Publications (5)0 Total impact
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ABSTRACT: Knowledge of the mass function in open clusters constitutes one way to
constrain the formation of low-mass stars and brown dwarfs as does the
knowledge of the frequency of multiple systems and the properties of disks. The
aim of the project is to determine the shape of the mass function in the
low-mass and substellar regimes in the pre-main sequence (27 Myr) cluster
IC4665, which is located at 350 pc from the Sun. We have cross-matched the
near-infrared photometric data from the Eighth Data Release of the UKIRT
Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey with previous
optical data obtained with the Canada-France-Hawaii wide-field camera to
improve the determination of the luminosity and mass functions in the low-mass
and substellar regimes. The availability of i and z photometry taken with the
CFH12K camera on the Canada France Hawaii Telescope added strong constraints to
the UKIDSS photometric selection in this cluster, which is located in a dense
region of our Galaxy. We have derived the luminosity and mass functions of the
cluster down to J=18.5 mag, corresponding to masses of ~0.025 Msun at the
distance and age of IC4665 according to theoretical models. In addition, we
have extracted new candidate members down to ~20 Jupiter masses in a previously
unstudied region of the cluster. We have derived the mass function over the
0.6-0.04 Msun mass range and found that it is best represented by a log-normal
function with a peak at 0.25-0.16 Msun, consistent with the determination in
the Pleiades.
06/2011;
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ABSTRACT: The so-called lithium depletion boundary (LDB) provides a secure and independent tool for deriving the ages of young open clusters.In this context, our goal is to determine membership for a sample of 147 photometrically selected candidates of the young open cluster IC 4665 and to use confirmed members to establish an age based on the LDB. Employing the FLAMES multi-object spectrograph on VLT/UT2, we have obtained intermediate-resolution spectra of the cluster candidates. The spectra were used to measure radial velocities and to infer the presence of the Li I 670.8 nm doublet and Halpha emission. We have identified 39 bona fide cluster members based on radial velocity, Halpha emission, and Li absorption. The mean radial velocity of IC 4665 is found to be vrad=-15.95 +/- 1.13 km/s. Confirmed cluster members display a sharp transition in magnitude between stars with and without lithium, both in the Im vs. Im-z and in the Ks vs. Im-Ks diagrams.From this boundary, we deduce a cluster age of 27.7^(+4.2)_(-3.5) +/- 1.1 +/- 2 Myr. IC 4665 is the fifth cluster for which an LDB age has been determined, and it is the youngest cluster among these five. Thus, the LDB is established from relatively bright stars still in the contracting pre-main sequence phase. The mass of the boundary is M*=0.24 +/- 0.04 Msun. The LDB age agrees well with the ages derived from isochrone fitting of both low and high mass, turn-off stars, a result similar to what is found in the slightly older NGC 2547. Comment: 13 pages, A&A in press
12/2007;
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ABSTRACT: We present the first deep, optical, wide-field imaging survey of the young open cluster Collinder 359, complemented by near-infrared follow-up observations. This study is part of a large programme aimed at examining the dependence of the mass function on environment and time. We have surveyed 1.6 square degrees in the cluster, in the I and z filters, with the CFH12K camera on the Canada-France-Hawaii 3.6-m telescope down to completeness and detection limits in both filters of 22.0 and 24.0 mag, respectively. Based on their location in the optical (I-z,I) colour-magnitude diagram, we have extracted new cluster member candidates in Collinder 359 spanning 1.3-0.03 Msun assuming an age of 60 Myr and a distance of 450 pc for the cluster. We have used the 2MASS database as well as our own near-infrared photometry to examine the membership status of the optically-selected cluster candidates. Comparison of the location of the most massive members in Collinder 359 in a (B-V,V) diagram with theoretical isochrones suggests that Collinder 359 is older than Alpha Per but younger than the Pleiades. We discuss the possible relationship between Collinder 359 and IC 4665 as both clusters harbour similar parameters, including proper motion, distance, and age. Comment: 13 pages, 9 figures, 4 tables, Table 4 only available in electronic format, accepted for publication in A&A on 30 Dec 2005
01/2006;
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W. J. de Wit,
J. Bouvier,
F Palla,
J. -C. Cuillandre,
D. J. James,
T. R. Kendall,
N. Lodieu,
M. J. McCaughrean,
E. Moraux,
S. Randich,
L. Testi
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ABSTRACT: We present a study of the young (30-100Myr) open cluster IC 4665 with the aim to determine the shape of the mass function well into the brown dwarf regime. We photometrically select 691 low-mass stellar and 94 brown dwarf candidate members over an area of 3.82 square degrees centred on the cluster. K-band follow-up photometry and Two-Micron All-Sky Survey data allow a first filtering of contaminant objects from our catalogues. A second filtering is performed for the brightest stars using proper motion data provided by the Tycho-2 and UCAC2 public catalogues. Contamination by the field population for the lowest mass objects is estimated using same latitude control fields. We fit observed surface densities of various cluster populations with King profiles and find a consistent tidal radius of 1.0 degree. The presence of possible mass segregation is discussed. In most respects investigated, IC 4665 is similar to other young open clusters at this age: (1) a power law fit to the mass function between 1 and 0.04Msun results in best fit for a slope of -0.6; (2) a cusp in the mass function is noticed at about the substellar boundary with respect to the power law description, the interpretation of which is discussed; (3) a fraction between 10-19% for BDs with M > 0.03Msun to total members; (4) a best-fit lognormal function to the full mass distribution shows an average member mass of 0.32Msun, if IC 4665 has an age of 50Myr. Comment: 14 pages, 13 figures. Accepted for publication in A&A. Catalogue with candidate members at CDS
11/2005;
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ABSTRACT: We have performed intermediate resolution (R = 5000), high signal-to-noise H-band spectroscopy of a small, initial sample of three massive embedded young stellar objects (YSOs), using VLT/ISAAC. The sample has been selected from sources characterised in previous literature as being likely of OB spectral type, to be unambiguously associated with bright (H < 14) single point sources in the 2MASS database, and to have no optical counterparts. Of the targets observed, one object shows a ~B3 spectrum, similar to a main sequence object of the same spectral type. A second object exhibits weak HeI and H emission, indicating an early-type source: we detect HeII absorption, which supports a previous indirect derivation of the spectral type as mid-O. The third object does not show absorption lines, so no spectral type can de derived. It does, however, exhibit a rich spectrum of strong, broad emission lines and is likely to be surrounded by dense circumstellar material and at a very early evolutionary stage. Our results from this very small sample are in agreement with those of Kaper et al. (2002), who also find spectra similar to optically visible main sequence stars, together with emission line objects representing a very early evolutionary phase, in their much larger sample of K-band spectra. Comment: 10 pages, 14 figures, A&A (accepted)
04/2003;
