- ID:
- ivo://CDS.VizieR/J/MNRAS/434/966
- Title:
- Measurements of Li in T-Tauri stars
- Short Name:
- J/MNRAS/434/966
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used medium-resolution spectra to search for evidence that proto-stellar objects accrete at high rates during their early 'assembly phase'. Models predict that depleted lithium and reduced luminosity in T-Tauri stars are key signatures of 'cold' high-rate accretion occurring early in a star's evolution. We found no evidence in 168 stars in NGC 2264 and the Orion nebula cluster for strong lithium depletion through analysis of veiling-corrected 6708{AA} lithium spectral line strengths. This suggests that 'cold' accretion at high rates (dM/dt>=5x10^-4^M_{sun}_/yr) occurs in the assembly phase of fewer than 0.5 percent of 0.3<=M*<=1.9M_{sun}_ stars. We also find that the dispersion in the strength of the 6708{AA} lithium line might imply an age spread that is similar in magnitude to the apparent age spread implied by the luminosity dispersion seen in colour-magnitude diagrams. Evidence for weak lithium depletion (<10% in equivalent width) that is correlated with luminosity is also apparent, but we are unable to determine whether age spreads or accretion at rates less than 5x10^-4^M_{sun}_/yr are responsible.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/159/282
- Title:
- Membership in Ophiuchus & Upper Scorpius complex
- Short Name:
- J/AJ/159/282
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a survey for new members of the Ophiuchus cloud complex using high-precision astrometry from the second data release of Gaia, proper motions measured with multi-epoch images from the Spitzer Space Telescope, and color-magnitude diagrams constructed with photometry from various sources. Through spectroscopy of candidates selected with those data, we have identified 155 new young stars. Based on available measurements of kinematics, we classify 102, 47, and 6 of those stars as members of Ophiuchus, Upper Sco, and other populations in Sco-Cen, respectively. We have also assessed the membership of all other stars in the vicinity of Ophiuchus that have spectroscopic evidence of youth from previous studies, arriving at a catalog of 373 adopted members of the cloud complex. For those adopted members, we have compiled mid-infrared photometry from Spitzer and the Wide-field Infrared Survey Explorer and have used mid-infrared colors to identify and classify circumstellar disks. We find that 210 of the members show evidence of disks, including 48 disks that are in advanced stages of evolution. Finally, we have estimated the relative median ages of the populations near the Ophiuchus clouds and the surrounding Upper Sco association using absolute K-band magnitudes (MK) based on Gaia parallaxes. If we adopt an age 10Myr for Upper Sco, then the relative values of MK imply median ages of ~2Myr for L1689 and embedded stars in L1688, 3-4Myr for low-extinction stars near L1688, and ~6Myr for the group containing {rho}Oph.
- ID:
- ivo://CDS.VizieR/J/A+A/637/A43
- Title:
- Membership in the Cepheus association
- Short Name:
- J/A+A/637/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young field stars are hardly distinguishable from older ones because their space motion rapidly mixes them with the stellar population of the Galactic plane.Nevertheless, a careful target selection allows for young stars to be spotted throughout the sky. We aim to identify additional sources associated with the four young comoving stars that we discovered towards the CO Cepheus void and to provide a comprehensive view of the Cepheus association. Based on multivariate analysis methods, we have built an extended sample of 193 young star candidates, which are the optical and infrared counterparts of ROSAT All-Sky Survey and XMM-Newton X-ray sources. From optical spectroscopic observations, we measured their radial velocity with the cross-correlation technique. We derived their atmospheric parameters and projected rotational velocity with the code ROTFIT. We applied the subtraction of inactive templates to measure the lithium equivalent width, from which we infer their lithium abundance and age. Finally, we studied their kinematics using the second Gaia data release. Our sample is mainly composed of young or active stars and multiple systems. We identify two distinct populations of young stars that are spatially and kinematically separated. Those with an age between 100 and 300Myr are mostly projected towards the Galactic plane. In contrast, 23 of the 37 sources younger than 30Myr are located in the CO Cepheus void, and 21 of them belong to the stellar kinematic group that we previously reported in this sky area. We report a total of 32 bona fide members and nine candidates for this nearby (distance=157+/-10pc) young (age=10-20Myr) stellar association. According to the spatial distribution of its members, the original cluster is already dispersed and partially mixed with the local population of the Galactic plane.
- 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/ApJS/160/353
- Title:
- Membership of the Orion nebula population
- Short Name:
- J/ApJS/160/353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Chandra Orion Ultradeep project (COUP) observation described in a companion paper by Getman et al. (2005, Cat. J/ApJS/160/319) provides an exceptionally deep X-ray survey of the Orion Nebula Cluster and associated embedded young stellar objects. Membership of the region is important for studies of the stellar IMF, cluster dynamics, and star formation. The COUP study detected 1616 X-ray sources. In this study we confirm cloud membership for 1315 stars, identify 16 probable foreground field stars having optical counterparts with discrepant proper motions, and classify the remaining 285 X-ray sources, of which 51 are lightly and 234 heavily obscured.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/1157
- Title:
- Members of ONC and Tau-Aur
- Short Name:
- J/MNRAS/444/1157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In light of recent substantial updates to spectral type estimations and newly established intrinsic colours, effective temperatures, and bolometric corrections for pre-main sequence (PMS) stars, we re-address the theory of accretion disc-regulated stellar angular momentum (AM) evolution. We report on the compilation of a consistent sample of fully convective stars within two of the most well-studied and youngest, nearby regions of star formation: the Orion nebula Cluster and Taurus-Auriga. We calculate the average specific stellar AM (j*) assuming solid body rotation, using surface rotation periods gathered from the literature and new estimates of stellar radii and ages. We use published Spitzer IRAC fluxes to classify our stars as Class II or Class III and compare their j_*_ evolution. Our results suggest that disc dispersal is a rapid process that occurs at a variety of ages. We find a consistent j_*_ reduction rate between the Class II and Class III PMS stars which we interpret as indicating a period of accretion disc-regulated AM evolution followed by near-constant AM evolution once the disc has dissipated. Furthermore, assuming our observed spread in stellar ages is real, we find that the removal rate of j_*_ during the Class II phase is more rapid than expected by contraction at constant stellar rotation rate. A much more efficient process of AM removal must exist, most likely in the form of an accretion-driven stellar wind or other outflow from the star-disc interaction region or extended disc surface.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A55
- Title:
- Metallicity of the {gamma} Vel cluster
- Short Name:
- J/A+A/567/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowledge of the abundance distribution of star forming regions and young clusters is critical to investigate a variety of issues, from triggered star formation and chemical enrichment by nearby supernova explosions to the ability to form planetary systems. In spite of this, detailed abundance studies are currently available for relatively few regions. In this context, we present the analysis of the metallicity of the Gamma Velorum cluster, based on the products distributed in the first internal release of the Gaia-ESO Survey. The Gamma Velorum candidate members have been observed with FLAMES, using both UVES and Giraffe, depending on the target brightness and spectral type. In order to derive a solid metallicity determination for the cluster, membership of the observed stars must be first assessed. To this aim, we use several membership criteria including radial velocities, surface gravity estimates, and the detection of the photospheric lithium line. Out of the 80 targets observed with UVES, we identify 14 high-probability members. We find that the metallicity of the cluster is slightly sub-solar, with a mean [Fe/H]=-0.057+/-0.018dex. Although J08095427-4721419 is one of the high-probability members, its metallicity is significantly larger than the cluster average. We speculate about its origin as the result of recent accretion episodes of rocky bodies of about 60 Msun hydrogen-depleted material from the circumstellar disc.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/484
- Title:
- MgII UV feature in T Tauri stars
- Short Name:
- J/MNRAS/448/484
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The atmospheric structure of T Tauri stars (TTSs) and its connection with the large-scale outflow is poorly known. Neither the effect of the magnetically mediated interaction between the star and the disc is well understood. The MgII multiplet is a fundamental tracer of TTSs atmospheres and outflows, and is the strongest feature in the near-ultraviolet spectrum of TTSs. The International Ultraviolet Explorer and Hubble Space Telescope data archives provide a unique set to study the main physical compounds contributing to the line profile and to derive the properties of the line formation region. The MgII profiles of 44 TTSs with resolution 13000-30000 are available in these archives. In this work, we use this data set to measure the main observables: flux, broadening, asymmetry, terminal velocity of the outflow, and the velocity of the discrete absorption components. For some few sources repeated observations are available and variability has been studied. There is a warm wind that at sub-au scales absorbs the blue wing of the MgII profiles. The main result found in this work is the correlation between the line broadening, MgII flux, terminal velocity of the flow and accretion rate. Both outflow and magnetospheric plasma contribute to the MgII flux. The flux-flux correlation between MgII and CIV or HeII is confirmed; however, no correlation is found between the MgII flux and the UV continuum or the H_2_ emission.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A83
- Title:
- MIDI atlas of low- and intermediate-mass YSOs
- Short Name:
- J/A+A/617/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Protoplanetary disks show large diversity regarding their morphology and dust composition. With mid-infrared interferometry the thermal emission of disks can be spatially resolved, and the distribution and properties of the dust within can be studied. Our aim is to perform a statistical analysis on a large sample of 82 disks around low- and intermediate-mass young stars, based on mid-infrared interferometric observations. We intend to study the distribution of disk sizes, variability, and the silicate dust mineralogy. Archival mid-infrared interferometric data from the MIDI instrument on the Very Large Telescope Interferometer are homogeneously reduced and calibrated. Geometric disk models are used to fit the observations to get spatial information about the disks. An automatic spectral decomposition pipeline is applied to analyze the shape of the silicate feature. We present the resulting data products in the form of an atlas, containing N band correlated and total spectra, visibilities, and differential phases. The majority of our data can be well fitted with a continuous disk model, except for a few objects, where a gapped model gives a better match. From the mid-infrared size-luminosity relation we find that disks around T Tauri stars are generally colder and more extended with respect to the stellar luminosity than disks around Herbig Ae stars. We find that in the innermost part of the disks (r<~1au) the silicate feature is generally weaker than in the outer parts, suggesting that in the inner parts the dust is substantially more processed. We analyze stellar multiplicity and find that in two systems (AB Aur and HD 72106) data suggest a new companion or asymmetric inner disk structure. We make predictions for the observability of our objects with the upcoming Multi-AperTure mid- Infrared SpectroScopic Experiment (MATISSE) instrument, supporting the practical preparations of future MATISSE observations of T Tauri stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/201/11
- Title:
- Mid-infrared spectral variability atlas of YSOs
- Short Name:
- J/ApJS/201/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The atlas presents medium-resolution mid-infrared spectra of low- and intermediate mass pre-main sequence objects obtained by the ISOPHOT-S spectrophotometer of the Infrared Space Observatory (ISO) and the Infrared Spectrograph (IRS) of the Spitzer Space Telescope.
