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

Gloria, E; Snellen, I. A. G.; Albrecht, S.

doi:10.1051/0004-6361/201526218

Cited by 54 publications

(87 citation statements)

References 36 publications

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“…We did not take into account their correction for star spots since it is well inside our errorbars. Our uncertainties are of course larger than the ones obtained with HST, but one-half smaller than those obtained by Di Gloria et al (2015) who analyzed the same dataset using a different analysis method. The uncertainties could be reduced by increasing the number of observed transits; this should be easier with ground-based observations than from space.…”

Section: Discussioncontrasting

confidence: 59%

“…Broadband transmission spectrum of HD 189733b as calculated with this method (black circles). For comparison, red triangles are HST observations by Pont et al (2013) and light blue squares are measurements from Di Gloria et al (2015) using the chromatic RM effect on the same dataset of this paper. The vertical shift is due to the different transit parameters used in the different papers.…”

Section: Comparison Of Single Transit Eventsmentioning

confidence: 99%

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Chromatic line-profile tomography to reveal exoplanetary atmospheres: application to HD 189733b

Borsa

Rainer

Poretti

2016

A&A

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Context. Transmission spectroscopy can be used to constrain the properties of exoplanetary atmospheres. During a transit, the light blocked from the atmosphere of the planet leaves an imprint in the light coming from the star. This has been shown for many exoplanets with both photometry and spectroscopy, using different analysis methods. Aims. We test chromatic line-profile tomography as a new tool to investigate exoplanetary atmospheres. The signal imprinted on the cross-correlation function (CCF) by a planet transiting its star is dependent on the planet-to-star radius ratio. We want to verify whether the precision reachable on the CCF obtained from a subset of the spectral orders of the HARPS spectrograph is high enough to determine the radius of a planet at different wavelengths. Methods. We analyze HARPS archival data of three transits of HD 189733b. We divide the HARPS spectral range into seven broadbands, calculating for each band the ratio between the area of the out-of-transit CCF and the area of the signal imprinted by the planet on it during the full part of the transit. We take into account the effect of the limb darkening using the theoretical coefficients of a linear law. Averaging the results of three different transits allows us to obtain a good-quality broadband transmission spectrum of HD 189733b with a greater precision than that of the chromatic Rossiter McLaughlin effect. Results. We proved that chromatic line-profile tomography is an interesting way to reveal broadband transmission spectra of exoplanets: our analysis of the atmosphere of HD 189733b is in agreement with other ground-and space-based observations. The independent analysis of different transits emphasizes the probability that stellar activity plays a role in the extracted transmission spectrum. Therefore, care should be taken when claiming that Rayleigh scattering is present in the atmosphere of exoplanets orbiting active stars using only one transit.

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Section: Discussioncontrasting

confidence: 59%

Section: Comparison Of Single Transit Eventsmentioning

confidence: 99%

Chromatic line-profile tomography to reveal exoplanetary atmospheres: application to HD 189733b

Borsa

Rainer

Poretti

2016

A&A

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“…These data have been extensively studied by other authors, e.g. Wyttenbach et al (2015), Louden & Wheatley (2015), Di Gloria et al (2015) and Barnes et al (2016). Three datasets taken at different nights are used by W2015 and Barnes et al (2016) for studying the Na i D, Hα and Ca ii H&K lines.…”

Section: The CLV Effect In the Hd 189733b Datamentioning

confidence: 99%

Effect of the stellar absorption line centre-to-limb variation on exoplanet transmission spectrum observations

Yan

Πάλλη

Fosbury

et al. 2017

A&A

109

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Transit spectroscopy is one of the most commonly used techniques for exoplanet atmosphere characterisation. This technique has been used to detect ionized and neutral species in exoplanet atmospheres by comparing the observed stellar lines in and out of transit. The centre-to-limb variation (CLV) of the stellar lines across the stellar disk is an important effect for transmission spectroscopy, since it results in a change of stellar line depth when the planet transits different parts of the stellar disk. We reanalyse the transit data of HD 189733b taken with the HARPS spectrograph to study the CLV effect during transit. The transmission light curve of the Na i D line so obtained shows a clear imprint of the CLV effect. We use a one-dimensional non-LTE stellar spectral model to simulate the CLV effect. After applying the correction, the measurement of the Na i absorption in the atmosphere of HD 189733b becomes better determined. We compare the CLV effect of HD 189733b to that of HD 209458b. The CLV effects are different for these two benchmark planetary systems and this is attributed to their different stellar effective temperatures and transit impact parameters. We then explore the general CLV effect that occurs during exoplanet transits. Normally, a star with a lower effective temperature exhibits a stronger CLV effect and its CLV feature extends over a relatively broad wavelength range. The transit impact parameter (b) describes the transit trajectory on the stellar disk and thus determines the actual manifestation of the CLV effect. We introduce a b-diagram which describes the behavior of the CLV effect as the function of different impact parameters. With improving observational precision, a careful modeling and correction of the CLV effect is necessary for exoplanet atmosphere characterisation using transit spectroscopy.

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“…All spectra are shifted to the rest frame of the star by correcting for the Earth's barycentric velocity and HD 189733's system radial velocity, for which we use the mean value −2.23 km s −1 from Di Gloria et al (2015). We used the latest version of Molecfit (Kausch et al 2014) in order to model telluric absorption in the Hα order.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

A Decade of Hα Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

Cauley

Redfield

Jensen

2017

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HD 189733 b is one of the most well-studied exoplanets due to its large transit depth and host star brightness. The focus on this object has produced a number of high-cadence transit observations using high-resolution optical spectrographs. Here we present an analysis of seven full Hα transits of HD 189733 b using HARPS on the 3.6 meter La Silla telescope and HIRES on Keck I, taken over the course of nine years from 2006 to 2015. Hα transmission signals are analyzed as a function of the stellar activity level, as measured using the normalized core flux of the Ca II H and K lines. We find strong variations in the strength of the Hα transmission spectrum from epoch to epoch. However, there is no clear trend between the Ca II core emission and the strength of the in-transit Hα signal, although the transit showing the largest absorption value also occurs when the star is the most active. We present simulations of the in-transit contrast effect and find that the planet must consistently transit active latitudes with very strong facular and plage emission regions in order to reproduce the observed line strengths. We also investigate the measured velocity centroids with models of planetary rotation and show that the small line profile velocities could be due to large velocities in the upper atmosphere of the planet. Overall, we find it more likely that the measured Hα signals arise in the extended planetary atmosphere, although a better understanding of active region emission for active stars such as HD 189733 are needed.

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

Cited by 54 publications

References 36 publications

Chromatic line-profile tomography to reveal exoplanetary atmospheres: application to HD 189733b

Chromatic line-profile tomography to reveal exoplanetary atmospheres: application to HD 189733b

Effect of the stellar absorption line centre-to-limb variation on exoplanet transmission spectrum observations

A Decade of Hα Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

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