- 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.
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752. Pleiades member list
- ID:
- ivo://CDS.VizieR/J/A+A/332/575
- Title:
- Pleiades member list
- Short Name:
- J/A+A/332/575
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The luminosity function (LF) of the Pleiades cluster stars was constructed for the study of the LF fine structure related to pre-main sequence (MS) stellar evolution. Theoretical luminosity functions based on present-day pre-MS and MS stellar models were constructed and compared with observations. We tested both power- and log-normal laws describing the cluster star Initial Mass Function (IMF). Both single star formation burst- and age spread-models were examined. The agreement between the observed Pleiades colour-magnitude diagram with the new HIPPARCOS distance and the theoretical ZAMS for a normal metallicity is excellent when the model positions in the HR diagram are corrected to the helium abundance Y=0.34. The corresponding age of the cluster is logt=7.95. Three features (dips) were found in the observed cluster LF in a magnitude range M_V_=5-12mag. Two of them (at M_V_=7.5mag and 9.5mag) are assumed to be field LF features: Wielen and Kroupa dips. Theoretical models fail to reproduce them. We attributed the third (brightest) detail (the dip at M_V_=5.5mag) to the pre-MS evolution of Pleiades stars. The observed Pleiades LF corresponds in its brighter part to the standard Population I IMF. The log-normal IMF fits the observations much better than a simple power-law IMF. The brightest LF feature could be reproduced in the theoretical LF if a substantial age spread of order of several tens of Myrs is supposed to exist among the Pleiades stars.
- ID:
- ivo://CDS.VizieR/J/AJ/153/101
- Title:
- Pleiades members stellar properties
- Short Name:
- J/AJ/153/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise measurements of eclipsing binary parameters and statistical studies of young clusters have suggested that some magnetically active low-mass dwarfs possess radii inflated by ~5%-15% relative to theoretical expectations. If true, this effect should be pronounced in young open clusters, due to the rapid rotation and strong magnetic activity of their most extreme members. We explore this possibility by determining empirical radii for 83 members of the nearby Pleiades open cluster, using spectral energy distribution fitting to establish F_bol_ with a typical accuracy of ~3% together with color and spectro-photometric indices to determine T_eff_. We find several Pleiades members with radii inflated above radius-T_eff_ models from state-of-the-art calculations, and apparent dispersions in radii for the K-dwarfs of the cluster. Moreover, we demonstrate that this putative radius inflation correlates strongly with rotation rate, consistent with inflation of young stars by magnetic activity and/or starspots. We argue that this signal is not a consequence of starspot-induced color anomalies, binarity, or depth effects in the cluster, employing Gaia DR1 distances as a check. Finally, we consider the lithium abundances of these stars, demonstrating a triple correlation between rotation rate, radius inflation, and enhanced lithium abundance. Our result-already significant to ~99.99% confidence-provides strong support for a magnetic origin of the inflated radii and lithium dispersion observed in young, low-mass stars.
- ID:
- ivo://CDS.VizieR/J/AJ/152/114
- Title:
- Pleiades members with K2 light curves. II.
- Short Name:
- J/AJ/152/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use K2 to continue the exploration of the distribution of rotation periods in Pleiades that we began in Paper I. We have discovered complicated multiperiod behavior in Pleiades stars using these K2 data, and we have grouped them into categories, which are the focal part of this paper. About 24% of the sample has multiple, real frequencies in the periodogram, sometimes manifesting as obvious beating in the LCs. Those having complex and/or structured periodogram peaks, unresolved multiple periods, and resolved close multiple periods are likely due to spot/spot group evolution and/or latitudinal differential rotation; these largely compose the slowly rotating sequence in P versus (V-K_s_)_0_ identified in Paper I. The fast sequence in P versus (V-K_s_)_0_ is dominated by single-period stars; these are likely to be rotating as solid bodies. Paper III continues the discussion, speculating about the origin and evolution of the period distribution in the Pleiades.
- ID:
- ivo://CDS.VizieR/J/AJ/152/115
- Title:
- Pleiades members with K2 light curves. III.
- Short Name:
- J/AJ/152/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use high-quality K2 light curves for hundreds of stars in the Pleiades to better understand the angular momentum evolution and magnetic dynamos of young low-mass stars. The K2 light curves provide not only rotational periods but also detailed information from the shape of the phased light curve that was not available in previous studies. A slowly rotating sequence begins at (V-K_s_)_0_~1.1 (spectral type F5) and ends at (V-K_s_)_0_~3.7 (spectral type K8), with periods rising from ~2 to ~11 days in that interval. A total of 52% of the Pleiades members in that color interval have periods within 30% of a curve defining the slow sequence; the slowly rotating fraction decreases significantly redward of (V-K_s_)_0_=2.6. Nearly all of the slow-sequence stars show light curves that evolve significantly on timescales less than the K2 campaign duration. The majority of the FGK Pleiades members identified as photometric binaries are relatively rapidly rotating, perhaps because binarity inhibits star-disk angular momentum loss mechanisms during pre-main-sequence evolution. The fully convective late M dwarf Pleiades members (5.0<(V-K_s_)_0_<6.0) nearly always show stable light curves, with little spot evolution or evidence of differential rotation. During pre-main-sequence evolution from ~3Myr (NGC2264 age) to ~125Myr (Pleiades age), stars of 0.3M_{Sun}_ shed about half of their angular momentum, with the fractional change in period between 3 and 125Myr being nearly independent of mass for fully convective stars. Our data also suggest that very low mass binaries form with rotation periods more similar to each other and faster than would be true if drawn at random from the parent population of single stars.
- ID:
- ivo://CDS.VizieR/J/AJ/152/113
- Title:
- Pleiades members with K2 light curves. I. Periods
- Short Name:
- J/AJ/152/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young (125Myr), populous (>1000 members), and relatively nearby, the Pleiades has provided an anchor for stellar angular momentum models for both younger and older stars. We used K2 to explore the distribution of rotation periods in the Pleiades. With more than 500 new periods for Pleiades members, we are vastly expanding the number of Pleiades with periods, particularly at the low-mass end. About 92% of the members in our sample have at least one measured spot-modulated rotation period. For the ~8% of the members without periods, non-astrophysical effects often dominate (saturation, etc.), such that periodic signals might have been detectable, all other things being equal. We now have an unusually complete view of the rotation distribution in the Pleiades. The relationship between P and (V-K_s_)_0_ follows the overall trends found in other Pleiades studies. There is a slowly rotating sequence for 1.1<~(V-K_s_)_0_<~3.7 and a primarily rapidly rotating population for (V-K_s_)_0_>~5.0. There is a region in which there seems to be a disorganized relationship between P and (V-K_s_)_0_ for 3.7<~(V-K_s_)_0_<~5.0. Paper II continues the discussion, focusing on multiperiod structures, and Paper III speculates about the origin and evolution of the period distribution in the Pleiades.
- ID:
- ivo://CDS.VizieR/I/258
- Title:
- Pleiades positions and proper motions
- Short Name:
- I/258
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on a preliminary reference catalogue, combined with the catalogues PPM, ACRS and those in Eichhorn et al (1970, Cat. <I/90>), Jones (1973A&AS....9..313J) and Hertzsprung (1947AnLei..19a...1H), 33 exposures on 11 plates taken with the Zo-Se 40cm refractor (f=6895mm) in 86 years are reduced with the central overlapping technique, and high-precision positions and proper motions of 441 stars in the Pleiades astrometric standard region are obtained. The standard errors of star positions are less than +/-0.05arcsec, and the standard errors of proper motions for 90% stars in our reduction are less than +/-0.001arcsec/yr.
- 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.
759. 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.
