Astronomy and Astrophysics, volume 458, 805-816 (2006/11-2)
Pleiades low-mass brown dwarfs: the cluster L dwarf sequence.
BIHAIN G., REBOLO R., BEJAR V.J.S., CABALLERO J.A., BAILER-JONES C.A.L., MUNDT R., ACOSTA-PULIDO J.A. and MANCHADO TORRES A.
Abstract (from CDS):
We present a search for low-mass brown dwarfs in the Pleiades open cluster. The identification of Pleiades members fainter and cooler than those currently known allows us to constrain evolutionary models for L dwarfs and to extend the study of the cluster mass function to lower masses. We conducted a 1.8deg2
near-infrared J-band survey at the 3.5 m Calar Alto Telescope, with completeness Jcpl
∼19.0. The detected sources were correlated with those of previously available optical I-band images (Icpl
∼22). Using a J versus I-J colour-magnitude diagram, we identified 18 faint red L-type candidates, with magnitudes 17.4<J<19.7 and colours I-J>3.2. If Pleiades members, their masses would span ∼0.040-0.020M☉
. We performed follow-up HKs
-band imaging to further confirm their cluster membership by photometry and proper motion. Out of 11 IJ candidates with proper motion measurements, we find six cluster members, two non-members and three whose membership is uncertain and depends on the intrinsic velocity dispersion of Pleiades brown dwarfs. This dispersion (>4mas/yr) is at least four times that of cluster stars with masses >1M☉
. Five of the seven other IJ candidates are discarded because their J-Ks
colours are bluer than those of confirmed members. Our least massive proper motion members are BRB 28
). The J versus I-J sequence of the L-type candidates at J>18 is not as red as theoretical models predict; it rather follows the field L-dwarf sequence translated to the cluster distance. This sequence overlapping, also observed in the J versus J-H and J-K diagrams, suggests that Pleiades and field L dwarfs may have similar spectral energy distributions and luminosities, and thus possibly similar radii. Also, we find α=0.5±0.2 for a power-law approximation dN/dM ∝M–α
of the survey mass spectrum in the mass range 0.5-0.026M☉
. This value is similar to that of much younger clusters, indicating no significant differential evaporation of low-mass Pleiades members relative to more massive ones.
galaxies: clusters: individual: Pleiades - stars: low-mass, brown dwarfs - stars: luminosity function, mass function
Table 1: Cl* Melotte 22 BRB NN (Nos 1-34).
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