Toward Spectral Classification of L and T Dwarfs: Infrared and Optical Spectroscopy and Analysis

By T. Geballe, G. Knapp, S. Leggett, Xiaohui Fan, D. Golimowski, S. Anderson, J. Brinkmann, István Csabai, J. Gunn, S. Hawley and 19 more. 2001

374 citations recorded by the source corpus.

We present 0.6-2.5 μm, R ≳ 400 spectra of 27 cool, low-luminosity stars and substellar objects. Based on these and previously published spectra, we develop a preliminary spectral classification system for L and T dwarfs. For late L and T types the classification system is based entirely on four spectral indices in the 1-2.5 μm interval. Two of these indices are derived from water absorption bands at 1.15 and 1.4 μm, the latter of which shows a smooth increase in depth through the L and T sequences and can be used to classify both spectral types. The other two indices make use of methane absorption features in the H and K bands, with the K-band index also applicable to mid-to-late L dwarfs. Continuum indices shortward of 1 μm used by previous authors to classify L dwarfs are found to be useful only through mid-L subclasses. We employ the 1.5 μm water index and the 2.2 μm methane index to complete the L classification through L9.5 and to link the new system with a modified version of the 2MASS "color-d" index. By correlating the depths of the methane and water absorption features, we establish a T spectral sequence from T0 to T8, based on all four indices, that is a smooth continuation of the L sequence. We reclassify two 2MASS L8 dwarfs as L9 and L9.5 and identify one SDSS object as L9. In the proposed system methane absorption appears in the K band approximately at L8, two subclasses earlier than its appearance in the H band. The L and T spectral classes are distinguished by the absence and presence, respectively, of H-band methane absorption.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a21c9a5a060e6e6f6e853dc69d9c291d34fefd62

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In Astronomy and Astrophysics

1. A. Burgasser
2. Michael C. Liu
3. J. D. Kirkpatrick
4. M. Marley
5. T. Dupuy
6. K. Luhman
7. Kelle Cruz
8. D. Schneider

In Instrumentation

1. A. Burgasser
2. J. D. Kirkpatrick
3. Michael C. Liu
4. T. Dupuy
5. M. Marley
6. Kelle Cruz
7. K. Luhman
8. D. Schneider

Citations in the corpus

• A Spitzer Infrared Spectrograph Spectral Sequence of M, L, and T Dwarfs (2004, background): “SDSS J0423−0414AB (hereafter SDSS 0423AB) was discovered by Geballe et al. (2002) and subsequently resolved into a binary separated by 0.”
• Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity (2004, methodology): “…TiO and VO, and the T dwarfs, characterized by methane-band absorption in the H and K spectral regions (Martı́n et al. 1997, 1999b; Kirkpatrick et al. 1999, 2000; Strauss et al. 1999; Leggett et al. 2000, 2002b; Geballe et al. 2002, hereafter G02; Burgasser et al. 2002a; Hawley et al. 2002).”
• BANYAN. VII. A NEW POPULATION OF YOUNG SUBSTELLAR CANDIDATE MEMBERS OF NEARBY MOVING GROUPS FROM THE BASS SURVEY (2015, methodology): “2MASS J08575849+5708514 has been discovered by Geballe et al. (2002) as an L8±1 BD. Stephens et al. (2009) used atmosphere model fitting to determine that this object is unusually cloudy and seems to have a low surface gravity (logg = 4.5).”
• Seventy-One New L and T Dwarfs from the Sloan Digital Sky Survey (2006, background): “…(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).”
• Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs (2002, methodology): “For this L3 ± 1 dwarf (Geballe et al. 2002), we may assume Teff ≈ 1800K (Table 2).”
• ε Indi Ba,Bb: The nearest binary brown dwarf (2003, background): “Near-IRH band spectral classification indices forε Indi Ba and ε Indi Bb following the schemes of Geballe et al. (2002) and Burgasser et al. (2002).”
• Individual Dynamical Masses of Ultracool Dwarfs (2017, methodology): “For the latter, we used optical-to-infrared spectra from Geballe et al. (2002), adopting the integrated-light spectrum of SDSS J0423−0414AB7 for each of its components and the spectrum of 2MASS J0559−14048 for the components of SDSS J0926+5847AB.”
• Titanium and Vanadium Chemistry in Low-Mass Dwarf Stars (2002, background): “This switch defines the beginning of the T dwarf regime with the onset of methane absorption in the K and H bands (Kirkpatrick et al. 1999, 2000;Martin et al. 1999; Geballe et al. 2002).”
• SpeX SPECTROSCOPY OF UNRESOLVED VERY LOW MASS BINARIES. I. IDENTIFICATION OF 17 CANDIDATE BINARIES STRADDLING THE L DWARF/T DWARF TRANSITION (2009, methodology): “This could indicate a 7Photometry shown in Figure 9 is based either on direct measurements (Geballe et al. 2002; Leggett et al. 2002; Knapp et al. 2004; Chiu et al. 2006) or synthetic filter corrections from 2MASS photometry as computed directly from the SpeX data; see Section 4.4.”
• MEETING THE COOL NEIGHBORS. X. ULTRACOOL DWARFS FROM THE 2MASS ALL-SKY DATA RELEASE (2008, methodology): “Initial investigations operated in discovery mode, pushing detection to lower and lower temperatures, and extending the spectral classification system to types L (K99;Mart́ın et al., 1999) and T (Geballe et al., 2002; Burgasser et al., 2003, 2006).”
• A NEAR-INFRARED SPECTROSCOPIC STUDY OF YOUNG FIELD ULTRACOOL DWARFS (2013, methodology): “Previous near-IR studies have shown that the H2O absorption bands, as measured by flux ratios (indices), are well-correlated with optical spectral type (e.g., Reid et al. 2001; Geballe et al. 2002; McLean et al. 2003).”
• The 2MASS Wide-Field T Dwarf Search. III. Seven New T Dwarfs and Other Cool Dwarf Discoveries (2004, background): “The scatter in these indices is in fact better than that seen in the classifications of Burgasser et al. (2002) and Geballe et al. (2002), reflecting overall higher signal-to-noise data and the improved spectral index definitions.”
• The First Substellar Subdwarf? Discovery of a Metal-poor L Dwarf with Halo Kinematics (2003, background): “These discoveries include many dozens of substellar objects and extend well beyond the M spectral class into the L (Kirkpatrick et al. 1999; Martı́n et al. 1999) and the T (Burgasser et al. 2002; Geballe et al. 2002) classes.”
• Hubble Space Telescope Observations of Binary Very Low Mass Stars and Brown Dwarfs (2003, background): “…Skrutskie et al. 1997; Cutri et al. 2000),3 and Sloan Digital Sky Survey (SDSS; York et al. 2000) have enabled the discovery of numerous cool dwarfs and led to the definition of new spectral types L (Kirkpatrick et al. 1999; Martı́n et al. 1999b) and T (Burgasser et al. 2002a; Geballe et al. 2002).”
• THE DISCOVERY OF Y DWARFS USING DATA FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE) (2011, background): “…of brown dwarfs at two different wavelengths is not unprecedented as both the L and the T dwarfs have classification systems based in the red optical (Kirkpatrick et al. 1999; Burgasser et al. 2003) and the near infrared (Geballe et al. 2002; Kirkpatrick et al. 2010; Burgasser et al. 2006).”
• THE HAWAII INFRARED PARALLAX PROGRAM. I. ULTRACOOL BINARIES AND THE L/T TRANSITION, (2012, neutral): “…(44) Fan et al. (2000); (45) Forrest et al. (1988); (46) Forveille et al. (2004); (47) Gatewood & Coban (2009); (48) Geballe et al. (2001); (49) Geballe et al. (2002); (50) Geyer et al. (1988); (51) Gizis (1997); (52) Gizis et al. (2000); (53) Gizis et al. (2001); (54) Gizis et al. (2002);…”