Simulations of starspot anomalies within TESS exoplanetary transit light curves -- I. The detection limits of starspot anomalies in TESS light curves

Abstract

20573 simulations of planetary transits around spotted stars were conducted using the transit-starspot model, \texttt{PRISM}. In total 3888 different scenarios were considered using three different host star spectral types, M4V, M1V and K5V. The mean amplitude of the starspot anomaly was measured and compared to the photometric precision of the light curve, to determine if the starspot anomaly's characteristic "blip" was noticeable in the light curve. The simulations show that, starspot anomalies will be observable in TESS 2\,min cadence data. The smallest starspot detectable in TESS transit light curves has a radius of $\approx1900$\,km. The starspot detection limits for the three host stars are: $4900\pm1700$\,km (M4V), $13800\pm6000$\,km (M1V) and $15900\pm6800$\,km (K5V). The smallest change in flux of the starspot ($\Delta F_\mathrm{spot} = 0.00015\pm0.00001$) can be detected when the ratio between the planetary and stellar radii, $k = 0.082\pm0.004$. The results confirm known dependencies between the amplitude of the starspot anomaly and the photometric parameters of the light curve. The results allowed the characterisation of the relationship between the change in flux of the starspot anomaly and the change in flux of the planetary transit for TESS transit light curves.