Detection of sodium in the atmosphere of WASP-69b

Abstract

Context. Transit spectroscopy is one of the most commonly used methods to characterize exoplanets' atmospheres. From the ground, these observations are very challenging due to the terrestrial atmosphere and its intrinsic variations, but high-spectral resolution observations overcome this difficulty by resolving the spectral lines and taking advantage of the different Doppler velocities of the Earth, the host star and the exoplanet. Aims. We analyze the transmission spectrum around the Na I doublet at 589 nm of the extrasolar planet WASP-69b, a hot Jupiter orbiting a K-type star with a period of 3.868 days, and compare the analysis to that of the well-know hot Jupiter HD 189733b. We also present the analysis of the Rossiter-McLaughlin effect for WASP-69b. Methods. We observed two transits of WASP-69b with the High Accuracy Radial velocity Planet Searcher (HARPS-North) spectrograph (R = 115 000) at the TNG telescope. We perform a telluric contamination subtraction based on the comparison between the observed spectra and a telluric water model. Then, the common steps of the differential spectroscopy are followed to extract the transmission spectrum. The method is tested with archival transit data of the extensively studied exoplanet HD 189733b, obtained with the HARPS-South spectrograph at ESO 3.6 m telescope, and then applied to WASP-69b data. Results. For HD 189733b, we spectrally resolve the Na I doublet and measure line contrasts of 0.72 ± 0.05 % (D2) and 0.51 ± 0.05 % (D1), and FWHMs of 0.64 ± 0.04 Å (D2) and 0.60 ± 0.06 Å (D1), in agreement with previously published results. For WASP-69b only the contrast of the D2 line can be measured (5.8 ± 0.3 %). This corresponds to a detection at the 5σ-level of excess absorption of 0.5±0.1 % in a passband of 1.5 Å. A net blueshift of ∼0.04 Å is measured for HD 189733b and no shift is obtained for WASP-69b. By measuring the Rossiter-McLaughlin (RM) effect, we get an angular rotation of 0.24 +0.02 −0.01 rad/day and a sky-projected angle between the stellar rotation axis and the normal of orbit plane (λ) of 0.4 +2.0 −1.9 o for WASP-69b. Similar results to those previously presented in the literature are obtained for the RM analysis of HD 189733b. Conclusions. Even if sodium features are clearly detected in the WASP-69b transmission spectrum, more transits are needed to fully characterize the lines profiles and retrieve accurate atmospheric properties.

Detection of He I λ10830 Å absorption on HD 189733 b with CARMENES high-resolution transmission spectroscopy

“…The remaining free parameters were the radius ratio, the rotation velocity of the host Ω, the inclination of the orbit i, and the obliquity λ. For the obliquity and the inclination, we find λ = −1.6 ± 1.1 • and i = 85.77 ± 0.11 • , consistent with literature values (e.g., Triaud et al 2009;Cegla et al 2016;Casasayas-Barris et al 2017). With a value of 0.162 ± 0.024, the radius ratio is only weakly confined by our data and consistent with all the literature values.…”

High-resolution Transit Spectroscopy of Warm Saturns

“…In contrast with our analysis, their observations led to a 5σ detection of atmospheric sodium absorption in just the D 2 line of the sodium doublet, at 588.995 nm (Casasayas-Barris et al 2017). In order to better compare our analysis with theirs we repeated the Doppler cross-correlation technique as well as the model injection/recovery tests with each line of the sodium doublet separately; however, this did not significantly change our results.…”

“…The atmosphere of WASP-69b has previously been studied by Casasayas-Barris et al (2017) with the medium-resolution HARPS-North spectrograph.…”

“…WASP-69 is a slightly faster rotator, with v sin i * = 2.2 ± 0.4 km/s (Anderson et al 2014). In their analysis using the HARPS-N spectrograph, Casasayas- Barris et al (2017) model the RM effect of WASP-69b. They de-rive a value of λ = 0.4 +2.0 −1.9…”

“…Sing et al (2016) followed up with the Space Telescope Imaging Spectrograph (STIS) to observe HAT-P-12b in the full optical range, and found evidence of cloud or haze aerosols as well as potassium. In the case of WASP-69b, Casasayas- Barris et al (2017) analyzed two transits observed with the High Accuracy Radial velocity Planet Searcher (HARPS-North) spectrograph and reported a 5σ detection of atmospheric sodium absorption in the D 2 line of the sodium doublet, but not in the D 1 line.…”