親子觀星會

https://www.researchgate.net/publication/336883458_TESS_Asteroseismology_of_the_Known_Red-giant_Host_Stars_HD_212771_and_HD_203949

http://www.sci-news.com/astronomy/tess-improbable-exoplanet-hd-203949b-07755.html
HD 212771 is a G8-type bright subgiant star located about 364 light-years away from Earth. It hosts a Jovian planet with a minimum mass of 2.3 Jupiter masses in a 373-day orbit.

HD 203949 is a K2-type bright giant star about 257 light-years away. It has a massive planet (8.2 Jupiter masses) in a 184-day circular orbit around it.

In the study, Dr. Tiago Campante, an astronomer at the University of Porto and the University of California, Santa Barbara, and colleagues determined the physical properties of both stars, such as their mass, size and age, through asteroseismology.

The researchers then focused on the evolutionary state of HD 203949. Their aim was to understand how its planet, HD 203949b, could have avoided engulfment, since the envelope of the star would have expanded well beyond the current planetary orbit during the red-giant phase of evolution.

Based upon extensive numerical simulations, the scientists think that star-planet tides might have brought HD 203949b inward from its original, wider orbit, placing it where we see it today.

“We determined how this planet could have reached its current location, and to do so whether or not the planet had to survive engulfment within the stellar envelope of the red giant star,” said co-author Dr. Dimitri Veras, a researcher at the University of Warwick.

“The work sheds new light on the survivability of planets when their parent stars begin to die, and might even reveal new aspects of tidal physics.”

“This study is a perfect demonstration of how stellar and exoplanetary astrophysics are linked together,” said co-author Dr. Vardan Adibekyan, an astronomer at the University of Porto.

“Stellar analysis seems to suggest that HD 203949 is too evolved to still host a planet at such a short orbital distance, while from the exoplanet analysis we know that the planet is there.”

“The solution to this scientific dilemma is hidden in the simple fact that stars and their planets not only form but also evolve together. In this particular case, the planet managed to avoid engulfment.”

https://www.cnbeta.com/articles/science/905805.htm

该小组研究了红巨星HD 212771和HD 203949，这两颗星也是美国国家航空航天局（NASA）的“系外行星勘探卫星”（TESS，苔丝）首次探测到表面星震的已知系外行星的主恒星。研究负责人蒂亚戈·坎庞特说：“TESS的观测非常精确，可以测量恒星表面的柔和震动。这两颗处于演化后期的恒星也拥有行星，为研究行星系统的演化提供了理想的实验平台。”

研究人员首先通过星震学确定了这两颗恒星的物理性质，例如其质量、大小和年龄，然后重点研究了HD 203949的演化状态，希望了解其行星如何避免被吞噬的命运。

研究人员称：“对恒星进行的分析似乎表明，这颗恒星演化得太过了，无法在这样短的轨道距离内容纳一颗行星；而我们现在对系外行星进行的分析表明，该行星的确存在。”

研究小组通过广泛的数值模拟得出结论称，恒星—行星之间的潮汐作用可能使该行星从其原始的、更宽的轨道向内移动，并使其位于我们今天看到的位置。他们表示：“解决这一科学难题的方法隐藏于一个简单的事实中：恒星及其行星形成以后，还会一起演化。在这种特殊情况下，行星设法避免了被吞噬的命运。”

在过去10年间，星震学对类日恒星和红巨星的研究产生了重大影响，相关研究数据主要来自于NASA的开普勒望远镜，在下一个10年，随着TESS获得的数据越来越多，相关研究也将取得更大进展。