- 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.
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- ID:
- ivo://CDS.VizieR/J/A+A/620/A139
- Title:
- Planet candidates in open clusters
- Short Name:
- J/A+A/620/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detecting exoplanets in clusters of different ages is a powerful tool for understanding a number of open questions, such as how the occurrence rate of planets depends on stellar metallicity, on mass, or on stellar environment. We present the first results of our HARPS long-term radial velocity (RV) survey which aims to discover exoplanets around intermediate-mass (between ~2 and 6M_{sun}_) evolved stars in open clusters. We selected 826 bona fide HARPS observations of 114 giants from an initial list of 29 open clusters and computed the half-peak to peak variability of the HARPS RV measurements, namely {Delta}RV/2, for each target, to search for the best planet-host candidates. We also performed time series analyses for a few targets for which we have enough observations to search for orbital solutions. Although we attempted to rule out the presence of binaries on the basis of previous surveys, we detected 14 new binary candidates in our sample, most of them identified from a comparison between HARPS and CORAVEL data. We also suggest 11 new planet-host candidates based on a relation between the stellar surface gravity and {Delta}RV/2. Ten of the candidates are less than 3M_{sun}_, showing evidence of a low planet occurrence rate for massive stars. One of the planet-host candidates and one of the binary candidates show very clear RV periodic variations, allowing us to confirm the discovery of a new planet and to compute the orbital solution for the binary. The planet is IC 4651 9122b, with a minimum mass of msini=6.3M_J_ and a semimajor axis a=2.0AU. The binary companion is NGC 5822 201B, with a very low minimum mass of msini=0.11M_{sun}_ and a semimajor axis a=6.5AU, which is comparable to the Jupiter distance to the Sun.
- ID:
- ivo://CDS.VizieR/J/A+A/563/A45
- Title:
- Pleiades cluster membership probabilities
- Short Name:
- J/A+A/563/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the advent of deep wide surveys, large photometric and astrometric catalogues of literally all nearby clusters and associations have been produced. The unprecedented accuracy and sensitivity of these data sets and their broad spatial, temporal and wavelength coverage make obsolete the classical membership selection methods that were based on a handful of colours and luminosities. We present a new technique designed to take full advantage of the high dimensionality (photometric, astrometric, temporal) of such a survey to derive self-consistent and robust membership probabilities of the Pleiades cluster. We aim at developing a methodology to infer membership probabilities to the Pleiades cluster from the DANCe multidimensional astro-photometric data set in a consistent way throughout the entire derivation. The determination of the membership probabilities has to be applicable to censored data and must incorporate the measurement uncertainties into the inference procedure. We use Bayes-theorem and a curvilinear forward model for the likelihood of the measurements of cluster members in the colour-magnitude space, to infer posterior membership probabilities. The distribution of the cluster members proper motions and the distribution of contaminants in the full multidimensional astro-photometric space is modelled with a mixture-of-Gaussians likelihood. We analyse several representation spaces composed of the proper motions plus a subset of the available magnitudes and colour indices. We select two prominent representation spaces composed of variables selected using feature relevance determination techniques based in Random Forests, and analyse the resulting samples of high probability candidates. We consistently find lists of high probability (p>0.9975) candidates with ~1000 sources, 4 to 5 times more than obtained in the most recent astro-photometric studies of the cluster. Multidimensional data sets require statistically sound multivariate analysis techniques to fully exploit their scientific information content. Proper motions in particular are, as expected, critical for the correct separation of contaminants. The methodology presented here is ready for application in data sets that include more dimensions, such as radial and/or rotational velocities, spectral indices, and variability.
- ID:
- ivo://CDS.VizieR/J/A+A/299/696
- Title:
- Pleiades field Membership probabilities
- Short Name:
- J/A+A/299/696
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalogue of proper motions and photographic B,V magnitudes for stars up to B=19 mag within a region centered near Alcyone is presented. The catalogue is based on MAMA measurements of 8 plates taken with the Tautenburg Schmidt telescope. The survey includes ca. 14500 stars and covers a total field of about 9 square degrees. Membership probabilities, proper motions and B,V magnitudes are listed for 442 stars up to B=19 mag in the Pleiades field.
- ID:
- ivo://CDS.VizieR/J/MNRAS/313/347
- Title:
- Pleiades low-mass stars and brown dwarfs
- Short Name:
- J/MNRAS/313/347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a six-square-degree Pleiades survey in I and Z, which is photometrically complete to approximately I_KP_=19.2mag (I_C_=19.6 in the Pleiades). We remove non-cluster contamination on the basis of proper motions and infrared photometry, and present 339 candidate cluster members, 30 of which are fainter than I_KP_=17.5, and are thus strong brown-dwarf candidates.
- 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.
837. 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.
