J/ApJ/710/1142 SpeX spectroscopy of low mass binaries. I. (Burgasser+, 2010)
SpeX spectroscopy of unresolved very low mass binaries.
I. Identification of 17 candidate binaries straddling the L dwarf/T dwarf
transition.
Burgasser A.J., Cruz K.L., Cushing M., Gelino C.R., Looper D.L.,
Faherty J.K., Kirkpatrick J.D., Reid I.N.
<Astrophys. J., 710, 1142-1169 (2010)>
=2010ApJ...710.1142B 2010ApJ...710.1142B
ADC_Keywords: Binaries, spectroscopic ; Photometry, infrared ; Spectral types ;
Stars, late-type ; Spectra, infrared
Keywords: binaries: general - brown dwarfs - stars: fundamental parameters -
stars: low-mass
Abstract:
We report the identification of 17 candidate brown dwarf binaries
whose components straddle the L dwarf/T dwarf transition. These
sources were culled from a large near-infrared spectral sample of L
and T dwarfs observed with the Infrared Telescope Facility SpeX
spectrograph. Candidates were selected on the basis of spectral ratios
which segregate known (resolved) L dwarf/T dwarf pairs from presumably
single sources. Composite templates, constructed by combining 13581
pairs of absolute flux-calibrated spectra, are shown to provide
statistically superior fits to the spectra of our 17 candidates as
compared to single templates. Ten of these candidates appear to have
secondary components that are significantly brighter than their
primaries over the 1.0-1.3um band, indicative of rapid condensate
depletion at the L dwarf/T dwarf transition. Our results support prior
indications of enhanced multiplicity amongst early-type T dwarfs;
53±7% of the T0-T4 dwarfs in our spectral sample are found to be
either resolved or unresolved (candidate) pairs, although this is
consistent with an intrinsic (volume complete) brown dwarf binary
fraction of only 15%. If verified, this sample of spectral binaries
more than doubles the number of known L dwarf/T dwarf transition
pairs, enabling a broader exploration of this poorly understood phase
of brown dwarf atmospheric evolution.
Description:
Our analysis is based on a large sample of low-resolution,
near-infrared spectra of L and T dwarfs obtained with SpeX, a
low-resolution, 0.8-5.4um spectrograph mounted on the 3m NASA Infrared
Telescope Facility. Ninety-nine L and T dwarfs were observed by the
authors over several runs spanning 2004 September through 2008
September, as summarized in Table 1.
In addition to our new observations, we compiled from the literature
SpeX observations of 134 L and T dwarfs with published optical and/or
near-infrared spectral types spanning L3 to T8 and with data having
median signal-to-noise ratios of 20 or greater over the 0.9-2.4um
window.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 99 98 New SpeX spectral observations
table2.dat 91 175 Spectral templates
table6.dat 73 20 Binary candidates
table10.dat 121 20 Summary of binary candidates
refs.dat 71 55 References
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/A+A/497/619 : New ultra-cool dwarfs from SDSS and 2MASS (Zhang+, 2009)
J/ApJ/676/1281 : L and T dwarfs in 2MASS/SDSS (Metchev+, 2008)
J/AJ/136/1290 : Ultracool dwarfs from the 2MASS (Reid+, 2008)
J/ApJ/689/1295 : Lithium test implications for brown dwarfs (Kirkpatrick+,
2008)
J/AJ/134/1162 : 11 new T dwarfs in 2MASS (Looper+, 2007)
J/AJ/133/439 : Luminosity function of M7-L8 ultracool dwarfs (Cruz+, 2007)
J/ApJ/637/1067 : Near-IR spectral classification of T dwarfs (Burgasser+, 2006)
J/AJ/131/2722 : New L and T dwarfs from the SDSS (Chiu+, 2006)
J/PASP/118/659 : RI photometry of 2MASS late M and L dwarfs (Liebert+, 2006)
J/AJ/127/3553 : JHK photometry and spectroscopy for L and T dwarfs (Knapp+,
2004)
J/AJ/127/2856 : Brown dwarfs in the 2MASS Survey (Burgasser+, 2004)
J/AJ/126/2487 : T dwarfs in the southern hemisphere (Burgasser+, 2003)
J/AJ/126/2421 : 2MASS-Selected sample of ultracool dwarfs (Cruz+, 2003)
J/AJ/125/3302 : HST binary very low mass stars and brown dwarfs (Gizis+, 2003)
J/ApJ/564/421 : Spectra of T dwarfs. I. (Burgasser+, 2002)
J/AJ/123/3409 : SDSS M, L, and T dwarfs (Hawley+, 2002)
http://www.vlmbinaries.org/ : Very low-mass binaries archive online
http://pono.ucsd.edu/~adam/browndwarfs/spexprism/ : The SpeX Prism spectral
libraries
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 27 A27 --- Name Source name
29- 32 A4 --- OSpT Optical MK spectral type
34- 37 A4 --- NSpT Near-IR MK spectral type
39- 41 F3.1 --- e_NSpT ? NSpT uncertainty
43 A1 --- l_Jmag Limit flag on Jmag
45- 49 F5.2 mag Jmag 2MASS Johnson J band magnitude
51- 54 F4.2 mag e_Jmag ? Uncertainty in Jmag
56- 65 A10 "YYYY/MM/DD" Date UT date of the observation
67- 69 A3 --- Obs Observer initials
71- 74 I4 s Exp Exposure time
76- 78 F3.1 arcsec Slit Slit size
80- 83 F4.2 --- Air Airmass
85- 99 A15 --- Cal Calibration star
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Name Source name
29- 30 A2 --- f_Name [b-f ] Flag(s) on Name (1)
32- 35 A4 --- OSpT Optical MK spectral type
37- 40 A4 --- NSpT Near-IR MK spectral type
42- 44 F3.1 --- e_NSpT ? NSpT uncertainty
46- 49 A4 --- SSpT SpeX MK spectral type
51 I1 --- e_SSpT ? SSpT uncertainty
53- 57 F5.2 mag Jmag 2MASS Johnson J band magnitude
59- 62 F4.2 mag e_Jmag Uncertainty in Jmag
64 A1 --- f_Jmag [e] Flag on Jmag (1)
66 A1 --- l_J-Ks Limit flag on J-Ks
68- 72 F5.2 mag J-Ks 2MASS (J-Ks) color index
74- 77 F4.2 mag e_J-Ks ? Uncertainty in J-Ks
79 A1 --- f_J-Ks [e] Flag on J-Ks (1)
81- 91 A11 --- Ref References (see refs.dat file) (2)
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Note (1): Flag as follows:
b = Source satisfied one spectral index selection criterion, used as a
template for spectral fitting.
c = Source satisfied two or more spectral index selection criteria
(Table 7) and not used as a template for spectral fitting.
d = Optical, near-infrared and/or SpeX classifications deviate by two
subtypes or more.
e = Undetected in 2MASS; photometry on the Mauna Kea Observatory (MKO)
system (Knapp et al. 2004, Cat. J/AJ/127/3553).
f = 2MASSI J1546291-332511 is a misprint for 2MASSI J1546271-332511;
flag added by CDS.
Note (2): Data reference followed by references for discovery, optical
spectral type and near-infrared spectral type, where available.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Set [Sg/Wk] Sg: strong vs Wk: weak candidates
4- 27 A24 --- Name Source name (1)
29- 32 A4 --- OSpT Optical MK spectral type
34- 37 A4 --- NSpT Near-IR MK spectral type
39- 41 F3.1 --- e_NSpT ? NSpT uncertainty
43- 46 A4 --- SSpT SpeX MK spectral type
48 I1 --- e_SSpT ? SSpT uncertainty
50- 54 F5.2 mag Jmag 2MASS J-band magnitude
56- 59 F4.2 mag e_Jmag Jmag uncertainty
61 A1 --- l_J-Ks Limit flag on J-Ks
62- 66 F5.2 mag J-Ks 2MASS J-Ks color index
68- 71 F4.2 mag e_J-Ks ? J-Ks uncertainty
73 I1 --- C [2,6] Number of selection criteria satisfied (2)
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Note (1): In tables 6 and 10, 2MASS J13243559+6358284 is a misprint for
2MASS J13243553+6358281; corrected at CDS.
Note (2): We identified six pairings that best segregated known L dwarf/T
dwarf binaries from the bulk of the spectral sample, as shown in
Figure 4. These pairings reflect peculiar traits, in particular the
strength of the H-band CH4 feature (CH4-K versus CH4-H and H-dip
versus H2O-H), the unusual brightness of the J-band peak (H2O-K
versus H2O-J, H2O-J/H2O-H and H2O-J/CH4-K versus spectral
type), and blue near-infrared colors (K/J versus CH4-H).
See section 3.2 for further explanations.
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Byte-by-byte Description of file: table10.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Class [Pbl/Oth] Pbl: Probable binaries or Oth: Other
sources
5- 28 A24 --- Name Source name (1)
30- 33 A4 --- SpT1p Published MK spectral type
35- 37 F3.1 --- e_SpT1p ? SpT1p uncertainty
39- 42 A4 --- SpT2p SpeX MK spectral type (3)
44 I1 --- e_SpT2p ? SpT2p uncertainty
46- 49 A4 --- SpT1 Primary MK spectral type
51- 53 F3.1 --- e_SpT1 SpT1 uncertainty
55- 58 A4 --- SpT2 Secondary MK spectral type
60- 62 F3.1 --- e_SpT2 SpT2 uncertainty
64- 68 F5.2 mag dJmag Jmag difference between primary and secondary
70- 73 F4.2 mag e_dJmag dJmag uncertainty
75 A1 --- l_CL Limit flag on CL
76- 77 I2 % CL Confidence limit (see Sect. 4.2)
79- 81 A3 --- Obs? [Yes/No ] Near-infrared HST or Keck AO
observations?
82 A1 --- f_Obs? [b] HST observation (4)
84-121 A38 --- Note Notes
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Note (1): In tables 6 and 10, 2MASS J13243559+6358284 is a misprint for
2MASS J13243553+6358281; corrected at CDS.
Note (3): In table 10, SSpT has been corrected (at CDS) to T2.5 as indicated in
text and table 6.
Note (4):
b = HST/WFPC2 observations in the F1042M band by Gizis et al. (2003,
Cat. J/AJ/125/3302) did not have sufficient sensitivity to detect
any putative T dwarf secondary in this system.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Ref Reference code
4- 22 A19 --- BibCode Bibcode
24- 42 A19 --- Aut First author's name
44- 71 A28 --- Comm Comment
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 16-Mar-2012