The First High-Resolution Spectra of 1.3 L Subdwarfs
The First High-Resolution Spectra of 1.3 L Subdwarfs
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第一个 1.3 L 亚矮星的高分辨率光谱
DOI：
10.1086/500298
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
G. Basri
中科院分区：
文献类型：
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作者：
Ansgar Reiners;G. Basri
我们给出了凉爽的L亚矮星(SDL2MASS0532+8246)的第一个高分辨率(R≈31,000)光谱，它最初被确定为早期类型的SDL1610-0040。我们的工作，结合库欣和瓦卡同时期的工作，清楚地表明，后者更有可能是一颗M中矮星，其不同寻常的组成赋予了它一些亚矮星的光谱特征。我们使用这些数据来推导出这两个物体的精确径向速度，并估计空间运动；两者都与晕运动学一致。我们测量了投影的自转速度，发现旧的SD？M6天体LSR1610-0040的自转速度非常慢。天体2MASS0532+8246的自转速度v sin i=65±15 km S-1，与L矮星的行为一致。这意味着L小矮人的刹车时间极长，或许他们永远不会减速。Rb、Cs原子谱线与L矮星场光谱的详细比较表明，2MASS0532+8246型谱线与中晚期L型谱线一致。LSR1610-0040的RbI线和KI线类似于L早期矮星的RbI线，而CsI线则类似于M中矮星的CsI线。如果它不像M6一样热，那么这个天体中吸收的CaII三联体的出现是很难理解的。我们使用一个适度缺乏金属的Mid-M模型，以一致的方式解释了这些影响。相对于正常的M矮星，M亚矮星具有弱的金属氧化物和增强的金属氢化物。LSR1610-0040显示出类似M矮星的金属氢化物，但像亚矮星的金属氧化物。解决原子线差异的相同解释也解释了这一点。我们的光谱覆盖了之前未知的吸收特征附近的光谱区域(9600？)和声称检测到TiH的区域(约9400？)。我们确定9600ä附近的吸收是由于钛的原子线和少量FeH的贡献，但我们不能确认在冷SDL的光谱中检测到TiH。在2MASS0532+8246中，相对于正常的L矮星，金属氧化物和金属氢化物都非常强。可以通过引用抑制尘埃形成的效应来解释2MASS 0532+8246中的强氧化物特征。高分辨率光谱学有助于开始了解金属缺乏和超冷大气中的复杂分子化学和光谱形成，以及早期超低质量天体的性质。
We present the first high-resolution (R ≈ 31,000) spectra of the cool L subdwarf (sdL) 2MASS 0532+8246 and what was originally identified as an early-type sdL, LSR 1610-0040. Our work, in combination with contemporaneous work by Cushing and Vacca, makes it clear that the latter object is more likely a mid-M dwarf with an unusual composition that gives it some subdwarf spectral features. We use the data to derive precise radial velocities for both objects and to estimate space motion; both are consistent with halo kinematics. We measure the projected rotational velocities, revealing a very slow rotation for the old sd?M6 object LSR 1610-0040. The object 2MASS 0532+8246 exhibits a rapid rotation of v sin i = 65 ± 15 km s-1, consistent with the behavior of L dwarfs. This means that the braking time for L dwarfs is extremely long, or that perhaps they never slow down. A detailed comparison of the atomic Rb and Cs lines with spectra of field L dwarfs shows that the spectral type 2MASS 0532+8246 is consistent with being mid- to late-L. The Rb I and K I lines of LSR 1610-0040 are like those of an early-L dwarf, but the Cs I line is like that of a mid-M dwarf. The appearance of the Ca II triplet in absorption in this object is very hard to understand if it is not at least as warm as M6. We explain these effects in a consistent way using a mildly metal-poor mid-M model. M subdwarfs have weak metal oxides and enhanced metal hydrides relative to normal M dwarfs. LSR 1610-0040 exhibits metal hydrides like an M dwarf but metal oxides like a subdwarf. The same explanation that resolves the atomic-line discrepancy explains this as well. Our spectra cover the spectral region around a previously unidentified absorption feature at 9600 Å and the region around 9400 Å in which detection of TiH has been claimed. We identify the absorption around 9600 Å as being due to atomic lines of Ti and a small contribution of FeH, but we cannot confirm a detection of TiH in the spectra of cool sdLs. In 2MASS 0532+8246, both metal oxides and metal hydrides are extremely strong relative to normal L dwarfs. It may be possible to explain the strong oxide features in 2MASS 0532+8246 by invoking effects due to inhibited dust formation. High-resolution spectroscopy has aided in beginning to understand the complex molecular chemistry and spectral formation in metal-deficient and ultracool atmospheres and the properties of early ultra-low-mass objects.