ON THE RELIABILITY OF STELLAR AGES AND AGE SPREADS INFERRED FROM PRE-MAIN-SEQUENCE EVOLUTIONARY MODELS
ON THE RELIABILITY OF STELLAR AGES AND AGE SPREADS INFERRED FROM PRE-MAIN-SEQUENCE EVOLUTIONARY MODELS
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DOI：
10.1088/0004-637x/738/2/140
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发表时间：
2011-01
期刊：
影响因子：
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通讯作者：
T. Hosokawa;S. Offner;M. Krumholz
中科院分区：
文献类型：
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作者：
T. Hosokawa;S. Offner;M. Krumholz
我们重新审视了低质量前主序恒星演化的问题及其在赫罗图（HRD）上恒星落在哪里的观测结果。与大多数先前的工作相比，我们的模型跟踪恒星从小质量通过吸积成长的过程，我们系统地研究了恒星的HRD演化如何受到它们的初始半径、吸积流的辐射特性和吸积历史的影响，使用简单的理想吸积历史和从星团形成的数值模拟中获得的历史。我们将我们的数值结果与非吸积等时线和观测到的恒星在HRD中的位置进行比较，目的是确定绝对年龄和从非吸积等时线推断的年龄色散是否可靠。我们发现，非吸积等时线有时会高估质量较大的恒星（有效温度高于~ 3500k）的恒星年龄，从而解释了为什么非吸积等时线通常表明同一星团中质量较大和较小的恒星之间存在系统年龄差异。然而，我们也发现，对较冷恒星的年龄产生类似高估的唯一方法是，如果这些恒星从~ 0.01 M☉种子原恒星生长，比当前理论模型预测的要小一个数量级，并且如果种子原恒星的大小与吸积结束时的最终恒星质量系统地相关。因此，我们得出结论，除非这两个条件都满足，否则推断出的冷恒星的年龄和年龄分布是可靠的，至少在观测到的放热光度和温度是准确的程度上是可靠的。最后，我们注意到质量吸积速率的时间依赖性对低质量恒星在HRD上的演化的影响非常小，并且除了有效温度高于~ 4000 K的恒星外，所有恒星的时间依赖性都可以忽略。
We revisit the problem of low-mass pre-main-sequence stellar evolution and its observational consequences for where stars fall on the Hertzsprung–Russell diagram (HRD). In contrast to most previous work, our models follow stars as they grow from small masses via accretion, and we perform a systematic study of how the stars’ HRD evolution is influenced by their initial radius, by the radiative properties of the accretion flow, and by the accretion history, using both simple idealized accretion histories and histories taken from numerical simulations of star cluster formation. We compare our numerical results to both non-accreting isochrones and to the positions of observed stars in the HRD, with a goal of determining whether both the absolute ages and the age dispersions inferred from non-accreting isochrones are reliable. We show that non-accreting isochrones can sometimes overestimate stellar ages for more massive stars (those with effective temperatures above ∼3500 K), thereby explaining why non-accreting isochrones often suggest a systematic age difference between more and less massive stars in the same cluster. However, we also find the only way to produce a similar overestimate for the ages of cooler stars is if these stars grow from ∼0.01 M☉ seed protostars that are an order of magnitude smaller than predicted by current theoretical models, and if the size of the seed protostar correlates systematically with the final stellar mass at the end of accretion. We therefore conclude that, unless both of these conditions are met, inferred ages and age spreads for cool stars are reliable, at least to the extent that the observed bolometric luminosities and temperatures are accurate. Finally, we note that the time dependence of the mass accretion rate has remarkably little effect on low-mass stars’ evolution on the HRD, and that such time dependence may be neglected for all stars except those with effective temperatures above ∼4000 K.