Radial velocity search for extrasolar planets around late M dwarfs

by Henrik Lukas Ruh
Doctoral thesis
Date of Examination:2025-04-25
Date of issue:2025-08-29
Advisor:Prof. Dr. Ansgar Reiners
Referee:Prof. Dr. Ansgar Reiners
Referee:Prof. Dr. Stefan Dreizler
Persistent Address: http://dx.doi.org/10.53846/goediss-11469

 

 

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Abstract

English

The radial velocity (RV) method has revealed the presence of rocky exoplanets in the habitable zones of M dwarf stars in the Solar neighborhood. Some of the potentially most Earth-like exoplanets have been found orbiting late-type M dwarfs. The search for exoplanets around late-type M dwarfs is challenging because these stars are often faint and exhibit high levels of stellar activity. Stellar activity refers to phenomena causally connect to stellar magnetic fields and gives rise to RV excess noise (RV jitter). Consequently, only few exoplanets have been discovered around late-type M dwarfs so far. The focus of this thesis is the characterization of the RV jitter in M dwarfs and the search for exoplanets around late-type M dwarfs with the RV method. We investigated the RV jitter in M dwarfs as a function of stellar equatorial rotation velocity and average magnetic fields based on a sample of 239 M dwarfs from the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs (CARMENES) survey. The RV jitter in our sample is primarily a function of stellar equatorial rotation velocity for stars with equatorial rotation velocities greater than 1 km/s. We observed an elevated RV jitter in a series of stars with distinctive distributions of magnetic filling factors, which could be related to their magnetic fields. We conducted an RV survey of ten late-type M dwarfs with the near-infrared Habitable Zone Planet Finder (HPF) spectrograph to search for exoplanets. Our measurements achieved a precision down to 3.4 m/s per RV epoch. After completing half of the anticipated total of 50 RV epochs per star, our measurements indicate a possible Neptune-mass planet candidate with an orbital period of 2.9 d and a second, tentative planet candidate. A third candidate is likely an equal-mass binary as indicated by archival imaging data. Further measurements and analysis are needed to reveal the true nature of these objects. Once completed, the survey will contribute to uncover the planet population of late-type M dwarfs.
Keywords: stars: activity; stars: low-mass; stars: magnetic field; stars: rotation; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Solar and Stellar Astrophysics; techniques: radial velocities
 
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