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Spectral Classification and Effective Temperatures of L and T Dwarfs Based on Near-Infrared Spectra
We have obtained near-infrared spectra of L dwarfs, L/T transitionobjects, and T dwarfs using the Subaru telescope. The resulting spectraare examined in detail to study their dependence on spectral types. Onequestion is where the methane feature appears: we suggest that itappears at L8 and marginally at L6.5. The water bands at 1.1 and 1.4μm do not necessarily show steady increase toward later L types butmay show inversion at late L types. This does not necessarily imply thatthe spectral types do not represent a temperature sequence, but rathercan be interpreted as the increasing water abundance being offset by theheavier dust extinction in the later L types. We confirm that the FeH0.99 μm bands appear not only in the late L dwarfs but also in theearly T dwarfs. We suggest that FeH could be dredged up by the surfaceconvective zone induced by the steep temperature gradient as a result ofthe large opacity of the dust cloud itself, and replenished constantlyby convection.We have obtained bolometric luminosities of the objectswith known parallaxes in our sample, first by integrating the spectrabetween 0.87 and 2.5 μm, and second by the K-band bolometriccorrection. Apart from an L3 dwarf, the bolometric luminosities obtainedby both methods agree well, and this implies that the K-band bolometriccorrection, which is obtained using the unified cloudy models, can beapplied to obtain the bolometric luminosities and effective temperaturesof the L and T dwarfs with known parallaxes from the literature. Therelation between the effective temperature and spectral type derivedfrom the K-band bolometric correction shows monotonic behaviorthroughout the L-T sequence.Based on the data collected at the Subaru Telescope, which is operatedby the National Astronomical Observatory of Japan.
| A catalog of precise reference star positions for the astrometry network of the international comet P/Halley compaign
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...71..525D&db_key=AST
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