PLANET ENGULFMENT BY {approx}1.5-3 M{sub sun} RED GIANTS
- Department of Earth and Planetary Sciences, Tokyo Institute of Technology (TokyoTech), 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan)
- Department of Cosmosciences, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810 (Japan)
Recent radial-velocity surveys for GK clump giants have revealed that planets also exist around {approx}1.5-3 M{sub sun} stars. However, no planets have been found inside 0.6 AU around clump giants, in contrast to solar-type main-sequence stars, many of which harbor short-period planets such as hot Jupiters. In this study, we examine the possibility that planets were engulfed by host stars evolving on the red-giant branch (RGB). We integrate the orbital evolution of planets in the RGB and helium-burning phases of host stars, including the effects of stellar tide and stellar mass loss. Then we derive the critical semimajor axis (or the survival limit) inside which planets are eventually engulfed by their host stars after tidal decay of their orbits. Specifically, we investigate the impact of stellar mass and other stellar parameters on the survival limit in more detail than previous studies. In addition, we make detailed comparisons with measured semimajor axes of planets detected so far, which no previous study has done. We find that the critical semimajor axis is quite sensitive to stellar mass in the range between 1.7 and 2.1 M{sub sun}, which suggests a need for careful comparison between theoretical and observational limits of the existence of planets. Our comparison demonstrates that all planets orbiting GK clump giants that have been detected are beyond the survival limit, which is consistent with the planet-engulfment hypothesis. However, on the high-mass side (>2.1M{sub sun}), the detected planets are orbiting significantly far from the survival limit, which suggests that engulfment by host stars may not be the main reason for the observed lack of short-period giant planets. To confirm our conclusion, the detection of more planets around clump giants, especially with masses {approx}> 2.5M{sub sun}, is required.
- OSTI ID:
- 21579948
- Journal Information:
- Astrophysical Journal, Vol. 737, Issue 2; Other Information: DOI: 10.1088/0004-637X/737/2/66; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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