- ID:
- ivo://CDS.VizieR/J/A+A/460/133
- Title:
- Chandra X-ray sources in NGC 2362
- Short Name:
- J/A+A/460/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed the young cluster NGC 2362 in X-rays with Chandra ACIS-I, and detected 387 point X-ray sources, most of which are shown to be cluster members. We report here the list of all detected X-ray sources and their basic X-ray properties, and report separately their identifications with optical stars, using data from Moitinho et al. (2001ApJ...563L..73M; UBVRI photometry) and Dahm (2005, Cat. <J/AJ/130/1805>; H{alpha} data). We include in the second table a classification of optically-identified X-ray sources, based on position in the HR diagram, which helps to separate rather clearly cluster members from field objects.
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- ID:
- ivo://CDS.VizieR/J/ApJ/582/382
- Title:
- Chandra X-ray sources in Orion Nebula Cluster
- Short Name:
- J/ApJ/582/382
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this first of two companion papers on the Orion Nebula Cluster (ONC), we present our analysis of a 63ks Chandra HRC-I observation that yielded 742 X-ray detections within the 30'x30' field of view. To facilitate our interpretation of the X-ray image, here we collect a multiwavelength catalog of nearly 2900 known objects in the region by combining 17 different catalogs from the recent literature. We define two reference groups: an infrared sample, containing all objects detected in the K band, and an optical sample comprising low-extinction, well-characterized ONC members. We show for both samples that field object contamination is generally low. Our X-ray sources are primarily low-mass ONC members. The detection rate for optical sample stars increases monotonically with stellar mass from zero at the brown dwarf limit to ~100% for the most massive stars but shows a pronounced dip between 2 and 10M_{sun}_. We determine L_X_ and L_X_/L_bol_ or all stars in our optical sample and utilize this information in our companion paper to study correlations between X-ray activity and other stellar parameters.
- ID:
- ivo://CDS.VizieR/J/AJ/142/59
- Title:
- Chemical abundance in 10 open clusters
- Short Name:
- J/AJ/142/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed chemical abundance study of evolved stars in 10 open clusters based on Hydra multi-object echelle spectra obtained with the WIYN 3.5m telescope. From an analysis of both equivalent widths and spectrum synthesis, abundances have been determined for the elements Fe, Na, O, Mg, Si, Ca, Ti, Ni, Zr, and for two of the 10 clusters, Al and Cr. To our knowledge, this is the first detailed abundance analysis for clusters NGC 1245, NGC 2194, NGC 2355, and NGC 2425.
- ID:
- ivo://CDS.VizieR/J/A+A/535/A30
- Title:
- Chemical abundance of 12 stars in open clusters
- Short Name:
- J/A+A/535/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters are ideal test particles for studying the chemical evolution of the Galactic disc. However, the number and accuracy of existing high-resolution abundance determinations, not only of [Fe/H], but also of other key elements, remains largely insufficient. We attempt to increase the number of Galactic open clusters that have high quality abundance determinations, and to gather all the literature determinations published so far.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A176
- Title:
- Chemical composition of Ruprecht 147
- Short Name:
- J/A+A/619/A176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ruprecht 147 (NGC 6774) is the closest old open cluster, with a distance of less than 300pc and an age of about 2.5Gyr. It is therefore well suited for testing stellar evolution models and for obtaining precise and detailed chemical abundance information. We combined photometric and astrometric information coming from literature and the Gaia mission with very high-resolution optical spectra of stars in different evolutionary stages to derive the cluster distance, age, and detailed chemical composition. We obtained spectra of six red giants using HARPS-N at the Telescopio Nazionale Galileo (TNG). We also used European Southern Observatory (ESO) archive spectra of 22 main sequence (MS) stars, observed with HARPS at the 3.6m telescope. The very high resolution (115000) and the large wavelength coverage (about 380-680nm) of the twin instruments permitted us to derive atmospheric parameters, metallicity, and detailed chemical abundances of 23 species from all nucleosynthetic channels. We employed both equivalent widths and spectrum synthesis. We also re-derived the cluster distance and age using Gaia parallaxes, proper motions, and photometry in conjunction with the PARSEC stellar evolutionary models. We fully analysed those stars with radial velocity and proper motion/parallax in agreement with the cluster mean values. We also discarded one binary not previously recognised, and six stars near the MS turn-off because of their high rotation velocity. Our final sample consists of 21 stars (six giants and 15 MS stars). We measured metallicity (the cluster average [Fe/H] is +0.08, rms=0.07) and abundances of light, alpha, Fe-peak, and neutron-capture elements. The Li abundance follows the expectations, showing a tight relation between temperature and abundance on the MS, at variance with M67, and we did not detect any Li-rich giant.
- 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/476/908
- Title:
- Chromospheric activity in 4 open clusters
- Short Name:
- J/MNRAS/476/908
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the LAMOST spectra of member stars in Pleiades, M34, Praesepe, and Hyades to study how chromospheric activity varies as a function of mass and rotation at different age. We measured excess equivalent widths of H{alpha}, H{beta}, and CaII K based on estimated chromospheric contributions from old and inactive field dwarfs, and excess luminosities are obtained by normalizing bolometric luminosity, for more than 700 late-type stars in these open clusters. Results indicate two activity sequences in cool spot coverage and H{alpha} excess emission among GK dwarfs in Pleiades and M dwarfs in Praesepe and Hyades, paralleling with well-known rotation sequences. A weak dependence of chromospheric emission on rotation exists among ultrafast rotators in saturated regime with Rossby number Ro<=0.1. In the unsaturated regime, chromospheric and coronal emission show similar dependence on Ro, but with a shift towards larger Ro, indicating chromospheric emission gets easily saturated than coronal emission, and/or convective turnover time-scales based on X-ray data do not work well with chromospheric emission. More interestingly, our analysis shows fully convective slow rotators obey the rotation-chromospheric activity relation similar to hotter stars, confirming the previous finding. We found correlations among H{alpha}, H{beta}, and CaII K emissions, in which H{alpha} losses are more important than CaII K for cooler and more active stars. In addition, a weak correlation is seen between chromospheric emission and photospheric activity that shows dependence on stellar spectral type and activity level, which provides some clues on how spot configuration varies as a function of mass and activity level.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A50
- Title:
- Classification of stellar spectra 644-681nm
- Short Name:
- J/A+A/566/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of spectral diagnostics available from optical spectra with R=17000 obtained with the VLT/Giraffe HR15n setup, using observations from the Gaia-ESO Survey, on the {gamma} Vel young cluster, with the purpose of classifying these stars and finding their fundamental parameters. We define several spectroscopic indices, sampling the amplitude of TiO bands, the H{alpha} line core and wings, and temperature- and gravity-sensitive sets of lines, each useful as a Teff or logg indicator over a limited range of stellar spectral types. H{alpha} line indices are also useful as chromospheric activity or accretion indicators. Furthermore, we use all indices to define additional global Teff- and logg-sensitive indices {tau} and {gamma}, valid for the entire range of types in the observed sample.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A156
- Title:
- Cluster formation toward Be87/ON2. I.
- Short Name:
- J/A+A/650/A156
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Disentangling line-of-sight alignments of young stellar populations is crucial for observational studies of star-forming complexes. This task is particularly problematic in a Cygnus-X subregion where several components, located at different distances, overlap: the Berkeley 87 young massive cluster, the poorly known [DB2001] Cl05 embedded cluster, and the ON2 star-forming complex, which in turn is composed of several HII regions. We provide a methodology for building an exhaustive census of young objects that can consistently treat large differences in extinction and distance. OMEGA2000 near-infrared observations of the Berkeley 87 / ON2 field were merged with archival data from Gaia, Chandra, Spitzer, and Herschel, and with cross-identifications from the literature. To address the incompleteness effects and selection biases that arise from the line-of-sight overlap, we adapted existing methods for extinction estimation and young object classification. We also defined the intrinsic reddening index, R_int_, a new tool for separating intrinsically red sources from those whose infrared color excess is caused by extinction. Finally, we introduce a new method for finding young stellar objects based on R_int_. We find 571 objects whose classification is related to recent or ongoing star formation. Together with other point sources with individual estimates of distance or extinction, we compile a catalog of 3005 objects to be used for further membership work. A new distance for Berkeley 87, (1673+/-17)pc, is estimated as a median of 13 spectroscopic members with accurate Gaia EDR3 parallaxes. The flexibility of our approach, especially regarding the R_int_ definition, allows overcoming photometric biases caused by large variations in extinction and distance, in order to obtain homogeneous catalogs of young sources. The multiwavelength census that results from applying our methods to the Berkeley 87 / ON2 field will serve as a basis for disentangling the overlapped populations.
210. Clusterix 2.0
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/5811
- Title:
- Clusterix 2.0
- Short Name:
- J/MNRAS/492/5811
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Clusterix 2.0 is a web-based, Virtual Observatory compliant, interactive tool for the determination of membership probabilities in stellar clusters based on proper-motion data using a fully non-parametric method. In an area occupied by a cluster, the frequency function is made up of two contributions: cluster and field stars. The tool performs an empirical determination of the frequency functions from the vector point diagram without relying on any previous assumption about their profiles. Clusterix 2.0 allows us to search the appropriate spatial areas in an interactive way until an optimal separation of the two populations is obtained. Several parameters can be adjusted to make the calculation computationally feasible without interfering with the quality of the results. The system offers the possibility to query different catalogues, such as Gaia, or upload a user's own data. The results of the membership determination can be sent via Simple Application Messaging Protocol (SAMP) to Virtual Observatory (VO) tools such as Tool for OPerations on Catalogues And Tables (TOPCAT). We apply Clusterix 2.0 to several open clusters with different properties and environments to show the capabilities of the tool: an area of five degrees radius around NGC 2682 (M67), an old, well-known cluster; a young cluster NGC 2516 with a striking elongated structure extended up to four degrees; NGC 1750 and NGC 1758, a pair of partly overlapping clusters; the area of NGC 1817, where we confirm a little-known cluster, Juchert 23; and an area with many clusters, where we disentangle two overlapping clusters situated where only one was previously known: Ruprecht 26 and the new Clusterix 1.
