A Search for L Dwarf Binary Systems

By I. Neill Reid, J. Gizis, J. D. Kirkpatrick, D. Koerner. 2000

196 citations recorded by the source corpus.

We present analysis of Hubble Space Telescope (HST) planetary camera images of 20 L dwarfs identified in the course of the Two Micron All Sky Survey. Four of the targets, 2MASSW J0746425+200032, 2MASSs J0850359+105716, 2MASSW J0920122+351742, and 2MASSW J1146345+223053, have faint red companions at separations between 0.″07 and 0.″29 (1.6–7.6 AU). Ground-based infrared imaging confirms the last as a common proper motion companion. The surface density of background sources with comparable colors is extremely low, and we identify all four as physical binaries. In three cases, the bolometric magnitudes of the components differ by less than 0.3 mag. Since the cooling rate for brown dwarfs is a strong function of mass, similarity in luminosities implies comparable masses. The faint component in the 2M0850 system, however, is over 1.3 mag fainter than the primary in the I band and ∼0.8 mag fainter in Mbol. Indeed, 2M0850B is ∼0.8 mag fainter in I than the lowest luminosity L dwarf currently known, while the absolute magnitude we deduce at J is almost identical with MJ for Gl 229B. We discuss the implications of these results for the temperature scale in the L/T transition region. 2M0850 is known to exhibit 6708 Å Li I absorption, indicating that the primary has a mass less than 0.06 M⊙. Theoretical models predict that the magnitude difference implies a mass ratio of ≈0.75. The apparent binary fraction of the current sample, 20%, is comparable to the results of previous surveys of late-type M dwarfs in the field and in the Hyades. However, the mean separation of the L dwarf binaries in the current sample is smaller than the M dwarf value by a factor of 2, and only one system would be detected at the distance of the Hyades. We discuss the likely binary frequency among L dwarfs in light of these new data.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/430c6810460c5bc985c93212325838683b2c8d2d

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Citations in the corpus

Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition (2006, methodology): “…of T dwarf binaries as compared to warmer M- and L-type brown dwarf systems is consistent with a maximum binary separation that scales with total systemmass (Reid et al. 2001; Burgasser et al. 2003c; Close et al. 2003), since cooler brown dwarfs have lower masses than warmer ones at a given age.”
MID-INFRARED PHOTOMETRY OF COLD BROWN DWARFS: DIVERSITY IN AGE, MASS, AND METALLICITY (2010, unknown): “…(2010); Bouy et al. (2003); Burgasser et al. (2003a, 2005, 2006c); Freed et al. (2003); Golimowski et al. (2004b); Heintz (1972); Koerner et al. (1999); Liu & Leggett (2005); Liu et al. (2006, 2010, and in preparation); Martin, Brandner and Basri (1999a); Reid et al. (2001); Stumpf et al. (2005).”
The Formation of Brown Dwarfs as Ejected Stellar Embryos (2001, background): “Binary Brown Dwarfs As more brown dwarfs become known and more detailed studies of individual objects are undertaken, the number of known brown dwarfs paired in binaries is certain to increase (e.g. Martı́n et al. 2000; Reid et al. 2001).”
MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS–AURIGA (2011, background): “Since migration typically moves companions inward, the massdependent maximum separation for binary systems (Reid et al. 2001; Burgasser et al. 2003; Kraus & Hillenbrand 2009a) could then be interpreted as a denoting the separation regime at which disk fragmentation occurs: ∼100 AU for early M…”
THE IMPACT OF STELLAR MULTIPLICITY ON PLANETARY SYSTEMS. I. THE RUINOUS INFLUENCE OF CLOSE BINARY COMPANIONS (2016, background): “The small number of targets with M<0.5 Me might have fewer companions at 500 au (e.g., Reid et al. 2001; Burgasser et al. 2003), but the companion frequency per dex of semimajor axis is remarkably constant in the 500 au regime across the mass range our entire sample (Duchêne & Kraus 2013).”
FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME (2015, unknown): “…(2007), (26) Luyten (1979a), (27) Dieterich et al. (2014), (28) Geballe et al. (2002), (29) Hawley et al. (2002), (30) Naud et al. (2014), (31) Reid et al. (2001), (32) Cruz et al. (2003), (33) Kirkpatrick et al. (2006), (34) K. Cruz et al. (2015, in preparation), (35) J. Faherty et al.…”
Hubble Space Telescope Observations of Binary Very Low Mass Stars and Brown Dwarfs (2003, methodology): “’’ Ten L dwarf systems in this study and Reid et al. (2001) have spectroscopic detections of lithium, placing them below the lithium-burning limit ( 0.055M ).7 Three are doubles.”
SpeX SPECTROSCOPY OF UNRESOLVED VERY LOW MASS BINARIES. I. IDENTIFICATION OF 17 CANDIDATE BINARIES STRADDLING THE L DWARF/T DWARF TRANSITION (2009, background): “However, many L dwarfs have never been typed in the near-infrared, and those with nearinfrared types have been classified following different schemes (e.g., Reid et al. 2001a; Testi et al. 2001; McLean et al. 2003; Nakajima et al. 2004; Burgasser 2007a).”
The formation of a star cluster: predicting the properties of stars and brown dwarfs (2002, background): “Both Reid et al. (2001) and Close et al. (2002) observed 20 brown dwarf primaries and found that 4 have companions giving binary frequencies of ≈ 20%.”
THE ORIGIN OF BINARY STARS (2002, methodology): “These include HST (WFPC2 & NICMOS) imaging (Padgett et al. 1997, 1999; Reid et al. 2001), submillimeter imaging (Smith et al. 2000), optical and infrared long-baseline interferometry (Quirrenback 2001a,b), millimeter and submillimeter interferometry (Launhardt et al. 2000, Launhardt 2001,…”
Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program (2004, methodology): “One is 2MASS J085035+1057, which is a binary of 0.16 arcsec separation (Reid et al. 2001, discussed in §15.4) and for which the IR and CCD programs also derive marginally different proper motion position angles.”
The formation mechanism of brown dwarfs (2002, background): “Reid et al. (2001) find that four out of 20 brown dwarf primaries have companions giving a fraction of <20 per cent.”
Infrared Parallaxes for Methane T Dwarfs (2003, methodology): “…for known binaries Several of the systems published in the photometric compilations listed above are known to be binaries, having been resolved either from the ground (Koerner et al. 1999; Leggett et al. 2001), or using HST (Martıǹ, Brander & Basri 1999; Reid et al. 2001; Burgasser et al. 2003a).”
Low-Luminosity Companions to White Dwarfs (2005, background): “For these low mass primaries, the binary fraction is estimated to be ∼ 20% (Reid et al. 2001; Close et al. 2002; Siegler et al. 2003; Burgasser et al. 2003).”