Binaries and the L Dwarf/T Dwarf Transition

By A. Burgasser. 2006

163 citations recorded by the source corpus.

High-resolution imaging has revealed an unusually high binary fraction among objects spanning the transition between the L dwarf and T dwarf spectral classes. In an attempt to reproduce and unravel the origins of this apparent binary excess, I present a series of Monte Carlo mass function and multiplicity simulations of field brown dwarfs in the vicinity of the Sun. These simulations are based on solar metallicity brown dwarf evolutionary models and incorporate empirical luminosity and absolute magnitude scales, measured multiplicity statistics, and observed spectral templates in the construction and classification of composite binary spectra. In addition to providing predictions for the number and surface density distributions of L and T dwarfs for volume-limited and magnitude-limited samples, these simulations successfully reproduce the observed binary fraction distribution assuming an intrinsic (resolved) binary fraction of 11% (95% confidence interval), consistent with prior determinations. However, the true binary fraction may be as high as 40% if, as suggested by Liu et al., a significant fraction of L/T transition objects (~66%) are tightly bound, unresolved multiples. The simulations presented here demonstrate that the binary excess among L/T transition objects arises primarily from the flattening of the luminosity scale over these spectral types and is not inherently the result of selection effects incurred in current magnitude-limited imaging samples. Indeed, the existence of a binary excess can be seen as further evidence that brown dwarfs traverse the L/T transition rapidly, possibly driven by a nonequilibrium submergence of photospheric condensates.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0897f619665ca69adf62c771ce02e553f89d5735

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In Astronomy and Astrophysics

1. Michael C. Liu
2. T. Dupuy
3. A. Burgasser
4. J. D. Kirkpatrick
5. Kelle Cruz
6. K. Luhman
7. K. Allers
8. M. Marley

In Instrumentation

1. Michael C. Liu
2. A. Burgasser
3. T. Dupuy
4. J. D. Kirkpatrick
5. Kelle Cruz
6. K. Allers
7. K. Luhman
8. M. Marley

Citations in the corpus

• THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, methodology): “…spectral types for the three late-L and early-T dwarfs in our sample (WISE J0206+2640, CFHT-Hy-20 and WISE J0754+7909), we compute the set of flux indices defined by Burgasser et al. (2006) and assign spectral types to each resulting index based on the Burgasser (2007) polynomial fits (Table 5).”
• FURTHER DEFINING SPECTRAL TYPE “Y” AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION (2012, background): “Also plotted are the results of luminosity function simulations by Burgasser (2007) (based on earlier work by Burgasser et al. 2004) that show the expected distribution of objects for power-law mass functions with various slopes of α, the functional form of which is given by dN/dM ∝ M−α, where N is…”
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams (2008, background): “The importance of binaries in brown dwarf population synthesis has been pointed out by Chabrier (2002) and Burgasser (2007).”
• THE BROWN DWARF KINEMATICS PROJECT I. PROPER MOTIONS AND TANGENTIAL VELOCITIES FOR A LARGE SAMPLE OF LATE-TYPE M, L, AND T DWARFS (2008, methodology): “Both optical 2The coefficients of this polynomial relation reported in Burgasser (2007) did not list sufficient significant digits, yielding a slightly different numerical relation than that used in the paper’s analysis.”
• THE HAWAII INFRARED PARALLAX PROGRAM. I. ULTRACOOL BINARIES AND THE L/T TRANSITION, (2012, methodology): “The strongest cases are SDSS J0805+4812AB and 2MASS J1404−3159AB, with 2MASS J0518−2828AB showing smaller residual scatter that we also tentatively attribute to orbital motion.”
• Discovery of Two Nearby Peculiar L Dwarfs from the 2MASS Proper-Motion Survey: Young or Metal-Rich? (2008, background): “Also, no known combination of L+L or L+T dwarfs can reproduce the triangular-shaped H-band present in the spectra of 2MASS J1821+1414 and 2MASS J2148+4003 (See Figure 4 of Burgasser 2007), so we must account for these features in some other way.”
• MEETING THE COOL NEIGHBORS. X. ULTRACOOL DWARFS FROM THE 2MASS ALL-SKY DATA RELEASE (2008, methodology): “Most lack trigonometric parallaxes, so we have used the (MK , spectral type) relation derived by Burgasser (2007a) to estimate spectroscopic parallaxes.”
• WEATHER ON OTHER WORLDS. II. SURVEY RESULTS: SPOTS ARE UBIQUITOUS ON L AND T DWARFS (2014, background): “There are two additional candidate binaries, both identified in the literature through the spectral decomposition technique (Burgasser 2007).”
• Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839–0446358 (2008, methodology): “The low luminosity of the secondary, log10 Lbol/L⊙ = -5.0±0.3 dex based on its inferred spectral type (Golimowski et al. 2004; Burgasser 2007b), suggests that 2MASS J0320−0446 could have a relatively low system mass ratio (q ≡ M2/M1).”
• SpeX SPECTROSCOPY OF UNRESOLVED VERY LOW MASS BINARIES. I. IDENTIFICATION OF 17 CANDIDATE BINARIES STRADDLING THE L DWARF/T DWARF TRANSITION (2009, methodology): “Average component types of T1±0.2 and T5±0.6 indicate a secondary component that may be slightly brighter than the primary at the 1.27 µm spectral flux peak (∆J = 0.06±0.24).”