论文标题
用Spitzer红外光谱仪观察到的Ultracool矮人。 ii。 L矮人中硅酸盐云的出现和沉淀，以及完整的M5-T9田间矮谱样品的分析
Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. II. Emergence and Sedimentation of Silicate Clouds in L Dwarfs, and Analysis of the Full M5--T9 Field Dwarf Spectroscopic Sample
论文作者
论文摘要
我们提供了对使用Spitzer红外光谱仪（IRS）获得的所有中红外$ r \ r \ of 90 $光谱的统一分析。该样品包含113个光谱，其中12个属于晚期的矮人，69至l矮人，而twarfs则属于32个。这些光谱中的68个首次提出。我们测量了IRS光谱中主要吸收带的优势，即h $ _2 $ o，在6.25 $ $ $ m，ch $ _4 $时，为7.65 $ $ $ m，NH $ _3 $ at 10.5 $ $ m $ m，以及8---11 $ $ m的硅酸盐。在所有光谱中都存在吸水，并以光谱类型的形式得到增强。甲烷和氨的发作分别发生在L8和T2.5类型上，尽管早在T1.5就可以检测到氨。在光谱型L2处的硅酸盐吸收集平均是L4-L6矮人中最强的，并且消失了L8。但是，在任何L亚型的光谱中也可能不存在硅酸盐吸收。我们发现在给定的L亚型下的硅酸盐吸收强度与近红外颜色的过量（与中位偏差）之间存在正相关，这支持了这样一个观念，即硅酸盐云厚度的变化会产生观察到的l矮人中观察到的彩色散射。我们还发现，可变的L3-L7矮人的硅酸盐吸收的可能性要高两倍。结果的合奏巩固了L矮人大气中硅酸盐冷凝水云的证据，并且在第一次观察时，它们的出现和沉积物分别分别为$ \ $ \ $ \ $ \ $ \ $ \ $ \ $ 1300 k。
We present a uniform analysis of all mid-infrared $R\approx90$ spectra of field M5--T9 dwarfs obtained with the Spitzer Infrared Spectrograph (IRS). The sample contains 113 spectra out of which 12 belong to late-M dwarfs, 69 to L dwarfs, and 32 to T dwarfs. Sixty-eight of these spectra are presented for the first time. We measure strengths of the main absorption bands in the IRS spectra, namely H$_2$O at 6.25 $μ$m, CH$_4$ at 7.65 $μ$m, NH$_3$ at 10.5 $μ$m, and silicates over 8--11 $μ$m. Water absorption is present in all spectra and strengthens with spectral type. The onset of methane and ammonia occurs at the L8 and T2.5 types, respectively, although ammonia can be detectable as early as T1.5. Silicate absorption sets in at spectral type L2, is on average the strongest in L4--L6 dwarfs, and disappears past L8. However, silicate absorption can also be absent from the spectra at any L subtype. We find a positive correlation between the silicate absorption strength and the excess (deviation from median) near-infrared colour at a given L subtype, which supports the idea that variations of silicate cloud thickness produce the observed colour scatter in L dwarfs. We also find that variable L3--L7 dwarfs are twice more likely to have above-average silicate absorption than non-variables. The ensemble of results solidifies the evidence for silicate condensate clouds in the atmospheres of L dwarfs, and for the first time observationally establishes their emergence and sedimentation between effective temperatures of $\approx$2000 K and $\approx$1300 K, respectively.
