Enshrouded Exoplanetary Systems

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. <br></br><br></br> 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.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

The Open University

Year dc:date.issued

2018

Author dc:creator

• Staab, Daniel

Language dc:language

en