Monitoring of transiting exoplanets and their host stars with small aperture telescopes

TL;DR

This study demonstrates that small 0.4m telescopes are effective for long-term monitoring of transiting hot Jupiters, providing precise system parameters and detecting potential period changes and stellar activity.

Contribution

It shows the viability of using small aperture telescopes for detailed exoplanet transit monitoring and ephemeris updates, including detection of possible period variations.

Findings

Detected a potential quadratic ephemeris for WASP-52b suggesting a period change.

Confirmed the inflated and circular orbit of HAT-P-23b.

Measured the stellar rotation period of HAT-P-23 as 7.015 days.

Abstract

Exoplanet research is now target rich with a wide diversity of systems making it difficult for high demand observatories to undertake follow up observations over extended periods of time. We investigate the effectiveness of using 0.4m-class telescopes for monitoring transiting hot Jupiters and their host stars. We consider two representative case studies: WASP-52b with 13 new transits, and HAT-P-23b with 17 new transits and concurrent photometric monitoring covering 78 days. We present updated system parameters and combine our new transit times with previously published results to calculate new ephemerides for both systems. Our analysis of transit mid-times for WASP-52b results in a slight preference for a quadratic ephemeris ($\Delta\chi_{\nu}^2 = 0.07$, $\Delta BIC = 1.53$ over a linear ephemeris. We discuss the reality of this quadratic ephemeris indicating a period change of $ \delta P / \delta t = -38.6\pm4{\rm ms~yr^{-1}}$ and consider possible causes. WASP-52 is known to be an active star with previous publications reporting many spot crossing events, however no such events are seen in our new photometry. Our analysis shows that WASP-52 is still active and that the latitude of the spots has likely migrated away from the transit chord. We confirm the inflated nature and circular orbit for HAT-P-23b. Our monitoring of HAT-P-23 reveals a periodicity of 7.015 days with an amplitude of 0.011 mag which we interpret as the rotation period of HAT-P-23. The photometric and transit timing precision achieved in the case studies shows that this class of telescope is capable of precise characterisation and long-term monitoring of transiting hot Jupiters in support of dedicated ongoing and future ground and space based observations.