the special reduction and calibration procedures which should be applied to the GTC/OSIRIS data. An assessment of the SHARDS data quality is also performed. We present science demonstration results on the detection and study of emission-line galaxies (star-forming objects and AGNs) at z=0-5. We also analyze the SEDs for a sample of 27 quiescent massive galaxies with spectroscopic redshifts in the range 1.0<z<~1.4.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A70
- Title:
- SHINE sample definition
- Short Name:
- J/A+A/651/A70
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Large surveys with new-generation high-contrast imaging instruments are needed to derive the frequency and properties of exoplanet populations with separations from 5 to 300au. A careful assessment of the stellar properties is crucial for a proper understanding of when, where, and how frequently planets form, and how they evolve. The sensitivity of detection limits to stellar age makes this a key parameter for direct imaging surveys. We describe the SpHere INfrared survey for Exoplanets (SHINE), the largest direct imaging planet-search campaign initiated at the VLT in 2015 in the context of the SPHERE Guaranteed Time Observations of the SPHERE consortium. In this rst paper we present the selection and the properties of the complete sample of stars surveyed with SHINE, focusing on the targets observed during the rst phase of the survey (from February 2015 to February 2017). This early sample composed of 150 stars is used to perform a preliminary statistical analysis of the SHINE data, deferred to two companion papers presenting the survey performance, main discoveries, and the preliminary statistical constraints set by SHINE. We describe the SpHere INfrared survey for Exoplanets (SHINE), the largest direct imaging planet-search campaign initiated at the VLT in 2015 in the context of the SPHERE Guaranteed Time Observations of the SPHERE consortium. In this rst paper we present the selection and the properties of the complete sample of stars surveyed with SHINE, focusing on the targets observed during the first phase of the survey (from February 2015 to February 2017). This early sample composed of 150 stars is used to perform a preliminary statistical analysis of the SHINE data, deferred to two companion papers presenting the survey performance, main discoveries, and the preliminary statistical constraints set by SHINE. Based on a large database collecting the stellar properties of all young nearby stars in the solar vicinity (including kinematics, membership to moving groups, isochrones, lithium abundance, rotation, and activity), we selected the original sample of 800 stars that were ranked in order of priority according to their sensitivity for planet detection in direct imaging with SPHERE. The properties of the stars that are part of the early statistical sample were revisited, including for instance measurements from the GAIA Data Release 2. Rotation periods were derived for the vast majority of the late-type objects exploiting TESS light curves and dedicated photometric observations. The properties of individual targets and of the sample as a whole are presented.
- ID:
- ivo://CDS.VizieR/J/AJ/158/68
- Title:
- Short-period variables in young open cluster Stock 8
- Short Name:
- J/AJ/158/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present time-series photometry in the field of Stock 8 and identified 130 short-period variable stars. Twenty-eight main-sequence and 23 pre-main-sequence variables are found to be part of cluster Stock 8. The main-sequence variables are classified as slow pulsators of the B-type, {beta} Cep, and {delta} Scuti stars. Fourteen main-sequence stars could be new class variables as discussed by Mowlavi et al. (2013, J/A+A/554/A108) and Lata et al. (2011MNRAS.418.1346L; 2012MNRAS.427.1449L; 2014, J/MNRAS/442/273; 2016MNRAS.456.2505L). The age and mass of pre-main-sequence variables are found to be ~<5 Myr and in the mass range of 0.5-2.8 M_{sun}_, respectively. These pre-main-sequence stars could be T-Tauri variables. We have found 5 and 2 of 23 pre-main-sequence variables as classical T-Tauri stars and Herbig Ae/Be stars, respectively, whereas 16 pre-main-sequence stars are classified as weak-line T-Tauri stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/740/92
- Title:
- SN.Ia host galaxies properties
- Short Name:
- J/ApJ/740/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We improve estimates of the stellar mass and mass-weighted average age of Type Ia supernova (SN Ia) host galaxies by combining UV and near-IR photometry with optical photometry in our analysis. Using 206 SNe Ia drawn from the full three-year Sloan Digital Sky Survey (SDSS-II) Supernova Survey and multi-wavelength host-galaxy photometry from SDSS, the Galaxy Evolution Explorer, and the United Kingdom Infrared Telescope Infrared Deep Sky Survey, we present evidence of a correlation (1.9{sigma} confidence level) between the residuals of SNe Ia about the best-fit Hubble relation and the mass-weighted average age of their host galaxies. The trend is such that older galaxies host SNe Ia that are brighter than average after standard light-curve corrections are made. We also confirm, at the 3.0{sigma} level, the trend seen by previous studies that more massive galaxies often host brighter SNe Ia after light-curve correction.
- ID:
- ivo://CDS.VizieR/J/ApJ/790/L23
- Title:
- Solar analogs and twins rotation by Kepler
- Short Name:
- J/ApJ/790/L23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new sample of solar analogs and twin candidates has been constructed and studied, paying particular attention to their light curves from NASA's Kepler mission. This Letter aims to assess their evolutionary status, derive their rotation and ages, and identify those which are solar analogs or solar twin candidates. We separate out the subgiants that compose a large fraction of the asteroseismic sample, and which show an increase in the average rotation period as the stars ascend the subgiant branch. The rotation periods of the dwarfs, ranging from 6 to 30 days and averaging 19 days, allow us to assess their individual evolutionary states on the main sequence and to derive their ages using gyrochronology. These ages are found to be in agreement with a correlation coefficient of r = 0.79 with independent asteroseismic ages, where available. As a result of this investigation, we are able to identify 34 stars as solar analogs and 22 of them as solar twin candidates.
- ID:
- ivo://CDS.VizieR/J/AJ/147/85
- Title:
- Solar neighborhood. XXXIII. 45 M dwarfs
- Short Name:
- J/AJ/147/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing Research Consortium On Nearby Stars photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have saturated X-ray emission (log(L_X_/L_bol_)>-3.5) based on X-ray fluxes from the ROSAT All-Sky Survey, and many are significantly more luminous than main-sequence stars of comparable color. We present parallaxes and proper motions, Johnson-Kron-Cousins VRI photometry, and multiplicity observations from the CTIOPI program on the CTIO 0.9m telescope. To this we add low-resolution optical spectroscopy and line measurements from the CTIO 1.5m telescope, and interferometric binary measurements from the Hubble Space Telescope Fine Guidance Sensors. We also incorporate data from published sources: JHK_S_ photometry from the Two Micron All Sky Survey point source catalog, X-ray data from the ROSAT All-Sky Survey, and radial velocities from literature sources. Within the sample of 45 systems, we identify 21 candidate low-mass pre-main-sequence members of nearby associations, including members of {beta} Pictoris, TW Hydrae, Argus, AB Doradus, two ambiguous {approx}30Myr old systems, and one object that may be a member of the Ursa Major moving group. Of the 21 candidate young systems, 14 are newly identified as a result of this work, and six of those are within 25pc of the Sun.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A130
- Title:
- Solar sibling candidates chemical abundances
- Short Name:
- J/A+A/619/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Finding solar siblings, that is, stars that formed in the same cluster as the Sun, will yield information about the conditions at the Sun's birthplace. Finding possible solar siblings is difficult since they are spread widely throughout the Galaxy. We search for solar sibling candidates in AMBRE, the very large spectra database of solar vicinity stars. Since the ages and chemical abundances of solar siblings are very similar to those of the Sun, we carried out a chemistry- and age-based search for solar sibling candidates. We used high-resolution spectra to derive precise stellar parameters and chemical abundances of the stars. We used these spectroscopic parameters together with Gaia DR2 astrometric data to derive stellar isochronal ages. Gaia data were also used to study the kinematics of the sibling candidates. From the about 17000 stars that are characterized within the AMBRE project, we first selected 55 stars whose metallicities are closest to the solar value (-0.1<=[Fe/H]<=0.1dex). For these stars we derived precise chemical abundances of several iron-peak, {alpha}- and neutron-capture elements, based on which we selected 12 solar sibling candidates with average abundances and metallicities between -0.03 to 0.03dex. Our further selection left us with 4 candidates with stellar ages that are compatible with the solar age within observational uncertainties. For the 2 of the hottest candidates, we derived the carbon isotopic ratios, which are compatible with the solar value. HD186302 is the most precisely characterized and probably the most probable candidate of our 4 best candidates. Very precise chemical characterization and age estimation is necessary to identify solar siblings. We propose that in addition to typical chemical tagging, the study of isotopic ratios can give further important information about the relation of sibling candidates with the Sun. Ideally, asteroseismic age determinations of the candidates could solve the problem of imprecise isochronal ages.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A73
- Title:
- Solar Twins age-chromospheric activity
- Short Name:
- J/A+A/619/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1-2Gyr that is followed by a relatively inactive constant phase. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. We measured the CaII H and K activity indices using 9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (S_MW_), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Te, and then computed an improved bolometric flux normalized activity index logR'_HK_(Teff) for the entire sample. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using logR'_HK_(Teff). We measured an average solar activity of S_MW_=0.1712+/-0.0017 during solar magnetic cycles 23-24 covered by HARPS observations, and we also inferred an average of S_MW_=0.1694+/-0.0025 for cycles 10-24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6-7Gyr, in agreement with previous works using open clusters and field stars with precise ages. Our research confirms that CaII H& K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6-7Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations eects. The Sun seems to have a normal activity level and variability for its age.
