Taurus stars membership in Pleiades open cluster

The Astrophysical Journal, 2000

We present near-infrared photometry and optical spectroscopy of very low mass stars and brown dwarf candidates in the Pleiades open cluster. The membership status of these objects is assessed using color-magnitude diagrams, lithium and spectral types. Eight objects out of 45 appear to be nonmembers. A search for companions among 34 very low mass Pleiades members in high spatial (M ¹ 0.09 M _ ) resolution images obtained with the Hubble Space T elescope (HST ) and the adaptive optics system of the Canada-France-Hawaii telescope produced no resolved binaries with separations larger than 0A .2 (a D 27 AU ; P D 444 yr). Nevertheless, we Ðnd evidence for a binary sequence in the color-magnitude diagrams, in agreement with the results of Steele & Jameson for higher mass stars. We apply the lithium test to two objects : CFHT-Pl-16, which lies in the cluster binary sequence but is unresolved in images obtained with the Hubble Space T elescope ; and CFHT-Pl-18, which is binary with separation. The 0A .33 Ðrst object passes the test, but the second object does not. We conclude that CFHT-Pl-16 is an Pleiades brown dwarf binary with separation less than 11 AU and that CFHT-Pl-18 is a foreground system. We compare the multiplicity statistics of the Pleiades very low mass stars and brown dwarfs with that of Gand K-type main-sequence stars in the solar neighborhood. We Ðnd that there is some evidence for a deÐciency of wide binary systems (separation [27 AU) among the Pleiades very low mass members. We brieÑy discuss how this result can Ðt with current scenarios of brown dwarf formation. We correct the Pleiades substellar mass function for the contamination of cluster nonmembers found in this work. We Ðnd a contamination level of 33% among the brown dwarf candidates identiÐed by Bouvier et al. Assuming a power-law IMF across the substellar boundary, we Ðnd a slope dN/dM D M~0.53, implying that the number of objects per mass bin is still rising but the contribution to the total mass of the cluster is declining in the brown dwarf regime.

Astronomy & Astrophysics, 2012

Context. It is widely recognized that binarity is a very common feature during star formation; however, different regions and clusters display significantly different binary fractions. This appears to be related to the initial density of the star forming region. The Pleiades cluster has been shown to have a binary fraction similar to that of field stars in the solar neighborhood. Aims. We have taken advantage of a passage of the Moon over the Pleiades cluster, to investigate at high angular resolution two small but similar and consistent samples of cluster members and field stars. Methods. We have employed the technique of lunar occultations (LO). Although LO in the Pleiades have been reported several times in the past, we have for the first time employed the superior performance of the VLT, achieving about 1 milliarcsecond (mas) resolution and detecting sources as faint as K ≈ 12 mag. Results. We have recorded 17 LO light curves of stars recognized as cluster members, and 17 of field stars. The average magnitude was K ≈ 8.5 mag and the average limiting resolution ≈0. 002, for both samples. We detect 5 binaries among the cluster members, and 2 among the sample of field stars. Three systems are new detections, while two were previously only suspected to be binaries. The projected separations are in the range 0. 017 to 0. 642 and the brightness ratios in the range 1 to 90. One more star is suspected to have a companion. Conclusions. Although the fraction of binary detections appears higher among the members than among the non-members, the two samples are too small to draw firm conclusions. Our observations show that, in spite of extensive investigations carried out previously in the Pleiades cluster, the binarity census is not yet complete. We have detected significant orbital motion in four binary systems, which stand up as candidates for dynamical mass estimations.

Monthly Notices of the Royal Astronomical Society, 2000

We present the results of a six-square-degree Pleiades survey in I and Z, which is photometrically complete to approximately I KP 19X2 I Cou 19X6 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 17X5Y and are thus strong brown-dwarf candidates.

The Astrophysical …, 2007

We make use of new near and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to define the single-star main sequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near and mid-IR photometry extend effectively two magnitudes deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low mass and sub-stellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new candidate members fainter than Ks =14 (corresponding to 0.1 Mo). These candidate members should eventually allow a better estimate of the cluster mass function to be made down to of order 0.04 solar masses. We also use new IRAC data, in particular the images obtained at 8 um, in order to comment briefly on interstellar dust in and near the Pleiades. We confirm, as expected, that-with one exception-a sample of low mass stars recently identified as having 24 um excesses due to debris disks do not have significant excesses at IRAC wavelengths. However, evidence is also presented that several of the Pleiades high mass stars are found to be impacting with local condensations of the molecular cloud that is passing through the Pleiades at the current epoch.

The Astronomical Journal, 2001

We present the results of a large scale search for new members of the Pleiades star cluster using 2MASS near-infrared photometry and proper motions derived from POSS 1 Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.

Star Clusters, 1980

From a proper motion survey by Pels and photometric measurement of selected stars it was found that the Pleiades cluster extends till at least 496 from the centre, corresponding to 10 pc at a distance of 125 pc. It turns out that the luminosity function of the Pleiades is a func tion of the distance to the centre, the proportion of faint stars in creasing with this distance. Because of this, the luminosity function as it was determined before flattened towards fainter stars, whereas for the total field with a diameter of 20 pc one finds a luminosity function that is still increasing at the faint end. Flare star observations in the Pleiades field show that the increase amounts to at least a factor 20 in the mass range 2 to 0.4 M @. Accurate proper motions of stars in the projected central field show a dispersion of velocities in the cluster of 700 m/sec. This could indicate a total mass of the Pleiades cluster of the order of 2000 M Q .

Astronomy and Astrophysics, 2018

Aims. This work analyses the spatial distribution of stars in Taurus with a specific focus on multiple stars and wide pairs in order to derive new constraints on star formation and early dynamical evolution scenarios. Methods. We collected the multiplicity data of stars in Taurus to build an up-to-date stellar/multiplicity catalog. We first present a general study of nearest-neighbor statistics on spatial random distribution, comparing its analytical distribution and moments to those obtained from Monte Carlo samplings. We introduce the one-point correlation Ψ function to complement the pair correlation function and define the spatial regimes departing from randomness in Taurus. We then perform a set of statistical studies to characterize the binary regime that prevails in Taurus. Results. The Ψ function in Taurus has a scale-free trend with a similar exponent as the correlation function at small scale. It extends almost 3 decades up to ∼60 kAU showing a potential extended wide binary regime. This was hidden in the correlation function due to the clustering pattern blending. Distinguishing two stellar populations, single stars versus multiple systems (separation ≤1 kAU), within Class II/III stars observed at high angular resolution, we highlight a major spatial neighborhood difference between the two populations using nearest-neighbor statistics. The multiple systems are three times more likely to have a distant companion within 10 kAU when compared to single stars. We show that this is due to the presence of most probable physical ultra-wide pairs (UWPs, defined as such from their mutual nearest neighbor property), that are themselves generally composed of multiple systems containing up to five stars altogether. More generally, our work highlights; 1) a new large population of candidate UWPs in Taurus within the range 1-60 kAU in Taurus and 2) the major local structural role they play up to 60 kAU. There are three different types of UWPs; either composed of two tight and comparatively massive stars (MM), by one single and one multiple (SM), or by two distant low-mass singles (SS) stars. These UWPs are biased towards high multiplicity and higher-stellar-mass components at shorter separations. The multiplicity fraction per ultra-wide pair with separation less than 10 kAU may be as high as 83.5 ± 19.6%. Conclusions. We suggest that these young pre-main sequence UWPs may be pristine imprints of their spatial configuration at birth resulting from a cascade fragmentation scenario of the natal molecular core. They could be the older counterparts, at least for those separated by less than 10 kAU, to the ≤0.5 Myr prestellar cores/Class 0 multiple objects observed at radio/millimeter wavelengths.

The Astrophysical Journal, 2009

We present the results of a search for new members of the Taurus star-forming region using data from the Spitzer Space Telescope and the XMM-Newton Observatory. We have obtained optical and near-infrared spectra of 44 sources that exhibit red Spitzer colors that are indicative of stars with circumstellar disks and 51 candidate young stars that were identified by Scelsi and coworkers using XMM-Newton. We also performed spectroscopy on four possible companions to members of Taurus that were reported by Kraus and Hillenbrand. Through these spectra, we have demonstrated the youth and membership of 41 sources, 10 of which were independently confirmed as young stars by Scelsi and coworkers. Five of the new Taurus members are likely to be brown dwarfs based on their late spectral types (>M6). One of the brown dwarfs has a spectral type of L0, making it the first known L-type member of Taurus and the least massive known member of the region (M ∼ 4-7 M Jup). Another brown dwarf exhibits a flat infrared spectral energy distribution, which indicates that it could be in the protostellar class I stage (star+disk+envelope). Upon inspection of archival images from various observatories, we find that one of the new young stars has a large edge-on disk (r = 2. ′′ 5 = 350 AU). The scattered light from this disk has undergone significant variability on a time scale of days in optical images from the Canada-France-Hawaii Telescope. Using the updated census of Taurus, we have measured the initial mass function for the fields observed by XMM-Newton. The resulting mass function is similar to previous ones that we have reported for Taurus, showing a surplus of stars at spectral types of K7-M1 (0.6-0.8 M ⊙) relative to other nearby star-forming regions like IC 348, Chamaeleon I, and the Orion Nebula Cluster.

Astronomy and Astrophysics Supplement Series, 1999

We present the results of a deep CCD-based IZ photometric survey of a ∼ 1 deg 2 area in the central region of the Pleiades Galactic open cluster. The magnitude coverage of our survey (from I ∼ 17.5 down to 22) allows us to detect substellar candidates with masses between 0.075 and 0.03 M. Details of the photometric reduction and selection criteria are given. Finder charts prepared from the I-band images are provided.

Monthly Notices of the Royal Astronomical Society, 2012

We present results of a variability search in the intermediate-age open cluster NGC 6866 from 29 nights over two observing seasons. We find 28 periodic variables, of which 19 are newly identified. The periods of these variables, which have V magnitudes from 11.5 to 19.3 mag, range from ∼ 48 min to 37 d. We detected several δ-Scuti stars, some of which are of high amplitude, as well as γ-Doradus, rotational variables and eclipsing binaries. In order to study the physical properties of the cluster, we obtained U BV RI photometry of all the stars on a good photometric night. The radial distribution of the stellar surface density shows that the cluster has a radial extent of about 7 arcmin (∼ 3 pc) with a peak density of 5.7 ± 0.7 stars/arcmin 2 at the cluster center. The colour-colour diagram indicates a reddening of E(B − V ) = 0.10 mag towards NGC 6866. A distance of ∼1.47 kpc and an age of ∼ 630 Myr is estimated from the colour-magnitude diagram using the theoretical isochrones of solar metallicity.