基于JVLA和ALMA资料的Mira射电光球新测量
New Measurements of the Radio Photosphere of Mira based on Data from the JVLA and ALMA
摘要：
我们提出了新的测量毫米波长连续发射的长周期变量米拉（$o$鲸）在46 GHz，96 GHz和229 GHz（$λ$ ~7毫米，3毫米和1毫米）的基础上获得的观测与Jansky甚大阵列（JVLA）和阿塔卡马大毫米/亚毫米阵列（ALMA）。测量的毫米波通量密度与以前观测得到的射电光球模型一致，其中通量密度为$S_ν\proptoν^{1.86}$。恒星盘被解析，测量结果表明射电光球层的大小在较高的频率下减小，正如预期的那样，如果不透明度在较短的波长下减小。射电光球的形状被发现是轻微拉长的，扁平度约为10- 20%。这些数据还揭示了米拉表面在无线电波长上亮度不均匀的证据。在所有三个观测到的波长上都探测到了Mira的热伴星Mira B，我们测量了它的无线电发射表面的半径为$\approx2.0\times10^{13}$ cm。这里提供的数据突出了JVLA和ALMA在研究演化恒星大气层方面的作用。
英文摘要：
We present new measurements of the millimeter wavelength continuum emission from the long period variable Mira ($o$ Ceti) at frequencies of 46 GHz, 96 GHz, and 229 GHz ($λ$~7 mm, 3 mm, and 1 mm) based on observations obtained with the Jansky Very Large Array (JVLA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The measured millimeter flux densities are consistent with a radio photosphere model derived from previous observations, where flux density, $S_ν\proptoν^{1.86}$. The stellar disk is resolved, and the measurements indicate a decrease in the size of the radio photosphere at higher frequencies, as expected if the opacity decreases at shorter wavelengths. The shape of the radio photosphere is found to be slightly elongated, with a flattening of ~10-20%. The data also reveal evidence for brightness non-uniformities on the surface of Mira at radio wavelengths. Mira's hot companion, Mira B was detected at all three observed wavelengths, and we measure a radius for its radio-emitting surface of $\approx2.0\times10^{13}$ cm. The data presented here highlight the power of the JVLA and ALMA for the study of the atmospheres of evolved stars.
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