J/ApJ/689/1295 Lithium test implications for brown dwarfs (Kirkpatrick+, 2008)
A sample of very young field L dwarfs and implications for the brown dwarf
"Lithium test" at early ages.
Kirkpatrick J.D., Cruz K.L., Barman T.S., Burgasser A.J., Looper D.L.,
Tinney C.G., Gelino C.R., Lowrance P.J., Liebert J., Carpenter J.M.,
Hillenbrand L.A., Stauffer J.R.
<Astrophys. J., 689, 1295-1326 (2008)>
=2008ApJ...689.1295K 2008ApJ...689.1295K
ADC_Keywords: Spectral types ; Equivalent widths ; Stars, late-type ;
Photometry, infrared
Keywords: binaries: general - stars: fundamental parameters - stars: late-type -
stars: low-mass, brown dwarfs
Abstract:
Using a large sample of optical spectra of late-type dwarfs, we
identify a subset of late-M through L field dwarfs that, because of
the presence of low-gravity features in their spectra, are believed to
be unusually young. From a combined sample of 303 field L dwarfs, we
find observationally that 7.6±1.6% are younger than 100Myr. This
percentage is in agreement with theoretical predictions once observing
biases are taken into account. We find that these young L dwarfs tend
to fall in the southern hemisphere (DEC<0°) and may be previously
unrecognized, low-mass members of nearby, young associations like
Tucana-Horologium, TW Hydrae, β Pictoris, and AB Doradus. We use
a homogeneously observed sample of ∼150 optical spectra to examine
lithium strength as a function of L/T spectral type and further
corroborate the trends noted by Kirkpatrick and coworkers. We use our
low-gravity spectra to investigate lithium strength as a function of
age. The data weakly suggest that for early- to mid-L dwarfs the line
strength reaches a maximum for a fewx100Myr, whereas for much older
(few Gyr) and much younger (<100Myr) L dwarfs the line is weaker or
undetectable.
Description:
Optical spectra were obtained with LRIS on the 10m Keck-I Observatory
atop Mauna Kea, Hawaii, between 2000 Aug 23 and 2003 Dec 24.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 140 68 L dwarf candidates sample from 2MASS
table3.dat 129 28 New spectroscopic observations of late-M or L
dwarfs from table 1
table4.dat 129 6 Observations of L dwarfs from litterature sample
table5.dat 103 5 Observations of T dwarfs from litterature sample
table6.dat 117 20 *Ultracool field dwarfs (≥M7) with spectroscopic
signatures of low gravity (Youth)
table7.dat 114 31 Log of additional spectroscopic observations for
objects shown in Figs. 7-13
table8.dat 47 41 Lithium equivalent width measurements for L0,
L2, L4, and L6.5 dwarfs
refs.dat 80 41 References
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Note on table6.dat: Other possible low-g dwarfs have been noted due to
color anomalies only, e.g. SDSS 0107+0041 in Knapp et al. (2004, Cat.
J/AJ/127/3553). For T dwarfs Knapp et al. (2004, Cat. J/AJ/127/3553)
and Burgasser et al. (2006ApJ...639.1095B 2006ApJ...639.1095B) have found that for fixed
Teff the H-K color is diagnostic of gravity because it measures the
importance of gravity- (pressure-) sensitive CIA H2. Based on the
combined work of these two groups, the lowest gravities probed by the
currently known set of T dwarfs is 4.5<logg<5.0.
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/A+A/338/1066 : Optical Spectra of DENIS Brown Dwarf Candidate (Tinney+
1998)
J/ApJ/564/421 : Spectra of T dwarfs. I. (Burgasser+, 2002)
J/AJ/123/3409 : SDSS M, L, and T dwarfs (Hawley+, 2002)
J/AJ/126/1526 : IR photometry of ultracool dwarfs (Bouy+, 2003)
J/AJ/126/2421 : 2MASS-Selected sample of ultracool dwarfs (Cruz+, 2003)
J/A+A/401/959 : 35 DENIS late-M dwarfs between 10 and 30pc (Phan-Bao+, 2003)
J/AJ/125/3302 : HST binary very low mass stars and brown dwarfs (Gizis+,
2003)
J/AJ/127/2856 : Brown dwarfs in the 2MASS Survey (Burgasser+, 2004)
J/A+A/414/699 : Spectra of southern late-type dwarfs (Cincunegui+, 2004)
J/AJ/127/3553 : JHK photometry and spectroscopy for L and T dwarfs (Knapp+,
2004)
J/AJ/131/2722 : New L and T dwarfs from the SDSS (Chiu+, 2006)
J/AJ/133/439 : Luminosity function of M7-L8 ultracool dwarfs (Cruz+, 2007)
J/AJ/136/1290 : Ultracool dwarfs from the 2MASS (Reid+, 2008)
J/A+A/503/639 : NIR spectral of M-T dwarfs (Testi, 2009)
J/A+A/497/619 : New ultra-cool dwarfs from SDSS and 2MASS (Zhang+, 2009)
J/MNRAS/404/1817 : 2MASS/SDSS data for 806 ultracool dwarfs (Zhang+, 2010)
http://dwarfarchives.org/ : Photometry, spectroscopy and astrometry of M, L
and T dwarfs archives page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- S [Ld/OT] Sample (1)
4- 8 A5 --- --- [2MASS]
10- 26 A17 --- 2MASS 2MASS name (JHHMMSSss+DDMMSSs)
28- 33 F6.3 mag Jmag 2MASS J-band magnitude
35- 39 F5.3 mag e_Jmag Jmag uncertainty
41- 46 F6.3 mag Hmag 2MASS H-band magnitude
48- 52 F5.3 mag e_Hmag Hmag uncertainty
54- 59 F6.3 mag Ksmag 2MASS Ks-band magnitude
61- 65 F5.3 mag e_Ksmag Ksmag uncertainty
67- 71 F5.3 mag J-Ks J-Ks color index
73- 77 F5.3 mag e_J-Ks J-Ks uncertainty
79- 86 A8 --- SpType MK optical spectral type (for Ld sample)
87 A1 --- f_SpType [c] Flag for 2MASS J15394189-0520428 (2)
89- 99 A11 --- Type Object type (for OT sample)
101-102 I2 --- r_Type ? Type reference; see refs.dat file
104-109 A6 --- Ref Discovery reference(s); see refs.dat file
111-139 A29 --- OName Other designation(s) or comment
140 A1 --- f_OName [b] Flag for 2MASS J14413716-0945590 (3)
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Note (1): Objects verified spectroscopically to be late-M or L dwarfs are
"Ld"; those objects known not to be late-M or L dwarfs are "OT".
Note (2): DENIS J1539-0520 is typed in the optical as L3.5 by Reid et al.
(2008, Cat. J/AJ/136/1290).
Note (3): Common proper motion for DENIS-P J1441-0945 and G 124-62A
confirmed by Seifahrt et al. (2005A&A...440..967S 2005A&A...440..967S).
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Byte-by-byte Description of file: table[34].dat
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Bytes Format Units Label Explanations
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1- 27 A27 --- Name Object designation
28 A1 --- f_Name [e] Flag for Gl 337CD (1)
30- 31 I2 --- Ref ? Discovery reference (only for table 4);
see refs.dat file
33- 42 A10 "YYYY/MM/DD" ObsDate Observation date (UT)
43 A1 --- f_ObsDate [m] for multidates (2)
45- 48 I4 s tint Integration time
50- 53 F4.2 --- CrH-a CrH-a spectral index (3)
55 A1 --- l_CrT Limit flag on CrT
56- 58 A3 --- CrT Spectral type from CrHa line
60- 63 F4.2 --- Rb/TiO ? Rb-b/TiO-b spectral index (3)
65 A1 --- l_RbT Limit flag on RbT
66- 68 A3 --- RbT Spectral type from Rb/TiO
70- 74 F5.2 --- Cs/VO ? Cs-a/VO-b spectral index (3)
76 A1 --- l_CsT Limit flag on CsT
77- 79 A3 --- CsT Spectral type from Cs/VO
81- 85 F5.2 --- Col ? Color-d spectral index (3)
87 A1 --- l_ColT Limit flag on ColT
88- 90 A3 --- ColT Spectral type from col
92 A1 --- l_KI [≲ ] Limit flag on KI
93- 95 A3 --- KI KI fit spectral type
97- 99 A3 --- Ox Oxyde fit spectral type
101-106 A6 --- SpType Final optical spectral type
107 A1 --- f_SpType [b] Flag for 2MASS J00145575-4844171 (4)
109-110 I2 pc Dist ? Distance (only for table 3)
111 A1 --- u_Dist Uncertainty flag on Dist
112 A1 --- f_Dist [p] Dist from trigonometric parallax (5)
114-115 A2 --- l_W(Ha) [≤ ] Limit flag on W(Ha)
116-120 F5.1 0.1nm W(Ha) Hα equivalent width
121 A1 --- f_W(Ha) [cd] Flag on W(Ha) (6)
123-124 A2 --- l_W(Li) [≤ ] Limit flag on W(Li)
125-128 F4.1 0.1nm W(Li) LiI equivalent width
129 A1 --- u_W(Li) Uncertainty flag on W(Li)
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Note (1): Gl 337CD is also known as 2MASS J09121469+1459396 and was identified
as a close double by Burgasser et al. (2005AJ....129.2849B 2005AJ....129.2849B).
Note (2): SDSSp J0423-0414 (table 3) was observed on four separate dates: 2001
November 13 (900s integration), 2002 January 1 (1200s integration),
2002 January 2 (1200s integration), and 2002 January 3 (1800s
integration). All analysis was performed on a co-added spectrum
combining all 5100s of integration.
SDSS J0830+4828 (table 4) was observed on two separate dates: 2002
January 1 (1200s integration) and 2002 January 2 (1200s integration).
All analysis was performed on a co-added spectrum combining all 2400s
of integration.
Note (3): Primary standards and spectral indices are defined in Kirkpatrick et
al. (1999ApJ...519..802K 1999ApJ...519..802K). The indices are defined as flux ratios in
spectral ranges (wavelength in Å):
CrH-a (CrH λ8611) = F(8580-8600)/F(8621-8641)
Rb-b (RbI λ7947.6) =
((F(7922.6-7932.6)+F(7962.6-7972.6))/2/(F(7942.6-7952.6)
TiO-b (TiO λ8432) = F(8400-8415)/F(8435-8470)
Cs-a (CsI λ8521.1) =
((F(8496.1-8506.1)+F(8536.1-8546.1))/2/F(8516.1-8526.1)
VO-b (VO λ7912) = ((F(7860-7880)+F(8080-8100))/F(7960-8000)
Color-d = F(9675-9875)/F(7350-7550)
Note (4): The optical spectrum of 2MASS J0014-4844 is slightly peculiar, perhaps
indicative of lower metallicity.
Note (5):
p = distances as measured through trignonometric parallax. All other
entries are distances derived from spectrophotometric parallaxes. For
SDSSp J0423-0414, the trigonometric parallax is from Vrba et al.
(2004AJ....127.2948V 2004AJ....127.2948V); for Gl 618.1B the distance is from its
association with the primary, Gl 618.1A, whose trigonometric parallax
was measured by Hipparcos (Perryman et al. 1997, Cat. I/239).
Note (6): Flag as follows:
c = 2MASS J0144-0716 shows variable Hα emission when spectra from
different epochs are compared. See Liebert et al. (2003AJ....125..343L 2003AJ....125..343L)
for further discussion.
d = 2MASS J0318-3421 shows a possible absorption trough of ∼10Å EW
at the location of Hα, but this is likely a data artifact
since it is aphysically broad.
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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- 25 A25 --- Name Object designation
27- 28 I2 --- Ref Discovery reference; see refs.dat file
30- 39 A10 "YYYY/MM/DD" ObsDate Observation date (UT)
40 A1 --- f_ObsDate [m] for multidates (1)
42- 46 I5 s tint Integration time
48- 51 F4.2 --- CsI CsI(A) spectral index (2)
53 A1 --- l_CsT Limit flag on CsT
54- 56 A3 --- CsT Spectral type from CsI
58- 61 F4.2 --- CrH/H2O CrH(A)/H2O spectral index (2)
63 A1 --- l_CrT Limit flag on CrT
64- 66 A3 --- CrT Spectral type from CrH/H20
68- 71 F4.2 --- FeH FeH(B) spectral type (2)
73 A1 --- u_FeT [∼ ] Approximative flag on FeT
74 I1 --- FeT ? Spectral type from FeH
76- 79 F4.2 --- Col Color-e spectral index (2)
81 A1 --- l_ColT Limit flag on ColT
82 I1 --- ColT ? Spectral type from Col
84- 88 A5 --- Type By-eye type
90- 95 A6 --- SpType Final optical spectral type
97 A1 --- l_W(Ha) Limit flag on W(Ha)
98- 99 I2 0.1nm W(Ha) ? Hα equivalent width
100 A1 --- f_W(Ha) [c] Non-significant equivalent widths (3)
102 A1 --- l_W(Li) Limit flag on W(Li)
103 I1 0.1nm W(Li) ? LiI equivalent width
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Note (1): SDSS J0837-0000 was observed on three separate dates:
2000 December 26 (7200s integration), 2000 December 27 (3600s
integration), and 2000 December 28 (3600s integration). All analysis
was performed on a co-added spectrum combining all 14400s of
integration. 2MASS J1209-1004 was observed on three separate dates:
2003 December 22 (2400s integration), 2003 December 23 (3600s
integration), and 2003 December 24 (3600s integration). All analysis
was performed on a co-added spectrum combining all 9600s of integration.
Note (2): Indices of T dwarf spectral ratios in the red optical are defined in
Burgasser et al. 2003ApJ...594..510B 2003ApJ...594..510B:
CsI(A) (8521Å) = <F8496.1-8506.1>+<F8536.1-8546.1>
CrH(A) (8611Å) = ∫F8560-8600
H2O (9250Å) = ∫F9220-9240
FeH(B) (9896Å) = ∫F9855-9885
Color-e (spectral slope) = <F9140-9240>
Note (3): 2MASS J0415-0935 has a flux measurement at or very close to zero
at these wavelengths, so meaningful equivalent width measures are not
possible.
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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- 24 A24 --- Name Object name
25 A1 --- f_Name [d] SSSPM J1102-3431 = 2MASS J11020983-3430355
27- 34 A8 --- SpType Optical spectral type
35 A1 --- f_SpType [e] Flag for 2MASSI J1615425+495321 (1)
37- 38 I2 --- r_SpType ? Optical reference; see refs.dat file
40- 49 A10 --- IRSpT Near-IR spectral type
51- 52 I2 --- r_IRSpT ? Near-IR reference; see refs.dat file
54- 57 F4.2 mag J-Ks ? 2MASS J-Ks color index
59- 62 F4.2 mag e_J-Ks ? J-Ks uncertainty
63 A1 --- f_J-Ks [c] SDSS J102552.43+321234.0 not detected at
2MASS J-band
65- 66 I2 --- Ref Discovery reference; see refs.dat file
68- 71 A4 --- Ref2 Youth reference(s); see refs.dat file
73-117 A45 --- Diag Diagnostics
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Note (1): Spectrum has poor signal-to-noise ratio and may prove to be
dusty rather than low gravity.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 23 A23 --- Name Object name
25- 48 A24 --- OName Other designation
50- 59 A10 "YYYY/MM/DD" Date Observation date (UT)
61 A1 --- f_Date [b-e] Multidate (1)
63- 70 A8 --- Tel Telescope
71 A1 --- f_Tel [f] Flag for Subaru (1)
73- 79 A7 --- Inst Instrument
81- 85 I5 s tint Integration time
87- 90 I4 s tint2 ? Second integration time
92- 93 I2 --- r_SpType ? Spectroscopic reference; see refs.dat file
95-107 A13 --- SpType Spectral type
109-112 A4 --- Cor Telluric corrected? (3)
114 A1 --- f_Cor [c] Flag for G 196-3B (1)
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Note (1): Flags as follows:
b = 2MASS J0850+1057 was observed on five different dates; the plotted
spectrum is a sum of all five. Exposure times were 2400s on 1997 November
9 (UT), 1200s on 1997 December 7 (UT), 1200s on 1997 December 8 (UT),
1200s on 1997 December 9 (UT), and 4800s on 1998 January 24 (UT).
c = G 196-3B was observed using a blue setup (3900-8700Å) on one night and
our standard red setup (6300-10100Å) on two other nights. Observations
for the blue setup were done in superior conditions, so the plotted
spectrum shortward of 8500Å is from this set, and data longward of
8500Å come from the poorer data taken with the red setup. Data taken
with the blue setup were corrected for telluric absorption; data with the
red setup were not telluric corrected. The exposure time for the blue set
up was 3600s on 2001 February 19 (UT). Exposure times for the red setup
were 2400s on 1999 March 04 (UT) and 3600s on 1999 March 5 (UT).
d = 2MASS J1022+0200 was observed for 600s on two different dates, 2003 April
04 (UT) and 2006 January 15 (UT). The plotted spectrum is the sum of
these two observations.
e = Gl 417B was observed on three different dates; the plotted spectrum is a
sum of all three. Exposure times were 1200s on 1998 December 14 (UT),
1200s on 1999 March 4 (UT), and 3600s on 1999 March 5 (UT).
f = Observation and reduction procedures for Subaru-FOCAS data are
discussed in Looper et al. (2008ApJ...686..528L 2008ApJ...686..528L).
Note (3): Indicates whether or not the spectrum was telluric corrected
using a G dwarf spectrum acquired near in time and near on sky to the
program object.
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- SpT Spectral type
6- 32 A27 --- Name Name
34 A1 --- f_Name [a-g] Flag on Name (1)
36- 37 A2 --- l_W(Li) [≤ ] Limit flag on W(Li)
38- 41 F4.1 0.1nm W(Li) Lithium equivalent width
43- 45 F3.1 0.1nm e_W(Li) ? W(Li) uncertainty
47 I1 --- f_SpT [1-4] Particularity of dwarfs (2)
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Note (1): Flag as follows:
a = 2MASS J0141-4633: age estimate from fitting of theoretical models to
spectra is 1-50Myr (Kirkpatrick et al. 2006ApJ...639.1120K 2006ApJ...639.1120K).
b = Kelu-1: age estimate from model fits is 300-800Myr (Liu & Leggett,
2005ApJ...634..616L 2005ApJ...634..616L).
c = G 196-3B: age estimates from the presence of the lithium in G 196-3B
itself as well as activity diagnostics in the primary is 20-300Myr
(Rebolo et al. 1998Sci...282.1309R 1998Sci...282.1309R); an age estimate using indicators
from the early-M primary alone is 60-300Myr (Kirkpatrick et al.
2001AJ....121.3235K 2001AJ....121.3235K).
d = Gl 417B: age estimate from the G dwarf primary is 80-300Myr (Kirkpatrick
et al. 2001AJ....121.3235K 2001AJ....121.3235K). Gl 417B is actually typed as L4.5 but is
included here as an L4 so that this bin of peculiar, low-gravity L4
dwarfs could be populated.
e = GD 165B: age estimate using the white dwarf primary is 1.2-5.5Gyr
(Kirkpatrick et al. 1999ApJ...519..834K 1999ApJ...519..834K).
f = 2MASS J2244+2043: This object has a normal L6.5 optical spectrum, but its
near-infrared spectrum is extremely peculiar. In this case, the
peculiarity may be attributable to low gravity (McLean et al.
2003ApJ...596..561M 2003ApJ...596..561M).
g = 2MASS J2148+4003: This object has a normal L6.5 optical spectrum, but its
near-infrared spectrum is extremely peculiar. In this case, the
peculiarity is best explained by excessive atmospheric dust (Looper et
al. 2008ApJ...686..528L 2008ApJ...686..528L).
Note (2): Dwarf type as follows:
1 = Normal dwarf without Lithium
2 = Normal dwarf with Lithium
3 = Peculiar dwarf (low-g)
4 = Very peculiar dwarf (very low-g)
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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 number
4- 22 A19 --- BibCode Bibcode
24- 41 A18 --- Aut Author's name
43- 80 A38 --- Com Comment
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 26-Jan-2011