A Spectroscopic Technique for Measuring Stellar Properties of Pre-Main-Sequence Stars
A Spectroscopic Technique for Measuring Stellar Properties of Pre-Main-Sequence Stars
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测量前主序星恒星特性的光谱技术
DOI：
10.1086/379292
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
D. Jaffe
中科院分区：
文献类型：
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作者：
G. Doppmann;D. Jaffe
我们描述了一种从高分辨率近红外光谱导出有效温度、表面重力、旋转速度和径向速度的技术。该技术将观察到的近红外光谱与从模型大气合成的光谱进行匹配。我们的分析旨在表征严重变红的前主序星，但该技术也可用于表征位于厚厚的星际尘埃云后面的主序和后主序恒星。对于前主序星，除了其他恒星参数外，我们还使用相同的匹配过程来测量过量的近红外发射量（可能出现在原恒星盘中）。从高分辨率光谱中获得的信息来自线形状和紧密间隔的线的相对线强度。因此，我们得出的恒星参数值与低分辨率光谱学和光度测定得出的参数值无关。新方法有望提高将年轻恒星物体放置在演化模型轨道上的准确性。使用典型恒星参数和信噪比为 50 的人工噪声频谱进行的测试表明，Teff 中的 1 σ 误差为 100 K，v sin i 中为 2 km s-1，输入遮蔽为 1 时连续谱遮蔽中的误差为 0.13。如果 2.2 μm 处的 Na、Sc 和 Si 线总和与 (2-0) 12CO 能带头之间的通量比已知 2.3 μm 的精度为 10%，log g 的最佳拟合值的误差将为 Δ log g = 0.1–0.2。我们讨论了对我们确定恒星参数可能产生的系统影响，并评估了高分辨率光谱得出的结果的准确性。在本次评估的背景下，我们定量地探索了温度和重力之间的简并性，这种简并性一直困扰着使用低分辨率光谱对年轻恒星物体进行分类的努力。对 MK 标准品的高分辨率近红外光谱的分析表明，该技术可以产生非常准确的有效温度值。将我们的结果与 MK 标准品的光谱类型进行比较时，最大的不确定性在于标准品本身的光谱类型到有效温度的转换。即使包括这种不确定性，矮星在 3000-5800 K 的光学温度和红外温度之间的 1 σ 差异也仅为 140 K。在一篇配套论文中，我们对 ρ Ophiuchi 分子云中严重灭绝的年轻恒星物体进行了分析。
We describe a technique for deriving effective temperatures, surface gravities, rotation velocities, and radial velocities from high-resolution near-IR spectra. The technique matches the observed near-IR spectra to spectra synthesized from model atmospheres. Our analysis is geared toward characterizing heavily reddened pre–main-sequence stars, but the technique also has potential applications in characterizing main-sequence and post–main-sequence stars when these lie behind thick clouds of interstellar dust. For the pre–main-sequence stars, we use the same matching process to measure the amount of excess near-IR emission (which may arise in the protostellar disks) in addition to the other stellar parameters. The information derived from high-resolution spectra comes from line shapes and the relative line strengths of closely spaced lines. The values for the stellar parameters we derive are therefore independent of those derived from low-resolution spectroscopy and photometry. The new method offers the promise of improved accuracy in placing young stellar objects on evolutionary model tracks. Tests with an artificial noisy spectrum with typical stellar parameters and a signal-to-noise ratio of 50 indicate a 1 σ error of 100 K in Teff, 2 km s-1 in v sin i, and 0.13 in continuum veiling for an input veiling of 1. If the flux ratio between the sum of the Na, Sc, and Si lines at 2.2 μm and the (2–0) 12CO band head at 2.3 μm is known to an accuracy of 10%, the errors in our best-fit value for log g will be Δ log g = 0.1–0.2. We discuss the possible systematic effects on our determination of the stellar parameters and evaluate the accuracy of the results derivable from high-resolution spectra. In the context of this evaluation, we quantitatively explore the degeneracy between temperature and gravity that has bedeviled efforts to type young stellar objects using low-resolution spectra. The analysis of high-resolution near-IR spectra of MK standards shows that the technique yields very accurate values for the effective temperature. The greatest uncertainty in comparing our results with optical spectral typing of MK standards is in the spectral type–to–effective temperature conversion for the standards themselves. Even including this uncertainty, the 1 σ difference between the optical and infrared temperatures for dwarfs at 3000–5800 K is only 140 K. In a companion paper, we present an analysis of heavily extincted young stellar objects in the ρ Ophiuchi molecular cloud.