- ID:
- ivo://CDS.VizieR/J/A+A/531/A141
- Title:
- Physical parameters of PMS in open clusters
- Short Name:
- J/A+A/531/A141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aims are twofold: To determine the physical parameters of PMS members in young open clusters (YOCs), and to check and compare the performances of different model isochrones. We compare UBVRI photometric observations of eleven YOCs to theoretical isochrones in the photometric diagrams. The comparison simultaneously provides membership assignments for MS and PMS stars and estimates for the masses, ages, and spatial distribution of the candidate members. The relations found between the different cluster parameters show that the procedure applied to assign cluster membership, and to measure physical parameters for the selected members, is well founded.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/539/A119
- Title:
- Pismis 24 stars with X-ray emission
- Short Name:
- J/A+A/539/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Circumstellar disks are expected to evolve quickly in massive young clusters harboring many OB-type stars. Two processes have been proposed to drive the disk evolution in such cruel environments: (1) gravitational interaction between circumstellar disks and nearby passing stars (stellar encounters), and (2) photoevaporation by UV photons from massive stars. The relative importance of both mechanisms is not well understood. Studies of massive young star clusters can provide observational constraints on the processes of driving disk evolution. We investigate the properties of young stars and their disks in the NGC 6357 complex, concentrating on the most massive star cluster within the complex: Pismis 24.
- ID:
- ivo://CDS.VizieR/J/A+A/335/183
- Title:
- Pleiades low-mass stars rotational velocities
- Short Name:
- J/A+A/335/183
- Date:
- 13 Dec 2021 10:00:41
- Publisher:
- CDS
- Description:
- We present new vsini measurements for 235 low-mass stars in the Pleiades. The differential rotational broadening has been resolved for all the stars in our sample. These results, combined with previously published measurements, provide a complete and unbiased rotation data set for stars in the mass range from 0.6 to 1.2M_{sun}_. Applying a numerical inversion technique on the vsini distributions, we derive the distributions of equatorial velocities for low-mass Pleiades members. We find that half of the Pleiades dwarfs with a mass between 0.6 to 1M_{sun}_ have rotation rates lower than 10km/s.
- ID:
- ivo://CDS.VizieR/J/AJ/121/1040
- Title:
- PMS members of upper Scorpius OB association
- Short Name:
- J/AJ/121/1040
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a large intermediate-resolution spectroscopic survey for pre-main-sequence (PMS) stars in the Upper Scorpius OB association, the nearest region of recent massive star formation. Utilizing the 2dF multiobject spectrograph at the Anglo-Australian Telescope, we obtained spectra of 576 stars with magnitudes 12.5<=R<=16.5 in a 6{deg}^2^ area in Upper Scorpius. Among these objects we were able to identify 98 new PMS stars, nearly all of them M-type stars, by their strong lithium absorption lines. We place the new PMS stars into the H-R diagram and find that their ages agree well with the mean age of 5Myr determined in our earlier investigation based on a smaller sample of stars. The number of low-mass (0.1M_{sun}_<~M*<~0.5M_{sun}) members is at least as high as expected from the known number of high-mass (M*>~3M_{sun}_) association members and from recent determinations of the field star initial mass function. Thus, there is no deficit of low-mass stars in Upper Scorpius.
315. PMS stars in h Per
- ID:
- ivo://CDS.VizieR/J/A+A/589/A113
- Title:
- PMS stars in h Per
- Short Name:
- J/A+A/589/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several studies showed that the magnetic activity of late-type main-sequence (MS) stars is characterized by different regimes and that their activity levels are well described by the Ross by number, Ro, defined as the ratio between the rotational period P_rot_ and the convective turnover time. Very young pre-main-sequence (PMS) stars show, similarly to MS stars, intense magnetic activity. However, they do not show clear activity-rotation trends, and it still debated which stellar parameters determine their magnetic activity levels. To bridge the gap between MS and PMS stars, we studied the activity-rotation relation in the young cluster h Persei, a ~13Myr old cluster, that contains both fast and slow rotators. The cluster members have ended their accretion phase and have developed a radiative core. It therefore offers us the opportunity of studying the activity level of intermediate-age PMS stars with different rotational velocities, excluding any interactions with the circumstellar environment We constrained the magnetic activity levels of h Per members by measuring their X-ray emission from a Chandra observation, while rotational periods were obtained previously in the framework of the MONITOR project. By cross-correlating these data, we collected a final catalog of 414 h Per members with known rotational period, effective temperature, and mass. In 169 of these, X-ray emission has also been detected.
- ID:
- ivo://CDS.VizieR/J/A+A/467/1397
- Title:
- PMS stars in open clusters: the DAY-I Catalogue
- Short Name:
- J/A+A/467/1397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the basic ideas and first results from the project we are carrying out at present, the search for and characterisation of pre-main sequence (PMS) stars among the members of Galactic young clusters. The observations of 10 southern clusters, nine of them located in the Carina-Sagittarius spiral arm of the Milky Way are presented. We aim at listing candidate PMS member stars in young clusters. The catalogued stars will serve as a basis for future spectroscopic studies of individual objects to determine the properties of stellar formation in the last phases before the main sequence stage. Properties such as the presence of residual envelopes or disks, age spread among PMS members, and the possible presence of several episodes of star formation in the clusters, are to be addressed. Multicolour photometry in the UBVRcIc system has been obtained for 10 southern young clusters in the fourth Galactic quadrant, located between Galactic longitudes l=238 and l=310. For six clusters in the sample, the observations presented here provide the first published study based on CCD photometry. A quantitative comparison is performed with post-MS isochrones, and PMS isochrones from three different evolutionary models are used in the photometric membership analysis for possible PMS stars. The observations produce photometric indices in the Johnson-Cousins photometric systems for a total of 26962 stars. The matching of our pixel coordinates with corresponding fields in the 2MASS data base provides astrometric calibration for all catalogued stars and JHK 2MASS photometric indices for 60% of them. Post-MS cluster ages range from 4 to 60Myr, whereas the photometric membership analysis assigns PMS membership assignment to a total of 842 stars, covering an age range between 1 and 10Myr. This information on the PMS candidate members has been collected into a catalogue, named DAY-I, which contains 16 entries for 842 stars in the field of 10 southern clusters.
- ID:
- ivo://CDS.VizieR/J/MNRAS/267/755
- Title:
- Polarimetry in the Chamaeleon I Dark Cloud
- Short Name:
- J/MNRAS/267/755
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Position angles and magnitudes of linear polarization in the H band have been measured for 66 stars embedded in or behind the Chamaeleon I dark cloud. These data are used to demonstrate that the magnetic field permeating the cloud has an ordered structure over the full extent of the dark cloud (~4pc), with the magnetic field direction changing smoothly from a position angle of ~100 degrees in the vicinity of HD 97300 in the north to ~140 degrees in the vicinity of HD 97048 in the south and west. The elongation of the dark cloud is consistent with collapse preferentially along magnetic field lines. The polarizing efficiency of the cloud decreases with increasing line-of-sight extinction. Cloud members show a larger range in degree of polarization and position angle, which is interpreted as due to anisotropic scattering local to these stars. The IRAS 11054-7706C bipolar CO outflow is unusual in that it is oriented at >60 degrees to the cloud magnetic field direction. The Chamaeleon Infrared Nebula is polarized at ~30 per cent in the H band and also is oriented at ~50 degrees to the local magnetic field. We suggest that gravitational forces may have overwhelmed magnetic support locally to form these relatively massive stars.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A25
- Title:
- (Possible spiral in the disk around HD34282
- Short Name:
- J/A+A/649/A25
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- During the evolution of protoplanetary disks into planetary systems we expect to detect signatures that trace mechanisms such as planet-disk interaction. Protoplanetary disks display a large variety of structures in recently published high-spatial resolution images. However, the three-dimensional morphology of these disks is often difficult to infer from the two-dimensional projected images we observe. We aim to detect signatures of planet-disk interaction by studying the scattering surface of the protoplanetary disk around HD34282 We spatially resolved the disk using the high-contrast imager VLT/SPHERE in polarimetric imaging mode. We retrieved a profile for the height of the scattering surface to create a height-corrected deprojection, which simulates a face-on orientation. The detected disk displays a complex scattering surface. An inner clearing or cavity extending up to r<0.28" (88au) is surrounded by a bright inclined (i=56{deg}) ring with a position angle of 119{deg}. The center of this ring is offset from the star along the minor axis with 0.07", which can be explained with a disk height of 26au above the midplane. Outside this ring, beyond its southeastern ansa we detect an azimuthal asymmetry or blob at r~0.4". At larger separation, we detect an outer disk structure that can be fitted with an ellipse, which is compatible with a circular ring seen at r=0.62" (=190au) and a height of 77au. After applying a height-corrected deprojection we see a circular ring centered on the star at 88 au; what had seemed to be a separate blob and outer ring could now both be part of a single-armed spiral. We present the first scattered-light image of the disk around HD 34282 and resolve a disk with an inner cavity up to r~90au and a highly structured scattering surface of an inclined disk at a large height H_scat_/r=0.29" above the midplane at the inner edge of the outer disk. Based on the current data it is not possible to conclude decisively whether H_scat_/r remains constant or whether the surface is flared with at most H_scat_ {prop.to} r^1.35^, although we favor the constant ratio based on our deprojections. The height-corrected deprojection allows for a more detailed interpretation of the observed structures, from which we discern the first detection of a single-armed spiral in a protoplanetary disk.
- ID:
- ivo://CDS.VizieR/J/AJ/124/1670
- Title:
- Post-T Tauri Stars in Sco-Cen Association
- Short Name:
- J/AJ/124/1670
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a spectroscopic survey of X-ray and proper-motion-selected samples of late-type stars in the Lower Centaurus-Crux (LCC) and Upper Centaurus-Lupus (UCL) subgroups of the nearest OB association: Scorpius-Centaurus. The primary goals of the survey are to determine the star formation history of the OB subgroups and to assess the frequency of accreting stars in a sample dominated by "post-T Tauri" pre-main-sequence (PMS) stars. We investigate two samples: (1) proper-motion candidates from the ACT Catalog (<I/246>) and Tycho Reference Catalog (TRC, <I/250>) with X-ray counterparts in the ROSAT All-Sky Survey (RASS) Bright Source Catalog and (2) G- and K-type stars in the Hipparcos catalog found to be candidate members by de Zeeuw et al. (1999, Cat. <J/AJ/117/354>). We obtained optical spectra of 130 candidates with the Siding Spring 2.3m dual-beam spectrograph.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/806
- Title:
- Pre-main-sequence isochrones. II. SFR
- Short Name:
- J/MNRAS/434/806
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived ages for 13 young (<30Myr) star-forming regions and find that they are up to a factor of 2 older than the ages typically adopted in the literature. This result has wide-ranging implications, including that circumstellar discs survive longer (=~10-12Myr) and that the average Class I lifetime is greater (=~1Myr) than currently believed. For each star-forming region, we derived two ages from colour-magnitude diagrams. First, we fitted models of the evolution between the zero-age main sequence and terminal-age main sequence to derive a homogeneous set of main-sequence ages, distances and reddenings with statistically meaningful uncertainties. Our second age for each star-forming region was derived by fitting pre-main-sequence stars to new semi-empirical model isochrones. For the first time (for a set of clusters younger than 50Myr), we find broad agreement between these two ages, and since these are derived from two distinct mass regimes that rely on different aspects of stellar physics, it gives us confidence in the new age scale. This agreement is largely due to our adoption of empirical colour-T_eff_ relations and bolometric corrections for pre-main-sequence stars cooler than 4000K. The revised ages for the star-forming regions in our sample are: ~2Myr for NGC 6611 (Eagle Nebula; M 16), IC 5146 (Cocoon Nebula), NGC 6530 (Lagoon Nebula; M 8) and NGC 2244 (Rosette Nebula); ~6Myr for {sigma} Ori, Cep OB3b and IC 348; ~10Myr for {lambda} Ori (Collinder 69); ~11Myr for NGC 2169; ~12Myr for NGC 2362; ~13Myr for NGC 7160; ~14Myr for {chi}Per (NGC 884); and ~20Myr for NGC 1960 (M 36).
