Enshrouded Exoplanetary Systems

Staab, Daniel (2018). Enshrouded Exoplanetary Systems. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000d204

Abstract

This thesis is based on the hypothesis that stars hosting short period planets can show anomalously low apparent stellar activity values caused by planetary mass-loss enshrouding the system. The resulting circumstellar absorption depresses the cores of the Ca II H&K lines, where the activity index log(R'HK) is measured. I searched for this effect in a sample of ∼2700 stars, identifying 39 objects with log(R'HK) below the main sequence basal limit, and 6 Hyades and Pleiades stars with activity levels well below the cluster distributions. I describe a radial velocity programme to search for short period planets orbiting these stars. Because nearby bright stars are targeted, their mass-losing companions will offer key opportunities to probe planetary composition through transmission spectroscopy. I present four planet candidates discovered through this programme orbiting HD11231 and HD38677. The former is a γ-Doradus pulsator hosting a Saturn-mass planet in a 6 day orbit, and the latter is a compact system containing planets with ∼18, 13 and 3 Earth masses and periods between 20 and 1.7 days.

In addition, the Robert Stobie Spectrograph was calibrated to measure log(R'HK) values. The activity index of the known Hot Jupiter hosts WASP-43, WASP-51/HAT-P-30, WASP-72 & WASP-103 was measured to search for anomalous values caused by the companions. The activity level of WASP-43 is extremely high in absolute terms and relative to its age and X-ray emission. The activity of WASP-103 is marginally higher than expected from the system age. In both cases, star-planet interactions may enhance Ca II H & K emission. WASP-51/HAT-P-30 and WASP-72 show anomalously low activity; the latter falls below the basal envelopes of main sequence and evolved stars. I highlight that a quarter of transiting, short period planets hosts with published activity data exhibit anomalously low activity. These 22 systems include Hot Jupiters and low mass companions.

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