A high resolution spectral atlas of brown dwarfs
A high resolution spectral atlas of brown dwarfs
复制标题
棕矮星高分辨率光谱图集
DOI：
10.1051/0004-6361:20077963
复制
发表时间：
2007
影响因子：
6.5
通讯作者：
F. Allard
中科院分区：
文献类型：
--
作者：
A. Reiners;D. Homeier;P. Hauschildt;F. Allard
本文介绍了一个UVES/VLT高分辨率的三个L型矮星和一个T型矮星系统的光谱图，在这两个光谱类中，大多数天体都是棕矮星。我们的图谱涵盖了从H到近红外的光学区域，M.我们目前的光谱细节超冷大气在非常高的分辨率（R = 33000）和比较的光谱模型计算。我们的比较表明，VO和CaH的分子特征以及Cs和Rb的原子特征与当前模型相当吻合。另一方面，由于TiO，CrH，和水，原子Na和K的功能揭示模型计算和我们的观测之间的巨大差异。关键词。线：识别-恒星：低质量，棕矮星-恒星：大气层1。介绍褐矮星的分析已经看到了巨大的进展，因为他们的第一次检测超过十年前。从那时起，恒星光谱序列在其冷端增加了光谱类L和T。L和T天体肯定比那些被归类为光谱类型M的天体更冷，但是通过L和T类的光谱演化的原因比更热的天体更复杂（参见例如，Kirkpatrick 2005）。分子的形成开始于典型的光谱类K和M的温度，并且它们的不透明度开始引起黑体光谱的强烈偏离。此外，尘埃云的凝结在M到L的转变中变得重要，并主导了光谱类天体的出现。在L-T转换时，尘埃颗粒的大气效应减弱，但这种转换仍然知之甚少（Burrows et al. 2006）。根据标准的演化模型，光谱类T的天体总是棕矮星（Chabrier & Bara e 2000）。然而，根据年龄，光谱类M或L的天体可能是棕矮星或氢燃烧星。年轻的棕矮星可以在与年老的低质量恒星相同的温度范围内被发现，因此不可能仅仅从光谱类型（作为反应温度的代理）来确定棕矮星的状态（Basri 2000; Chabrier et al. 2005）。由于棕矮星是由质量定义的，因此没有明显的大气特征可以通过观察物体的光谱来确定棕矮星的状态。虽然Li测试（例如，Basri 2000）是一个在年轻对象中有用的工具，它不适合大多数老（场）对象。年龄也可以通过
ABSTRACT We present a UVES/VLT high resolution atlas of three L dwarfs and one T dwarf system, spectral classes at which most of theobjects are brown dwarfs. Our atlas covers the optical region from H up to the near infrared at 1m. We present spectral details ofultra-cool atmospheres at very high resolution (R ˘33000) and compare the spectra to model calculations. Our comparison showsthat molecular features from VO and CaH, and atomic features from Cs and Rb are reasonably well fit by current models. On theother hand, features due to TiO, CrH, and water, and atomic Na and K reveal large discrepancies between model calculations and ourobservations. Key words. Line: identification – Stars: low-mass, brown dwarfs – Stars: atmospheres 1. Introduction The analysis of brown dwarfs has seen tremendous progresssince their first detection more than ten years ago. Since then,the stellar spectral sequence was augmented by spectral classesL and T at its cool end. L and T objects must certainly be coolerthan those classified as spectral type M, but the reasons for thespectral evolution through the L- and T-classes turned out to bemore complex than in the hotter objects (see e.g., Kirkpatrick2005). The formation of molecules sets in at temperatures typ-ical for spectral classes K and M, and their opacities begin tocause strong deviations from blackbody spectra. Furthermore,the condensation of dust clouds becomes important at the transi-tion from M to L and dominates the appearance of spectral classL objects. At the L to T transition, the atmospheric e ects of thedust grains weaken, but this transition is still poorly understood(Burrows et al. 2006).Objects of spectral class T are always brown dwarfs accord-ing to standard evolutionary models (Chabrier & Bara e 2000).Depending on age, however, objects of spectral classes M or Lmay be either brown dwarfs or hydrogen-burning stars. Youngbrown dwarfs can be found in the same temperature range asold low-mass stars, hence it is not possible to determine browndwarf status from the spectral type (taken as proxy for e ectivetemperature) alone (Basri 2000; Chabrier et al. 2005).As brown dwarfs are defined by mass, there is no obviousatmospheric feature that determines brown dwarf status by justlooking at an object’s spectrum. While the Li-test (e.g., Basri2000) is a useful tool in young objects, it is not suitable for themajority of old (field) objects. Age can as well be determined in
新 Na I D 线轮廓在凉爽大气中的效果
影响因子：
6.5
作者：
Johnas;C. M. S;Hauschildt;Schweitzer;Mullamphy;D. F. T;Whittingham
通讯作者：
Whittingham