Detalles de publicación
PP 06035
Pleiades low-mass brown dwarfs: the cluster L dwarf sequence
(1) IAC, (2) CSIC, (3) GTC Project, (4) MPIA
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 1.8~deg$^2$ near-infrared $J$-band survey at
the 3.5~m Calar Alto Telescope, with completeness
$J_{cpl}\sim$~19.0. The detected sources were correlated with
those of previously available optical $I$-band images
($I_{cpl}\sim$~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 $\sim$0.040--0.020~$M_{\sun}$.
We performed follow-up $HK_{\rm s}$-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 ($>$4~mas~yr$^{-1}$) is at
least four times that of cluster stars with masses
$\ga$1~$M_{\sun}$. Five of the seven other $IJ$ candidates are
discarded because their $J-K_{\rm s}$ colours are bluer than those
of confirmed members. Our least massive proper motion members are
\object{BRB~28} and 29 ($\sim$25~$M_{Jup}$). 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 $\alpha=$~$0.5\pm0.2$ for a power-law
approximation $dN/dM \propto M^{-\alpha}$ of the survey mass
spectrum in the mass range 0.5--0.026~$M_{\sun}$. 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.
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 1.8~deg$^2$ near-infrared $J$-band survey at
the 3.5~m Calar Alto Telescope, with completeness
$J_{cpl}\sim$~19.0. The detected sources were correlated with
those of previously available optical $I$-band images
($I_{cpl}\sim$~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 $\sim$0.040--0.020~$M_{\sun}$.
We performed follow-up $HK_{\rm s}$-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 ($>$4~mas~yr$^{-1}$) is at
least four times that of cluster stars with masses
$\ga$1~$M_{\sun}$. Five of the seven other $IJ$ candidates are
discarded because their $J-K_{\rm s}$ colours are bluer than those
of confirmed members. Our least massive proper motion members are
\object{BRB~28} and 29 ($\sim$25~$M_{Jup}$). 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 $\alpha=$~$0.5\pm0.2$ for a power-law
approximation $dN/dM \propto M^{-\alpha}$ of the survey mass
spectrum in the mass range 0.5--0.026~$M_{\sun}$. 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.