Ephemeris refinement of 21 hot Jupiter exoplanets with high timing uncertainties

Abstract

Transit events of extrasolar planets offer a wealth of information for planetary characterization. However, for many known targets, the uncertainty of their predicted transit windows prohibits an accurate scheduling of follow-up observations. In this work, we refine the ephemerides of 21 hot Jupiter exoplanets with the largest timing uncertainties. We collected 120 professional and amateur transit light curves of the targets of interest, observed with a range of telescopes of 0.3m to 2.2m, and analyzed them along with the timing information of the planets discovery papers. In the case of WASP-117b, we measured a timing deviation compared to the known ephemeris of about 3.5 hours, and for HAT-P-29b and HAT-P-31b the deviation amounted to about 2 hours and more. For all targets, the new ephemeris predicts transit timings with uncertainties of less than 6 minutes in the year 2018 and less than 13 minutes until 2025. Thus, our results allow for an accurate scheduling of follow-up observations in the next decade.

WASP-117 b: An Eccentric Hot Saturn as a Future Complex Chemistry Laboratory

“…Our derived period is 1.2 s shorter than that from Mallonn et al (2019). We improved the accuracy of the period and thus reduced the current uncertainty on the transit time with respect to the results from Mallonn et al (2019). The observed minus calculated residuals, along with the fitted TESS light curves are shown in Figure 5 while the fitted mid-times can be found in Table 4.…”

“…The transits of WASP-117 b from HST and TESS were seen to arrive early compared to the predictions from Lendl et al (2014). The ephemeris of WASP-117 b was recently refined by Mallonn et al (2019). We used the observations from Mallonn et al (2019), the original ephemeris from Lendl et al (2014), and the new data analyzed here to update the period and transit time for the planet.…”

Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b

“…This HST observation benefited from reobservations of the WASP-117b transit in July 2017 with broadband photometry using two small telescopes: one in Chile, the Chilean-Hungarian Automated Telescope 0.7 m (CHAT, PI: Jordán), and one in South Africa (1m, Los Cumbres Observatory). The combined observations allowed us to improve the uncertainties in mid-transit time from 2 h (based on Lendl et al 2014) to 2 min (Mallonn et al 2019).…”

“…In addition to the parameters for the systematics model described above, parameters of the transit mid-time, the transit depth, and the limb-darkening coefficient were optimized using the emcee code (Foreman-Mackey et al 2013). The other planetary-system related parameters, including the orbital period, system semimajor axis, eccentricity, inclination, and the longitude of periastron, were fixed using values from the literature (Lendl et al 2014;Mallonn et al 2019), which were already good enough for the fit. We then conducted the fit to spectroscopic light curves using the same method except fixing the transit mid-time using the best-fitting value from the broadband fit.…”

“…Furthermore, WASP-117b orbits its quiet F-type mainsequence star on an eccentric orbit (e = 0.3) with a relatively long orbital period of ≈10 days (Lendl et al 2014;Mallonn et al 2019). Lendl et al (2014) further report equilibrium temperatures of 900 and 1200 K during apastron and periastron, respectively, assuming an albedo of α = 0 and efficient, uniform redistribution of absorbed stellar energy over the whole planet.…”