Gran Telescopio Canarias OSIRIS transiting exoplanet atmospheric survey: detection of potassium in XO-2b from narrowband spectrophotometry

Sing, David K.; Désert, Jean Michel; Fortney, Jonathan J.; Étangs, A. Lecavelier des; Ballester, G. E.; Cepa, J.; Ehrenreich, D.; López‐Morales, Mercedes; Pont, F.; Shabram, Megan; Vidal‐Madjar, A.

doi:10.1051/0004-6361/201015579

Cited by 131 publications

(141 citation statements)

References 56 publications

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“…HST/NICMOS has been used to detect H 2 O and CH 4 (Swain et al 2008), though the H 2 O feature has been challenged by a more sensitive search using filter photometry (Sing et al 2009;Désert et al 2009Désert et al , 2010 showing the presence of haze condensate at high altitude as previously observed in the optical using HST/ACS (Pont et al 2008;Lecavelier des Etangs et al 2008a). In addition to HST, groundbased, high-resolution spectra have also allowed sodium detection in HD 189733 b (Redfield et al 2008), confirmed sodium in HD 209458 b (Snellen et al 2008), detected CO and even winds in the planetary atmosphere (Snellen et al 2010), while the other important alkali metal potassium has been detected in XO-2b using narrowband photometry (Sing et al 2011). Sing et al (2008a) revisited all the existing HST/STIS spectroscopic data of HD 209458 b transits gathered over the years.…”

Section: Introductionmentioning

confidence: 99%

The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines

Vidal‐Madjar

Sing

Étangs

et al. 2011

A&A

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A complete reassessment of the Hubble Space Telescope (HST) observations of the transits of the extrasolar planet HD 209458 b has provided a transmission spectrum of the atmosphere over a wide range of wavelengths. Analysis of the NaI absorption line profile has already shown that the sodium abundance has to drop by at least a factor of ten above a critical altitude. Here we analyze the profile in the deep core of the NaI doublet line from HST and high-resolution ground-based spectra to further constrain the vertical structure of the HD 209458 b atmosphere. With a wavelength-dependent cross section that spans more than 5 orders of magnitude, we use the absorption signature of the NaI doublet as an atmospheric probe. The NaI transmission features are shown to sample the atmosphere of HD 209458 b over an altitude range of more than 6500 km, corresponding to a pressure range of 14 scale heights spanning 1 millibar to 10 −9 bar pressures. By comparing the observations with a multi-layer model in which temperature is a free parameter at the resolution of the atmospheric scale height, we constrain the temperature vertical profile and variations in the Na abundance in the upper part of the atmosphere of HD 209458 b. We find a rise in temperature above the drop in sodium abundance at the 3 mbar level. We also identify an isothermal atmospheric layer at 1500 ± 100 K spanning almost 6 scale heights in altitude, from 10 −5 to 10 −7 bar. Above this layer, the temperature rises again to 2500 +1500 −1000 K at ∼10 −9 bar, indicating the presence of a thermosphere. The resulting temperature-pressure (T-P) profile agrees with the Na condensation scenario at the 3 mbar level, with a possible signature of sodium ionization at higher altitudes, near the 3×10 −5 bar level. Our T-P profile is found to be in good agreement with the profiles obtained with aeronomical models including hydrodynamic escape.

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Section: Introductionmentioning

confidence: 99%

The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines

Vidal‐Madjar

Sing

Étangs

et al. 2011

A&A

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“…One way to mitigate these issues is by using ground-based highdispersion spectroscopy. For example, detections of sodium and potassium have been presented in the optical (Redfield et al 2008;Snellen et al 2008;Sing et al 2011a;Wood et al 2011;Jensen et al 2011;Zhou & Bayliss 2012;Wyttenbach et al 2015), and detections of carbon monoxide and water in the infrared (Brogi et al 2012(Brogi et al , 2014Rodler et al 2012;de Kok et al 2013;Birkby et al 2013;Lockwood et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Using the chromatic Rossiter-McLaughlin effect to probe the broadband signature in the optical transmission spectrum of HD 189733b

Gloria

Snellen

Albrecht

2015

A&A

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Context. Transmission spectroscopy is a powerful technique for probing exoplanetary atmospheres. A successful ground-based observational method uses a differential technique that uses high-dispersion spectroscopy, but it only preserves narrow features in transmission spectra. Broadband features, such as the remarkable Rayleigh-scattering slope from possible hazes in the atmosphere of HD 189733b as observed by the Hubble Space Telescope, cannot be probed in this way. Aims. Here we use the chromatic Rossiter-McLaughlin (RM) effect to measure the Rayleigh-scattering slope in the transmission spectrum of HD 189733b with the aim to show that it can be effectively used to measure broadband transmission features. The amplitude of the RM effects depends on the effective size of the planet, and in the case of an atmospheric contribution therefore depends on the observed wavelength. Methods. We analysed archival HARPS data of three transits of HD 189733b, covering a wavelength range of 400 to 700 nm. The radial velocity (RV) time-series were determined for white light and for six wavelength bins each 50 nm wide, using the crosscorrelation profiles as provided by the HARPS data reduction pipeline. The RM effect was first fitted to the white-light RV time series using the publicly available code AROME. The residuals to this best fit were subsequently subtracted from the RV time series of each wavelength bin, after which they were also fitted using the same code, leaving only the effective planet radius to vary. Results. We measured the slope in the transmission spectrum of HD 189733b at a 2.5σ significance. Assuming it is due to Rayleigh scattering and not caused by stellar activity, it would correspond to an atmospheric temperature, as set by the scale height, of T = 2300 ± 900 K, well in line with previously obtained results. Conclusions. Ground-based high-dispersion spectral observations can be used to probe broad-band features in the transmission spectra of extrasolar planets, such as the optical Rayleigh-scattering slope of HD 189733b, by using the chromatic Rossiter-McLaughlin effect. The precision achieved with HARPS per transit is about an order of magnitude lower than that with STIS on the Hubble Space Telescope. This method will be particularly interesting in conjunction with the new echelle spectrograph ESPRESSO, which currently is under construction for ESO's Very Large Telescope, which will provide a gain in signal-to-noise ratio of about a factor 4 compared to HARPS. This will be of great value because of the limited and uncertain future of the Hubble Space Telescope and because the future James Webb Space Telescope will not cover this wavelength regime.

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“…Nevertheless, signatures from the atmospheres of hot-Jupiters have been detected Photometric time series are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/538/A46 in transmission spectra, both from atoms, including sodium (e.g. Charbonneau et al 2002;Snellen et al 2008;Redfield et al 2008), potassium (Sing et al 2011a;Colon et al 2012), hydrogen (Vidal-Madjar et al 2003), carbon (Vidal-Madjar et al 2004) and oxygen (Vidal-Madjar et al 2004), as well as from molecules such as water (Tinetti et al 2007), although this is disputed by Désert et al (2009), methane (Swain et al 2008), which has been challenged by Sing et al (2009) and Gibson et al (2011), and carbon monoxide (Snellen et al 2010). In addition, a gradual increase of the planet-to-star radius ratio of HD 189733b has been detected toward shorter wavelengths, which has been attributed to the scattering by haze particles (Pont et al 2008;Sing et al 2011b).…”

Section: Introductionmentioning

confidence: 99%

Optical to near-infrared transit observations of super-Earth GJ 1214b: water-world or mini-Neptune?

Mooij

Brogi

Kok

et al. 2012

A&A

103

127

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Context. GJ 1214b, the 6.55 Earth-mass transiting planet recently discovered by the MEarth team, has a mean density of ∼35% of that of the Earth. It is thought that this planet is either a mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. Aims. In the case of a hydrogen-rich atmosphere, molecular absorption and scattering processes may result in detectable radius variations as a function of wavelength. The aim of this paper is to measure these variations. Methods. We have obtained observations of the transit of GJ 1214b in the r-and I-band with the Isaac Newton Telescope (INT), in the g-, r-, i-and z-bands with the 2.2 m MPI/ESO telescope, in the K s -band with the Nordic Optical Telescope (NOT), and in the K c -band with the William Herschel Telescope (WHT). By comparing the transit depth between the the different bands, which is a measure for the planet-to-star size ratio, the atmosphere is investigated. Results. We do not detect clearly significant variations in the planet-to-star size ratio as function of wavelength. Although the ratio at the shortest measured wavelength, in g-band, is 2σ larger than in the other bands. The uncertainties in the K s and K c bands are large, due to systematic features in the light curves. Conclusions. The tentative increase in the planet-to-star size ratio at the shortest wavelength could be a sign of an increase in the effective planet-size due to Rayleigh scattering, which would require GJ 1214b to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have both clouds, to suppress planet-size variations at red optical wavelengths, as well as a sub-solar metallicity, to suppress strong molecular features in the near-and mid-infrared. However, star spots, which are known to be present on the hoststar's surface, can (partly) cancel out the expected variations in planet-to-star size ratio, because the lower surface temperature of the spots causes the effective size of the star to vary with wavelength. A hypothetical spot-fraction of ∼10%, corresponding to an average stellar dimming of ∼5% in the i-band, would be able to raise the near-and mid-infrared points sufficiently with respect to the optical measurements to be inconsistent with a water-dominated atmosphere. Modulation of the spot fraction due to the stellar rotation would in such case cause the observed flux variations of GJ 1214.

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Gran Telescopio Canarias OSIRIS transiting exoplanet atmospheric survey: detection of potassium in XO-2b from narrowband spectrophotometry

Cited by 131 publications

References 56 publications

The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines

The upper atmosphere of the exoplanet HD 209458 b revealed by the sodium D lines

Using the chromatic Rossiter-McLaughlin effect to probe the broadband signature in the optical transmission spectrum of HD 189733b

Optical to near-infrared transit observations of super-Earth GJ 1214b: water-world or mini-Neptune?

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