Pleiades low-mass brown dwarfs: the cluster L dwarf sequence
Pleiades low-mass brown dwarfs: the cluster L dwarf sequence
复制标题
昴宿星团低质量褐矮星：L型矮星团序列
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
A. Torres
中科院分区：
文献类型：
--
作者：
G. Bihain;R. Rebolo;V. Béjar;J. Caballero;C. Bailer;R. Mundt;J. Acosta;A. Torres
Aims. 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. Methods. We conducted a 1.8 deg 2 near-infrared J -band survey at the 3.5 m Calar Alto Telescope, with completeness $J_{
m cpl}sim 19.0$. The detected sources were correlated with those of previously available optical I -band images ($I_{
m cpl}sim 22$). Using a J versus $I-J$ colour–magnitude diagram, we identified 18 faint red L-type candidates, with magnitudes $17.4 3.2$. If Pleiades members, their masses would span ~$0.040{-}0.020~M_{odot}$. We performed follow-up HK s -band imaging to further confirm their cluster membership by photometry and proper motion. Results. 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 $M_{odot}$. Five of the seven other IJ candidates are discarded because their $J-K_{
m s}$ colours are bluer than those of confirmed members. Our least massive proper motion members are BRB 28 and 29 (~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 $alpha= 0.5pm0.2$ for a power-law approximation ${
m d}N/{
m d}M propto M^{-alpha}$ of the survey mass spectrum in the mass range $0.5{-}0.026~M_{odot}$. 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.
Aims. 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. Methods. We conducted a 1.8 deg 2 near-infrared J -band survey at the 3.5 m Calar Alto Telescope, with completeness $J_{
m cpl}sim 19.0$. The detected sources were correlated with those of previously available optical I -band images ($I_{
m cpl}sim 22$). Using a J versus $I-J$ colour–magnitude diagram, we identified 18 faint red L-type candidates, with magnitudes $17.4 3.2$. If Pleiades members, their masses would span ~$0.040{-}0.020~M_{odot}$. We performed follow-up HK s -band imaging to further confirm their cluster membership by photometry and proper motion. Results. 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 $M_{odot}$. Five of the seven other IJ candidates are discarded because their $J-K_{
m s}$ colours are bluer than those of confirmed members. Our least massive proper motion members are BRB 28 and 29 (~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 $alpha= 0.5pm0.2$ for a power-law approximation ${
m d}N/{
m d}M propto M^{-alpha}$ of the survey mass spectrum in the mass range $0.5{-}0.026~M_{odot}$. 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.