Characterizing Extrasolar Planets from Transit Light Curves obtained at the Universidad de Monterrey Observatory – Part 3

At the Universidad de Monterrey Observatory (MPC 720) we carried out a program for observing exoplanet transits and registering their light curves using telescopes of modest aperture and standard photometric filters between 2005 and 2016. In our archives we have over 340 transits of over 75 known systems. Our goal is to combine individual transit light curves of the same system taken at different times but with the same equipment. We then analyze the combined light curves in conjunction with the radial velocity information available from the literature in order to confirm, improve or revise the main parameters that characterize the transiting system. It is important to systematically continue observing these systems not only to improve and refine our understanding of them, but also to record any possible transient phenomenon and monitor for possible period changes, as reflected in the mid-transit times. We report our observations of 48 individual exoplanet transit light curves and the results from successfully combining 7 light curves for GJ 436 (Ic), 7 for HAT-P-20 (Ic), 5 for WASP-14 (Rc), 4 for WASP-26 (Ic), 5 for WASP-43 (Ic), 6 for WASP-50 (Ic), 6 for XO-2 (Ic), 4 for XO-3 (Ic), and 4 for XO-4 (Ic). From these we then derive planet sizes (Rp/R*), orbital distances (a/R*) and orbital inclinations (i) for these systems using standard modeling software such as EXOFAST and TAP. In most cases we confirm the parameters reported in the literature. For the GJ 436, WASP-50 and XO-2 systems we derive planet sizes which are marginally larger than literature values. For the WASP-43 and GJ 436 systems we derive slightly higher inclinations accompanied by slight increases in orbital distance compared with HST results. Our WASP-26 results show an anomalous 20% larger planet size, but we suspect that to be an artifact of light contamination in the light curve due to a nearby star. From our mid-transit times and those of the literature we do not find any statistically significant deviations from a fixed orbital period for these systems. Our results validate the presented methodology and show that college observatories with small telescopes are able to adopt usefull extrasolar planet transit follow-up observing programs.