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Register a new userRotation and winds of exoplanet HD 189733 b measured with high-dispersion transmission spectroscopy
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Giant exoplanets orbiting very close to their parent star (hot Jupiters) are subject to tidal forces expected to synchronize their rotational and orbital periods on short timescales (tidal locking). However, spin rotation has never been measured directly for hot Jupiters. Furthermore, their atmospheres can show equatorial super-rotation via strong eastward jet streams, and/or high-altitude winds flowing from the day- to the night-side hemisphere. Planet rotation and atmospheric circulation broaden and distort the planet spectral lines to an extent that is detectable with measurements at high spectral resolution. We observed a transit of the hot Jupiter HD 189733 b around 2.3 {mu}m and at a spectral resolution of R~10$^5$ with CRIRES at the ESO Very Large Telescope. After correcting for the stellar absorption lines and their distortion during transit (the Rossiter-McLaughlin effect), we detect the absorption of carbon monoxide and water vapor in the planet transmission spectrum by cross-correlating with model spectra. The signal is maximized (7.6{sigma}) for a planet rotational velocity of $(3.4^{+1.3}_{-2.1})$ km/s, corresponding to a rotational period of $(1.7^{+2.9}_{-0.4})$ days. This is consistent with the planet orbital period of 2.2 days and therefore with tidal locking. We find that the rotation of HD 189733 b is longer than 1 day (3{sigma}). The data only marginally (1.5{sigma}) prefer models with rotation versus models without rotation. We measure a small day- to night-side wind speed of $(-1.7^{+1.1}_{-1.2})$ km/s. Compared to the recent detection of sodium blue-shifted by (8$pm$2) km/s, this likely implies a strong vertical wind shear between the pressures probed by near-infrared and optical transmission spectroscopy.
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Aims: We explore the capabilities of CARMENES for characterizing hot-Jupiter atmospheres by targeting multiple water bands, in particular, those at 1.15 and 1.4 $mu$m. Hubble Space Telescope observations suggest that this wavelength region is relevant for distinguishing between hazy/cloudy and clear atmospheres. Methods: We observed one transit of the hot Jupiter HD 189733 b with CARMENES. Telluric and stellar absorption lines were removed using Sysrem, which performs a principal component analysis including proper error propagation. The residual spectra were analysed for water absorption with cross-correlation techniques using synthetic atmospheric absorption models. Results: We report a cross-correlation peak at a signal-to-noise ratio (SNR) of 6.6, revealing the presence of water in the transmission spectrum of HD 189733 b. The absorption signal appeared slightly blueshifted at -3.9 $pm$ 1.3 kms$^{-1}$. We measured the individual cross-correlation signals of the water bands at 1.15 and 1.4 $mu$m, finding cross-correlation peaks at SNRs of 4.9 and 4.4, respectively. The 1.4 $mu$m feature is consistent with that observed with the Hubble Space Telescope. Conclusions: The water bands studied in this work have been mainly observed in a handful of planets from space. The ability of also detecting them individually from the ground at higher spectral resolution can provide insightful information to constrain the properties of exoplanet atmospheres. Although the current multiband detections can not yet constrain atmospheric haze models for HD 189733 b, future observations at higher signal-to-noise ratio could provide an alternative way to achieve this aim.
We present the first exoplanet atmosphere detection made as part of the SPIRou Legacy Survey, a Large Observing Program of 300 nights exploiting the capabilities of SPIRou, the new near-infrared high-resolution (R ~ 70 000) spectro-polarimeter installed on the Canada-France-Hawaii Telescope (CFHT; 3.6-m). We observed two transits of HD 189733, an extensively studied hot Jupiter that is known to show prominent water vapor absorption in its transmission spectrum. When combining the two transits, we successfully detect the planets water vapor absorption at 5.9 sigma using a cross-correlation t-test, or with a Delta BIC >10 using a log-likelihood calculation. Using a Bayesian retrieval framework assuming a parametrized T-P profile atmosphere models, we constrain the planet atmosphere parameters, in the region probed by our transmission spectrum, to the following values: VMR[H2O] = -4.4^{+0.4}_{-0.4}, and P_cloud >~ 0.2 bar (grey clouds), both of which are consistent with previous studies of this planet. Our retrieved water volume mixing ratio is slightly sub-solar although, combining it with the previously retrieved super-solar CO abundances from other studies would imply super-solar C/O ratio. We furthermore measure a net blue shift of the planet signal of -4.62^{+0.46}_{-0.44} km s-1, which is somewhat larger than many previous measurements and unlikely to result solely from winds in the planets atmosphere, although it could possibly be explained by a transit signal dominated by the trailing limb of the planet. This large blue shift is observed in all the different detection/retrieval methods that were performed and in each of the two transits independently.
We report detections of atomic species in the atmosphere of MASCARA-2 b, using the first transit observations obtained with the newly commissioned EXPRES spectrograph. EXPRES is a highly stabilised optical echelle spectrograph, designed to detect stellar reflex motions with amplitudes down to 30 cm/s, and was recently deployed at the Lowell Discovery Telescope. By analysing the transmission spectrum of the ultra-hot Jupiter MASCARA-2 b using the cross-correlation method, we confirm previous detections of Fe I, Fe II and Na I, which likely originate in the upper regions of the inflated atmosphere. In addition, we report significant detections of Mg I and Cr II. The absorption strengths change slightly with time, possibly indicating different temperatures and chemistry in the day-side and night-side terminators. Using the effective stellar line-shape variation induced by the transiting planet, we constrain the projected spin-orbit misalignment of the system to $1.6pm3.1$ degrees, consistent with an aligned orbit. We demonstrate that EXPRES joins a suite of instruments capable of phase-resolved spectroscopy of exoplanet atmospheres.
Context. The atmosphere of exoplanets has been studied extensively in recent years, using numerical models to retrieve chemical composition, dynamical circulation or temperature from data. One of the best observational probes in transmission is the sodium doublet, due to its large cross section. However, modelling the shape of the planetary sodium lines has proven to be challenging. Models with different assumptions regarding the atmosphere have been employed to fit the lines in the literature, yet statistically sound direct comparisons of different models are needed to paint a clear picture. Aims. We will compare different wind and temperature patterns and provide a tool to distinguish them driven by their best fit for the sodium transmission spectrum of the hot Jupiter HD 189733b. We parametrise different possible wind patterns already tested in literature and introduce the new option of an upwards driven vertical wind. Methods. We construct a forward model where the wind speed, wind geometry and temperature are injected into the calculation of the transmission spectrum. We embed this forward model in a nested sampling retrieval code to rank the models via their Bayesian evidence. Results. We retrieve a best-fit to the HD 189733b data for vertical upward winds $|vec{v}_{mathrm{ver}}(mathrm{mean})|=40pm4$ km/s at altitudes above $10^{-6}$ bar. With the current data from HARPS, we cannot distinguish wind patterns for higher pressure atmospheric layers. Conclusions. We show that vertical upwards winds in the upper atmosphere are a possible explanation for the broad sodium signature in hot Jupiters. We highlight other influences on the width of the doublet and explore strong magnetic fields acting on the lower atmosphere as one possible origin of the retrieved wind speed.
We present the open-source Bayesian Atmospheric Radiative Transfer (BART) retrieval package, which produces estimates and uncertainties for an atmospheres thermal profile and chemical abundances from observations. Several BART components are also stand-alone packages, including the parallel Multi-Core Markov chain Monte Carlo (MC3), which implements several Bayesian samplers; a line-by-line radiative-transfer model, transit; a code that calculates Thermochemical Equilibrium Abundances, TEA; and a test suite for verifying radiative-transfer and retrieval codes, BARTTest. The codes are in Python and C. BART and TEA are under a Reproducible Research (RR) license, which requires reviewed-paper authors to publish a compendium of all inputs, codes, and outputs supporting the papers scientific claims. BART and TEA produce the compendiums content. Otherwise, these codes are under permissive open-source terms, as are MC3 and BARTTest, for any purpose. This paper presents an overview of the code, BARTTest, and an application to eclipse data for exoplanet HD 189733 b. Appendices address RR methodology for accelerating science, a reporting checklist for retrieval papers, the spectral resolution required for synthetic tests, and a derivation of the effective sample size required to estimate any Bayesian posterior distribution to a given precision, which determines how many iterations to run. Paper II, by Cubillos et al., presents the underlying radiative-transfer scheme and an application to transit data for exoplanet HAT-P-11b. Paper III, by Blecic et al., discusses the initialization and post-processing routines, with an application to eclipse data for exoplanet WASP-43b. We invite the community to use and improve BART and its components at http://GitHub.com/ExOSPORTS/BART/.
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