- ID:
- ivo://CDS.VizieR/J/AJ/101/1408
- Title:
- Massive stars in Cyg OB2.
- Short Name:
- J/AJ/101/1408
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The galactic association Cygnus OB2, which contains heavily reddened O and B stars, has been studied using CCD UBV photometry and spectroscopy. The file "mt91.dat" contains precise coordinates, UBV photometry, and spectral types from the study of Cygnus OB2, and merges the tables 2, 5 and 6 from the paper.
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- ID:
- ivo://CDS.VizieR/J/A+A/626/A50
- Title:
- Massive stars in NGC 346
- Short Name:
- J/A+A/626/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopy for 247 stars towards the young cluster NGC 346 in the Small Magellanic Cloud has been combined with that for 116 targets from the VLT-FLAMES Survey of Massive Stars. Spectral classification yields a sample of 47 O-type and 287 B-type spectra, while radial-velocity variations and/or spectral multiplicity have been used to identify 45 candidate single-lined (SB1) systems, 17 double-lined (SB2) systems, and one triple-lined (SB3) system. Atmospheric parameters (T_eff_ and log g) and projected rotational velocities (v_e_sini) have been estimated usingTLUSTY model atmospheres; independent estimates of v_e_sini were also obtained using a Fourier Transform method. Luminosities have been inferred from stellar apparent magnitudes and used in conjunction with the T_eff_ and v_e_sini estimates to constrain stellar masses and ages using theBONNSAI package. We find that targets towards the inner region of NGC 346 have higher median masses and projected rotational velocities, together with smaller median ages than the rest of the sample. There appears to be a population of very young targets with ages of less than 2Myr, which have presumably all formed within the cluster. The more massive targets are found to have lower projected rotational velocities consistent with previous studies. No significant evidence is found for differences with metallicity in the stellar rotational velocities of early-type stars, although the targets in the Small Magellanic Cloud may rotate faster than those in young Galactic clusters. The rotational velocity distribution for single non-supergiant B-type stars is inferred and implies that a significant number have low rotational velocity (~=10% with v_e_<40km/s), together with a peak in the probability distribution at v_e_~=300km/s. Larger projected rotational velocity estimates have been found for our Be-type sample and imply that most have rotational velocities between 200-450km/s.
- ID:
- ivo://CDS.VizieR/J/ApJ/662/413
- Title:
- 2MASS survey of wide multiplicity in 3 associations
- Short Name:
- J/ApJ/662/413
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for wide binary systems among 783 members of three nearby young associations: Taurus-Auriga, Chamaeleon I, and two subgroups of Upper Scorpius. Near-infrared (JHK) imagery from 2MASS was analyzed to search for wide (1"-30"; ~150-4500AU) companions to known association members, using color-magnitude cuts to reject likely background stars. We identify a total of 131 candidate binary companions with colors consistent with physical association, of which 39 have not been identified previously in the literature.
- ID:
- ivo://CDS.VizieR/J/AN/328/889
- Title:
- Mean Radial Velocities of open clusters
- Short Name:
- J/AN/328/889
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the 2nd version of the Catalogue of Radial Velocities with Astrometric Data (CRVAD-2, Cat. <III/254>) for a new determination of mean RVs of 363 open clusters and stellar associations considering their defined members from proper motions and photometry in the All-Sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5, Cat. <I/280>). For 330 clusters and associations we compiled previously published RVs from the literature, critically reviewed and partly revised them. The resulting Catalogue of Radial Velocities of Open Clusters and Associations (CRVOCA) provides RVs for 516 open clusters and stellar associations in the Solar neighbourhood. Objects in the catalogue are sorted in the order of increasing right ascension J2000.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A71
- Title:
- Members for 20 open clusters
- Short Name:
- J/A+A/643/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity. We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters. Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving RV distributions and studying the position of the kinematic selections in the EW(Li) versus Teff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections. We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members, as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers. This work is the first step towards the calibration of the lithium-age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A52
- Title:
- Membership in stellar kinematic groups
- Short Name:
- J/A+A/567/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Over the last century, the overdensities in the velocity distributions of nearby stars were attributed to stellar kinematic groups or moving groups. Although their reality was initially questioned, their existence is now supported by a confluence of evidence. To pursue investigations, quantitative methods should be clearly defined to identify new stars belonging to these groups. Here, we present two probabilistic methods to determine the likelihood of kinematic membership for possible candidates in five of the known young stellar kinematic groups - namely, Pleiades, IC2391, Castor, Ursa Major, and Hyades - in which all are younger than 650Myr. We tried different methods to handle kinematic data of their known members. We succeeded in developing two independent procedures able to identify new candidates of these five stellar stream. We tested the robustness of our two approaches by means of extensive Monte Carlo simulations. Our methods are consistent with one another in more than 90% of cases and for almost all the stellar kinematic groups under scrutiny. The IC2391 supercluster is an exception. Applying our statistical methods to a large sample of young low-mass stars, we confirmed almost all the likely members and good candidates of these stellar streams. We also proposed 39 additional candidates based on the agreement and the high likelihood of age and kinematic membership. These probabilistic methods are very powerful to reliably identify new candidate members of young stellar kinematic groups. However, the kinematic criteria alone are not sufficient to distinguish between coeval stars that are evaporated from open clusters and other field stars trapped by dynamical processes generated by galactic perturbations. The identification of stars belonging to the remnant of a past star-forming event can be possible with the help of additional information, such as indicators of chromospheric activity, age proxies (lithium abundance), and chemical composition.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/1325
- Title:
- Membership of the {epsilon} Cha association
- Short Name:
- J/MNRAS/435/1325
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive investigation of the {epsilon} Chamaeleontis association, one of several young moving groups spread across the southern sky. We re-assess the putative membership of {epsilon} Cha using the best available proper motion and spectroscopic measurements, including new ANU 2.3-m/Wide Field Spectrograph observations. After applying a kinematic analysis, our final membership comprises 35-41 stars from B9 to mid-M spectral types. Theoretical evolutionary models suggest {epsilon} Cha is 3-5Myr old, distinguishing it as the youngest moving group in the solar neighbourhood. 15 members show 3-22um spectral energy distributions attributable to circumstellar discs, including 11 stars which appear to be actively accreting. {epsilon} Cha's disc and accretion fractions are both consistent with a typical 3-5Myr old population. Multi-epoch spectroscopy reveals three M-type members with broad and highly variable Ha emission as well as several new spectroscopic binaries. We reject 11 stars proposed as members in the literature and suggest they may belong to the background Cha I and II clouds or other nearby young groups. Our analysis underscores the importance of a holistic and conservative approach to assigning young stars to kinematic groups, many of which have only subtly different properties and ill-defined memberships. We conclude with a brief discussion of {epsilon} Cha's connection to the young open cluster eta Cha and the Scorpius- Centaurus OB association. Contrary to earlier studies which assumed eta and {epsilon} Cha are coeval and were born in the same location, we find the groups were separated by ~30pc when eta Cha formed 4-8Myr ago in the outskirts of Sco-Cen, 1-3Myr before the majority of {epsilon} Cha members.
- ID:
- ivo://CDS.VizieR/J/AJ/159/166
- Title:
- Membership & properties of moving groups with Gaia
- Short Name:
- J/AJ/159/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the membership probability of young stars belonging to nearby moving groups with Gaia DR2 data. The sample of 1429 stars was identified from "The Catalog of Suspected Nearby Young Moving Group Stars" (CSNYMGS; see Riedel+, J/AJ/153/95). Good-quality parallax and proper motion values were retrieved for 890 stars from the Gaia DR2 database. The analysis for membership probability is performed in the framework of the LACEwING algorithm (Riedel 2016IAUS..314...33R). From the analysis it is confirmed that 279 stars do not belong to any of the known moving groups. We estimated the U, V, W space velocity values for 250 moving group members, which were found to be more accurate than previous values listed in the literature. The velocity ellipses of all the moving groups are well constrained within the "good box," a widely used criterion to identify moving group members. The age of moving group members are uniformly estimated from the analysis of the Gaia color-magnitude diagram with MIST isochrones. We found a spread in the age distribution of stars belonging to some moving groups, which needs to be understood from further studies.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A102
- Title:
- Milky Way nuclear star cluster HKs photometry
- Short Name:
- J/A+A/641/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The environment of Sagittarius A* (Sgr A*), the central black hole of the Milky Way, is the only place in the Universe where we can currently study the interaction between a nuclear star cluster and a massive black hole and infer the properties of a nuclear cluster from observations of individual stars. This work aims to explore the star formation history of the nuclear cluster and the structure of the innermost stellar cusp around Sgr A*. We combined and analysed multi epoch high quality AO observations. For the region close to Sgr A* we apply the speckle holography technique to the AO data and obtain images that are >=50% complete down to Ks~19 within a projected radius of 5" around Sgr A*. We used $H$-band images to derive extinction maps. We provide Ks photometry for roughly 39000 stars and H-band photometry for ~11000 stars within a field of about 40"x40", centred on Sgr A*. In addition, we provide Ks photometry of ~3000 stars in a very deep central field of 10"x10", centred on Sgr A*. We find that the Ks luminosity function (KLF) is rather homogeneous within the studied field and does not show any significant changes as a function of distance from the central black hole on scales of a few 0.1pc. By fitting theoretical luminosity functions to the KLF, we derive the star formation history of the nuclear star cluster. We find that about 80% of the original star formation took place 10Gyr ago or longer, followed by a largely quiescent phase that lasted for more than 5Gyr. We clearly detect the presence of intermediate-age stars of about 3Gyr in age. This event makes up about 15% of the originally formed stellar mass of the cluster. A few percent of the stellar mass formed in the past few 100Myr. Our results appear to be inconsistent with a quasi-continuous star formation history. The mean metallicity of the stars is consistent with being slightly super solar. The stellar density increases exponentially towards Sgr A* at all magnitudes between Ks=15-19. We also show that the precise properties of the stellar cusp around Sgr A* are hard to determine because the star formation history suggests that the star counts can be significantly contaminated, at all magnitudes, by stars that are too young to be dynamically relaxed. We find that the probability of observing any young (non-millisecond) pulsar in a tight orbit around Sgr A* and beamed towards Earth is very low. We argue that typical globular clusters, such as they are observed in and around the Milky Way today, have probably not contributed to the nuclear cluster's mass in any significant way. The nuclear cluster may have formed following major merger events in the early history of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/548/A24
- Title:
- 1.3mm observations of CrA cluster
- Short Name:
- J/A+A/548/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The importance of the physical environment in the evolution of newly formed low-mass stars remains an open question. In particular, radiation from nearby more massive stars may affect both the physical and chemical structure of these kinds of young stars. We constrain the physical characteristics of a group of embedded low-mass protostars in Corona Australis in the vicinity of the young luminous Herbig Be star R CrA.
