Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity

By G. Knapp, S. Leggett, Xiaohui Fan, M. Marley, T. Geballe, D. Golimowski, Douglas P. Finkbeiner, J. Gunn, J. Hennawi, Željko Ivezic´ and 19 more. 2004

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We present new JHK photometry on the MKO-NIR system and JHK spectroscopy for a large sample of L and T dwarfs. Photometry has been obtained for 71 dwarfs, and spectroscopy for 56. The sample comprises newly identified very red objects from the Sloan Digital Sky Survey (SDSS) and known dwarfs from the SDSS and the Two Micron All Sky Survey (2MASS). Spectral classification has been carried out using four previously defined indices from Geballe et al. that measure the strengths of the near infrared water and methane bands. We identify nine new L8–9.5 dwarfs and 14 new T dwarfs from SDSS, including the latest yet found by SDSS, the T7 dwarf SDSS J175805.46+463311.9. We classify 2MASS J04151954-0935066 as T9, the latest and coolest dwarf found to date. We combine the new results with our previously published data to produce a sample of 59 L dwarfs and 42 T dwarfs with imaging data on a single photometric system and with uniform spectroscopic classification. We compare the near-infrared colors and absolute magnitudes of brown dwarfs near the L–T transition with predictions made by models of the distribution and evolution of photospheric condensates. There is some scatter in the Geballe et al. spectral indices for L dwarfs, suggesting that these indices are probing different levels of the atmosphere and are affected by the location of the condensate cloud layer. The near-infrared colors of the L dwarfs also show scatter within a given spectral type, which is likely due to variations in the altitudes, spatial distributions, and thicknesses of the clouds. We have identified a small group of late-L dwarfs that are relatively blue for their spectral type and that have enhanced FeH, H2O, and K I absorption, possibly due to an unusually small amount of condensates. The scatter seen in the H-K color for late-T dwarfs can be reproduced by models with a range in surface gravity. The variation is probably due to the effect on the K-band flux of pressure-induced H2 opacity. The correlation of H-K color with gravity is supported by the observed strengths of the J-band K I doublet. Gravity is closely related to mass for field T dwarfs with ages greater than108 yr and the gravities implied by the H-K colors indicate that the T dwarfs in our sample have masses in the range 15–75MJupiter. One of the SDSS dwarfs, SDSS J111010.01+011613.1, is possibly a very low mass object, with log g ∼ 4.2–4.5 and mass ∼ 10–15MJupiter.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

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Citations in the corpus

A SURVEY OF z ∼ 6 QUASARS IN THE SLOAN DIGITAL SKY SURVEY DEEP STRIPE. I. A FLUX-LIMITED SAMPLE AT zAB < 21 (2007, background): “The open circles in Figure 2 represent known L/T dwarfs from Golimowski et al. (2004), Knapp et al. (2004), and Chiu et al. (2006).”
L and T Dwarf Models and the L to T Transition (2005, background): “Though one is still unsure about the latest Ls and the brightening in J near T3, this conclusion seems reasonable and has also been reached by Burrows et al. (2002b) and Knapp et al. (2004) using different arguments.”
The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs (2020, background): “• SDSS 0758+3247: This early T dwarf was discovered by Knapp et al. (2004).”
Binaries and the L Dwarf/T Dwarf Transition (2006, methodology): “…Tokunaga et al. (2002). derived by fitting an eighth-order polynomial toMK data 9 based on photometry (Geballe et al. 2002; Leggett et al. 2002; Knapp et al. 2004) and parallax data (Dahn et al. 2002; Tinney et al. 2003; Vrba et al. 2004) for 26 unresolved field L and T dwarfs with combined…”
ON THE STELLAR POPULATIONS AND EVOLUTION OF STAR-FORMING GALAXIES AT 6.3 < z ⩽ 8.6 (2009, background): “Figure 3 shows the synthesized colors of brown–dwarf stars (us- ing spectra of brown dwarfs from S. Leggett6, with the data from Golimowski et al. (2004), Knapp et al. (2004) and Chiu et al. (2006)).”
THE HAWAII INFRARED PARALLAX PROGRAM. I. ULTRACOOL BINARIES AND THE L/T TRANSITION, (2012, methodology): “…resolution searches for ultracool binaries were derived primarily from three magnitude-limited searches: the SDSS ultracool dwarf search (e.g., Knapp et al. 2004; Chiu et al. 2006), the 2MASS L dwarf search (e.g., Cruz et al. 2007; Reid et al. 2008b), and the 2MASS T dwarf search (e.g.,…”
Individual Dynamical Masses of Ultracool Dwarfs (2017, neutral): “…Dupu12 = Dupuy & Liu (2012); Dupu14 = Dupuy et al. (2014); Dupu15 = Dupuy et al. (2015b); Dupu16 = this work; Gizi03 = Gizis et al. (2003); Knap04 = Knapp et al. (2004); Kono10 = Konopacky et al. (2010); Lane01 = Lane et al. (2001); Legg00 = Leggett et al. (2000); Legg02a = Leggett et al. (2002);…”
A Spitzer Infrared Spectrograph Spectral Sequence of M, L, and T Dwarfs (2004, background): “In particular, the suppression of the K-band is a result of collision-induced H2 1−0 dipole absorption (CIA H2) centered at 2.4 µm (Borysow 2002; Knapp et al. 2004) which is enhanced in such environments.”
FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME (2015, result): “(1) Cutri et al. (2003), (2) Leggett et al. (2002a), (3) Knapp et al. (2004), (4) Leggett et al. (2010), (5) Naud et al. (2014), (6) Leggett et al. (1998), (7) Chiu et al. (2006), (8) Leggett et al. (2000), (9) Hewett et al. (2006), (10) Leggett et al. (2002b), (11) Lawrence et al. (2007), (12)…”
NEAR-INFRARED SPECTROSCOPY OF THE EXTRASOLAR PLANET HR 8799 b (2010, neutral): “K < 0 mag; e.g., Knapp et al. 2004).”
NEGLECTED CLOUDS IN T AND Y DWARF ATMOSPHERES (2012, background): “Indeed, a large increase infsed with lower Teff values is one way to quickly clear away the silicate and iron clouds (Knapp et al. 2004) 4.2.3.”
BANYAN. VII. A NEW POPULATION OF YOUNG SUBSTELLAR CANDIDATE MEMBERS OF NEARBY MOVING GROUPS FROM THE BASS SURVEY (2015, background): “2MASS J11555389+0559577 was discovered by Knapp et al. (2004) as an L7.”
Discovery of Two T Dwarf Companions with the Spitzer Space Telescope (2006, background): “In comparison, these lines become weaker with lower gravity for late-M and early-L dwarfs (McGovern et al. 2004; Kirkpatrick et al. 2006) but grow stronger with lower gravity at late-T types (Knapp et al. 2004).”
A PATCHY CLOUD MODEL FOR THE L TO T DWARF TRANSITION (2010, background): “In addition to the L to T transition, patchy clouds have been suggested by Folkes et al. (2007) as a possible mechanism to explain those L dwarfs that have unusually blue nearinfrared colors (Cruz et al. 2003; Knapp et al. 2004; Burgasser et al. 2008).”
The Evolution of L and T Dwarfs in Color-Magnitude Diagrams (2008, methodology): “Tsuji & Nakajima (2003), Knapp et al. (2004), and Burrows et al. (2006) have suggested that variations in gravity (i.e., a spread in mass and age) account for the broadening.”
MEETING THE COOL NEIGHBORS. X. ULTRACOOL DWARFS FROM THE 2MASS ALL-SKY DATA RELEASE (2008, background): “However, Knapp et al.(2004) derived a near-infrared spectral type of L9.”
LARGE AREA SURVEY FOR z = 7 GALAXIES IN SDF AND GOODS-N: IMPLICATIONS FOR GALAXY FORMATION AND COSMIC REIONIZATION (2009, methodology): “Figure 1 plots the model spectra of a z ∼ 7 galaxy as well as red objects including low-z galaxies and one of the reddest T dwarf stars (Knapp et al. 2004) which are likely to be prominent interlopers in our photometric sample.”