L′ and M′ photometry of ultracool dwarfs
L′ and M′ photometry of ultracool dwarfs
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DOI：
10.1086/420709
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发表时间：
2004-06-01
影响因子：
5.3
通讯作者：
Brinkmann, J
中科院分区：
文献类型：
--
作者：
Golimowski, DA;Leggett, SK;Brinkmann, J
我们利用莫纳克亚天文台的滤光片装置，对英国红外望远镜上获得的63颗单星和双星M、L和T矮星的L(3.4-4.1um)和M‘(4.6-4.8um)光度进行了汇编。汇编包括L对8颗L矮星和13颗T矮星的新测量，以及对7颗L矮星、5颗T矮星和M1矮星G1229A的新M‘测量。这些新数据分别使L和M‘报道的超冷矮星(T-Eff小于或类似于2400K)的数目增加了0.6倍和1.6倍。我们计算了42颗已有通量校准JHK光谱、L测光和三角视差的矮星的L-BOL、BCK和T-Eff，并估计了另外9颗已获得视差和通量校准光谱的矮星的这些量。BCK是一种性能良好的近红外光谱型函数，对于M6-T5型，其色散类似于0.1MAG；对于T5-T9型，它明显更分散。对于M6-L7型和T4-T9型，T-Eff急剧单调下降，但对于假定年龄类似于3Gyr的L7-T4型，在1450K附近几乎是恒定的。在L6型和T3型之间，L‘-M’的值几乎不变，证明了这种恒定的T-Eff。它还支持最近的模型，这些模型将L-T转变过程中近红外光度和光谱特征的变化归因于凝析云在狭窄的T-Eff范围内的快速迁移、破坏和/或变薄。早期T矮星的L和M‘发光度并不像以前在I到K波段所指出的那样出现明显的驼峰或拐点，但对于L6-T5型来说，没有足够的数据来断言M-L’和M-M‘在这个类型范围内是严格单调的。我们将观测到的L矮星和T矮星的K、L和M‘发光度与降水云和无云模式在不同表面重力和沉积效率下的预测值进行了比较。模型表明，L3-T4.5矮星的引力(logg=5.0-5.5)普遍高于T6-T9矮星(logg=4.5-5.0)。预测的T晚期矮星的M‘光度比我们样本中的T晚期矮星的经验计算值大1.5-2.5倍。这种差异归因于CO在4.5-4.9微米处的吸收，在模型中假设的热化学平衡条件下，这不是预期的。光度和测辐射热学计算表明，L3矮星KELU-1和T0矮星SDSSJ042348.57-041403.5可能是双星系统。我们计算了T9矮星2MASSI J0415195-093506的LOG(L-BOL/L-.)=-5.73+/-0.05，T-Eff=600-750K，它取代了G1570D，成为目前已知的最弱、最冷的褐矮星。
We have compiled L' (3.4 - 4.1 mum) and M' (4.6 - 4.8 mum) photometry of 63 single and binary M, L, and T dwarfs obtained at the United Kingdom Infrared Telescope using the Mauna Kea Observatory filter set. This compilation includes new L' measurements of eight L dwarfs and 13 T dwarfs and new M' measurements of seven L dwarfs, five T dwarfs, and the M1 dwarf Gl 229A. These new data increase by factors of 0.6 and 1.6, respectively, the numbers of ultracool dwarfs (T-eff less than or similar to2400 K) for which L' and M' measurements have been reported. We compute L-bol, BCK, and T-eff for 42 dwarfs whose flux-calibrated JHK spectra, L' photometry, and trigonometric parallaxes are available, and we estimate these quantities for nine other dwarfs whose parallaxes and flux-calibrated spectra have been obtained. BCK is a well-behaved function of near-infrared spectral type with a dispersion of similar to 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 it is nearly constant at similar to 1450 K for types L7 - T4 with assumed ages of similar to 3 Gyr. This constant T-eff is evidenced by nearly unchanging values of L'-M' between types L6 and T3. It also supports recent models that attribute the changing near-infrared luminosities and spectral features across the L-T transition to the rapid migration, disruption, and/or thinning of condensate clouds over a narrow range of T-eff. The L' and M' luminosities of early-T dwarfs do not exhibit the pronounced humps or inflections previously noted in the I through K bands, but insufficient data exist for types L6 - T5 to assert that M-L' and M-M' are strictly monotonic within this range of types. We compare the observed K, L', and M' luminosities of L and T dwarfs in our sample with those predicted by precipitating-cloud and cloud-free models for 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 late-T dwarfs are 1.5 - 2.5 times larger than those derived empirically for the late-T dwarfs in our sample. This discrepancy is attributed to absorption at 4.5 - 4.9 mum by CO, which is not expected under the condition of thermochemical equilibrium assumed in the models. Our photometry and bolometric calculations indicate that the L3 dwarf Kelu-1 and the T0 dwarf SDSS J042348.57 - 041403.5 are probable binary systems. We compute log (L-bol/L-.) = - 5.73 +/- 0.05 and T-eff = 600 - 750 K for the T9 dwarf 2MASSI J0415195 - 093506, which supplants Gl 570D as the least luminous and coolest brown dwarf presently known.