早期恒星演化过程中星周参数的变化
The Variation of Circumstellar Parameters through Early Stellar Evolution
- University of Hawaii at Mānoa（夏威夷大学马诺阿分校）
- Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales（迭戈帕拉莱斯大学工程与科学学院天体物理研究所）
- Departamento de Física, Universidad de Santiago de Chile（智利圣地亚哥大学物理系）
- Planetary Science Institute（行星科学研究所）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究通过分析109个年轻恒星天体的观测数据，揭示了消光、质量吸积率和光谱指数随年龄的演化规律，发现吸积约在5百万年时结束，且Class I与Class II天体物理性质相似。
AI中文摘要：
我们报告了基于SpeX观测和AllWISE光谱能量分布分析得到的消光、质量吸积率和光谱指数的演化，并与从先前报道和新分析的同一批年轻恒星天体（YSOs）的iSHELL观测中推导出的恒星参数（质量、年龄和veiling）进行了比较。通过使用恒星重力作为年龄指示器，我们能够在不对星周环境做任何假设的情况下推断年龄。我们的样本包括109个Class I、II和III YSOs。光谱指数总体上随时间下降，但存在足够的离散度，使得Class I-III YSOs可以在相同年龄被发现。消光（A_V）范围很广，从接近0到大于30星等，年龄可达5 Myr，且与年龄无明显趋势。质量吸积率从约1 Myr时的中位数10^-8太阳质量/年下降到年龄大于10 Myr时的低于10^-10太阳质量/年，质量吸积率的离散度为±1 dex。吸积似乎在约5 Myr时有效结束，此时获得的中位数质量为0.05太阳质量。我们发现Class I和II YSOs的veiling（rK）范围很广，从零到三（受限于我们检测光球谱线的需要），中位数veiling在约2 Myr后下降。Class I YSOs在物理上与Class II YSOs非常相似，具有相似的吸积率以及重叠的年龄和质量分布。没有发现高光谱指数和低消光的天体，这表明一旦星周物质匮乏，光谱指数会迅速下降。
英文摘要：
We report on the evolution of extinction, mass accretion rate, and spectral index from analysis of SpeX observations and AllWISE spectral energy distributions, compared to stellar parameters (mass, age, and veiling) derived from analysis of previously reported and newly analyzed iSHELL observations of the same young stellar objects (YSOs). By using stellar gravity as an age indicator, we are able to infer age without any assumptions about the circumstellar environment. Our sample consists of 109 Class I, II, and III YSOs. The spectral index broadly decreases with time but with sufficient scatter that Class I-III YSOs can all be found at the same age. There is a wide range of extinction (A_V) from nearly 0 to greater than 30 mag for ages up to 5 Myr, showing no clear trend with age. The mass accretion rate declines from a median of 10^-8 solar masses per year at ~1 Myr to less than 10^-10 solar masses per year at ages greater than 10 Myr, with a scatter of the mass accretion rate of +/- 1 dex. Accretion seems to effectively end by ~ 5 Myr, by which time the median mass gained is 0.05 solar masses. We find a wide range of veiling (rK) from zero to three (limited by our need to detect photospheric lines) for Class I and II YSOs, with the median veiling declining after ~2 Myr. Class I YSOs appear to be physically very similar to Class II YSOs, with similar accretion rates and overlapping age and mass distributions. There are no objects with a high spectral index and low extinction, suggesting that once starved of circumstellar material, the spectral index rapidly declines.
