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Register a new userA photometric study of the hot exoplanet WASP-19b
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Context: When the planet transits its host star, it is possible to measure the planetary radius and (with radial velocity data) the planet mass. For the study of planetary atmospheres, it is essential to obtain transit and occultation measurements at multiple wavelengths. Aims: We aim to characterize the transiting hot Jupiter WASP-19b by deriving accurate and precise planetary parameters from a dedicated observing campaign of transits and occultations. Methods: We have obtained a total of 14 transit lightcurves in the r-Gunn, IC, z-Gunn and I+z filters and 10 occultation lightcurves in z-Gunn using EulerCam on the Euler-Swiss telescope and TRAPPIST. We have also obtained one lightcurve through the narrow-band NB1190 filter of HAWK-I on the VLT measuring an occultation at 1.19 micron. We have performed a global MCMC analysis of all new data together with some archive data in order to refine the planetary parameters and measure the occultation depths in z-band and at 1.19 micron. Results: We measure a planetary radius of R_p = 1.376 (+/-0.046) R_j, a planetary mass of M_p = 1.165 (+/-0.068) M_j, and find a very low eccentricity of e = 0.0077 (+/-0.0068), compatible with a circular orbit. We have detected the z-band occultation at 3 sigma significance and measure it to be dF_z= 352 (+/-116) ppm, more than a factor of 2 smaller than previously published. The occultation at 1.19 micron is only marginally constrained at dF_1190 = 1711 (+/-745) ppm. Conclusions: We have shown that the detection of occultations in the visible is within reach even for 1m class telescopes if a considerable number of individual events are observed. Our results suggest an oxygen-dominated atmosphere of WASP-19b, making the planet an interesting test case for oxygen-rich planets without temperature inversion.
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High resolution precision spectroscopy provides a multitude of robust techniques for probing exoplanetary atmospheres. We present multiple VLT/ESPRESSO transit observations of the hot-Jupiter exoplanet WASP-19b with previously published but disputed atmospheric features from low resolution studies. Through spectral synthesis and modeling of the Rossiter-McLaughlin (RM) effect we calculate stellar, orbital and physical parameters for the system. From narrow-band spectroscopy we do not detect any of H,I, Fe,I, Mg,I, Ca,I, Na,I and K,I neutral species, placing upper limits on their line contrasts. Through cross correlation analyses with atmospheric models, we do not detect Fe,I and place a 3$sigma$ upper limit of $log,(X_{textrm{Fe}}/X_odot) approx -1.83,pm,0.11$ on its mass fraction, from injection and retrieval. We show the inability to detect the presence of H$_2$O for known abundances, owing to lack of strong absorption bands, as well as relatively low S/N ratio. We detect a barely significant peak (3.02,$pm$,0.15,$sigma$) in the cross correlation map for TiO, consistent with the sub-solar abundance previously reported. This is merely a hint for the presence of TiO and does textit{not} constitute a confirmation. However, we do confirm the presence of previously observed enhanced scattering towards blue wavelengths, through chromatic RM measurements, pointing to a hazy atmosphere. We finally present a reanalysis of low resolution transmission spectra of this exoplanet, concluding that unocculted starspots alone cannot explain previously detected features. Our reanalysis of the FORS2 spectra of WASP-19b finds a $sim$,100$times$ sub-solar TiO abundance, precisely constrained to $log,X_{textrm{TiO}} approx -7.52 pm 0.38$, consistent with the TiO hint from ESPRESSO. We present plausible paths to reconciliation with other seemingly contradicting results.
Observations of ultra-hot Jupiters indicate the existence of thermal inversion in their atmospheres with day-side temperatures greater than 2200 K. Various physical mechanisms such as non-local thermal equilibrium, cloud formation, disequilibrium chemistry, ionisation, hydrodynamic waves and associated energy, have been omitted in previous spectral retrievals while they play an important role on the thermal structure of their upper atmospheres.We aim at exploring the atmospheric properties of WASP-19b to understand its largely featureless thermal spectra using a state-of-the-art atmosphere code that includes a detailed treatment of the most important physical and chemical processes at play in such atmospheres.We used the one-dimensional line-by-line radiative transfer code PHOENIX in its spherical symmetry configuration including the BT-Settl cloud model and C/O disequilibrium chemistry to analyse the observed thermal spectrum of WASP-19b. Results. We find evidence for a thermal inversion in the day-side atmosphere of the highly irradiated ultra-hot Jupiter WASP-19b with Teq ~ 2700 K. At these high temperatures we find that H2O dissociates thermally at pressure below 10^-2 bar. The inverted temperature-pressure profiles of WASP-19b show the evidence of CO emission features at 4.5 micron in its secondary eclipse spectra.We find that the atmosphere ofWASP-19b is thermally inverted.We infer that the thermal inversion is due to the strong impinging radiation. We show that H2O is partially dissociated in the upper atmosphere above about tau = 10^-2, but is still a significant contributor to the infrared-opacity, dominated by CO. The high-temperature and low-density conditions cause H2O to have a flatter opacity profile than in non-irradiated brown dwarfs.Altogether these factors makes H2O more difficult to identify in WASP-19b.
We present an occultation of the newly discovered hot Jupiter system WASP-19, observed with the HAWK-I instrument on the VLT, in order to measure thermal emission from the planets dayside at ~2 um. The light curve was analysed using a Markov-Chain Monte-Carlo method to find the eclipse depth and the central transit time. The transit depth was found to be 0.366+-0.072 %, corresponding to a brightness temperature of 2540+-180 K. This is significantly higher than the calculated (zero-albedo) equilibrium temperature, and indicates that the planet shows poor redistribution of heat to the night side, consistent with models of highly irradiated planets. Further observations are needed to confirm the existence of a temperature inversion, and possibly molecular emission lines. The central eclipse time was found to be consistent with a circular orbit.
In the past few years, the study of exoplanets has evolved from being pure discovery, then being more exploratory in nature and finally becoming very quantitative. In particular, transmission spectroscopy now allows the study of exoplanetary atmospheres. Such studies rely heavily on space-based or large ground-based facilities, because one needs to perform time-resolved, high signal-to-noise spectroscopy. The very recent exchange of the prisms of the FORS2 atmospheric diffraction corrector on ESOs Very Large Telescope should allow us to reach higher data quality than was ever possible before. With FORS2, we have obtained the first optical ground-based transmission spectrum of WASP-19b, with 20 nm resolution in the 550--830 nm range. For this planet, the data set represents the highest resolution transmission spectrum obtained to date. We detect large deviations from planetary atmospheric models in the transmission spectrum redwards of 790 nm, indicating either additional sources of opacity not included in the current atmospheric models for WASP-19b or additional, unexplored sources of systematics. Nonetheless, this work shows the new potential of FORS2 for studying the atmospheres of exoplanets in greater detail than has been possible so far.
Ultra-hot Jupiters offer interesting prospects for expanding our theories on dynamical evolution and the properties of extremely irradiated atmospheres. In this context, we present the analysis of new optical spectroscopy for the transiting ultra-hot Jupiter WASP-121b. We first refine the orbital properties of WASP-121b, which is on a nearly polar (obliquity $psi^{rm North}$=88.1$pm$0.25$^{circ}$ or $psi^{rm South}$=91.11$pm$0.20$^{circ}$) orbit, and exclude a high differential rotation for its fast-rotating (P$<$1.13 days), highly inclined ($i_mathrm{star}^{rm North}$=8.1$stackrel{+3.0}{_{-2.6}}^{circ}$ or $i_mathrm{star}^{rm South}$=171.9$stackrel{+2.5}{_{-3.4}}^{circ}$) star. We then present a new method that exploits the reloaded Rossiter-McLaughlin technique to separate the contribution of the planetary atmosphere and of the spectrum of the stellar surface along the transit chord. Its application to HARPS transit spectroscopy of WASP-121b reveals the absorption signature from metals, likely atomic iron, in the planet atmospheric limb. The width of the signal (14.3$pm$1.2 km/s) can be explained by the rotation of the tidally locked planet. Its blueshift (-5.2$pm$0.5 km/s) could trace strong winds from the dayside to the nightside, or the anisotropic expansion of the planetary thermosphere.
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