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

Abstract

We present 0.6È2.5 km, spectra of 27 cool, low-luminosity stars and substellar objects. Based R Z 400 on these and previously published spectra, we develop a preliminary spectral classiÐcation system for L and T dwarfs. For late L and T types the classiÐcation system is based entirely on four spectral indices in the 1È2.5 km interval. Two of these indices are derived from water absorption bands at 1.15 and 1.4 km, 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 km used by previous authors to classify L dwarfs are found to be useful only through mid-L subclasses. We employ the 1.5 km water index and the 2.2 km methane index to complete the L classiÐcation through L9.5 and to link the new system with a modiÐed version of the 2MASS "" color-d ÏÏ 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.

The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

“…Figure 8 shows the distribution of photometric distances obtained from the z magnitudes without (solid line) and with (dotted line) contamination and completeness correction of the sample. It mostly contains brown dwarfs within 20 pc and 120 pc, which most probably belongs to the galactic disc, although it may contain close subdwarfs that can be revealed by high kinematics or low-metallicity features in the spectrum Geballe et al 2002;Burgasser et al 2009;Burningham et al 2010a). The distribution peaks between 60 and 100 pc, which is about the maximal detection distance for late-L and mid-T dwarfs.…”

“…Spectral types for L and T dwarfs are given according to the infrared classification scheme described in Geballe et al (2002) and Burgasser et al (2006), respectively.…”

Parallaxes and physical properties of 11 mid-to-late T dwarfs

“…4 we present three absolute magnitude -IR spectral type diagrams. The IR spectral type classification follows the scheme described in Geballe et al (2002) for L dwarfs and the scheme described in Burgasser et al (2006a) for T dwarfs. The over plotted curves are polynomial fits derived in Liu et al (2006), with the dotted line representing the polynomial obtained excluding from the fit all the known and possible binaries, while the dashed line is the one obtained excluding only the known binaries.…”

Binary frequency of planet-host stars at wide separations

“…Skrutskie et al 2006;Burgasser et al 1999Burgasser et al , 2003bCruz et al 2007), the Sloan Digital Sky Survey (SDSS; e.g. York et al 2000;Leggett et al 2000b;Geballe et al 2002;Chiu et al 2006), the UKIRT Infrared Deep Sky Survey (UKIDSS; Lawrence et al 2007;Lodieu et al 2007;Pinfield et al 2008;Burningham et al 2010Burningham et al , 2013, and the Wide-field Infrared Survey Explorer (WISE; Wright et al 2010;Kirkpatrick et al 2011;Mace et al 2013;Thompson et al 2013). However, only one wide brown dwarf companion co-moving with a planet-host star has been reported to date, HD 3651B (T7.5; d = 11.1 ± 0.1 pc; Mugrauer et al 2006b;Liu et al 2007; Leggett et al 2007;Burgasser 2007).…”