arXiv 1506.075362015-06-24astro-ph.SR

参宿四扩展大气的尺度和温度的时间演化

Temporal Evolution of the Size and Temperature of Betelgeuse's Extended Atmosphere

Eamon O'Gorman, Graham M. Harper, Alexander Brown, Edward F. Guinan, Anita M. S. Richards, Wouter Vlemmings, Richard Wasatonic

DOI：: 10.1051/0004-6361/201526136

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摘要：

我们使用的超大阵列（VLA）在A配置与派镇（PT）甚长基线阵列（VLBA）天线空间解决了扩展的参宿四的大气在多个时期在0.7，1.3，2.0，3.5，和6.1厘米。扩展大气在所有波长上都偏离了圆对称，而在某些时期，我们发现了可能的证据，表明小的气体口袋明显比全球平均温度低。我们发现没有证据表明最近报道的e-MERLIN无线电热点在我们的多历元VLA/PT数据，尽管有足够的空间分辨率和灵敏度在短波长，并得出结论，这些无线电热点最有可能是干涉文物。扩展大气的平均气体温度在2 $R_{\star}$时的典型值为3000 K，在6 $R_{\star}$时降至1800 K，与Lim等人（1998）的单历元研究结果基本一致。在$2 R_{\star} \lesssim r \lesssim 6 R_{\star}$之间的扩展大气的总体温度廓线可以用$T_{\mathrm{gas}}(r) \propto r^{-0.6}$形式的幂律来描述，在某些时期有明显的几个100 K的时间变化。最后，我们提出了超过12年的V波段测光，其中一部分重叠我们的多历元无线电数据。我们发现，在V波段的部分通量密度变化与大多数无线电波长之间的相关性。这种相关性可能是由于恒星脉动引起的冲击波，它加热了内部大气层，并通过辐射方式使更广泛的大气层变热。恒星脉动可能在激发参宿四的扩展大气层中发挥重要作用。

英文摘要：

We use the Very Large Array (VLA) in the A configuration with the Pie Town (PT) Very Long Baseline Array (VLBA) antenna to spatially resolve the extended atmosphere of Betelgeuse over multiple epochs at 0.7, 1.3, 2.0, 3.5, and 6.1 cm. The extended atmosphere deviates from circular symmetry at all wavelengths while at some epochs we find possible evidence for small pockets of gas significantly cooler than the mean global temperature. We find no evidence for the recently reported e-MERLIN radio hotspots in any of our multi-epoch VLA/PT data, despite having sufficient spatial resolution and sensitivity at short wavelengths, and conclude that these radio hotspots are most likely interferometric artefacts. The mean gas temperature of the extended atmosphere has a typical value of 3000 K at 2 $R_{\star}$ and decreases to 1800 K at 6 $R_{\star}$, in broad agreement with the findings of the single epoch study from Lim et al. (1998). The overall temperature profile of the extended atmosphere between $2 R_{\star} \lesssim r \lesssim 6 R_{\star}$ can be described by a power law of the form $T_{\mathrm{gas}}(r) \propto r^{-0.6}$, with temporal variability of a few 100 K evident at some epochs. Finally, we present over 12 years of V band photometry, part of which overlaps our multi-epoch radio data. We find a correlation between the fractional flux density variability at V band with most radio wavelengths. This correlation is likely due to shock waves induced by stellar pulsations, which heat the inner atmosphere and ionize the more extended atmosphere through radiative means. Stellar pulsations may play an important role in exciting Betelgeuse's extended atmosphere.

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