- ID:
- ivo://CDS.VizieR/J/MNRAS/434/2238
- Title:
- Cepheids in open clusters
- Short Name:
- J/MNRAS/434/2238
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cepheids in open clusters (cluster Cepheids: CCs) are of great importance as zero-point calibrators of the Galactic Cepheid period-luminosity relationship (PLR). We perform an 8-dimensional all-sky census that aims to identify new bona-fide CCs and provide a ranking of membership confidence for known CC candidates according to membership probabilities. The probabilities are computed for combinations of known Galactic open clusters and classical Cepheid candidates, based on spatial, kinematic, and population-specific membership constraints. Data employed in this analysis are taken largely from published literature and supplemented by a year-round observing program on both hemispheres dedicated to determining systemic radial velocities of Cepheids. In total, we find 23 bona-fide CCs, 5 of which are candidates identified for the first time, including an overtone-Cepheid member in NGC 129. We discuss a subset of CC candidates in detail, some of which have been previously mentioned in the literature. Our results indicate unlikely membership for 7 Cepheids that have been previously discussed in terms of cluster membership. We furthermore revisit the Galactic PLR using our bona fide CC sample and obtain a result consistent with the recent calibration by Turner (2010). However, our calibration remains limited mainly by cluster uncertainties and the small number of long-period calibrators. In the near future, Gaia will enable our study to be carried out in much greater detail and accuracy, thanks to data homogeneity and greater levels of completeness.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/562/A71
- Title:
- Chemical abundances of solar neighbourhood dwarfs
- Short Name:
- J/A+A/562/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed elemental abundance study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The analysis is based on high-resolution spectra obtained with MIKE on the Magellan telescope, FEROS on the ESO 1.5m and 2.2m telescopes, HARPS on the ESO 3.6m telescope, UVES on the ESO Very Large Telescope, SOFIN and FIES on the Nordic Optical Telescope. Our data show that there is an old and alpha-enhanced disk population, and a younger and less alpha-enhanced disk population. While they overlap greatly in metallicity between -0.7<[Fe/H]<+0.1, they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff<5400K) are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between stellar populations are to be revealed. In addition, we find that the alpha-enhanced population has orbital parameters placing the stellar birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk, fully consistent with the recent claims of a short scale-length for the alpha-enhanced Galactic thick disk. We have also investigated the properties of the Hercules stream and the Arcturus moving group.
- ID:
- ivo://CDS.VizieR/J/A+A/275/101
- Title:
- Chemical evolution of the galactic disk I.
- Short Name:
- J/A+A/275/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From high resolution, high S/N spectroscopic observations of carefully selected northern and southern stars, abundances of O, Na, Mg, Al, Si, Ca, Ti, Fe, Ni, Y, Zr, Ba and Nd, as well as photometric ages, are derived for 189 nearby field F and G stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/481/3244
- Title:
- Chemo-kinematics from MARVELS
- Short Name:
- J/MNRAS/481/3244
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Combining stellar atmospheric parameters, such as effective temperature, surface gravity, and metallicity, with barycentric radial velocity data provides insight into the chemo-dynamics of the Milky Way and our local Galactic environment. We analyse 3075 stars with spectroscopic data from the Sloan Digital Sky Survey III MARVELS radial velocity survey and present atmospheric parameters for 2343 dwarf stars using the spectral indices method, a modified version of the equivalent width method. We present barycentric radial velocities for a sample of 2610 stars with a median uncertainty of 0.3km/s. We determine stellar ages using two independent methods and calculate ages for 2335 stars with a maximum-likelihood isochronal age-dating method and for 2194 stars with a Bayesian age-dating method. Using previously published parallax data, we compute Galactic orbits and space velocities for 2504 stars to explore stellar populations based on kinematic and age parameters. This study combines good ages and exquisite velocities to explore local chemo-kinematics of the Milky Way, which complements many of the recent studies of giant stars with the APOGEE survey, and we find our results to be in agreement with current chemo-dynamical models of the Milky Way. Particularly, we find from our metallicity distributions and velocity-age relations of a kinematically defined thin disc that the metal-rich end has stars of all ages, even after we clean the sample of highly eccentric stars, suggesting that radial migration plays a key role in the metallicity scatter of the thin disc. All stellar parameters and kinematic data derived in this work are catalogued and published online in machine-readable form.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A198
- Title:
- CHIPS II. O stars in Trumpler 14 CHIPS-Tr14
- Short Name:
- J/A+A/658/A198
- Date:
- 25 Feb 2022 07:07:49
- Publisher:
- CDS
- Description:
- Most massive stars belong to multiple systems, yet the formation process leading to such high multiplicity remain insufficiently understood. To help constrain the different formation scenarios that exist, insights on the low-mass end of the companion mass function of such stars is crucial. However, this is a challenging endeavour as (sub-)solar mass companions at angular separations {rho} below 1" (corresponding to 1000-3000au in nearby young open clusters and OB associations) are difficult to detect due to the large brightness contrast with the central star. With the Carina High-contrast Imaging Project of massive Stars (CHIPS), we aim to obtain statistically significant constraints on the presence and properties of low-mass companions around massive stars at a previously unreachable observing window ({Delta}mag>=10 at {rho}<= 1"). In this second paper in the series, we focus on the Trumpler 14 cluster, which harbours some of the youngest and most massive O-type stars in the Milky Way. We obtained VLT-SPHERE observations of seven O-type objects in Trumpler 14 using the IRDIFS_EXT mode. These allow us to search for companions at separations larger than 0.15" (~360au) and down to magnitude contrast >10 mag in the near-infrared. We used angular and spectral differential imaging along with PSF fitting to detect sources and measure their flux relative to that of the central object. We detected 211 sources with near-infrared magnitude contrast in the range of 2 to 12. The closest companion, at only 0.26", is characterised as a 1.4M_{sun}_ stars with an age of 0.6Myr, in excellent agreement with previous age estimates for Tr14. The mass function peaks at about 0.4M_{sun}_ and presents a dearth of stars in the 0.5 to 0.8M_{sun}_ mass range compared to previous estimates of the initial mass function in Tr14.
- ID:
- ivo://CDS.VizieR/J/MNRAS/298/332
- Title:
- Chromospheric activity-age relation
- Short Name:
- J/MNRAS/298/332
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We show that there is a relationship between the age excess, defined as the difference between the stellar isochrone and chromospheric ages, and the metallicity as measured by the index [Fe/H] for late-type dwarfs. The chromospheric age tends to be lower than the isochrone age for metal-poor stars, and the opposite occurs for metal-rich objects. We suggest that this could be an effect of neglecting the metallicity dependence of the calibrated chromospheric emission-age relation. We propose a correction to account for this dependence. We also investigate the metallicity distributions of these stars, and show that there are distinct trends according to the chromospheric activity level. Inactive stars have a metallicity distribution which resembles the metallicity distribution of solar neighbourhood stars, while active stars appear to be concentrated in an activity strip on the log(R'_HK_)*[Fe/H] diagram. We provide some explanations for these trends, and show that the chromospheric emission-age relation probably has different slopes on the two sides of the Vaughan-Preston gap.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/875
- Title:
- Chromospheric activity for CPS stars
- Short Name:
- J/ApJ/725/875
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present time series measurements of chromospheric activity for more than 2600 main-sequence and subgiant stars on the California Planet Search (CPS) program with spectral types ranging from about F5V to M4V for main-sequence stars and from G0IV to about K5IV for subgiants. The large data set of more than 44000 spectra allows us to identify an empirical baseline floor for chromospheric activity as a function of color and height above the main sequence. We define {Delta}S as an excess in emission in the CaII H and K lines above the baseline activity floor and define radial velocity jitter as a function of {Delta}S and B-V for main-sequence and subgiant stars. Although the jitter for any individual star can always exceed the baseline level, we find that K dwarfs have the lowest level of jitter. The lack of correlation between observed jitter and chromospheric activity in K dwarfs suggests that the observed jitter is dominated by instrumental or analysis errors and not astrophysical noise sources. Thus, given the long-term precision for the CPS program, radial velocities are not correlated with astrophysical noise for chromospherically quiet K dwarf stars, making these stars particularly well suited for the highest precision Doppler surveys. Chromospherically quiet F and G dwarfs and subgiants exhibit higher baseline levels of astrophysical jitter than K dwarfs. Despite the fact that the rms in Doppler velocities is correlated with the mean chromospheric activity, it is rare to see one-to-one correlations between the individual time series activity and Doppler measurements, diminishing the prospects for correcting activity-induced velocity variations in F and G dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A77
- Title:
- Chromospheric activity from AMBRE-HARPS
- Short Name:
- J/A+A/646/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The main objective of this project is to characterise chromospheric activity of FGK stars from the HARPS archive. We start, in this first paper, by presenting a catalogue of homogeneous determined chromospheric emission (CE), stellar atmospheric parameters and ages for 1,674 FGK main sequence (MS), subgiant, and giant stars. The analysis of CE level and variability is also performed. We measured CE in the CaII lines using more than 180000 high-resolution spectra from the HARPS spectrograph, as compiled in the AMBRE project, obtained between 2003 and 2019. We converted the fluxes to bolometric and photospheric corrected chromospheric emission ratio, R'_HK_. Stellar atmospheric parameters T_eff_, logg, and [Fe/H] were retrieved from the literature or determined using an homogeneous method. M_{star}_, R_{star}_, and ages were determined from isochrone fitting. We show that our sample has a distribution of CE for MS stars that is consistent with an unbiased sample of solar-neighbour MS stars. We analysed the CE distribution for the different luminosity classes and spectral types and confirmed the existence of the very inactive stars (VIS) and very active stars (VAS) populations at R'_HK_<-5.1 and >-4.2dex, respectively. We found indications that the VIS population is composed mainly of subgiant and giant stars and that R'_HK_=-5.1dex marks a transition in stellar evolution. Overall, CE variability decreases with decreasing CE level but its distribution is complex. There appears to be at least three regimes of variability, for inactive, active and very active stars, with the inactive and active regimes separated by a diagonal, extended Vaughan-Preston (VP) gap. We show that stars with low activity levels do not necessarily have low variability. In the case of K dwarfs which show high CE variability, inactive and active stars have similar levels of activity variability. This means that activity levels alone are not enough to infer about the activity variability of a star. We also explained the shape of the VP gap observed in the distribution of CE by using the CE variability-level diagram. In the CE variability-level diagram, the Sun is located in the high variability region of the inactive MS stars zone. A method to extract the probability density function of the CE variability for a given R'_HK_ level is discussed, and a python code to retrieve it is provided.
- ID:
- ivo://CDS.VizieR/J/A+A/551/L8
- Title:
- Chromospheric activity of field stars
- Short Name:
- J/A+A/551/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Compilation of S-index measurements available in the literature cross-correlated with the CDS catalog. The S-index is a measure of the strength of the chromospheric emission in the core of the CaII H and K lines, and it is a proxy for chromospheric activity. Its conversion into logR'HK is also reported, along with temperature, age and metallicity from the CDS.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/70
- Title:
- Chromospheric activity of Southern stars
- Short Name:
- J/ApJ/734/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present chromospheric-activity measurements of ~670 F, G, K, and M main-sequence stars in the Southern Hemisphere, from ~8000 archival high-resolution echelle spectra taken at Las Campanas Observatory since 2004. These stars were targets from the Old Magellan Planet Search, and are now potential targets for the New Magellan Planet Search that will look for rocky and habitable planets. Activity indices (S values) are derived from CaII H and K line cores and then converted to the Mount Wilson system. From these measurements, chromospheric (log R'_HK_) indices are derived, which are then used as indicators of the level of radial-velocity jitter, age, and rotation periods these stars present.
