The effect of accretion on the pre-main-sequence evolution of low-mass stars and brown dwarfs
The effect of accretion on the pre-main-sequence evolution of low-mass stars and brown dwarfs
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DOI：
10.1051/0004-6361/201630356
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发表时间：
2017-06
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通讯作者：
E. Vorobyov;V. Elbakyan;T. Hosokawa;Y. Sakurai;M. Guedel;Harold Yorke Institute of Fluid Mechanics;Heat Transfer Research Institute of Physics;Southern Federal University;R. Vienna;Department of Applied Physics;Kyoto Sangyo University Department of Physics;Graduate School of Science;T. L. H. J. P. Laboratory;C. I. O. Technology.
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作者：
E. Vorobyov;V. Elbakyan;T. Hosokawa;Y. Sakurai;M. Guedel;Harold Yorke Institute of Fluid Mechanics;Heat Transfer Research Institute of Physics;Southern Federal University;R. Vienna;Department of Applied Physics;Kyoto Sangyo University Department of Physics;Graduate School of Science;T. L. H. J. P. Laboratory;C. I. O. Technology.
从一颗原恒星/原棕矮星的形成出发，考虑到在演化的最初几年中对中心天体的质量吸积，用数值方法研究了低质量恒星和棕矮星的前主序列演化。恒星演化计算使用的恒星演化代码是由York&Bodenheimer开发的，最近由Hosokawa等人进行了修改。质量吸积率取自Vorobyov&Basu的数值流体力学模型，计算了不同质量和角动量的前星云核引力崩塌开始的星盘演化。所得到的恒星演化轨迹与使用非吸积模型计算的等时线和异构体进行了比较。我们发现，在原恒星演化的最初几个MYR中的质量吸积可以对随后的年轻恒星和棕矮星的演化产生强烈的影响。吸积和非吸积模型在恒星总光度L_st、恒星半径R_st和有效温度T_ef方面的不一致取决于吸积的热效率，即中心天体吸收的吸积能的分数。最大的失配出现在冷吸积情形，在冷吸积情形中，基本上所有的吸积能量都被辐射出去。在这种情况下，对于1.0百万岁的天体，L_st和R_st的相对偏差可以达到50%，即使对于10百万岁的天体，它们的相对偏差也是显著的。在热吸积和混合吸积情形中，吸积能量的恒定比例被吸收，吸积和非吸积模型之间的不一致变得不那么明显，但对于1.0-Myr-old天体仍然值得注意。在使用基于非吸积模型的等时线时，这些分歧可能会导致对(次)太阳质量天体的错误年龄估计(略)。
The pre-main-sequence evolution of low-mass stars and brown dwarfs is studied numerically starting from the formation of a protostellar/proto-brown dwarf seed and taking into account the mass accretion onto the central object during the initial several Myr of evolution. The stellar evolution was computed using the STELLAR evolution code developed by Yorke & Bodenheimer with recent modifications by Hosokawa et al. The mass accretion rates were taken from numerical hydrodynamics models of Vorobyov & Basu computing the circumstellar disk evolution starting from the gravitational collapse of pre-stellar cloud cores of various mass and angular momentum. The resulting stellar evolution tracks were compared with the isochrones and isomasses calculated using non-accreting models. We find that mass accretion in the initial several Myr of protostellar evolution can have a strong effect on the subsequent evolution of young stars and brown dwarfs. The disagreement between accreting and non-accreting models in terms of the total stellar luminosity L_st, stellar radius R_st and effective temperature T_eff depends on the thermal efficiency of accretion, i.e., on the fraction of accretion energy absorbed by the central object. The largest mismatch is found for the cold accretion case, in which essentially all accretion energy is radiated away. The relative deviations in L_st and R_st in this case can reach 50% for 1.0-Myr-old objects and remain notable even for 10-Myr-old objects. In the hot and hybrid accretion cases, in which a constant fraction of accretion energy is absorbed, the disagreement between accreting and non-accreting models becomes less pronounced, but still remains notable for 1.0-Myr-old objects. These disagreements may lead to the wrong age estimate for objects of (sub-)solar mass when using the isochrones based on non-accreting models (abridged).