J/ApJ/705/1416 Volume-limited sample of M7-M9.5 dwarfs <20pc (Reiners+, 2009)
A volume-limited sample of 63 M7-M9.5 dwarfs.
I. Space motion, kinematic age, and lithium.
Reiners A., Basri G.
<Astrophys. J., 705, 1416-1424 (2009)>
=2009ApJ...705.1416R 2009ApJ...705.1416R
ADC_Keywords: Stars, M-type ; Radial velocities ; Stars, dwarfs ;
Space velocities ; Stars, distances
Keywords: stars: kinematics - stars: low-mass, brown dwarfs -
stars: luminosity function, mass function
Abstract:
In a volume-limited sample of 63 ultracool dwarfs of spectral type
M7-M9.5, we have obtained high-resolution spectroscopy with UVES at
the Very Large Telescope and HIRES at Keck Observatory. In this first
paper we introduce our volume-complete sample from DENIS and 2MASS
targets, and we derive radial velocities and space motion. Kinematics
of our sample are consistent with the stars being predominantly
members of the young disk. The kinematic age of the sample is 3.1Gyr.
We find that six of our targets show strong Li lines implying that
they are brown dwarfs younger than several hundred million years. Five
of the young brown dwarfs were unrecognized before. Comparing the
fraction of Li detections to later spectral types, we see a hint of an
unexpected local maximum of this fraction at spectral type M9. It is
not yet clear whether this maximum is due to insufficient statistics,
or to a combination of physical effects including spectral appearance
of young brown dwarfs, Li line formation, and the star formation rate
at low masses.
Description:
This is the first of two papers in which we report on high-resolution
spectroscopy in a volume-complete sample of ultracool M dwarfs. In
this one, we introduce the sample and search for young brown dwarfs
via the lithium test. We derive radial velocities and report space
velocities, from which we derive the kinematic age. We constructed a
sample of known M dwarfs of spectral type M7-M9.5 that is almost
volume-complete (dist<20pc). The targets are taken from several
catalogs and discoveries from the Deep Near Infrared Survey of the
Southern Sky (DENIS) and the Two Micron All Sky Survey (2MASS)
surveys.
Observations for our 63 sample targets were collected using the
High-Resolution Echelle Spectrometer (HIRES) spectrograph at Keck
observatory for targets in the northern hemisphere, and using the
Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large
Telescope at Paranal observatory for targets in the southern
hemisphere (PIDs 080.D-0140 and 081.D-0190). HIRES data were taken
with a 1.15" slit providing a resolving power of R=31000.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 80 63 Sample targets and their space motion
--------------------------------------------------------------------------------
See also:
B/denis : The DENIS database (DENIS Consortium, 2005)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/MNRAS/404/1817 : 2MASS/SDSS data for 806 ultracool dwarfs (Zhang+, 2010)
J/AJ/137/1 : Proper motions and astrometry of late-type dwarfs (Faherty+,
2009)
J/MNRAS/394/857 : UKIDSS-2MASS proper motion survey (Deacon+, 2009)
J/AJ/136/1290 : Ultracool dwarfs from the 2MASS (Reid+, 2008)
J/AJ/133/439 : Luminosity function of M7-L8 ultracool dwarfs (Cruz+, 2007)
J/A+A/446/515 : Distances of nearby ultracool dwarfs (Phan-Bao+, 2006)
J/A+A/441/653 : 32 DENIS nearby red dwarfs (Crifo+, 2005)
J/AJ/126/2421 : 2MASS-Selected sample of ultracool dwarfs (Cruz+, 2003)
J/AJ/126/1526 : IR photometry of ultracool dwarfs (Bouy+, 2003)
J/A+A/401/959 : 35 DENIS late-M dwarfs between 10 and 30pc (Phan-Bao+, 2003)
J/A+A/380/590 : 30 DENIS late-M dwarfs between 15 and 30pc (Phan-Bao+, 2001)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [2MASS]
7- 22 A16 --- Name 2MASS-I name (JHHMMSSs+DDMMSSA) (Cat. II/241)
24- 38 A15 --- OName Other name
40- 43 A4 --- SpT MK spectral type
45- 49 F5.2 mag Jmag Apparent 2MASS J-band magnitude
51- 55 F5.2 pc Dist Spectrophotometric distance (1)
56 A1 --- r_Dist [a-f] Distance reference (2)
58- 60 I3 km/s U Velocity component U
62- 64 I3 km/s V Velocity component V
66- 68 I3 km/s W Velocity component W
70- 74 F5.1 km/s Vrad Radial velocity (Vrad) (3)
76 I1 --- r_Vrad ? Vrad reference (4)
78- 80 A3 --- Note Note about binarity and Li presence (5)
--------------------------------------------------------------------------------
Note (1): The uncertainties of the spectrophotometric distance are
typically on the order of ∼10%.
Note (2): Distance reference as follows:
a = Reiners, A. 2009ApJ...702L.119R 2009ApJ...702L.119R
b = Costa et al. 2005AJ....130..337C 2005AJ....130..337C
c = Costa et al. 2006AJ....132.1234C 2006AJ....132.1234C
d = Lepine et al. 2009AJ....137.4109L 2009AJ....137.4109L
e = Monet et al. 1992, Cat. J/AJ/103/638
f = Bartlett, J.L. 2007PhDT.........2B 2007PhDT.........2B
Note (3): Radial velocities were measured relative to a spectrum of a
standard star. We used Gl 406 as radial velocity standard
(Vrad=19±1km/s; Martin et al. 1997A&A...327L..29M 1997A&A...327L..29M) using the
cross-correlation technique and correcting for barycentric motion.
The typical uncertainty for Vrad is 1-3km/s depending on rotational
line broadening.
Note (4): Proper motion usually taken from Faherty et al. 2009,
Cat. J/AJ/137/1, except for the following references:
1 = Phan-Bao et al. 2001, Cat. J/A+A/380/590;
2 = Phan-Bao et al. 2003, Cat. J/A+A/401/959;
3 = Salim & Gould, 2003, Cat. J/ApJ/582/1011
Note (5): Object type as follows:
Li = lithium brown dwarf;
SB1 = single lined binary;
SB2 = double lined binary.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 06-Dec-2011