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arXiv 0909.4160astro-ph.SR
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亮蓝变星AFGL2298的热光度变化

Bolometric luminosity variations in the Luminous Blue Variable AFGL2298

J. S. Clark, P. A. Crowther, V. M. Larionov, I. A. Steele, B. W. Ritchie, A. A. Arkharov

摘要:

我们研究了1989-2008年期间发光蓝色变星AFGL 2298的物理性质的变化。结合1989年至2001年公布的数据,我们已经进行了长期(2001年至2008年)近红外光谱和光度观测活动,这颗星,并利用非LTE模型大气代码来解释这些数据。我们发现AFGL 2298在观测数据集所涵盖的二十年中变化很大。在JHK波段观测到的光度变化大于1.6等;然而,这些变化并不伴随着近红外颜色的相关变化。对2001年至2007年期间获得的4个时期的K波段光谱的非LTE模型大气分析表明,光度变化是由恒星光球的膨胀和收缩驱动的,伴随着恒星温度的相对较小的变化。在此期间未聚集的质量损失率是温和的,直接可比的其他高度发光的LBV。然而,AFGL 2298的热光度在1989年至2008年之间变化了至少2倍,它是银河系中最明亮的恒星之一。与其他经历过非测热光度守恒“爆发”的LBV相比,这种事件是不均匀的,AFGL 2298是最不极端的例子。这些结果-和不同性质的静止LBV和相关的喷出物-可能提供支持的建议,一个以上的物理机制是负责这种行为。[删节]

英文摘要:

We characterise the variability in the physical properties of the luminous blue variable AFGL2298 between 1989-2008. In conjunction with published data from 1989-2001, we have undertaken a long term (2001-2008) near-IR spectroscopic and photometric observational campaign for this star and utilise a non-LTE model atmosphere code to interpret these data. We find AFGL2298 to have been highly variable during the two decades covered by the observational datasets. Photometric variations of >1.6 mag have been observed in the JHK wavebands; however, these are not accompanied by correlated changes in near-IR colour. Non-LTE model atmosphere analysis of 4 epochs of K band spectroscopy obtained between 2001-7 suggests that the photometric changes were driven by expansion and contraction of the stellar photosphere accompanied by comparatively small changes in the stellar temperature. Unclumped mass loss rates throughout this period were modest and directly comparable to those of other highly luminous LBVs. However, the bolometric luminosity of AFGL2298 appears to have varied by at least a factor of ~2 between 1989-2008, with it being one of the most luminous stars in the Galaxy during maximum. Comparison to other LBVs that have undergone non bolometric luminosity conserving `eruptions' shows such events to be heterogeneous, with AFGL2298 the least extreme example. These results - and the diverse nature of both the quiescent LBVs and associated ejecta - may offer support to the suggestion that more than one physical mechanism is responsible for such behaviour. [ABRIDGED]

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