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The Astronomical Journal, 131:2722 2736, 2006 May
# 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A.

A

SEVENTY-ONE NEW L AND T DWARFS FROM THE SLOAN DIGITAL SKY SURVEY
K. Chiu,1 X. Fan,2 S. K. Leggett,3 D. A. Golimowski,1 W. Zheng, T. R. Geballe,4 D. P. Schneider,5 and J. Brinkmann6
Received 2005 September 15; accepted 2006 January 3
1

ABSTRACT We present near-infrared observations of 71 newly discovered L and T dwarfs, selected from imaging data of the Sloan Digital Sky Survey (SDSS) using the i-dropout technique. Sixty-five of these dwarfs have been classified spectroscopically according to the near-infrared L dwarf classification scheme of Geballe et al. and the unified T dwarf classification scheme of Burgasser et al. The spectral types of these dwarfs range from L3 to T7 and include the latest types yet found in the SDSS. Six of the newly identified dwarfs are classified as early to mid-L dwarfs according to their photometric near-infrared colors, and two others are classified photometrically as M dwarfs. We also present new near-infrared spectra for five previously published SDSS L and T dwarfs, and one L dwarf and one T dwarf discovered by Burgasser et al. from the Two Micron All Sky Survey. The new SDSS sample includes 27 T dwarfs and 30 dwarfs with spectral types spanning the complex L-T transition ( L7 T3). We continue to see a large ($0.5 mag) spread in J ю H for L3 T1 types and a similar spread in H ю K for all dwarfs later than L3. This color dispersion is probably due to a range of grain sedimentation properties, metallicity, and gravity. We also find L and T dwarfs with unusual colors and spectral properties that may eventually help to disentangle these effects. Key words: infrared: stars -- stars: low-mass, brown dwarfs Online material: machine-readable tables

1. INTRODUCTION Over the last decade, the search for rare astronomical objects has undergone an explosion of productivity, thanks in part to the specialized labor associated with modern digital sky surveys. Innovative programmers and instrumentalists designing highly automated software pipelines and large imaging arrays have laid the groundwork for massive databases that can now be mined for objects once only thought to exist. The result of these efforts has been the most productive period in history for the discovery of rare objects, which range from the brightest and most distant quasars ( Fan et al. 1999, 2000b, 2001a, 2001b, 2003, 2004; Zheng et al. 2000) to the faintest and nearest stars and brown dwarfs ( Kirkpatrick et al. 1999, 2000; Burgasser et al. 1999, 2002b; Fan et al. 2000a; Leggett et al. 2000; Geballe et al. 2002, hereafter G02; Knapp et al. 2004, hereafter K04). Since the first discoveries of L and T dwarfs in the early 1990s, the ranks of these spectral classes have been populated through systematic searches of large-area, optical and near-infrared surveys such as the Deep Near Infrared Survey of the Southern Sky ( Epchtein 1997), the Two Micron All Sky Survey (2MASS; Skrutskie et al. 1997), and the Sloan Digital Sky Survey (SDSS; York et al. 2000). Although time intensive, these searches are more productive and efficient than the tedious, pointed surveys that preceded them. The optical and near-infrared spectra of the many known L and T dwarfs have yielded well-defined classi1

Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218. 2 Steward Observatory, The University of Arizona, Tucson, AZ 85721. 3 United Kingdom Infrared Telescope, Joint Astronomy Center, 660 North A'ohoku Place, Hilo, HI 96720. 4 Gemini Observatory, 670 North A'ohoku Place, Hilo, HI 96720. 5 Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802. 6 Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349.

fication schemes and valuable information about the chemical compositions, temperatures, and other physical characteristics of ultracool dwarfs ( Kirkpatrick et al. 2000; Burgasser et al. 2002b, 2006a; G02; K04; Golimowski et al. 2004a). L and T dwarfs, which link the lowest mass stars and the highest mass planets, are the subjects of a broad range of observational and theoretical studies ( Kirkpatrick 2005). A principal goal of these studies is the determination of the substellar mass function, which is fundamental to understanding the star formation process at the lowest mass end and how it is related to the formation and evolution of planetary systems ( Burgasser 2004; Allen et al. 2005). The hundreds of L dwarfs and more than 50 T dwarfs discovered from 2MASS and SDSS data compose a statistical sample of brown dwarfs essential to understanding the demographics and eventually the luminosity and mass functions of substellar objects ( X. Fan et al. 2006, in preparation). Since 1999 we have used SDSS imaging data to select L and T dwarf candidates and carry out follow-up observations of their photometric and spectroscopic properties (Strauss et al. 1999; Tsvetanov et al. 2000; Fan et al. 2000a; Leggett et al. 2000, 2002; Schneider et al. 2002; G02; Hawley et al. 2002; K04; Golimowski et al. 2004a). The SDSS i ю z color, which is our primary selection criterion, is sensitive to brown dwarfs of all effective temperatures as long as they are bright enough to be detected in the z band. Near-infrared selection criteria, such as those employed by the 2MASS group (e.g., Burgasser et al. 2002b), are more sensitive to late T dwarfs, which are optically faint, but they are less efficient in detecting dwarfs at the L-T transition because their near-infrared colors are indistinguishable from those of the more numerous M dwarfs. Therefore, the SDSS selection criteria are better suited for defining a complete, magnitude-limited sample of field brown dwarfs. In this paper we report the discovery and properties of 71 L and T dwarfs drawn from over 3500 deg 2 of SDSS imaging data. We describe the techniques for identifying and confirming these 2722

NEW L AND T DWARFS FROM SDSS dwarfs based on their SDSS and near-infrared colors. We classify 65 of the L and T dwarfs from their near-infrared spectra, and we identify six L dwarfs and two M dwarfs from their photometric colors. The observations are presented in x 2, spectral classification of the sample is presented in x 3, and variations in the photometric and spectroscopic properties are discussed in x 4. Our conclusions are given in x 5. 2. OBSERVATIONS The search for nearby ultracool dwarfs at optical wavelengths is fortuitously related to the search for the most distant galaxies and quasars in the universe. Because both types of objects have very red optical colors caused by rising flux into the near-infrared, a search for one yields the other (or from another perspective, one is the unwanted contaminant of the other). The ``i-dropout'' and related techniques have been employed in nearly all highredshift observing programs, so a joint effort to find L and T dwarfs with these techniques benefits both programs. 2.1. General Selection Method We select candidate L and T dwarfs using the i and z magnitudes of sources listed in the SDSS photometric catalog. The SDSS uses a dedicated 2.5 m telescope in a drift-scanning mode to acquire digital images. The hardware and software pipelines that produce the final astrometry and photometry have been described by the project collaborators elsewhere in detail: Fukugita et al. (1996), Gunn et al. (1998), Hogg et al. (2001), Lupton et al. (1999), Stoughton et al. (2002), Smith et al. (2002), Pier et al. (2003), and Abazajian et al. (2004). Fan et al. (2001a) described the i-dropout selection and identification procedures used in this program. The photometric selection criteria are z < 20:4; (z) < 0:12; i ю z > 2: 2: П 1ч

2723

law. Ultracool dwarfs are more easily discovered than quasars because they are much redder, and therefore, significantly brighter in the J band. Applying the selection criteria above to a 6600 deg2 survey area, we have confirmed 53 T dwarfs and over 100 L dwarfs (including those found in this work), but only 19 quasars with redshifts >5.7. Finally, we obtained near-infrared spectra of candidates whose colors matched those of L and T dwarfs, at the wavelength resolution needed to determine the dwarf classification indices. 2.2. Photometric Observations The area of sky covered in this work is 3526 deg 2, comprising imaging runs recorded from early 2003 to 2005 and a few earlier runs that had been reprocessed through the SDSS photometric pipeline. Eighty-four i-dropout candidates were selected using the criteria in equation (1) and then examined with the 2MASS catalog or follow-up z and J imaging. A few additional candidates with attributes outside of our formal selection limits were also selected in order to fill gaps during observations. We obtained z-band images with the SPICAM imager on the Astrophysical Research Consortium (ARC ) 3.5 m telescope at the Apache Point Observatory. The typical exposure time needed to verify the presence of a z ј 20:4 source was $60 s. We obtained J-band images with the 256 ; 256 NICMOS camera on Steward Observatory's 2.3 m Bok Telescope, and the GRIM II and NICFPS imagers on the ARC 3.5 m telescope. Candidates surviving our initial photometric screening were then imaged through the Mauna Kea Observatory ( MKO) J, H, and K bands (Simons & Tokunaga 2002; Tokunaga et al. 2002) using the UKIRT Fast-Track Imager ( UFTI; Roche et al. 2003) or the NASA Infrared Telescope Facility ( IRTF ) imager /spectrometer SpeX ( Rayner et al. 2003). United Kingdom Infrared Telescope ( UKIRT ) Faint Standards ( Hawarden et al. 2001) were used to calibrate the data. Typical exposure times were 60 s, with a five- or nine-point dither pattern. Table 1 lists the SDSS designations, SDSS iz and MKO JHK magnitudes, and observation details for the 73 M, L, and T dwarfs discovered in this work.7 Although the SDSS i-band 5 detection limit is 22.5, the SDSS photometric pipeline yields asinh magnitudes below this flux limit ( Lupton et al. 1999). For this reason, we identify with brackets those SDSS i magnitudes in Table 1 that imply nondetections. The SDSS designations contain the J2000.0 right ascensions and declinations in sexigesimal format, truncated to the significant digit shown. The positions are accurate to better than 0B1 in each coordinate. For brevity, we hereafter refer to the dwarfs by the abbreviated form, SDSS JHHMMф DDMM. One T dwarf, SDSS J1534+1615AB, has recently been resolved into a close binary using the laser guide star and adaptive optics systems at the Keck Observatory ( Liu et al. 2006). Figure 1 displays 3 0 ; 3 0 z-band finding charts for the 73 dwarfs in our sample. Table 2 lists MKO JHK magnitudes for three 2MASS dwarfs (2MASS J0034+0523, 2MASS J1209ю1004, and 2MASS J2101+ 1756), as well as UFTI Z magnitudes for 2MASS J1209ю1004 and seven previously published SDSS L and T dwarfs ( Burgasser et al. 2004; K04). The Z-band data are not used in this analysis but are presented for future reference.
7 The SDSS iz magnitudes are based on the AB system, whereas the MKO JHK magnitudes are based on the Vega system. The photometric errors of these objects in the SDSS public data releases may differ from those published here due to reprocessing of the data.

Because most of the SDSS area is imaged only once and our i-dropout technique favors one-band detections, our initial list of L and T dwarf candidates is heavily contaminated by cosmic rays. False detections from cosmic rays and intrinsic faintness are the main problems preventing the SDSS itself from discovering these objects, as well as z > 5:7 quasars, in its automated spectroscopic observing program ( Richards et al. 2002). We conservatively remove cosmic rays from our list by visual inspection. The reality of the remaining bright candidates can be immediately confirmed by correlating the list with the 2MASS Point Source Catalog, which contains near-infrared photometry down to a 10 detection limit of J ј 15:8. We matched our SDSS candidates with 2MASS sources, allowing for small astrometric errors caused by the proper motions of these nearby dwarfs. Although the z ю J colors of ultracool dwarfs are very red (z ю J > 2; Fan et al. 2001a), our fainter candidates often do not appear in the 2MASS catalog because of 2MASS's shallower imaging depth. Those fainter candidates not confirmed by 2MASS were further examined through independent J-band imaging. Additional SDSS i and z imaging was carried out to secure our primary color criterion of i ю z > 2:2. The follow-up J-band photometry allows us to distinguish very red L and T dwarf candidates from bluer high-redshift quasar candidates. Quasars at redshifts >5.7 have z ю J < 1:5 because their intrinsic continua are dominated by a blue power

TABLE 1 New M, L , a nd T Dw a rf P ho t o met ry UT Date ( yyyy mm dd) 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2005 2004 2004 2003 2003 2005 2004 2003 2003 2004 2003 2002 2002 2004 2003 2003 2005 2001 2004 2004 2003 2003 2003 2003 2002 2003 2003 2003 2002 2002 2002 2004 2003 2004 09 09 09 09 09 09 12 12 12 10 10 12 10 03 12 12 01 11 03 04 03 02 04 03 03 12 04 03 03 01 05 12 04 04 04 05 04 05 04 03 04 06 05 05 06 06 04 23 17 15 21 21 21 15 14 14 15 15 13 15 12 12 13 25 20 10 16 26 01 16 31 12 13 13 24 31 17 18 13 25 01 26 30 28 08 26 11 27 09 08 08 14 22 15 UT Date ( yyyy mm dd) 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2005 2004 2005 2005 2004 2004 2005 2004 2004 2004 2004 2004 2005 2004 2005 2005 2005 2004 2004 2004 2004 2004 2005 2004 2004 2004 2004 2004 2005 2005 2004 2004 07 07 08 02 08 11 08 08 08 02 08 01 04 04 01 01 01 01 04 06 01 01 12 01 01 01 06 01 06 03 01 04 06 01 01 06 01 04 01 01 01 02 02 04 03 06 06 27 27 11 08 12 07 12 11 12 08 12 21 07 07 21 21 14 21 07 26 18 21 29 18 18 18 26 21 26 05 21 07 26 18 18 26 20 07 18 18 20 10 14 07 06 26 26

SDSS Name J000250.98+245413.8 ...................... J003609.26+241343.3 ...................... J011912.22+240331.6 ...................... J020608.97+223559.2 ...................... J020608.97+223559.2 ...................... J024256.98+212319.6 ...................... J024749.90ю163112.6 ..................... J032553.17+042540.1 ...................... J032553.17+042540.1 ...................... J035104.37+481046.8 ...................... J035104.37+481046.8 ...................... J065405.63+652805.4 ...................... J073922.26+661503.5 ...................... J082030.12+103737.0 ...................... J083506.16+195304.4 ...................... J085116.20+181730.0 ...................... J085834.42+325627.7 ...................... J090900.73+652527.2 ...................... J100711.74+193056.2 ...................... J102552.43+321234.0 ...................... J102751.48+400931.7b .................... J103321.92+400549.5 ...................... J103931.35+325625.5 ...................... J104335.08+121314.1 ...................... J104829.21+091937.8 ...................... J105213.51+442255.7 ...................... J111320.16+343057.9 ...................... J112118.57+433246.5 ...................... J114220.63+114440.3b .................... J120602.51+281328.7 ...................... J121440.95+631643.4 ...................... J121659.17+300306.3 ...................... J121951.45+312849.4 ...................... J123330.63+423948.8c .................... J125011.65+392553.9 ...................... J134203.11+134022.2 ...................... J134403.84+083950.9d .................... J134525.57+521634.0 ...................... J135852.68+374711.9 ...................... J140023.12+433822.3 ...................... J140255.66+080055.2 ...................... J141530.05+572428.7 ...................... J141659.78+500626.4 ...................... J141659.78+500626.4 ...................... J142227.25+221557.1 ...................... J143553.25+112948.6 ...................... J143945.86+304220.6 ......................

SDSS i (AB)a 22:20 [22:97 [24:07 22:42 22:42 22:24 [23:24 [23:59 [23:59 [22:84 [22:84 20:97 [23:90 [22:75 21:10 21:92 22:09 [23:46 [22:93 [22:67 22:14 21:94 [22:78 21:99 [24:31 [22:94 21:99 22:31 22:46 [24:11 [24:90 22:41 21:97 [22:79 [23:78 22:31 [23:09 22:02 [25:34 [22:52 [22:87 [22:56 22:18 22:18 22:16 [23:40 [23:64 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:16 0:39] 0:49] 0:17 0:17 0:18 0:39] 0:57] 0:57] 0:30] 0:30] 0:05 0:33] 0:25] 0:07 0:15 0:15 0:38] 0:29] 0:30] 0:16 0:16 0:31] 0:19 0:60] 0:40] 0:14 0:19 0:25 0:85] 0:78] 0:24 0:15 0:27] 0:48] 0:20 0:31] 0:17 0:45] 0:20] 0:31] 0:30] 0:23 0:23 0:14 0:44] 0:49]

SDSS z (AB) 19:99 20:07 20:46 19:25 19:25 20:02 19:83 19:75 19:75 19:57 19:57 18:89 19:86 20:03 18:84 19:68 19:07 18:75 19:76 19:69 19:98 19:54 19:41 18:86 19:69 19:11 19:76 19:93 20:24 19:48 19:65 19:71 18:85 19:92 19:95 19:86 19:98 19:84 19:89 19:08 19:93 19:87 19:70 19:70 19:71 20:13 20:24 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:08 0:11 0:11 0:04 0:04 0:09 0:11 0:08 0:08 0:06 0:06 0:04 0:08 0:09 0:05 0:08 0:05 0:05 0:09 0:08 0:08 0:06 0:06 0:04 0:08 0:06 0:07 0:09 0:11 0:07 0:10 0:10 0:04 0:09 0:09 0:09 0:08 0:10 0:08 0:04 0:08 0:09 0:10 0:10 0:09 0:10 0:10

SDSS Run 4851 4836 4829 4844 4844 4844 5069 5065 5065 4887 4887 5060 4887 5194 5045 5061 3606 4264 5183 4576 3818 3647 4576 3836 3031 3530 4550 3813 3836 5112 2304 5061 4599 3840 3900 3971 3909 3177 3900 3716 3903 3225 3177 3177 4678 3996 4570

MKO J ( Vega) 17:02 17:08 16:86 16:40 16:31 17:05 16:73 15:88 15:92 16:33 16:27 16:08 16:75 17:03 15:94 16:68 16:33 15:81 16:75 16:89 17:10 16:74 16:16 15:82 16:39 15:89 16:92 17:04 17:89 16:10 16:05 16:89 15:85 17:24 16:12 16:90 17:22 17:05 16:17 16:16 16:85 16:49 16:81 16:76 16:87 17:04 16:97 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:03 0:05 0:03 0:05 0:03 0:03 0:03 0:03 0:03 0:05 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:05 0:05 0:05 0:03 0:03 0:03 0:03 0:03 0:03 0:05 0:06 0:03 0:03 0:05 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:05 0:03 0:03 0:03

MKO H ( Vega) 16:09 16:28 16:46 15:56 15:62 16:19 16:31 16:24 16:26 15:80 15:81 15:35 16:31 16:09 15:12 15:80 15:45 15:32 15:85 15:98 16:49 16:05 15:47 14:87 15:95 15:09 16:00 16:56 17:40 15:83 15:80 16:19 14:98 16:33 16:07 15:95 16:45 16:30 16:41 15:18 16:25 16:09 16:04 16:01 16:12 16:52 16:53 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:03 0:03 0:03 0:05 0:03 0:03 0:03 0:03 0:03 0:05 0:03 0:03 0:03 0:05 0:03 0:04 0:03 0:03 0:05 0:03 0:03 0:04 0:03 0:03 0:03 0:03 0:03 0:04 0:05 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:04 0:03

MKO K ( Vega) 15:42 15:48 16:26 15:03 15:05 15:43 15:81 16:48 16:45 15:15 15:20 14:59 16:05 15:58 14:41 14:97 14:72 15:19 15:15 15:16 15:87 15:60 15:01 14:20 15:87 14:46 15:26 16:13 16:84 15:97 15:73 15:56 14:30 15:65 16:07 15:13 15:98 15:54 16:66 14:47 15:73 15:55 15:35 15:35 15:64 16:15 16:34 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:03 0:03 0:03 0:05 0:03 0:03 0:03 0:03 0:05 0:05 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:05 0:03 0:03 0:03 0:03 0:03 0:04 0:09 0:03 0:04 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:05 0:03 0:03 0:03 0:03 0:03 0:03 0:06 0:05

Instrument UFTI UFTI SpeX UFTI SpeX SpeX SpeX SpeX SpeX UFTI SpeX SpeX SpeX SpeX SpeX SpeX UFTI SpeX SpeX UFTI UFTI SpeX UFTI UFTI UFTI UFTI UFTI SpeX UFTI UFTI SpeX SpeX UFTI UFTI UFTI UFTI UFTI SpeX UFTI UFTI UFTI UFTI UFTI SpeX UFTI UFTI UFTI

2724

TABLE 1--Continued UT Date ( yyyy mm dd) 2002 2003 2001 2002 2003 2003 2005 2005 2003 2003 2004 2002 2003 2005 2005 2003 2003 2005 2003 2003 2003 2002 2004 2000 2005 2005 2004 2001 2000 2000 05 04 06 05 06 03 03 05 05 05 06 06 05 03 05 05 06 06 06 06 06 05 06 04 06 06 09 09 09 11 08 25 16 08 23 26 12 11 29 29 13 09 29 12 12 01 22 05 22 25 26 08 14 04 11 22 12 18 27 27 UT Date ( yyyy mm dd) 2004 2004 2005 2004 2004 2004 2005 2005 2004 2004 2005 2005 2004 2005 2005 2004 2004 2005 2004 2004 2004 2005 2005 2005 2005 2005 2005 2005 2005 2005 02 01 03 02 02 02 03 08 02 02 03 04 07 04 03 07 01 08 07 07 07 08 08 03 08 08 08 08 08 08 14 20 06 11 11 11 05 11 14 14 05 07 28 08 07 28 18 11 28 28 28 13 11 07 01 11 01 13 13 14

SDSS Name J144128.52+504600.4 ...................... J150411.63+102718.4 ...................... J151114.66+060742.9 ...................... J151506.11+443648.3 ...................... J151643.01+305344.4 ...................... J152039.82+354619.8 ...................... J153417.05+161546.1AB ................ J153453.33+121949.2 ...................... J154009.36+374230.3 ...................... J154508.93+355527.3 ...................... J154849.02+172235.4 ...................... J161731.65+401859.7 ...................... J162051.17+323732.1 ...................... J162255.27+115924.1 ...................... J162429.36+125144.0d .................... J162838.77+230821.1 ...................... J163022.92+081822.0 ...................... J163359.23ю064056.5 ..................... J163607.48+233601.6d .................... J164916.89+464340.0 ...................... J170005.43+154128.8d .................... J171147.17+233130.5 ...................... J171902.15+373453.6d .................... J173101.41+531047.9 ...................... J204317.69ю155103.4 ..................... J205235.31ю160929.8 ..................... J213154.43ю011939.3 ..................... J213240.36+102949.4 ...................... J213352.72+101841.0 ...................... J232804.58ю103845.7 ..................... Note.--Table 1 is a Bracketed value b Photometrically c Photometrically d Photometrically

SDSS i (AB) 21:83 [24:66 21:88 22:07 [23:18 21:86 [24:17 20:48 [22:67 22:28 21:32 22:09 [23:44 21:93 20:79 [24:40 [23:82 21:31 21:82 22:39 21:53 21:90 21:87 21:55 [23:74 [22:72 [22:68 21:49 21:96 21:44 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф

a

SDSS z (AB) 19:87 20:34 19:09 19:50 19:99 18:31 20:20 18:18 19:03 19:87 18:82 19:81 20:01 19:43 18:97 20:23 20:13 18:76 19:57 19:73 19:14 19:95 20:28 19:34 19:72 19:06 20:01 19:25 19:76 19:76 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:08 0:14 0:06 0:06 0:11 0:03 0:12 0:03 0:06 0:09 0:04 0:10 0:11 0:06 0:05 0:10 0:10 0:04 0:06 0:09 0:05 0:13 0:11 0:07 0:10 0:05 0:10 0:05 0:10 0:12

SDSS Run 3180 3894 2391 3180 4002 3818 5194 5317 3965 3965 4674 3226 3964 5194 5323 3927 3996 5384 3997 4011 4014 3177 4679 1336 5415 5421 4822 2566 1739 1891

MKO J ( Vega) 16:86 16:49 15:83 16:54 16:79 15:47 16:62 15:27 16:33 16:97 16:09 16:83 17:17 16:89 16:44 16:25 16:18 16:00 16:86 17:09 16:21 16:84 17:65 16:32 16:87 16:04 17:29 16:38 16:92 16:77 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:04 0:05 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:05 0:03 0:03 0:04 0:03 0:03 0:03 0:03

MKO H ( Vega) 15:98 16:92 15:16 15:63 15:86 14:56 16:37 14:42 15:42 16:04 15:24 15:69 16:23 16:15 15:72 16:63 16:35 15:25 16:21 16:33 15:65 16:00 17:08 15:50 16:02 15:45 16:45 15:52 16:19 15:99 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:04 0:03 0:03 0:03 0:03 0:03 0:03 0:04 0:03 0:03 0:03 0:03 0:03 0:03 0:03

MKO K ( Vega) 15:18 17:02 14:52 14:86 15:12 14:02 16:06 13:69 14:65 15:29 14:49 14:84 15:40 15:46 15:18 16:72 16:41 14:54 15:61 15:74 15:12 15:25 16:50 14:78 15:41 15:00 15:75 14:76 15:61 15:20 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03 0:03

Instrument UFTI UFTI UFTI UFTI UFTI UFTI UFTI SpeX UFTI UFTI UFTI SpeX UFTI SpeX UFTI UFTI UFTI SpeX UFTI UFTI UFTI SpeX SpeX UFTI UFTI SpeX UFTI SpeX SpeX SpeX

0:15 0:78] 0:19 0:15 0:35] 0:12 0:61] 0:05 0:26] 0:18 0:08 0:16 0:48] 0:17 0:15 0:58] 0:61] 0:08 0:19 0:19 0:10 0:24 0:13 0:14 0:71] 0:23] 0:31] 0:10 0:16 0:15

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also available in the electronic edition of the Astronomical Journal. s denote asinh magnitudes of dwarfs not detected in SDSS i. identified M dwarf; no spectrum obtained. identified mid-L dwarf; no spectrum obtained. identified early L dwarf; no spectrum obtained.

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CHIU ET AL.

Vol. 131

Fig. 1.--SDSS z finding charts for the 73 new M, L, and T dwarfs found in this work. North is up, and east is left. The fields of view are 3 0 ; 3 0 .

2.3. Spectroscopic Observations We obtained near-infrared spectra of 65 newly identified SDSS dwarfs whose near-infrared colors are consistent with types mid-L and later. We also obtained spectra of the T dwarf 2MASS J1209ю1004 ( Burgasser et al. 2004), the mid-L dwarf 2MASS J2101+1756 ( Kirkpatrick et al. 2000), three L dwarfs identified by K04 on the basis of their colors (SDSS J0740+ 2009, SDSS J0756+2314, and SDSS J0809+4434), one L dwarf with uncertain spectral type (SDSS J0805+4812; K04), and one T dwarf with incomplete spectral coverage (SDSS J2124+0100; K04). The new spectra allow more accurate classification of these previously reported L and T dwarfs. We did not obtain spectra of the two M dwarfs and six early to mid-L dwarfs because of observing time constraints.

The spectra were obtained using the UKIRT Imaging Spectrometer ( UIST; Ramsay-Howat et al. 2000) and Cooled Grating Spectrometer (CGS4; Wright et al. 1993) on UKIRT, as well as SpeX at the IRTF. The UKIRT instrument configurations and observational procedures are described by K04. SpeX was used in the low-resolution prism mode with a slit width of 0B5, giving a wavelength coverage of 0.8 2.5 m and a resolution of $150. The on-target exposure time was 120 s, and each star was nodded along the slit for a total observation time of 48 80 minutes. Flat fields and arc spectra for wavelength calibration were obtained using the SpeX calibration box lamps. A0 stars were observed as telluric calibrators, and the data were reduced using the Spextool package (Cushing et al. 2004; Vacca et al. 2003). The flux calibration of the spectra was improved by adjusting the relative flux level to match our JHK photometry. Tables 3 and 4 list the

No. 5, 2006

NEW L AND T DWARFS FROM SDSS

2727

Fig. 1.-- Continued

instruments and dates of observation for each dwarf in our spectral sample. Figure 2 shows spectra of selected L and T dwarfs representing the range of types in our sample.8 Most spectra cover the wavelength range $1 2.5 m. Interesting and diagnostic absorption features are identified above the displayed spectra. 3. SPECTRAL CLASSIFICATION The near-infrared classification of L and T dwarfs is generally accomplished either by directly comparing the spectra with
More extensive spectral and photometric data for this and other samples can be found at http://www.jach.hawaii.edu /~ skl / LTdata.html.
8

standard dwarf templates or by measuring indices defined for their diagnostic spectral bands (i.e., H2O and CH4). As in our past work, we use the spectral-index approach, which is robust even with medium to low signal-to-noise ratios and spectral resolution. To place our present sample of SDSS L dwarfs in the context of those presented by G02 and K04, we classified the L dwarfs using the near-infrared spectral indices of G02. However, we classified the T dwarfs using the new spectral indices of Burgasser et al. (2006a), which unify the similar T classification schemes of G02 and Burgasser et al. (2002b). The unified scheme uses five primary indices: H2O-J centered at 1.15 m, CH4-J at 1.32 m, H2O-H at 1.4 m, CH4-H at 1.65 m, and CH4-K at 2.2 m. The values of the unified indices are inverted with respect to

2728

CHIU ET AL.

Fig. 1.-- Continued

those of G02, i.e., the values of the unified indices decrease with later T type. We used both the G02 and unified indices to classify the suspected L-T transition dwarfs, as in some cases one scheme suggests a late L type and the other scheme suggests an early T type. Table 3 lists the G02 indices of 61 L and early T dwarfs for which we have obtained new near-infrared spectra. Of these, 56 are newly identified from the SDSS and 5 are previously known SDSS and 2MASS dwarfs, as described in x 2.3. Values in square brackets are uncertain and have not been included in the final spectral classification. When only a single index could be measured reliably, the spectra were visually compared with standard subtypes for more accurate classification. Table 4 lists the indices for 45 late L and T dwarfs from the unified scheme of Burgasser

et al. (2006a).9 In both tables the uncertainty in the mean spectral type is ф0.5 subtypes, unless otherwise stated. Table 5 lists, in order of spectral type, the optical and /or nearinfrared colors of the 72 dwarfs for which we have new spectra, plus 2MASS J0034+0523. Multiple photometric and spectroscopic measurements (including data from K04) were averaged before determining the final colors and types. The i ю z colors for dwarfs not detected in i were computed using the SDSS 5 detection limit of i ј 22:5. The spectral types of all newly discovered L and T dwarfs are taken from Tables 3 and 4,
9 Revised spectral types for previously published SDSS T dwarfs and two late L dwarfs (SDSS J1104+5548 and SDSS J2047ю0718) are given in Table 14 of Burgasser et al. (2006a).

Fig. 1.-- Continued

TABLE 2 Additi onal ZJ HK Photometry UT Date ( yyyy mm dd) 2004 2004 2004 2004 2004 2004 2004 2004 2004 2005 08 03 03 03 02 02 03 02 02 08 30 29 29 29 22 22 29 22 22 14

Name 2MASS J00345157+0523050.............................. SDSS J075840.33+324723.4 ............................... SDSS J080531.80+481233.0 ............................... SDSS J093109.56+032732.5 ............................... SDSS J111010.01+011613.1 ............................... SDSS J115700.50+061105.2 ............................... 2MASS J12095613ю1004008 ............................. SDSS J133148.90ю011651.4 .............................. SDSS J152103.24+013142.7 ............................... 2MASS J21011544+1756586 ..............................

UFTI Z .. . 16:47 ф 16:42 ф 18:40 ф 18:00 ф 18:82 ф 17:52 ф 17:04 ф 17:99 ф .. .

MKO J 15:11 ф 0:03 .. . .. . .. . .. . .. . 15:55 ф 0:03 .. . .. . 16:81 ф 0:03

MKO H 15:55 . . . . . 15:24 . . 15:89 ф 0:03 .. .. .. .. .. ф 0:03 .. .. ф 0:03

MKO K 15:96 ф 0:03 .. . .. . .. . .. . .. . 15:17 ф 0:03 .. . .. . 15:00 ф 0:03

Instrument UFTI UFTI UFTI UFTI UFTI UFTI UFTI UFTI UFTI SpeX

0: 0: 0: 0: 0: 0: 0: 0:

05 05 05 05 05 05 05 05

TABLE 3 Spec tr al Indices o f L T1 Dwarfs (Geball e e t a l. 2002 Scheme ) H2O- J Name SDSS J000250.98+245413.8 ................. SDSS J000250.98+245413.8 ................. SDSS J003609.26+241343.3 ................. SDSS J020608.97+223559.2 ................. SDSS J024256.98+212319.6 ................. SDSS J035104.37+481046.8 ................. SDSS J065405.63+652805.4 ................. SDSS J074007.30+200921.9 ................. SDSS J075656.54+231458.5 ................. SDSS J080531.80+481233.0 ................. SDSS J080959.01+443422.2 ................. SDSS J082030.12+103737.0 ................. SDSS J083506.16+195304.4 ................. SDSS J085116.20+181730.0 ................. SDSS J085834.42+325627.7 ................. SDSS J085834.42+325627.7 ................. SDSS J100711.74+193056.2 ................. SDSS J102552.43+321234.0 ................. SDSS J102552.43+321234.0 ................. SDSS J103321.92+400549.5 ................. SDSS J103931.35+325625.5 ................. SDSS J103931.35+325625.5 ................. SDSS J104335.08+121314.1 ................. SDSS J105213.51+442255.7 ................. SDSS J111320.16+343057.9 ................. SDSS J112118.57+433246.5 ................. SDSS J121659.17+300306.3 ................. SDSS J121951.45+312849.4 ................. SDSS J134203.11+134022.2 ................. SDSS J134525.57+521634.0 ................. SDSS J140023.12+433822.3 ................. SDSS J140255.66+080055.2 ................. SDSS J140255.87+080055.6 ................. SDSS J141659.78+500626.4 ................. SDSS J141659.78+500626.4 ................. SDSS J142227.25+221557.1 ................. SDSS J144128.52+504600.4 ................. SDSS J151114.66+060742.9 ................. SDSS J151506.11+443648.3 ................. SDSS J151643.01+305344.4 ................. SDSS J152039.82+354619.8 ................. SDSS J153453.33+121949.2 ................. SDSS J154009.36+374230.3 ................. SDSS J154508.93+355527.3 ................. SDSS J154849.02+172235.4 ................. SDSS J161731.65+401859.7 ................. SDSS J162051.17+323732.1 ................. SDSS J162255.27+115924.1 ................. SDSS J163359.23ю064056.5 ................ SDSS J164916.89+464340.0 ................. SDSS J171147.17+233130.5 ................. SDSS J173101.41+531047.9 ................. SDSS J204317.69ю155103.4 ................ SDSS J204317.69ю155103.4 ................ SDSS J205235.31ю160929.8 ................ 2MASS J21011544+1756586 ................ SDSS J213154.43ю011939.3 ................ SDSS J213154.43ю011939.3 ................ SDSS J213240.36+102949.4 ................. SDSS J213352.72+101841.0 ................. SDSS J232804.58ю103845.7 ................
a

H2O- H Index Type

CH4-H Index Type

CH4-K Index .. . 1.06 1.06 1.04 0.92 1.11 1.04 1.13 0.98 1.14 1.02 1.12 0.99 0.91 1.08 1.07 1.07 .. . 1.04 1.02 .. . 1.44 1.17 1.26 0.86 1.14 0.99 1.15 1.05 0.94 1.13 1.40 1.43 0.99 1.01 1.17 0.95 1.11 1.05 1.28 1.25 1.02 1.09 1.14 0.99 0.94 1.06 0.99 1.04 1.04 1.02 0.98 .. . 1.29 1.28 1.06 .. . 1.14 0.95 1.04 0.93 Type . .. L6 L6 L6 L3.5 L7.5 L6 L7.5 L4.5 L8 L5.5 L7.5 L5 < L3 L6.5 L6.5 L6.5 . .. L5.5 L5.5 . .. T1 L8.5 L9.5
Index

Type

.. . ... 1.57 L5 0.97
2 1.5 1 1.5 2 1.5 1.5 1.5 1.5 2.5 2.5

1 1

1

1 1 1.5 1 2 2 1.5 1.5 1.5 1.5

1.5

1.5 1.5 1 1 1 1 1 1

Note.--Table 3 is also available in the electronic edition of the Astronomical Journal. The uncertainty in mean types is ф0.5 subtypes, unless otherwise noted.

NEW L AND T DWARFS FROM SDSS
TABLE 4 Spec tr al Indices o f L 8 T Dwarfs (B urgasser et a l. 2006 a Scheme ) H2O- J Name SDSS J011912.22+240331.6 ................ SDSS J024749.90ю163112.6 ............... SDSS J032553.17+042540.1 ................ SDSS J035104.37+481046.8 ................ SDSS J073922.26+661503.5 ................ SDSS J080531.80+481233.0 ................ SDSS J082030.12+103737.0 ................ SDSS J085834.42+325627.7 ................ SDSS J085834.42+325627.7 ................ SDSS J090900.73+652527.2 ................ SDSS J100711.74+193056.2 ................ SDSS J103931.35+325625.5 ................ SDSS J103931.35+325625.5 ................ SDSS J104829.21+091937.8 ................ SDSS J105213.51+442255.7 ................ SDSS J120602.51+281328.7 ................ SDSS J120602.51+281328.7 ................ 2MASS J12095613ю1004008 .............. SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS SDSS J121440.95+631643.4 ................ J121951.45+312849.4 ................ J125011.65+392553.9 ................ J135852.68+374711.9 ................ J135852.68+374711.9 ................ J140255.66+080055.2 ................ J140255.66+080055.2 ................ J141530.05+572428.7 ................ J143553.25+112948.6 ................ J143553.25+112948.6 ................ J143945.86+304220.6 ................ J143945.86+304220.6 ................ J150411.63+102718.4 ................ J151114.66+060742.9 ................ J151643.01+305344.4 ................ J152039.82+354619.8 ................ J153417.05+161546.1AB .......... J154009.36+374230.3 ................ J162838.77+230821.1 ................ J163022.92+081822.0 ................ J204317.69ю155103.4 ............... J205235.31ю160929.8 ............... J212413.89+010000.3 ................ J213154.43ю011939.3 ............... J213154.43ю011939.3 ............... CH4- J H2O-H CH4-H CH4-K

2731

Index Type Index Type Index Type Index Type Index Type Mean Typea 0.42 0.41 0.20 0.48 0.61 0.70 0.61 .. . 0.55 0.54 0.65 .. . 0.54 0.47 0.57 .. . 0.45 0.44 0.34 .. . 0.36 0.30 0.31 .. . .. . 0.37 .. . 0.41 .. . 0.45 0.08 0.67 .. . 0.76 0.34 0.61 0.07 0.29 0.69 0.67 0.25 .. . 0.68 T3 T3 T5.5 T2
Instrument and UT Date (yymmdd)

SpeX 050812 1.5 SpeX 050814 SpeX 050813 1 SpeX 050121 1 SpeX 050406 1 SpeX 050122 SpeX 050407 UIST H, K 040409 SpeX 050123 SpeX 050123 SpeX 050406 CGS4 H 041229 SpeX 050122 1 CGS4 J 040514, UIST H. K 1 CGS4 J 040430, UIST H, K CGS4 H 050306 SpeX 050408 CGS4 Z 040627, J 040430, UIST H, K 040430 1 SpeX 050123 UIST H, K 040703 CGS4 J 040513, UIST H, K CGS4 J 040531 1 SpeX 050408 UIST H, K 040429 UIST H, K 040511 1 CGS4 J 040609, UIST H, K CGS4 H 041229 1 SpeX 050407 1 CGS4 H 041229 SpeX 050123 CGS4 J 040613, UIST H, K SpeX 050406 1 UIST H, K 040605 1 CGS4 J 040622, UIST H, K SpeX 050406 SpeX 050813 CGS4 J 040729, H 040916 CGS4 J 040502, UIST H, K 1 SpeX 050812 1 SpeX 050812 1 SpeX 050811 CGS4 H 050801 SpeX 050811

040409 040405

040408

040430

040615

040405

040429

Note.--Table 4 is also available in the electronic edition of the Astronomical Journal. a The uncertainty in mean types is ф0.5 subtypes, unless otherwise noted.

respectively. The subtypes adopted for the L8 T1 dwarfs are those produced by the classification scheme that exhibited the more definitive and complete set of indices for its resulting subtype. If both schemes indicated a late L type, then the G02 designation was adopted. If both schemes indicated an early T type, then the unified T classification of Burgasser et al. (2006a) was used. The only exception to these rules is SDSS J1511+0607 (T0 ф 2), for which a definitive set of indices was derived only in the G02 scheme. The uncertainty of all the subtypes listed in Table 5 is ф0.5 subtypes, unless otherwise stated. The uncertainties of the L6 T1 dwarfs are typically >1 subtype, which suggests that the presence of condensate cloud decks undermines the internal consistency of the spectral indices.

Consequently, the indices become more a probe of cloud optical depth than a measure of effective temperature (Stephens 2003; K04; Leggett et al. 2005). Approximately 75% of the dwarfs whose mean spectral types are very uncertain have CH4-K spectral types that are significantly earlier than indicated by their J- and H-band indices. This effect is also seen in the L8 T0 sample of K04. Because the optical and K-band fluxes emerge from more opaque regions of the atmosphere (specifically from regions above the cloud decks), they are likely to be better indicators of Teff than the flux emerging from the clear J- and H-band windows. Golimowski et al. (2004a) showed that Teff is approximately constant for L7 T4 types, so it might be expected that the L-T transition dwarfs have a constant optical and K-band

2732

CHIU ET AL.

Fig. 2.--Representative optical and near-infrared spectra of the L and T dwarfs discovered in this work. The typical spectral resolution is $150. SDSS designations are given above the dashed line corresponding to the zero flux level. The locations of significant spectral features are indicated at the top of each panel. Left, L4.5 T1; right, T2.5 T7.

spectral type of $L8, while their J- and H-band indices reflect changes in optical depth caused by varying condensate clouds. The newly identified L dwarf SDSS J1025+3212 ( L7:5 ф 2:5) has particularly scattered spectral indices ( Tables 3 and 4), indicating that it may be multiple and/or variable. Figure 3 shows the SpeX and CGS4 spectra of SDSS J1025+3212 along with comparison L5 and T1 spectra. Its H2O-J index suggests a T0 type, while its CH4-J, H2O-H, and CH4-K indices suggest a mid-L type. Evidence of CH4 absorption at 1.6 m is seen in the CGS4 spectrum but not in the SpeX spectrum obtained 1 month later. Attempts to reproduce the spectrum as a composite of L and T spectra failed. High-resolution imaging and photometric monitoring are needed to investigate the nature of this peculiar brown dwarf. Ambiguous types such as SDSS J1025+3212 give cause for reexamining the near-infrared classification scheme for L dwarfs, especially near the L-T transition. Moreover, two of the first known early T dwarfs, SDSS J0423ю0414 and SDSS J1021ю 0304, have recently been found to be binary ( Burgasser et al. 2006b; A. J. Burgasser et al. 2006, in preparation). These binary dwarfs contributed significantly to the definition of G02's standard indices at the L-T transition. Revision of these indices must be based on single dwarfs, so knowing which transition dwarfs are multiple is prerequisite to merging a revised L infrared classification scheme with the unified T classification scheme of Burgasser et al. (2006a). Several high-resolution imaging searches for close-binary brown dwarfs are being conducted with the Hubble Space Telescope and ground-based adaptive optics imagers ( Burgasser et al. 2003; Bouy et al. 2003; McCaughrean et al. 2004; Golimowski et al. 2004b; Liu & Leggett 2005; Liu et al. 2006; Burgasser et al. 2006b). Segregating the single and multiple transition dwarfs will not only help define the ``standard'' L and T sequences but will clarify our understanding of the breakup of the condensate cloud decks across the L-T transition, which is currently a controversial aspect of ultracool atmosphere models ( Burgasser et al. 2002a; Tsuji & Nakajima 2003; K04; Burrows et al. 2006).

4. SPECTRAL TYPE AND NEAR-INFRARED COLORS Figure 4 shows plots of SDSS and MKO colors versus spectral type for the L and T dwarfs listed in Table 5 of this paper and in Table 9 of K04. Most of the spectral types have been assigned by us from our own spectra, but a few types are adopted from other published work. (See the notes for Table 5 and K04's Table 9.) While the colors are generally correlated with spectral type, they are also significantly scattered. The J ю H colors of L3 T1 dwarfs show a dispersion of $0.5 mag, as do the H ю K colors of all dwarfs later than type L3. These dispersions are likely due to wide ranges of grain sedimentation properties and metallicity in the L dwarfs and wide ranges of gravity and metallicity in the T dwarfs ( K04 and references therein). As noted by K04, a small population of L dwarfs has unusually blue near-infrared colors, and we have found in this sample a small population of T dwarfs with unusually red colors. These unusual dwarfs are marked in Figure 4. Figure 5 shows the spectra of the anomalously blue mid-L dwarfs SDSS J1033+ 4005, SDSS J1422+2215, and SDSS J1121+4332, along with the spectrum of the normal L6 dwarf SDSS J0654+6528. The spectra of the blue dwarfs show strong H2O and FeH absorption bands, which may be due to subsolar metallicity and /or thinner condensate cloud decks. Figure 6 shows the spectra of the unusually red early-T dwarfs SDSS J1516+3053 and SDSS J1415+5724, along with two normal reference spectra. SDSS J1516+3053 shows weak CH4 bands but strong H2O bands. SDSS J1415+5724 displays unusually weak K-band CH4 absorption. Attempts to reproduce these spectra as composite binary systems failed, but, as previously discussed, we may not know the true spectra of single L-T transition dwarfs. Liu et al. (2006) show that one of our new T dwarfs, SDSS J1534+1615, is a close T1 T2 and T5 T6 binary whose brighter J-band component is the fainter one in H and K. This near-infrared flux inversion suggests that the system straddles the ``early T hump'' in the absolute magnitude color diagrams (e.g., K04; Golimowski et al. 2004a). Clearly, high-resolution imaging of dwarfs with

TABLE 5 L and T Dwarf Colors ve rsus Sp ectral Type Name SDSS J111320.16+343057.9 .................................. SDSS J144128.52+504600.4 .................................. SDSS J075656.54+231458.5 .................................. SDSS J121659.17+300306.3 .................................. SDSS J134525.57+521634.0 .................................. SDSS J171147.17+233130.5 .................................. SDSS J232804.58ю103845.7 ................................. SDSS J153453.33+121949.2 .................................. SDSS J024256.98+212319.6 .................................. SDSS J161731.65+401859.7 .................................. SDSS J083506.16+195304.4 .................................. SDSS J085116.20+181730.0 .................................. SDSS J213240.36+102949.4 .................................. SDSS J154849.02+172235.4 .................................. SDSS J164916.89+464340.0 .................................. SDSS J213352.72+101841.0 .................................. SDSS J000250.98+245413.8 .................................. SDSS J003609.26+241343.3 .................................. SDSS J020608.97+223559.2 .................................. SDSS J134203.11+134022.2 .................................. SDSS J141659.78+500626.4 .................................. SDSS J065405.63+652805.4 .................................. SDSS J173101.41+531047.9 .................................. SDSS J074007.30+200921.9 .................................. SDSS J080959.01+443422.2 .................................. SDSS J103321.92+400549.5 .................................. SDSS J162051.17+323732.1 .................................. SDSS J162255.27+115924.1 .................................. SDSS J163359.23ю064056.5 ................................. SDSS J142227.25+221557.1 .................................. 2MASS J21011544+1756586 ................................. SDSS J104335.08+121314.1 .................................. SDSS J140023.12+433822.3 .................................. SDSS J102552.43+321234.0 .................................. SDSS J112118.57+433246.5 .................................. SDSS J151506.11+443648.3 .................................. SDSS J154508.93+355527.3 .................................. SDSS J100711.74+193056.2 .................................. SDSS J121951.45+312849.4 .................................. SDSS J154009.36+374230.3 .................................. SDSS J204317.69ю155103.4 ................................. SDSS J213154.43ю011939.3 ................................. SDSS J080531.80+481233.0 .................................. SDSS J082030.12+103737.0 .................................. SDSS J151114.66+060742.9 .................................. SDSS J152039.82+354619.8 .................................. SDSS J105213.51+442255.7 .................................. SDSS J151643.01+305344.4 .................................. SDSS J035104.37+481046.8 .................................. SDSS J085834.42+325627.7 .................................. SDSS J103931.35+325625.5 .................................. SDSS J205235.31ю160929.8 ................................. SDSS J073922.26+661503.5 .................................. SDSS J090900.73+652527.2 .................................. SDSS J140255.66+080055.2 .................................. SDSS J011912.22+240331.6 .................................. SDSS J024749.90ю163112.6 ................................. SDSS J143553.25+112948.6 .................................. SDSS J104829.21+091937.8 .................................. SDSS J143945.86+304220.6 .................................. SDSS J120602.51+281328.7 .................................. 2MASS J12095613ю1004008 ................................ SDSS J141530.05+572428.7 .................................. SDSS J121440.95+631643.4 .................................. SDSS J153417.05+161546.1ABd ........................... Type
a

i ю zb 2:23 ф 0:16 1:96 ф 0:17 >2.68 2:70 ф 0:26 2:18 ф 0:20 1:95 ф 0:27 1:68 ф 0:19 2:30 ф 0:06 2:22 ф 0:20 2:28 ф 0:19 2:26 ф 0:09 2:24 ф 0:17 2:24 ф 0:11 2:50 ф 0:08 2:66 ф 0:21 2:20 ф 0:19 2:21 ф 0:18 >2.43 3:17 ф 0:17 2:45 ф 0:22 2:48 ф 0:25 2:08 ф 0:06 2:21 ф 0:16 >2.72 2:54 ф 0:17 2:40 ф 0:17 >2.49 2:50 ф 0:18 2:55 ф 0:09 2:45 ф 0:17 2:76 ф 0:28 3:13 ф 0:19 >3.42 >2.81 2:38 ф 0:21 2:57 ф 0:16 2:41 ф 0:20 >2.74 3:12 ф 0:16 >3.47 >2.78 >2.49 2:20 ф 0:05 >2.47 2:79 ф 0:20 3:55 ф 0:12 >3.39 >2.51 >2.93 3:02 ф 0:16 >3.09 >3.44 >2.64 >3.75 >2.57 >2.04 >2.67 >2.37 >2.81 >2.26 >3.02 .. . >2.63 >2.85 >2.30

zюJ ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф . .. 3:38 ф 3:60 ф 3:58 ф 2:84 3:01 3:02 2:82 2:79 3:11 2:99 2:91 2:97 2:98 2:90 3:00 2:87 2:73 2:64 2:84 2:97 2:99 2:91 2:96 2:91 2:81 3:02 3:11 2:91 2:80 2:84 2:54 2:76 2:84 2:87 3:04 2:92 2:80 2:89 2:96 2:90 3:01 3:00 2:70 2:85 2:72 3:01 3:00 3:26 2:84 3:22 3:20 3:28 2:74 3:25 3:02 3:11 2:94 3:08 3:60 3:10 3:09 3:30 3:27 3:38 0:08 0:09 0:07 0:11 0:10 0:13 0:12 0:04 0:09 0:10 0:06 0:09 0:06 0:05 0:09 0:10 0:09 0:12 0:05 0:09 0:10 0:05 0:08 0:10 0:07 0:07 0:12 0:08 0:05 0:09 0:09 0:05 0:05 0:09 0:10 0:07 0:09 0:10 0:05 0:07 0:10 0:10 0:04 0:09 0:07 0:04 0:07 0:11 0:07 0:06 0:07 0:06 0:09 0:06 0:09 0:11 0:11 0:10 0:09 0:10 0:08 0:09 0:10 0:12

J юH 0:92 0:88 0:98 0:70 0:75 0:84 0:78 0:85 0:86 1:14 0:82 0:88 0:86 0:85 0:76 0:73 0:93 0:80 0:75 0:95 0:76 0:73 0:82 0:85 1:12 0:69 0:94 0:74 0:75 0:75 0:92 0:95 0:98 0:91 0:48 0:91 0:93 0:90 0:87 0:91 0:85 0:84 0:60 0:94 0:67 0:91 0:80 0:93 0:48 0:88 0:69 0:59 0:44 0:49 0:60 0:40 0:42 0:52 0:44 0:44 0:27 0:31 0:40 0:25 0:25 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:04 0:04 0:04 0:06 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:05 0:04 0:04 0:04 0:04 0:04 0:06 0:05 0:04 0:05 0:04 0:04 0:04 0:04 0:05 0:05 0:06 0:04 0:04 0:04 0:04 0:04 0:06 0:06 0:04 0:04 0:07 0:04 0:04 0:04 0:04 0:04 0:06 0:04 0:04 0:04 0:04 0:05 0:04 0:04 0:05 0:04 0:04 0:04 0:04 0:04 0:05 0:04 0:04 0:04 0:04 0:04 0:04 0:04

H юK 0:74 0:80 0:82 0:63 0:76 0:75 0:79 0:73 0:76 0:85 0:71 0:83 0:76 0:75 0:59 0:58 0:67 0:80 0:56 0:82 0:68 0:76 0:72 0:71 0:94 0:45 0:83 0:69 0:71 0:48 0:89 0:67 0:71 0:82 0:43 0:77 0:75 0:70 0:68 0:77 0:61 0:70 0:50 0:51 0:64 0:54 0:63 0:74 0:63 0:73 0:46 0:45 0:26 0:13 0:52 0:20 0:50 0:37 0:08 0:19 ю0:14 0:07 0:54 0:07 0:31 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:05 0:04 0:04 0:04 0:04 0:04 0:04 0:05 0:04 0:04 0:04 0:04 0:04 0:04 0:06 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:06 0:04 0:04 0:06 0:04 0:04 0:04 0:04 0:04 0:06 0:04 0:04 0:04 0:04 0:05 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:07 0:04 0:06 0:04 0:04 0:04 0:05 0:04

J юK 1:66 1:68 1:80 1:33 1:51 1:59 1:57 1:58 1:62 1:99 1:53 1:71 1:62 1:60 1:35 1:31 1:60 1:60 1:30 1:77 1:44 1:49 1:54 1:56 2:06 1:14 1:77 1:43 1:46 1:23 1:81 1:62 1:69 1:73 0:91 1:68 1:68 1:60 1:55 1:68 1:46 1:54 1:10 1:45 1:31 1:45 1:43 1:67 1:11 1:61 1:15 1:04 0:70 0:62 1:12 0:60 0:92 0:89 0:52 0:63 0:13 0:38 0:94 0:32 0:56 ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф ф 0:04 0:04 0:04 0:06 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:06 0:05 0:04 0:05 0:04 0:04 0:04 0:04 0:06 0:05 0:06 0:04 0:04 0:04 0:04 0:04 0:06 0:06 0:04 0:04 0:06 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:05 0:04 0:04 0:05 0:04 0:04 0:04 0:04 0:04 0:07 0:04 0:06 0:04 0:04 0:04 0:05 0:04

J

c

L3.0 L3.0 L3.5 ф L3.5 ф L3.5 L3.5 ф L3.5 L4.0 ф L4.0 L4.0 L4.5 L4.5 ф L4.5 ф L5.0 L5.0 L5.0 ф L5.5 L5.5 L5.5 L5.5 L5.5 ф L6.0 ф L6.0 ф L6.0 ф L6.0 L6.0 L6.0 L6.0 ф L6.0 L6.5 ф L6.5 ф L7.0 ф L7.0 ф L7.5 ф L7.5 L7.5 ф L7.5 L8.0 ф L8.0 L9.0 ф L9.0 L9.0 L9.5 ф L9.5 ф T0.0 ф T0.0 ф T0.5 ф T0.5 ф T1.0 ф T1.0 T1.0 T1.0 ф T1.5 ф T1.5 T1.5 T2.0 T2.0 ф T2.0 ф T2.5 T2.5 T3.0 T3.0 T3.0 ф T3.5 ф T3.5

1.0 1.0 1.5 1.5

1.5 1.0

1.0

2.0 1.0 1.5 1.5

1.5 2.0 1.0 1.0 1.0 2.5 1.5 1.5 1.5

1.5 2.0 2.0 1.0 1.0 1.0 1.5

1.0 1.0

1.5 1.0

1.0 1.0

16.92 16.86 16.80 16.89 17.05 16.84 16.77 15.27 17.05 16.83 15.94 16.68 16.38 16.09 17.09 16.92 17.02 17.08 16.34 16.90 16.79 16.08 16.32 16.67 16.37 16.74 17.17 16.89 16.00 16.87 16.81 15.82 16.16 16.89 17.04 16.54 16.97 16.75 15.85 16.33 16.87 17.29 14.61 17.03 15.83 15.47 15.89 16.79 16.29 16.33 16.16 16.04 16.75 15.81 16.85 16.86 16.73 17.04 16.39 16.97 16.10 15.55 16.49 16.05 16.62

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CHIU ET AL.
TABLE 5-- Continued Name Typea T4.0 T4.5 ф 1.0 T5.0 T5.5 T5.5 T6.5 T7.0 T7.0 i ю zb >2.55 >2.61 >2.79 >2.75 >2.37 .. . >2.16 >2.27 zюJ 3:83 3:72 3:83 3:85 3:95 ф ф ф ф ф . .. 3:85 ф 3:98 ф 0:09 0:09 0:12 0:09 0:10 0:14 0:10 J юH 0:05 ю0:24 ю0:24 ю0:35 ю0:17 ю0:44 ю0:43 ю0:38 ф ф ф ф ф ф ф ф 0:04 0:04 0:04 0:04 0:04 0:04 0:04 0:05 0 ю0 0 ю0 ю0 ю0 ю0 ю0 H юK :00 :25 :05 :22 :06 :41 :10 :09 ф ф ф ф ф ф ф ф 0:04 0:06 0:04 0:05 0:04 0:04 0:04 0:05 J юK 0:05 ю0:49 ю0:19 ю0:57 ю0:23 ю0:85 ю0:53 ю0:47 ф ф ф ф ф ф ф ф 0:04 0:06 0:04 0:05 0:04 0:04 0:04 0:04

Vol. 131

J

c

SDSS J125011.65+392553.9 .................................. SDSS J135852.68+374711.9 .................................. SDSS J212413.89+010000.3 .................................. SDSS J032553.17+042540.1 .................................. SDSS J163022.92+081822.0 .................................. 2MASS J00345157+0523050e ............................... SDSS J150411.63+102718.4 .................................. SDSS J162838.77+230821.1 ..................................

16.12 16.17 15.88 15.88 16.18 15.11 16.49 16.25..

Note.--Table 5 is also available in the electronic edition of the Astronomical Journal. a The uncertainty in spectral types is ф0.5 subtypes, unless otherwise noted. b The i ю z colors of dwarfs not detected in i are calculated using a 5 detection limit of i ј 22:5 and are indicated with greater than signs to show lower limits. c J photometry errors are typically 0.03 mag (also see Table 1). d Identified by Liu et al. (2006) as a close binary with T1 T2 and T5 T6 components. e Spectral type from Burgasser et al. (2006a).

unusual colors is warranted, as are parallax and velocity studies to determine their kinematic properties. 5. SUMMARY Thanks to the great gains in detection efficiency provided by large digital sky surveys, observers have reached the onceunimaginable position of routinely discovering nearby field brown dwarfs. In this paper we report the discovery of 71 L and T dwarfs identified during our ongoing search for high-redshift quasars and brown dwarfs in SDSS imaging data. Using nearinfrared photometry and spectra obtained over the past 2 years at UKIRT and IRTF, we have classified these dwarfs using the L classification scheme of G02 and the new unified T classification scheme of Burgasser et al. (2006a). The near-infrared colors of the 71 dwarfs exhibit the same trends, scatter, and anomalies noted in previously reported samples. The unusual spectral features exhibited by some dwarfs may lead to a better understanding of their underlying atmospheric properties. We plan to apply our results to the revision of the spectral infrared indices used in the near-infrared classification of L dwarfs. We will also integrate the 71 new L and T dwarfs into a complete magnitudelimited catalog for the purpose of determining the substellar luminosity function.

Fig. 3.--Unusual spectra of the L7:5 ф 2:5 dwarf, SDSS J1025+3212 (thick lines). The spectra show 1.1 m H2O and 1.4, 2.2 m CH4 absorption features usually associated with T0 dwarfs, as well as H2O features typical of L5 dwarfs. The 1.6 mCH4 absorption features seen in the CGS4 and SpeX spectra appear variable. Spectra of SDSS J0539ю0059 (L5) and SDSS J0837ю0000 ( T1) are shown for reference ( Leggett et al. 2000).

Fig. 4.-- Optical and near-infrared colors of the dwarfs listed in Table 5 of this work ( filled circles) and reported previously by K04 and Leggett et al. (2002) (open circles). Five dwarfs with unusual colors are labeled, as discussed in x 4: SDSS J1033+4005 ( first panel ), SDSS J1422+2215 (second panel ), SDSS J1121+4332 (third panel ), SDSS J1516+3053 ( fourth panel ), and SDSS J1415+5724 ( fifth panel ). Horizontal error bars are shown for those dwarfs whose spectral types are more uncertain than ф0.5 subtypes. The small vertical error bar in the top right corner of each panel indicates the typical color error. In the top panel, the i ю z colors of dwarfs not detected in SDSS i are shown with arrows as lower limits based on a 5 detection limit of i ј 22:5. Dwarfs with type >T0 are almost all nondetections in SDSS i, shown by the large barred arrow in i ю z.

No. 5, 2006

NEW L AND T DWARFS FROM SDSS

2735

Fig. 5.--Spectra of unusually blue L dwarfs with strong H2O and FeH absorption bands. These features may be due to subsolar metallicity and /or thinner condensate cloud decks. A spectrum of the typical L6 dwarf SDSS J0654+6528 is shown for reference.

Fig. 6.--Spectra of unusually red early T dwarfs (thick curves) compared with spectra of typical T dwarfs. SDSS J1516+3053 has weak methane bands but strong water bands. SDSS J1415+5724 has unusually weak K-band methane.

We thank the staff at APO, IRTF, and UKIRT for their assistance with the observations and data acquisition. Some data were obtained through the UKIRT Service Programme. UKIRT is operated by the Joint Astronomy Centre on behalf of the UK Particle Physics and Astronomy Research Council. APO is owned and operated by the Astrophysical Research Consortium (ARC ). The IRTF is operated by the University of Hawaii under Cooperative Agreement NCC5-538 with the National Aeronautics and Space Administration ( NASA), Office of Space Science, Planetary Astronomy Program. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center ( IPAC )/California Institute of Technology, funded by NASA and the National Science Foundation ( NSF ). This research has also made use of the NASA / IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. X. F. acknowledges support from NSF grant AST 03-07384, a Sloan Research Fellowship, and a David and Lucile Packard

Fellowship. T. R. G.'s research is supported by the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., on behalf of the international Gemini partnership of Argentina, Australia, Brazil, Canada, Chile, the United Kingdom, and the United States of America. The Sloan Digital Sky Survey is managed by ARC for the Participating Institutions: the University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Korean Scientist Group, Los Alamos National Laboratory, the Max Planck Institute for Astronomy, the Max Planck Institute for Astrophysics, New Mexico State University, the University of Pittsburgh, the University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. Funding for SDSS has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, NASA, the NSF, the US Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS Web site is http://www.sdss.org.

REFERENCES Abazajian, K., et al. 2004, AJ, 128, 502 Burrows, A., Sudarsky, D., & Hubeny, I. 2006, ApJ, 640, 1063 Allen, P. R., Koerner, D. W., Reid, I. N., & Trilling, D. E. 2005, ApJ, 625, 385 Cushing, M. C., Vacca, W. D., & Rayner, J. T. 2004, PASP, 116, 362 Bouy, H., Brandner, W., Martin, E. L., Delfosse, X., Allard, F., & Basri, G. ґ Epchtein, N. 1997, in The Impact of Large Scale Near-IR Sky Surveys, ed. ґ 2003, AJ, 126, 1526 F. Garzon et al. ( Dordrecht: Kluwer), 15 Burgasser, A. J. 2004, ApJS, 155, 191 Fan, X., et al. 1999, AJ, 118, 1 Burgasser, A. J., Geballe, T. R., Leggett, S. K., Kirkpatrick. J. D., & ------. 2000a, AJ, 119, 928 Golimowski, D. A. 2006a, ApJ, 637, 1067 ------. 2000b, AJ, 120, 1167 Burgasser, A. J., Kirkpatrick, J. D., Reid, I. N., Brown, M. E., Miskey, C. L., & ------. 2001a, AJ, 121, 54 Gizis, J. E. 2003, ApJ, 586, 512 ------. 2001b, AJ, 122, 2833 Burgasser, A. J., Marley, M. S., Ackerman, A. S., Saumon, D., Lodders, K., ------. 2003, AJ, 125, 1649 Dahn, C. C., Harris, H. C., & Kirkpatrick, J. D. 2002a, ApJ, 571, L151 ------. 2004, AJ, 128, 515 Burgasser, A. J., McElwain, M. W., Kirkpatrick. J. D., Cruz, K. L., Tinney, C. G., Fukugita, M., Ichikawa, T., Gunn, J. E., Doi, M., Shimasaku, K., & Schneider, & Reid, I. N. 2004, AJ, 127, 2856 D. P. 1996, AJ, 111, 1748 Burgasser, A. J., Reid, I. N., Leggett, S. K., Kirkpatrick, J. D., Liebert, J., & Geballe, T. R., et al. 2002, ApJ, 564, 466 (G02) Burrows, A. 2006b, ApJ, 634, L177 Golimowski, D. A., et al. 2004a, AJ, 127, 3516 Burgasser, A. J., et al. 1999, ApJ, 522, L65 ------. 2004b, AJ, 128, 1733 ------. 2002b, ApJ, 564, 421 Gunn, J. E., et al. 1998, AJ, 116, 3040

2736

CHIU ET AL.
Ramsay-Howat, S. K., Ellis, M. A., Gostick, D. C., Hastings, P. R., Strachan, M., & Wells, M. 2000, Proc. SPIE, 4008, 1067 Rayner, J. T., Toomey, D. W., Onaka, P. M., Denault, A. J., Stahlberger, W. E., Vacca, W. D., Cushing, M. C., & Wang, S. 2003, PASP, 115, 362 Richards, G. T., et al. 2002, AJ, 123, 2945 Roche, P. F., et al. 2003, Proc. SPIE, 4841, 901 Schneider, D. P., et al. 2002, AJ, 123, 458 Simons, D. A., & Tokunaga, A. T. 2002, PASP, 114, 169 Skrutskie, M. F., et al. 1997, in The Impact of Large Scale Near-IR Sky ґ Surveys, ed. F. Garzon et al. ( Dordrecht: Kluwer), 25 Smith, J., et al. 2002, AJ, 123, 2121 Stephens, D. C. 2003, in IAU Symp. 211, Brown Dwarfs, ed. E. Martin (San ґ Francisco: ASP), 355 Stoughton, C., et al. 2002, AJ, 123, 485 Strauss, M. A., et al. 1999, ApJ, 522, L61 Tokunaga, A. T., Simons, D. A., & Vacca, W. D. 2002, PASP, 114, 180 Tsuji, T., & Nakajima, T. 2003, ApJ, 585, L151 Tsvetanov, Z. I., et al. 2000, ApJ, 531, L61 Vacca, W. D., Cushing, M. C., & Rayner, J. T. 2003, PASP, 115, 389 Wright, G. S., Mountain, C. M., Bridger, A., Daly, P. N., Griffin, J. L., & Ramsay-Howat, S. K. 1993, Proc. SPIE, 1946, 547 York, D. G., et al. 2000, AJ, 120, 1579 Zheng, W., et al. 2000, AJ, 120, 1607

Hawarden, T. G., Leggett, S. K., Letawsky, M. B., Ballantyne, D. R., & Casali, M. M. 2001, MNRAS, 325, 563 Hawley, S., et al. 2002, AJ, 123, 3409 Hogg, D. W., Finkbeiner, D. P., Schlegel, D. J., & Gunn, J. E. 2001, AJ, 122, 2129 Kirkpatrick, J. D. 2005, ARA&A, 43, 195 Kirkpatrick, J. D., et al. 1999, ApJ, 519, 802 ------. 2000, AJ, 120, 447 Knapp, G. R., et al. 2004, AJ, 127, 3553 ( K04) Leggett, S. K., Allard, F., Burgasser, A. J., Jones, H. R. A., Marley, M. S., & Tsuji, T. 2005, in 13th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, ed. F. Favata, G. A. J. Hussain, & B. Battrick ( ESA SP-560; Noordwijk: ESA), 143 Leggett, S. K., et al. 2000, ApJ, 536, L35 ------. 2002, ApJ, 564, 452 Liu, M. C., & Leggett, S. K. 2005, ApJ, 634, 616 Liu, M. C., Leggett, S. K., Golimowski, D. A., Chiu, K., Fan, X., Geballe, T. R., Schneider, D. P., & Brinkmann, J. 2006, ApJ, submitted Lupton, R. H., Gunn, J. E., & Szalay, A. S. 1999, AJ, 118, 1406 McCaughrean, M. J., Close, L. M., Scholz, R.-D., Lenzen, R., Biller, B., Brandner, W., Hartung, M., & Lodieu, N. 2004, A&A, 413, 1029 Pier, J. R., Munn, J. A., Hindsley, R. B., Hennessy, G. S., Kent, S. M., Lupton, R. H., & Ivezic, Z. 2003, AJ, 125, 1559