Exoplanet Transit Observations with Small Aperture Ground-Based Telescopes

Salisbury, Mark (2021). Exoplanet Transit Observations with Small Aperture Ground-Based Telescopes. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00013d4d

Abstract

In this thesis I investigate using small aperture ground-based telescopes to contribute to transiting exoplanet science. 95 transits were obtained of three case study systems, HAT-P-23b, WASP-12b and WASP-52b over multiple seasons, using three (~0.4m) telescopes. Observations were made either side of GPS timing control installation at the OU OpenScience Observatories and its impact quantified. The transit lightcurves were analysed using open-source applications combined with published data providing precise timing and system parameters. HAT-P-23 and WASP-12 were monitored separately outside of transits.

Transit timing analysis confirms and refines the linear ephemeris for HAT-P-23b and quadratic ephemeris for WASP-12b. Transit timing of WASP-52b indicates preference for a previously unreported non-linear ephemeris.

HAT-P-23 monitoring revealed variability with a period of 7.015d, interpreted as stellar rotation due to surface spots. No variability was unambiguously detected for WASP-12 over 4 seasons. J0630+2942, located 2' from WASP-12 and commonly used as a comparison star for observations of WASP-12b was discovered to be variable with an amplitude that declined over four seasons. The results show OSO PIRATE telescope can achieve a monitoring precision better than 0.01Magnitude over multiple seasons.

I confirm the disputed eccentricity for HAT-P-23b is consistent with zero and determine a planetary radius and mass of 1.157+0.023-0.022Rsun and 1.063+0.063-0.060Msun, 3.8% and 5.9% smaller respectively than reported at discovery. WASP-52b lightcurves exhibit no detectable spot crossings as seen in previous seasons while the star remains variable, indicating the spot latitude has likely migrated from the transit chord.

The effects of different observing modes are quantified and general best practice identified for photometry of transiting exoplanets with small aperture ground-based telescopes. This includes observing transits using the CCD in 1x1 binning mode and an ideal minimum Transit SNR (TSNR) of 10-12. GPS implementation at the OSO halved the transit timing measurement scatter. The results demonstrate the capability and efficiency of small aperture ground-based telescopes to contribute to our understanding of transiting hot Jupiter systems.