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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
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:
FileName Lrecl Records Explanations
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
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) 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.
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) : Photometry, spectroscopy and astrometry of M, L and T dwarfs archives page Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
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)
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).
Byte-by-byte Description of file: table[34].dat
Bytes Format Units Label Explanations
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)
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). 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). 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); 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) 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.
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
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)/H_2_O 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
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: 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.
Byte-by-byte Description of file: table6.dat
Bytes Format Units Label Explanations
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
Note (1): Spectrum has poor signal-to-noise ratio and may prove to be dusty rather than low gravity.
Byte-by-byte Description of file: table7.dat
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)
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). 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.
Byte-by-byte Description of file: table8.dat
Bytes Format Units Label Explanations
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)
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). b = Kelu-1: age estimate from model fits is 300-800Myr (Liu & Leggett, 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); an age estimate using indicators from the early-M primary alone is 60-300Myr (Kirkpatrick et al. 2001AJ....121.3235K). d = Gl 417B: age estimate from the G dwarf primary is 80-300Myr (Kirkpatrick et al. 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). 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). 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). 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)
Byte-by-byte Description of file: refs.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Ref Reference number 4- 22 A19 --- BibCode Bibcode 24- 41 A18 --- Aut Author's name 43- 80 A38 --- Com Comment
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 26-Jan-2011
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