论文标题
所有低质量恒星都会经历额外的混合过程吗？
Do All Low-Mass Stars Undergo Extra Mixing Processes?
论文作者
论文摘要
仅将对流视为将恒星内部材料混合的物理过程的标准恒星演化模型预测，低质量恒星中的3He（M <2 msun）的产生，峰值丰度为3He/h〜几个x 10-3按数量。在银河系的终生中，这应该产生3he/h的丰度，随着半半径的增加而减少。然而，整个银河磁盘中HII区域中3HE+的观察结果显示，3He丰度的变化很小，其值为3HE/H的值类似于前期丰度（3HE/H）P〜10-5。这种差异被称为“ 3HE问题”，可以通过在恒星进化中调用由于热盐素不稳定性而引起的混合机制来解决。在这里，我们在行星Nebula J320（PN G190.3-17.7）中观察到3He+，Jansky非常大的阵列（JVLA）确认了用VLA制成的前3HE+检测，该检测支持标准恒星产量。仅此测量表明并非所有恒星都会进行额外的混合。我们更敏感的观察结果在将数据平滑至11.4 km/s的速度分辨率之后，无法检测到J320的3HE+发射。我们使用数值辐射传输代码星云估计3He/h <= 2.75 x 10-3的丰度极限。该结果使PN中3HE+的最后一个显着检测无效，并允许所有恒星都经历额外的混合过程。
Standard stellar evolution models that only consider convection as a physical process to mix material inside of stars predict the production of significant amounts of 3He in low-mass stars (M < 2 Msun), with peak abundances of 3He/H ~ few x 10-3 by number. Over the life-time of the Galaxy, this ought to produce 3He/H abundances that diminish with increasing Galactocentric radius. Observations of 3He+ in HII regions throughout the Galactic disk, however, reveal very little variation in the 3He abundance with values of 3He/H similar to the primoridal abundance, (3He/H)p ~ 10-5 . This discrepancy, known as the "3He Problem", can be resolved by invoking in stellar evolution models an extra-mixing mechanism due to the thermohaline instability. Here, we observe 3He+ in the planetary nebula J320 (PN G190.3-17.7) with the Jansky Very Large Array (JVLA) to confirm a previous 3He+ detection made with the VLA that supports standard stellar yields. This measurement alone indicates that not all stars undergo extra mixing. Our more sensitive observations do not detect 3He+ emission from J320 with an RMS noise of 58.8 microJy/beam after smoothing the data to a velocity resolution of 11.4 km/s . We estimate an abundance limit of 3He/H <= 2.75 x 10-3 by number using the numerical radiative transfer code NEBULA. This result nullifies the last significant detection of 3He+ in a PN and allows for the possibility that all stars undergo extra mixing processes.
