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J/ApJ/564/421 Spectra of T dwarfs. I. (Burgasser+, 2002)
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The spectra of T dwarfs. I. Near-infrared data and spectral classification.
Burgasser A.J., Kirkpatrick J.D., Brown M.E., Reid I.N., Burrows A.,
Liebert J., Matthews K., Gizis J.E., Dahn C.C., Monet D.G., Cutri R.M.,
Skrutskie M.F.
<Astrophys. J. 564, 421 (2002)>
=2002ApJ...564..421B (SIMBAD/NED BibCode)
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ADC_Keywords: Stars, dwarfs ; Spectral types ; Photometry, infrared
Keywords: infrared: stars - stars: fundamental parameters -
stars: low-mass, brown dwarfs - techniques: spectroscopic
Abstract:
We present near-infrared spectra for a sample of T dwarfs, including
11 new discoveries made using the 2 Micron All Sky Survey. These
objects are distinguished from warmer (L-type) brown dwarfs by the
presence of methane absorption bands in the 1-2.5{mu}m spectral
region. A first attempt at a near-infrared classification scheme for T
dwarfs is made, based on the strengths of CH_4_ and H_2_O bands and
the shapes of the 1.25, 1.6, and 2.1{mu}m flux peaks. Subtypes T1 VT8
V are defined, and spectral indices useful for classification are
presented.
Description:
The final confirmation of a candidate object as a T dwarf was made
through the identification of CH_4_ absorption bands in 1-2.5{mu}m
spectral data. Observations were made using the Near Infrared Camera
(NIRC), mounted on the Keck I 10m, a similar instrument, D78, mounted
on the Palomar 5 m Hale Telescope and using OSIRIS, mounted on the
CTIO 4 m Blanco Telescope.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 130 373 2MASS IDR2 Sources Unconfirmed in Second Epoch
Imaging
table4.dat 77 42 Log of NIRC and OSIRIS Observations
table5.dat 89 20 Comparison of NIRC Spectrophotometric colors to
2MASS photometry
table6.dat 66 11 New T Dwarfs Identified in the 2MASS Catalog
table7.dat 81 24 Known T Dwarfs
table10.dat 68 9 Spectral diagnostics for L and T dwarf standards
table11.dat 105 15 T dwarf spectral indices: NIRC and D78 data
table12.dat 105 14 T dwarf spectral indices: OSIRIS data
table13.dat 110 8 T dwarf spectral indices: data from literature
table15.dat 60 20 K I pseudoequivalent widths: OSIRIS data
table16.dat 62 30 K I pseudoequivalent widths: data from literature
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See also:
J/A+AS/130/65 : A standard stellar library. II. (Lejeune+ 1998)
J/AJ/105/1962 : K and M stars photometry (Weis, 1993)
B/2mass : The 2MASS database (IPAC/UMass, 2000)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- --- [2MASSI]
8- 22 A15 --- 2MASSI Object name (1)
24- 27 I4 yr 2MASS.Y The UT year of 2MASS observation
29- 31 A3 "month" 2MASS.M The UT month of 2MASS observation
33- 34 I2 d 2MASS.D The UT day of 2MASS observation
36- 40 F5.2 mag Jmag The 2MASS J band magnitude
42- 45 F4.2 mag e_Jmag Uncertainty in Jmag
47- 51 F5.2 mag Hmag The 2MASS H band magnitude
53- 56 F4.2 mag e_Hmag Uncertainty in Hmag
58 A1 --- l_Ksmag The limit flag in Ksmag
59- 63 F5.2 mag Ksmag The 2MASS K_s_ band magnitude
65- 68 F4.2 mag e_Ksmag ? Uncertainty in Ksmag
70- 80 A11 --- Inst Instrument used in additional observations (2)
82- 85 I4 yr Add.Y The UT year of the additional observation
87- 89 A3 "month" Add.M The UT month of the additional observation
91- 92 I2 d Add.D The UT day of the additional observation
94-129 A36 --- n_Inst Note on Inst (3)
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Note (1): Source designations for 2MASS sources in the Incremental Release
Catalogs are given as ``2MASSI JHHMMSSs+/-DDMMSS''. The suffix
conforms to IAU nomenclature convention and is the sexagesimal R.A.
and decl. at J2000 equinox.
Note (2):
P60 = Palomar 60 inches;
CTIO = Cerro Tololo 1.5m;
KECK = Keck 10m.
Note (3): Unconfirmed objects near asteroid positions are likely missed
associations due to errors in ephemerides. Separations for these
objects are given in arcseconds. See text for discussion.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Obs Observations (NIRC or OSIRIS)
8- 24 A17 --- Object Object designation
25 A1 --- n_Object [b] b: Previously identified M and L dwarfs
observed for spectral comparison
27- 32 A6 --- Type Dwarf type (L, M or T) (G1)
35- 44 A10 "YYYY/MM/DD" Date UT Date of observation
46- 49 I4 s Tint Integration time
51- 54 F4.2 --- AirMass Airmass
55 A1 --- --- [-]
56- 59 F4.2 --- AirMass2 ? Upper value of airmass when interval
61- 70 A10 --- Cal Calibrator name
72- 77 A6 --- SpType Spectral type of the calibrator,
from SIMBAD database
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Object Object name
18 A1 --- n_Object [b] b: Separate observations obtained on
2000 January 23-24 (UT)
20- 24 F5.2 mag (J-H)2 2MASS photometric J-H colour index
26- 29 F4.2 mag e_(J-H)2 rms uncertainty on J-H
31- 35 F5.2 mag (J-H)N NIRC spectrophotometric J-H colour index
37- 41 F5.2 mag D(J-H) (J-H) difference, 2MASS minus NIRC
43 A1 --- l_(H-Ks)2 Limit flag on H-Ks
44- 48 F5.2 mag (H-Ks)2 2MASS photometric H-Ks colour index
50- 54 F5.2 mag e_(H-Ks)2 ? rms uncertainty on H-Ks
56- 60 F5.2 mag (H-Ks)N NIRC spectrophotometric J-H colour index
62- 66 F5.2 mag D(H-Ks) ? (H-Ks) difference, 2MASS minus NIRC
67 A1 --- l_(J-Ks)2 Limit flag on J-Ks
68- 72 F5.2 mag (J-Ks)2 2MASS photometric J-Ks colour index
74- 77 F4.2 mag e_(J-Ks)2 ? rms uncertainty on J-Ks
79- 83 F5.2 mag (J-Ks)N NIRC spectrophotometric J-H colour index
85- 89 F5.2 mag D(J-Ks) ? (J-Ks) difference, 2MASS minus NIRC
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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- 6 A6 --- --- [2MASSI]
8- 22 A15 --- 2MASSI Designation in 2MASS catalogue
25- 31 A7 --- Sample Primary sample (1)
33- 37 F5.2 mag Jmag 2MASS J magnitude
39- 42 F4.2 mag e_Jmag rms uncertainty on Jmag
45- 49 F5.2 mag Hmag 2MASS H magnitude
51- 54 F4.2 mag e_Hmag rms uncertainty on Hmag
57- 61 F5.2 mag Ksmag 2MASS Ks magnitude
63- 66 F4.2 mag e_Ksmag rms uncertainty on Ksmag
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Note (1): Some objects found in multiple samples because of overlapping search
criteria.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 25 A25 --- Object Object name
26 A1 --- Note [bc] Note on photometry (1)
28- 33 A6 --- Type Dwarf type (G1)
35- 39 F5.2 mag Jmag ? J magnitude
41- 44 F4.2 mag e_Jmag ? rms uncertainty on Jmag
46- 50 F5.2 mag J-H ? J-H colour index
52- 55 F4.2 mag e_J-H ? rms uncertainty on J-H
57 A1 --- l_H-Ks Limit flag on H-Ks
58- 62 F5.2 mag H-Ks ? H-Ks colour index
64- 67 F4.2 mag e_H-Ks ? rms uncertainty on H-Ks
69 A1 --- l_J-Ks Limit flag on J-Ks
70- 74 F5.2 mag J-Ks J-Ks colour index
76- 79 F4.2 mag e_J-Ks ? rms uncertainty on J-Ks
81 I1 --- Ref Reference for photometry (2)
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Note (1): Type of photometry:
b: UKIRT JHK photometry from Leggett et al., 1999ApJ...517L.139L
c: JK photometry from Cuby et al., 1999A&A...349L..41C
else: 2MASS photometry
Note (2): References:
1: This paper
2: Burgasser et al., 2000AJ....120..473B
3: Nakajima et al., 1995Natur.378..463N
4: Leggett et al., 2000ApJ...536L..35L
5: Burgasser et al., 1999ApJ...522L..65B
6: Cuby et al., 1999A&A...349L..41C
7: Tsvetanov et al., 2000ApJ...531L..61T
8: Burgasser et al., 2000ApJ...531L..57B
9: Strauss et al., 1999ApJ...522L..61S
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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- 15 A15 --- Object Object name
17- 20 A4 --- Type Dwarf type (G1)
22- 26 F5.3 --- H2O-A H_2_O-A spectral diagnostic (G2)
28- 32 F5.3 --- H2O-B H_2_O-B spectral diagnostic (G2)
34- 38 F5.3 --- CH4-A CH_4_-A spectral diagnostic (G2)
40- 44 F5.3 --- CH4-B CH_4_-B spectral diagnostic (G2)
46- 50 F5.3 --- CH4-C CH_4_-C spectral diagnostic (G2)
52- 56 F5.3 --- H/J H/J spectral diagnostic (G2)
58- 62 F5.3 --- K/J K/J spectral diagnostic (G2)
64- 68 F5.3 -- 2.11/2.07 2.11/2.07 spectral diagnostic (G2)
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Byte-by-byte Description of file: table11.dat table12.dat table13.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Object Object name
16 A1 --- n_Object [b] b: Indices averaged from multiple
spectra
18- 22 F5.3 --- H2O-A ? H_2_O-A spectral diagnostic (G2)
24- 26 A3 --- T(H2O-A) T sub-type from H_2_O-A
28- 32 F5.3 --- H2O-B H_2_O-B spectral diagnostic (G2)
34- 36 A3 --- T(H2O-B) T sub-type from H_2_O-B
38- 42 F5.3 --- CH4-A CH_4_-A spectral diagnostic (G2)
44- 46 A3 --- T(CH4-A) T sub-type from CH_4_-A
48- 52 F5.3 --- CH4-B CH_4_-B spectral diagnostic (G2)
54- 56 A3 --- T(CH4-B) T sub-type from CH4-B
58- 62 F5.3 --- CH4-C ? CH_4_-C spectral diagnostic (G2) (2)
64- 66 A3 --- T(CH4-C) T sub-type from CH4-C
68- 72 F5.3 --- H/J H/J spectral diagnostic (G2) (2)
74- 76 A3 --- T(H/J) T sub-type from H/J
78- 82 F5.3 --- K/J K/J spectral diagnostic (G2) (2)
84- 86 A3 --- T(K/J) T sub-type from K/J
88- 92 F5.3 -- 2.11/2.07 ? 2.11/2.07 spectral diagnostic (G2)
94- 96 A3 --- T(2.11/2.07) T sub-type from 2.11/2.07
98-100 F3.1 --- Type Final dwarf T sub-type (G1)
101 A1 --- u_Type Uncertainty flag on Type Spectral due to
poor quality spectrum
103-105 F3.1 --- e_Type ? rms uncertainty on Type
107-109 A3 --- Ref References for table13.dat (3)
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Note (2): Index ambiguous for subtypes T7 V - T8 V.
Note (3): Literature references:
1: Leggett et al., 200ApJ...536L..35L
2: Burgasser et al., 2000AJ....120.1100B
3: Strauss et al., 1999ApJ...522L..61S
4: Tsvetanov et al., 2000ApJ...531L..61T
5: Cuby et al., 1999A&A...349L..41C
6: Geballe et al., 1996ApJ...467L.101G
7: Oppenheimer et al., 1998ApJ...502..932O
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Byte-by-byte Description of file: table15.dat table16.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Object Object name
17- 22 A6 --- Type Dwarf type (G1)
25- 30 F6.4 um lambdac1 Central wavelength for 1.2432{mu}m line
32 A1 --- l_PEW1 Limit flag on PEW1
33- 37 F5.2 0.1nm PEW1 Pseudoequivalent width for 1.2432{mu}m line
39- 42 F4.2 0.1nm e_PEW1 ? rms uncertainty on PEW1
44- 49 F6.4 um lambdac2 Central wavelength for 1.2522{mu}m line
51- 55 F5.2 0.1nm PEW2 Pseudoequivalent width for 1.2522{mu}m line
57- 60 F4.2 0.1nm e_PEW2 ? rms uncertainty on PEW2
62 I1 --- Ref ? References for table16.dat (1)
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Note (1): Literature reference:
1: Leggett et al., 2001ApJ...548..908L
2: Reid et al., 2001AJ....121.1710R
3: Leggett et al., 2000ApJ...536L..35L
4: Tsvetanov et al., 2000ApJ...531L..61T
5: Strauss et al., 1999ApJ...522L..61S
6: Geballe et al., 1996ApJ...467L.101G
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GLobal notes:
Note (G1): Dwarf sub-types:
L: the L spectral class is comprised of a mix of stars and brown
dwarfs, characterized in the red optical (6300-10100{AA}) by
weakening bands of TiO and VO (dominant features in M dwarfs),
strengthening bands of FeH, CrH, and H2O, and strengthening lines
of the alkali metals Na I, K I, Cs I, and Rb I (Kirkpatrick et
al., 1999ApJ...519..802K; Martin et al., 1999AJ....118.2466M)
T: the T spectral class is comprised of brown dwarfs that exhibit
CH_4_ absorption bands between 1.0 and 2.2{mu}m.
See Kirkpatrick et al., 1999ApJ...519..802K.
Table8: Near-Infrared Spectral Properties of T Dwarf Subtypes
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Type Description Standard
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T1 V Weak CH_4_ bands seen at 1.3, 1.6, and 2.2{mu}m SDSS 0837-0000
Distinct 1.07 and 1.27{mu}m peaks separated by
1.15{mu}m H_2_O/CH_4_ feature
K-band peak noticeably depressed relative to J and H
CH_4_ and CO bands at K equal in strength
K I lines at 1.25{mu}m strong
T2 V CH_4_ bands strengthening SDSS 1254-0122
Flux at 1.15{mu}m feature roughly 50% J-band peak
K-band CH_4_ stronger than CO
K-band peak rounded
T3 V Flux at 1.15{mu}m feature roughly 40% J-band peak SDSS 1021-0304
Flux at 1.6{mu}m feature roughly 60% H-band peak
CO barely visible at K band
T5 V Flux at 1.6{mu}m trough roughly 50% H-band peak 2MASS 0559-1404
No CO present
H band suppressed relative to J and K
K I lines at 1.25{mu}m peak in strength
T6 V Flux at 1.15{mu}m feature roughly 20% J-band peak 2MASS 0243-2453
Flux at 1.6{mu}m feature roughly 30% H-band peak
1.25{mu}m K I lines beginning to weaken
1.3{mu}m CH_4_ band blended with 1.4{mu}m H_2_O
2.2{mu}m CH_4_ absorption nearly saturated
K band beginning to flatten, asymmetric peak centered at 2.11{mu}m
T7 V Flux at 1.15{mu}m feature roughly 10% 2MASS 0727+1710
J-band peak
Flux at 1.6{mu}m feature roughly 10% H-band peak
1.25{mu}m K I lines barely discernible
H- and K-band peaks maximally suppressed relative to J
J-band peak increasingly narrow
T8 V Flux at 1.15{mu}m feature nearly saturated 2MASS 0415-0935
Flux at 1.6{mu}m feature nearly saturated
No 1.25{mu}m K I lines present
Slight increase in H- and K-band peaks relative to J
K-band peak more sharply peaked and symmetric about 2.07{mu}m
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Global Notes:
Note (G2): Ratios Used as T Dwarf Spectral Diagnostics
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Diagnostic Numerator (um) Denominator (um) Feature Measured
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H_2_O-A <F_1.12-1.17_> <F_1.25-1.28_> 1.15 {mu}m H_2_O/CH_4_
H_2_O-B <F_1.505-1.525_> <F_1.575-1.595_> 1.4 {mu}m H_2_O
H_2_O-C <F_2.00-2.04_> <F_2.09-2.13_> 1.9 {mu}m H_2_O
CH_4_-A <F_1.295-1.325_> <F_1.25-1.28_> 1.3 {mu}m CH_4_
CH_4_-B <F_1.64-1.70_> <F_1.575-1.595_> 1.6 {mu}m CH_4_
CH_4_-C <F_2.225-2.275_> <F_2.09-2.13_> 2.2 {mu}m CH_4_
H/J <F_1.50-1.75_> <F_1.20-1.325_> NIR color
K/J <F_2.00-2.30_> <F_1.20-1.325_> NIR color
2.11/2.07 <F_2.10-2.12_> <F_2.06-2.08_> K-band shape/CIA H_2_
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History:
From electronic version of the journal
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(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 25-Feb-2002