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L' and M' Photometry of Ultracool Dwarfs | | D. A. Golimowski
; S. K. Leggett
; M. S. Marley
; X. Fan
; T. R. Geballe
; G. R. Knapp
; F. J. Vrba
; A. A. Henden
; C. B. Luginbuhl
; H. H. Guetter
; J. A. Munn
; B. Canzian
; W. Zheng
; Z. I. Tsvetanov
; K. Chiu
; K. Glazebrook
; E. A. Hoversten
; D. P. Schneider
; J. Brinkmann
; | | Date: |
20 Feb 2004 | | Journal: | Astron.J. 127 (2004) 3516 | | Subject: | astro-ph | | Abstract: | We have compiled L’ and M’ photometry of 63 single and binary M, L,and T dwarfs obtained at UKIRT using the MKO filter set. This compilation includes new L’ data for 8 L dwarfs and 13 T dwarfs and new M’ data for 7 L dwarfs, 5 T dwarfs, and Gl 229A. We compute L_bol, BC_K, and T_eff for 42 dwarfs whose flux-calibrated JHK spectra, L’ photometry, and trigonometric parallaxes are available, and we estimate these quantities for 9 other dwarfs whose parallaxes and flux-calibrated spectra have been obtained. BC_K is a well-behaved function of near-IR spectral type with a dispersion of ~0.1 mag for types M6-T5; it is significantly more scattered for types T5-T9. T_eff declines steeply and monotonically for types M6-L7 and T4-T9, but is nearly constant at ~1450 K for types L7-T4 with assumed ages of ~3 Gyr. This constant T_eff is evidenced by nearly unchanging values of L’-M’ between types L6 and T3. We compare the observed K, L’, and M’ luminosities of L and T dwarfs in our sample with those predicted by model atmospheres with varying surface gravities and sedimentation efficiencies. The models indicate that the L3-T4.5 dwarfs generally have higher gravities (log g = 5.0-5.5) than the T6-T9 dwarfs (log g = 4.5-5.0). The predicted M’ luminosities of T dwarfs are 1.5-2.5 times larger than those derived empirically for the T dwarfs in our sample. This discrepancy is attributed to absorption at 4.5-4.9 um by CO, which is not expected under the condition of chemical equilibrium assumed in the models. We determine that the L3 dwarf Kelu-1 and the T0 dwarf SDSS J0423-0414 are probable binary systems. We compute log(L_bol/L_sun) = -5.73 +/- 0.05 and T_eff = 600-750 K for the T9 dwarf 2MASS J0415-0935, which supplants Gl 570D as the least luminous and coolest brown dwarf presently known. | | Source: | arXiv, astro-ph/0402475 | | Services: | Forum | Review | PDF | Favorites | |
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