Imaging the Radio Photospheres of Long-Period Variable Stars

PI将进行一系列射电观测，以研究具有凉爽尘埃风的旧恒星的大气。驱动风的过程尚不清楚，但了解它是重要的，在这个项目中获得的新观测将会有所帮助。尘埃风中损失的质量大小可以决定恒星的命运，从恒星脱落的物质最终会扩散到星际介质中。现在，使用新墨西哥州的Jansky甚大阵列(JVLA)射电望远镜可以测量这些恒星的大小、形状和大气中的气体运动。PI和她的合作者将进行这样的测量，并用它们来了解凉爽的尘埃风是如何发出的。一个以“无线电之星”为主题的教育播客(正在进行的系列节目中的第四个)将与公众分享该节目的成果。PI将指导干草堆天文台本科研究项目的一名本科生。该项目将利用JVLA最近获得的观测数据，生成迄今最敏感的(按数量级)射电光球图像，其中包括五颗最近、研究最深入的AGB恒星的样本。将使用一种特殊的校准技术来“冻结”大气的相位变化，提供近乎完美的、衍射受限的射电观测，并产生角分辨率约为40毫秒(在100毫微秒距离下约为4 AU)的图像。超乎寻常的灵敏度将允许精确测量基本恒星参数，包括半径和亮度温度，这些参数将与模型预测和其他多波长观测进行比较。其中四颗样本恒星之前曾拍摄过厘米波长的图像，其中两颗显示出明显偏离球对称的证据。新的观测(在恒星脉动周期的不同阶段进行)将揭示光球形状是否随时间变化，并将用于区分非球形形状的可能原因。对于表现出SiO脉泽发射的恒星，同步观测将提供关于大气动力学的补充信息。这些将提供对脉泽泵浦和激发过程以及密度和温度的径向变化的洞察。

The PI will carry out a series of radio observations to study the atmospheres of old stars with cool, dusty winds. The process that drives the winds is unknown, but understanding it is important, and the new observations obtained in this program will help. The amount of mass lost in dusty winds can determine the star's fate, and the material shed from the star eventually spreads into the interstellar medium. It is now possible to measure the size, shape, and gas motions in the atmospheres of these stars using the Jansky Very Large Array (JVLA) radio telescope in New Mexico. The PI and her collaborators will make such measurements and use them to understand how the cool, dusty winds are launched. An educational podcast centered on the theme "Radio Stars" (the fourth in an ongoing series) will share results from this program with the general public. The PI will mentor an undergraduate student from Haystack Observatory's Research Experience for Undergraduate program.Using recent observations obtained with the JVLA, this program will produce the most sensitive (by an order of magnitude) images to date of the radio photospheres of a sample of five of the nearest, best-studied AGB stars. A special calibration technique will be employed to "freeze" atmospheric phase variations, providing near perfect, diffraction-limited radio seeing, and yielding images with an angular resolution of ~40 mas (~4 AU at a distance of 100 pc). The extraordinary sensitivity will allow accurate measurements of fundamental stellar parameters, including the radius and brightness temperature, which will be compared with model predictions and other multi-wavelength observations. Four of the sample stars have been imaged previously at centimeter wavelengths, and two show clear evidence for deviation from spherical symmetry. The new observations (taken at different phases of the stellar pulsation cycle) will reveal whether the photospheric shape is time-variable and will be used to distinguish between possible causes of non-spherical shapes. For the stars exhibiting SiO maser emission, simultaneous observations will provide complementary information on the atmospheric dynamics. These will provide insight into the maser pumping and excitation processes and radial variations in density and temperature.