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Register a new userTESS unveils the phase curve of WASP-33b. Characterization of the planetary atmosphere and the pulsations from the star
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We present the detection and characterization of the full-orbit phase curve and secondary eclipse of the ultra-hot Jupiter WASP-33b at optical wavelengths, along with the pulsation spectrum of the host star. We analyzed data collected by the Transiting Exoplanet Survey Satellite (TESS) in sector 18. WASP-33b belongs to a very short list of highly irradiated exoplanets that were discovered from the ground and were later visited by TESS. The host star of WASP-33b is of delta Scuti-type and shows nonradial pulsations in the millimagnitude regime, with periods comparable to the period of the primary transit. These completely deform the photometric light curve, which hinders our interpretations. By carrying out a detailed determination of the pulsation spectrum of the host star, we find 29 pulsation frequencies with a signal-to-noise ratio higher than 4. After cleaning the light curve from the stellar pulsations, we confidently report a secondary eclipse depth of 305.8 +/- 35.5 parts-per-million (ppm), along with an amplitude of the phase curve of 100.4 +/- 13.1 ppm and a corresponding westward offset between the region of maximum brightness and the substellar point of 28.7 +/- 7.1 degrees, making WASP-33b one of the few planets with such an offset found so far. Our derived Bond albedo, A_B = 0.369 +/- 0.050, and heat recirculation efficiency, epsilon = 0.189 +/- 0.014, confirm again that he behavior of WASP-33b is similar to that of other hot Jupiters, despite the high irradiation received from its host star. By connecting the amplitude of the phase curve to the primary transit and depths of the secondary eclipse, we determine that the day- and nightside brightness temperatures of WASP-33b are 3014 +/- 60 K and 1605 +/- 45 K, respectively. From the detection of photometric variations due to gravitational interactions, we estimate a planet mass of M_P = 2.81 +/- 0.53 M$_J.
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We present the detection and analysis of the phase curve of KELT-1b at optical wavelengths, analyzing data taken by the Transiting Exoplanet Survey Satellite (TESS). With a mass of ~27 M_J, KELT-1b is a low-mass brown dwarf. Due to the high mass and close proximity of its companion, the host star has a TESS light curve which shows clear ellipsoidal variations. We model the data with a six-component model: secondary eclipse, phase curve accounting for reflected light and thermal emission, Doppler beaming, ellipsoidal variations, stellar activity and the primary transit. We determine the secondary eclipse depth in the TESS bandpass to be 304 +/- 75 parts-per-million (ppm), the most accurate eclipse depth determined so far for KELT-1b. We measure the amplitude of the phase curve to be 128 +/- 27 ppm, with a corresponding eastward offset between the region of maximum brightness and the substellar point of 19.2 +/- 9.6 degrees, in good agreement with Spitzer measurements. We determine day and night brightness temperatures of 3201 +/- 147 K and 1484 +/- 110 K, respectively, slightly higher than those from Spitzer 3.6 and 4.5 micrometer data. A one-dimensional self-consistent atmospheric model can explain the TESS and Spitzer day side brightness temperatures with thermal emission alone and no reflected light. The night side data can be explained by a model with an internal temperature of ~1100 K, which may be related to the inflated radius. The difference between the TESS and Spitzer brightness temperatures can be explained by stronger molecular opacity in the Spitzer bands. On the night side, this opacity is due primarily to CH4 and CO while on the day side it is due to H2-H2 and H2-He collision-induced absorption.
We study the red-optical photometry of the ultra-hot Jupiter WASP-121 b as observed by the Transiting Exoplanet Survey Satellite (TESS) and model its atmosphere through a radiative transfer simulation. Given its short orbital period of $sim1.275$ days, inflated state and bright host star, WASP-121 b is exceptionally favorable for detailed atmospheric characterization. Towards this purpose, we use texttt{allesfitter} to characterize its full red-optical phase curve, including the planetary phase modulation and the secondary eclipse. We measure the day and nightside brightness temperatures in the TESS passband as $3012substack{+40 -42}$ K and $2022substack{+254 -602}$ K, respectively, and do not find a statistically significant phase shift between the brightest and substellar points. This is consistent with an inefficient heat recirculation on the planet. We then perform an atmospheric retrieval analysis to infer the dayside atmospheric properties of WASP-121 b such as its bulk composition, albedo and heat recirculation. We confirm the temperature inversion in the atmosphere and suggest H$^-$, TiO and VO as potential causes of the inversion, absorbing heat at optical wavelengths at low pressures. Future HST and JWST observations of WASP-121 b will benefit from its first full phase curve measured by TESS.
We report ground-based observations at 0.91 microns of the occultation of the hot Jupiter WASP-33b by its A5 host star. We measure the planet to be 0.109 +/- 0.030 per cent as bright as its host star at 0.91 microns. This corresponds to a brightness temperature, T_B = 3620 +200 -250 K, significantly higher than the zero-albedo equilibrium temperature for both isotropic re-radiation (2750 +/- 37 K) and uniform day-side only re-radiation (3271 +/- 44 K), but consistent with the zero-redistribution temperature (3515 +/- 47 K). This indicates that the heat redistribution from the day-side of WASP-33b to the night side is inefficient, and further suggest that there is immediate re-radiation, and therefore little or no redistribution, of heat within the day-side. We also detected the stellar pulsations of WASP-33, which we model as the sum of four sinusoids, with periods of between 42 and 77 minutes and amplitudes of 0.5 to 1.5 mmag.
WASP-33b is a retrograde hot Jupiter with a period of 1.2 days orbiting around a rapidly rotating and pulsating A-type star. A previous study found that the transit chord of WASP-33b had changed slightly from 2008 to 2014 based on Doppler tomographic measurements. They attributed the change to orbital precession caused by the non-zero oblateness of the host star and the misaligned orbit. We aim to confirm and more precisely model the precession behavior using additional Doppler tomographic data of WASP-33b obtained with the High Dispersion Spectrograph on the 8.2m Subaru telescope in 2011, as well as the datasets used in the previous study. Using equations of a long-term orbital precession, we constrain the stellar gravitational quadrupole moment $J_{2}=(9.14pm 0.51)times 10^{-5}$ and the angle between the stellar spin axis and the line of sight $i_{star}=96^{+10}_{-14}$ deg. These values update that the host star is more spherical and viewed more equator than the previous study. We also estimate that the precession period is $sim$840 years. We also find that the precession amplitude of WASP-33b is $sim$67 deg and WASP-33b transits in front of the host star for only $sim$20% of the whole precession period.
We measured the optical phase curve of the transiting brown dwarf KELT-1b (TOI 1476, Siverd et al. 2012) using data from the TESS spacecraft. We found that KELT-1b shows significant phase variation in the TESS bandpass, with a relatively large phase amplitude of $234^{+43}_{-44}$ ppm and a secondary eclipse depth of $371^{+47}_{-49}$ ppm. We also measured a marginal eastward offset in the dayside hotspot of $18.3^circpm7.4^circ$ relative to the substellar point. We detected a strong phase curve signal attributed to ellipsoidal distortion of the host star, with an amplitude of $399pm19$ ppm. Our results are roughly consistent with the Spitzer phase curves of KELT-1b (Beatty et al. 2019), but the TESS eclipse depth is deeper than expected. Our cloud-free 1D models of KELT-1bs dayside emission are unable to fit the full combined eclipse spectrum. Instead, the large TESS eclipse depth suggests that KELT-1b may have a significant dayside geometric albedo of $mathrm{A}_mathrm{g}sim0.5$ in the TESS bandpass, which would agree with the tentative trend between equilibrium temperature and geometric albedo recently suggested by Wong et al. 2020. We posit that if KELT-1b has a high dayside albedo, it is likely due to silicate clouds (Gao et al. 2020) that form on KELT-1bs nightside (Beatty et al. 2019, Keating et al. 2019) and are subsequently transported onto the western side of KELT-1bs dayside hemisphere before breaking up.
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