arXiv 0708.30892007-08-22astro-ph

候选后T金牛星的Keck Hires光谱

Keck Hires Spectroscopy of Candidate Post T Tauri Stars

Eric J. Bubar, Jeremy R. King, David R. Soderblom, Constantine P. Deliyannis, Ann M. Boesgaard

备注：: Accepted to AJ, 35 pages, 12 figures
发表信息：: Astron.J.134:2328-2339,2007
DOI：: 10.1086/522626

摘要：

我们使用高信噪比（$\sim$ 150-450），高分辨率（$R{\sim}45,000$）凯克HIRES光谱的13个候选后T金牛星的基本物理参数，锂丰度和径向速度。我们把我们的恒星在M $_v$ -T $_{eff}$平面用于确定近似年龄的前主序等时线，并确认这些使用三个相对年龄指标在我们的分析：锂丰度，色球发射和运动{ \it U-V}平面。使用三个年龄标准，我们确定5颗恒星（HIP 54529，HIP 62758，HIP 63322，HIP 74045和HIP 104864）可能是后T金牛座恒星，年龄在10到1亿年之间。我们确认HIP 54529是SB 2星，HIP 63322是SB 1星。我们还使用{ \it HIPPARCOS}光度附件检查了PTT的不规则光度变化。我们的两个PTT明星表现出近红外线过剩相比，库鲁茨模型流量，而最近的工作表明，经典金牛座T星表现出类似的{ \it JHK}过剩大概表示非光球（磁盘）的排放，我们的结果可能是虚幻的文物所选择的{ \it I}带归一化。我们在基于文献的PTT样本中看到的近红外过量似乎是先前基于光谱类型的$T_{\rm eff}$值的伪影。事实上，他们观察到的和模型的光球SED的同源性的比较表明，测光温度比温度更可靠的光谱标准的基础上，在这个样本中的恒星的温度较低的范围。我们的结论是，我们的年龄为导向的分析是一个强大的手段来选择附近的样本，年轻的，孤立的后金牛座T星，否则伪装成正常的场星。

英文摘要：

We use high-signal-to-noise ($\sim$150-450), high resolution ($R{\sim}45,000$) Keck HIRES spectroscopy of 13 candidate post T Tauri stars to derive basic physical parameters, lithium abundances and radial velocities. We place our stars in the M$_v$-T$_{eff}$ plane for use in determining approximate ages from pre-main sequence isochrones, and confirm these using three relative age indicators in our analysis: Li abundances, chromospheric emission and the kinematic {\it U-V} plane. Using the three age criteria we identify 5 stars (HIP 54529, HIP 62758, HIP 63322, HIP 74045, and HIP 104864) as probable post T Tauri stars with ages between 10 and 100 Myr. We confirm HIP 54529 as an SB2 and HIP 63322 as an SB1 star. We also examine irregular photometric variability of PTTs using the {\it HIPPARCOS} photometry annex. Two of our PTT stars exhibit near-IR excesses compared to Kurucz model flux; while recent work suggests classical T Tauri stars evince similar {\it JHK} excesses presumably indicative of non-photospheric (disk) emission, our results may be illusory artifacts of the chosen {\it I}-band normalization. Near-IR excesses we see in a literature-based sample of PTTs appear to be artifacts of previous spectral type-based $T_{\rm eff}$ values. Indeed, comparison of the homology of their observed and model photospheric SED's suggests that photometric temperatures are more reliable than temperatures based on spectral standards for the cooler temperature ranges of the stars in this sample. We conclude that our age oriented analysis is a robust means to select samples of nearby, young, isolated post T Tauri stars that otherwise masquerade as normal field stars.

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