Homogeneously derived transit timings for 17 exoplanets and reassessed TTV trends for WASP-12 and WASP-4

Abstract

We homogeneously analyse ∼3.2 × 105 photometric measurements for ∼1100 transit light curves belonging to 17 exoplanet hosts. The photometric data cover 16 years (2004–2019) and include amateur and professional observations. Old archival light curves were reprocessed using up-to-date exoplanetary parameters and empirically debiased limb-darkening models. We also derive self-consistent transit and radial-velocity fits for 13 targets. We confirm the non-linear transit timing variation (TTV) trend in the WASP-12 data at a high significance, and with a consistent magnitude. However, Doppler data reveal hints of a radial acceleration of about −7.5 ± 2.2 m s−1 yr−1, indicating the presence of unseen distant companions, and suggesting that roughly 10 per cent of the observed TTV was induced via the light-travel (or Roemer) effect. For WASP-4, a similar TTV trend suspected after the recent TESS observations appears controversial and model dependent. It is not supported by our homogeneous TTV sample, including 10 ground-based EXPANSION light curves obtained in 2018 simultaneously with TESS. Even if the TTV trend itself does exist in WASP-4, its magnitude and tidal nature are uncertain. Doppler data cannot entirely rule out the Roemer effect induced by possible distant companions.

WASP-4 Is Accelerating toward the Earth

“…These transits were observed from the 3.58m New Technology Telescope and the Danish 1.54m telescope at La Silla, Chile, and the South African Astronomical Observatory 1.0m telescope. Additional timing measurements were also reported recently by Baluev et al (2019), based on a homogeneous analysis of archival groundbased observations. We included their transit times from the TRAPPIST telescope (six transits), the El Sauce 36 cm (four transits), and Petrucci et al (2013) (two transits).…”

“…For hot Jupiters that have been monitored over baselines exceeding 10 years, secular changes in their orbital periods are currently being constrained to a precision of 10 msec yr −1 (Wilkins et al 2017;Maciejewski et al 2018;Baluev et al 2019;Petrucci et al 2020;Patra et al 2020). This is roughly commensurate with the level of signal many outer companions are expected to induce ( Figure 5).…”

“…Soon thereafter, Southworth et al (2019) reported an additional 22 transit times and recalculated the period derivative to bė P = −9.2 ± 1.1 milliseconds per year. A separate study by Baluev et al (2019) reported on additional transit times, and pointed out that the period decrease was statistically significant only when analyzing the data with the highest precision.…”

Transit timing variations of five transiting planets

“…The mid-transit times from the literature have been determined by making use of various models and software packages. Therefore, we have started an effort to homogenize the data sets (as in [5]) that we use, starting with the detrending of the light curves and ending with the measurements of the mid-transit times and their uncertainty by ourselves with the same tools consistently. We think that comparison of the results of this contribution with that from the upcoming work will be helpful in terms of getting all transit observers prepare for future observations with similar standards, and researchers decide which data sets to use and which to discard in such a tedious work as the analysis of transit timing variations.…”

Simultaneous TESS and NGTS transit observations of WASP-166 b

“…The precise transit ephemerides achievable with this observing method will also allow NGTS to monitor the transit timing variations of shortperiod Jupiter-like planets to search for signs of orbital decay (e.g. Baluev et al 2019;Patra et al 2020;Yee et al 2020). In addition to measuring transit timing variations, the precise ephemerides achievable with NGTS multitelescope observations will also be of use for the scheduling of future transmission spectroscopic measurements, and other characterization efforts.…”