Refined System Parameters and TTV Study of Transiting Exoplanetary System Hat-P-20

Abstract

We report new photometric observations of the transiting exoplanetary system HAT-P-20, obtained using CCD cameras at Yunnan Observatories and Ho Koon Nature Education cum Astronomical Centre, China, from 2010 to 2013, and Observatori Ca l'Ou, Sant Marti Sesgueioles, Spain, from 2013 to 2015. The observed data are corrected for systematic errors according to the coarse de-correlation and SYSREM algorithms, so as to enhance the signal of the transit events. In order to consistently model the star spots and transits of this exoplanetary system, we develop a highly efficient tool STMT based on the analytic models of Mandel & Agol and Montalto et al. The physical parameters of HAT-P-20 are refined by homogeneously analyzing our new data, the radial velocity data, and the earlier photometric data in the literature with the Markov chain Monte Carlo technique. New radii and masses of both host star and planet are larger than those in the discovery paper due to the discrepancy of the radius among K-dwarfs between predicted values by standard stellar models and empirical calibration from observations. Through the analysis of all available mid-transit times calculated with the normal model and spotted model, we conclude that the periodic transit timing variations in these transit events revealed by employing the normal model are probably induced by spot crossing events. From the analysis of the distribution of occulted spots by HAT-P20b, we constrain the misaligned architecture between the planetary orbit and the spin of the host star.

Kepler-411: a four-planet system with an active host star

“…We employ the Spot and Transit Modeling Tool (STMT), as described in Sun et al (2017), to model the normal transit light curves of Kepler-411. The recently updated STMT has not only the capability to model the combined effect of spots and planets on the light curve simultaneously, but can also be used to efficiently simulate double transit curves of an active host star using the analytic formulae derived by Pál (2012) and Montalto et al (2014).…”

“…We note that we only select the transit light curves near the local flux maximum to calculate the physical parameters, since these local maxima tend to be less affected by star spots. These fiducial models form the basis for modeling spot crossing events and double-transit events, because there is a strong degeneracy between transit parameters and spot properties derived from spot-distorted transit light curves (Sun et al 2017). The short-cadence data constrain the parameters of a transiting body better than the long-cadence data.…”

“…Stellar activity can not only create bumps on a transit light curve when star spots (or faculae) are occulted by the planet, but can also lead to variable depths of normalized transit light curves due to the influence of stellar activity on the total flux of the host star (Czesla et al 2009;Sun et al 2017).…”

“…Star spots can deform the transit light curves, for example through Article number, page 1 of 11 arXiv:1902.09719v1 [astro-ph.EP] 26 Feb 2019 A&A proofs: manuscript no. 34275corr_final_two-column spot-crossing events, and can thus possibly mimic the TTV signals induced by the gravitational perturbations of other planets (Oshagh et al 2013b;Daassou et al 2014;Ioannidis et al 2014Sun et al 2017). Therefore, appropriately accounting for the effects of stellar activity on transit light curves becomes absolutely necessary for characterizing exoplanets orbiting relatively active host stars.…”

The extraneous eclipses on binary light curves: KIC 5255552, KIC 10091110, and KIC 11495766

“…The 4.2185174 d period eclipses have secondary minimums that can be explicitly seen in panel Due to the lack of secondary eclipse (no secondary eclipse was found after the data folding and binning), its solution bears much more uncertainty. In view of this point, the 8.5303353 d period eclipses were also analyzed by the Spot and Transit Modeling Tool (STMT, Sun et al 2017), and the results are listed in the last column of Table 2 for comparison. The comparison shows that, generally, only the primary mean densities coincide with each other, and the differences of the other parameters reach 50%.…”