Hot Jupiters orbiting pulsating stars: the cases of HD 31221b and WASP-167b

Kurzfassung

Hot Jupiters orbiting pulsating A/F stars represent a significant subset of the exoplanetary population, offering valuable insights into exoplanetary atmospheres and planet-to-star interactions. In this study, we analyze the TESS (Transiting Exoplanet Survey Satellite) light curves of two such systems featuring considerable stellar activity: HD 31221, a V = 8.02 mag, A2 star displaying hybrid pulsations of δ Scuti/γ Doradus type, and WASP-167, a V = 10.52 mag, F1 star exhibiting gamma Doradus type pulsations or spots. Our comprehensive analysis involves modeling transits and out-of-transit variability, encompassing Doppler beaming, ellipsoidal variations, and the reflection effect using the Transit and Light Curve Modeller (TLCM). For HD 31221 b, we determine an orbital period of 4.66631 ± 0.00011 days, a radius of 1.32 ± 0.14 R_jup, and a mass of 11.5 ± 10.3M_jup (from the ellipsoidal effect), consistent with either a brown dwarf or a giant planet. As HD 31221 is a rapid rotator (v sin I = 175.31 ± 1.74 km/s), we infer a projected spin-orbit misalignment of -121.6 ± 14.4 degrees and I = 55.9 +/- 11.3 degrees by modeling gravity darkening. The out-of-transit variations are dominated by the reflection effect, characterized by a geometric albedo of 1.58 ± 0.50. We confirm HD 31221 as the signal source through speckle interferometry, ground-based photometry, and detailed pixel photometry. For WASP-167b, transit parameters align with literature values (e.g. P = 2.02195830 ± 0.00000053 days, R = 1.621 R_jup), with an occultation depth of 106.8 +/- 27.3 ppm (geometric albedo of 0.34 ± 0.11). We employ a simple model to investigate WASP-167b's dayside, nightside, and intrinsic temperatures, revealing a dayside temperature of 2790 ± 100 K, categorizing WASP-167b as an Ultra Hot Jupiter (UHJ). A 2 sigma upper limit of 0.51 is placed on its Bond albedo. Resonant 2/P stellar signals interfere with the phase curve analysis of WASP-167b. Following rigorous signal treatment, we derive M = 0.34 ± 0.22 M_jup. Radial velocity-based mass estimation is challenging due to significant stellar activity and rapid rotation (v sin I = 52 ± 8 km/s for WASP-167) in these two systems. We show that both companions likely influence the activity of their host, evidenced by near resonance of the 3rd, 81st, and 225th orbital harmonics in HD 31221 and the 2nd harmonic in WASP-167 and the respective stellar signal. These systems offer promising candidates for follow-up atmospheric studies, particularly at thermal wavelengths less influenced by stellar pulsations (with e.g. Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey). Future observations, such as those by PLATO (PLAnetary Transits and Oscillations of stars), could provide multiband photometry for better understanding of stellar activity and improved separation of stellar and planetary signals, facilitating more precise modeling of out-of-transit variations and ultimately a better retrieval of the atmospheric parameters. Our analyses provide insights into managing stellar activity in similar systems while also shedding light on planet-to-star interactions, aiding future observations by PLATO or similar missions.