M dwarf/L dwarf Binaries Resolved with SpeX

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M dwarf/L dwarf Binaries Resolved with SpeX

• Adam J. Burgasser (MIT)
• Michael W. McElwain (UCLA)

Resolved Spectroscopy of M Dwarf/L Dwarf
Binaries. I. DENIS J220002.05-303832.9AB Burgasse
r McElwain 2006, AJ, 131, 1007 Resolved
Spectroscopy of M Dwarf/L Dwarf Binaries. II.
2MASS J17072434-0558249AB McElwain Burgasser
2006, AJ, submitted
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M dwarfs and L dwarfs are stellar spectroscopic
classes encompassing the lowest temperature,
lowest mass Hydrogen burning stars.At the
transition between these classes (Teff 2400 K),
gases such as TiO, VO and Fe condense into solid
and liquid grains (e.g., perovskite, enstatite
e.g., Lodders 1999), forming floating clouds of
dirt. The process of cloud formation (e.g.,
Ackerman Marley 2001) and the properties of
these clouds remains controversial, but they do
have a profound impact on the spectral properties
and atmospheric chemistry of L dwarfs.
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J
H
K
J
J
2MASS 1707-0558AB
H
DENIS 2200-3038AB
K
As part of a program to obtain low resolution,
near infrared spectra of late-type stars and
brown dwarfs with SpeX, we uncovered two M
dwarf/L dwarf binaries with separations of
roughly 1 arcsecond 2MASS 1707-0558AB and DENIS
2200-3038AB
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The pairs were both sufficiently resolved to
obtain spectra of their individual components.
These are among the few low mass binaries with
resolved spectroscopy of any kind.
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Spectra were classified by comparison to NIR
spectral standards 2MASS 1707-0558AB is an M9L3
binary, DENIS 2200-3038AB is an M9L0 binary
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Optical spectroscopy of 2MASS 1707-0558AB shows
no signature of the 6708 Å Li I line, implying
that the primary component must have a mass gt
0.065 Msun. This provides a constraint on the
age of the system and mass of the secondary.
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With projected separations of 17 and 38 AU, these
systems are relatively wide compared to most very
low mass binary systems, which are generally
separated by 20 AU or less. However, if the
maximum separation of binaries is mass-dependent,
these systems match a trend amax 1400xMtot2 AU
previously identified amongst brown dwarf
binaries (Burgasser et al. 2003).As presumably
coeval pairs, 2MASS 1707-0558AB and DENIS
2200-3038AB are valuable new probes of
atmospheric processes across the M dwarf/L dwarf
transition.
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Breaking News!
We have uncovered a new L dwarf binary selected
from a near infrared proper motion survey using
2MASS data. 2MASS 1520-4422 is composed of an
L1.5L4.5 with a 1.17 separation. Like 2MASS
1707-0558 and DENIS 2200-3038, it is a prime
source for resolved spectroscopic studies tracing
trends across the M and L dwarf regime.
Burgasser, Looper, Kirkpatrick Liu 2006, AJ,
submitted