Exoplanets Around Subgiant Stars

Dutta, Arkaprova (2025) Exoplanets Around Subgiant Stars. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Arkaprova Dutta (20MS007)) 20MS007_Thesis_file.pdf Restricted to Repository staff only Download (4MB)

Abstract

Evolved stars, particularly sub-giants, have been underrepresented in most planet search surveys, which traditionally focus on solar-type main-sequence stars. The quest for exoplanets around sub-giant stars offers crucial insights into planet formation and evolution in the context of evolved stellar environments. This study comprehensively reviews well-studied 190 exoplanets around 154 sub-giant stars from the NASA exoplanet archive, emphasising their detection methods, orbital properties, and atmospheric characterisation and compares them with well-studied properties of exoplanets around main-sequence stars. We also discuss the broader implications of our findings for understanding exoplanet frequency and migration mechanisms across different spectral types through occurrence studies. This work lays the groundwork for our long-term planet search and population studies around sub-giant stars using the radial velocity (RV) method. In order to achieve this goal we curate a candidate list of 82 subgiant stars with brightness of < 11.5 magnitude, observable from northern hemisphere, for potentially suitable stars to host planets using homogeneous properties from the GAIA DR3 and LAMOST DR10 catalogue to follow up using high-resolution spectroscopy aimed at detecting new exoplanets around sub-giant stars (including the stars in the list with limited or no high-precision radial velocity measurements) and modelling their orbits. Overall, we find that even modest stellar evolution off the main sequence imprints detectable changes in planet occurrence, orbital configuration, and system multiplicity. To this end, we have proceeded with occurrence rate studies and finished studying 45 stars in covering regions from 6700 K to 7000 K. We find a lower than mainsequence occurrence rate for considering < 10 days planets within 1-20 R⊕ radius. The assembled catalogue and methodologies furnish a benchmark for future spectroscopic and theoretical investigations into planet survival, migration, and tidal realignment in evolving systems.

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