IMPRS-HD Alumni 2022

Alumni 2022

Paz Bluhm  (15.2.)  -  Jonas Kemmer  (16.2.)

    Jonas Kemmer   (Germany)                                                                                                                               16.2.2022

Earth-sized planets orbiting M-dwarf stars: Detection and mass measurement with CARMENES and TESS ( thesis pdf )

The technical progress of the last decades has enabled us to study ever smaller planets with increasing precision. The characterisation of Earth-sized planets is particularly exciting, since they can provide important insights into the formation and development of our own Earth. M-dwarf stars are especially suited to search for Earth-sized planets with the radial velocity (RV) and transit method, because the planetary signals are more pronounced for these stars due to their larger planet-to-star mass and radius ratios. In my dissertation, I deal with the CARMENES spectrograph, which was constructed exactly for this purpose. The first part is an error budget for the visual channel of the spectrograph, in which I investigate what comprises the uncertainty of the measured RVs and what the technical limits of the instrument are. In the second part of the thesis, I present the discovery of two Earth-sized planets using CARMENES observations. The two short-period, Earth-sized planets GJ 3473 b and GJ 3929 b orbit M-dwarf stars and were initially identified as transiting planet candidates by the TESS survey satellite. Our follow-up observations using the RV method confirmed their planetary nature and revealed in the case of GJ 3473 another non-transiting, temperate planet with sub-Neptune mass, GJ 3473 c. Joint modelling of the transit and RV data made it possible to determine precise masses and radii for the two transiting planets. The densities determined from this are most consistent with a MgSiO3 composition for both planets. Due to their short orbital periods and therefore high equilibrium temperatures, both are particularly well suited for future atmospheric characterisation using transit spectroscopy.

Supervisor:    Andreas Quirrenbach  (LSW)

    Paz Bluhm   (Chile)                                                                                                                               15.2.2022

Detection and characterization of exoplanets around M dwarfs in the presence of stellar activity  ( thesis pdf )

M dwarfs are the most numerous type of stars in the Universe. Their low masses and their large planet-to-star size ratios offer big advantages to study orbiting exoplanets around these stars. On one hand, the radial velocities signals have greater amplitudes and are easier to identify than in FGK stars. On the other, the small size of M dwarfs leads to transiting planets leaving a stronger imprint in the light curve. Additionally, their low temperatures places their habitable zone close to the host star, which makes them excellent targets to search for temperate or habitable worlds. Despite the advantages that M dwarfs offer, these do not come for free. Typically they are active entities, and most of the M-dwarfs have strong magnetic fields, which can heat their stellar chromospheres, creating magnetic activity which drives the occurrence of stellar spots in their photosphere. Consequently, stellar activity can mimic the signal of an orbiting planet which is one of the most problematic sources of noise. This thesis is focused on the discovery and characterization of exoplanets around M dwarfs, where I highlight the importance of careful modeling of the intrinsic stellar noise present in the data for to avoid false planet claims.

Supervisor:    Andreas Quirrenbach  (LSW)

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