渐近巨星分支尖端OH脉泽的寿命
Lifetime of OH masers at the tip of the asymptotic giant branch
摘要：
背景：大部分其他类似的渐近巨星分支星（AGB）没有显示OH脉泽发射。如最近所示，一个有限的寿命可能会给一个自然的解释，为什么只有一部分的任何样品发射微波激射发射在一个给定的时代。目的：研究AGB星拱壳层中1612 MHz OH脉泽的寿命。研究方法：我们重新观察了28年前发现的OH/IR恒星样本，以确定可能已经失去脉泽的恒星数量。结果：我们重新探测到了全部114个OH脉泽。推断的最小寿命为2800年（1 sigma）。这个脉泽寿命适用于具有强烈质量损失的AGB恒星，导致非常红的红外颜色。自发现以来，速度和平均通量密度水平没有变化。由于最小寿命与风穿越时间具有相同的量级，因此质量损失过程中的强烈变化不太可能影响约3000年或更短时间尺度上的激励条件。关键词：OH脉泽-恒星：AGB和后AGB-星周物质
英文摘要：
Context: A large fraction of otherwise similar asymptotic giant branch stars (AGB) do not show OH maser emission. As shown recently, a restricted lifetime may give a natural explanation as to why only part of any sample emits maser emission at a given epoch. Aims: We wish to probe the lifetime of 1612 MHz OH masers in circumstellar shells of AGB stars. Methods: We reobserved a sample of OH/IR stars discovered more than 28 years ago to determine the number of stars that may have since lost their masers. Results: We redetected all 114 OH masers. The minimum lifetime inferred is 2800 years (1 sigma). This maser lifetime applies to AGB stars with strong mass loss leading to very red infrared colors. The velocities and mean flux density levels have not changed since their discovery. As the minimum lifetime is of the same order as the wind crossing time, strong variations in the mass-loss process affecting the excitation conditions on timescales of ~3000 years or less are unlikely. Keywords: OH masers -- Stars: AGB and post-AGB -- circumstellar matter
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