Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg
Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg
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DOI：
10.3847/1538-4357/ac0c7e
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发表时间：
2021-06
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影响因子：
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通讯作者：
R. Norris;F. Baron;J. Monnier;C. Paladini;M. Anderson;A. O. Martinez;G. Schaefer;X. Che;A. Ch
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文献类型：
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作者：
R. Norris;F. Baron;J. Monnier;C. Paladini;M. Anderson;A. O. Martinez;G. Schaefer;X. Che;A. Ch
我们介绍了用密歇根红外组合器(MIRC)在高角度分辨率天文中心(CHARA)的六望远镜中心对红超巨星(RSG)AZ Cyg进行的H波段干涉观测。观测的时间跨度为5年(2011-2016)，提供了对RSGS上地表特征的短期和长期演变的洞察。利用NASA红外望远镜设备上的SPEX获得的AZ Cyg的光谱，以及球面MARCS、球面菲尼克斯和SATLAS模型大气计算的合成光谱，我们推导出Tef在3972K到4000K之间，logg在−0.50到0.00之间，这取决于所使用的恒星模型。利用对平方能见度和Gaia视差的拟合，我们测量了它的平均半径R=911−50+57R⊙。使用我们的模型无关成像程序Squeeze和OITOOLS.jl重建的恒星表面显示了一个复杂的表面，具有小的明亮特征，似乎在不到一年的时间尺度上变化，而较大的特征持续一年以上。这些图像的一维功率谱表明，对于较大的、寿命较长的特征，其特征尺寸为0.52-0.69R⋆。这接近从恒星表面的3DRHD模型得到的0.51RHD值-0.53RRHD。我们的结论是，这颗恒星的干涉成像与3D RHD模型的预测是一致的，但需要短期成像来更严格地测试RSGs中对流的预测。
We present H-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011–2016), which offers insight into the short and long-term evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we derive T eff is between 3972 K and 4000 K and logg between −0.50 and 0.00, depending on the stellar model used. Using fits to the squared visibility and GAIA parallaxes, we measure its average radius R=911−50+57R⊙ . Reconstructions of the stellar surface using our model-independent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. The 1D power spectra of these images suggest a characteristic size of 0.52–0.69 R ⋆ for the larger, long lived features. This is close to the values of 0.51–0.53 R ⋆ that are derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that short-term imaging is needed to more stringently test predictions of convection in RSGs.