Three close-in planets found around red-clump giants that should have been engulfed
Astronomers report three planets orbiting red-clump giants at separations where engulfment theory says they should not have survived.
A new arXiv paper reports three systems in which planets orbit close to red-clump giant stars, at distances where current theory says they should not have survived. The systems are 24 Boo b, HD 12648 b and TYC 4282-605-1 b. The paper, by Wen-Xu Lin and 11 other authors, was submitted on 3 November.
The host stars are confirmed as red-clump giants through asteroseismology, which the authors say shows that each has already expanded and contracted dramatically following helium ignition. The planets now sit at orbital separations smaller than the maximum stellar radii the stars reached during the red-giant-branch phase.
Tidal-engulfment theory predicts that planets within about 1 au of Sun-like stars should be engulfed during red-giant-branch expansion. Only one such "forbidden" planet had been identified before this work.
Of the three, 24 Boo b orbits at only 0.183 au with a 30-day period. The authors say that makes it the closest planet known around a red-clump giant.
Sourcearxiv.org