Physical properties of the HAT-P-23 and WASP-48 planetary systems from multi-colour photometry

Abstract

Context. Accurate and repeated photometric follow-up observations of planetary transit events are important to precisely characterize the physical properties of exoplanets. A good knowledge of the main characteristics of the exoplanets is fundamental in order to trace their origin and evolution. Multi-band photometric observations play an important role in this process. Aims. By using new photometric data, we computed precise estimates of the physical properties of two transiting planetary systems at equilibrium temperatures of ∼2000 K. Methods. We present new broadband, multi-colour photometric observations obtained using three small class telescopes and the telescope-defocussing technique. In particular we obtained 11 and 10 light curves covering 8 and 7 transits of HAT-P-23 and WASP-48, respectively. For each of the two targets, one transit event was simultaneously observed through four optical filters. One transit of WASP-48 b was monitored with two telescopes from the same observatory. The physical parameters of the systems were obtained by fitting the transit light curves with jktebop and from published spectroscopic measurements.Results. We have revised the physical parameters of the two planetary systems, finding a smaller radius for both HAT-P-23 b and WASP-48 b, R b = 1.224 ± 0.037 R Jup and R b = 1.396 ± 0.051 R Jup , respectively, than those measured in the discovery papers (R b = 1.368 ± 0.090 R Jup and R b = 1.67 ± 0.10 R Jup ). The density of the two planets are higher than those previously published (ρ b ∼ 1.1 and ∼0.3 ρ jup for HAT-P-23 and WASP-48, respectively) hence the two hot Jupiters are no longer located in a parameter space region of highly inflated planets. An analysis of the variation of the planet's measured radius as a function of optical wavelength reveals flat transmission spectra within the experimental uncertainties. We also confirm the presence of the eclipsing contact binary NSVS-3071474 in the same field of view of WASP-48, for which we refine the value of the period to be 0.459 d.

The Continuing Search for Evidence of Tidal Orbital Decay of Hot Jupiters

“…Maciejewski et al (2018) presented several new transit times and renanalyzed some light curves drawn from the literature. Their revised transit times differ from those reported by Ciceri et al (2015) by several minutes, for unknown reasons. We have adopted their rean- alyzed transit times, figuring that the more homogeneous analysis was preferable.…”

“…Timing residuals for HAT-P-23 b. White points are data obtained and reanalyzed byMaciejewski et al (2018) and originally reported byBakos et al (2011);Ramón-Fox & Sada (2013);Ciceri et al (2015) andSada & Ramón-Fox (2016). Black points represent new data.…”

The GTC exoplanet transit spectroscopy survey

“…For the dayside emission spectra they fitted a blackbody model with an effective temperature of T eff = 2158 ± 100 K. Using the models of Fortney et al (2008) and Burrows et al (2008) to fit their data, they deduced that WASP48b has a weak or absent temperature inversion. Ciceri et al (2015) presents a follow up of this system using multicolor broadband photometry; this work updated the stellar parameters of WASP-48 (M = 1.062 ± 0.074 M , R = 1.519 ± 0.007 R ), measured a smaller planetary radius (R = 1.396 ± 0.051 R Jup ), and found a flat transmission spectrum using broadband filters. Turner et al (2016) presents ground-based near-UV data of several transiting systems including WASP-48b, and found a R p /R s for the U band of 0.0916 ± 0.0017, a shallower transit depth than the one found by Enoch et al (2011).…”

“…The orbital eccentricity and period were fixed to 0 and 2.14363544 days (Ciceri et al 2015), respectively. In addition to the free transit parameters, we also set as free the coefficients used to model the systematic trends present in the light curves.…”

“…The atmospheric scale for WASP-48b is H = 614.9 km (using µ = 2.3 times the proton mass, T p = 2000 K, and g p = 11.5 m/s 2 taken from Ciceri et al 2015). To analyze our transmission spectrum results, we computed theoretical atmosphere models using Exo-Transmit (Kempton et al 2016).…”