Exoplanetary atmospheric sodium revealed by orbital motion

Khalafinejad, S.; Essen, C. von; Hoeijmakers, H. J.; Zhou, G.; Klocová, T.; Schmitt, J. H. M. M.; Dreizler, S.; López-Morales, M.; Husser, Tim-Oliver; Schmidt, T. O. B.; Collet, Remo

doi:10.1051/0004-6361/201629473

Cited by 57 publications

(63 citation statements)

References 60 publications

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“…This is important since a transiting planet with no atmosphere can produce a transmission signal, even if there are no active regions present on the stellar surface, due to the fact that the ratio of the line core to the continuum changes as a function of the transit (see Figures 1-5 of Czesla et al 2015). This effect was recently included in Na I transit modeling by Khalafinejad et al (2016).…”

Section: Contrast and Limb-darkening/brighteningmentioning

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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Section: Contrast and Limb-darkening/brighteningmentioning

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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“…Here, we present high-resolution transit observations of the ultra-hot Jupiter WASP-121b (Delrez et al 2015) with the UV-Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT; Dekker et al 2000), which has been previously used for measuring exoplanet spectra (e.g. Snellen 2004;Czesla et al 2015;Khalafinejad et al 2017;Gibson et al 2019). WASP-121b orbits a bright, V∼10.5 F6V host with a period of only 1.27 days, giving it an equilibrium temperature of over 2400 K. Coupled with its inflated radius, it is an excellent target for transmission spectroscopy.…”

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confidence: 99%

Detection of Fe i in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy

Gibson

Merritt

Nugroho

et al. 2020

Monthly Notices of the Royal Astronomical Society

181

222

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High-resolution Doppler-resolved spectroscopy has opened up a new window into the atmospheres of both transiting and non-transiting exoplanets. Here, we present VLT/UVES observations of a transit of WASP-121b, an 'ultra-hot' Jupiter previously found to exhibit a temperature inversion and detections of multiple species at optical wavelengths. We present initial results using the blue arm of UVES (≈3700 -5000Å), recovering a clear signal of neutral Fe in the planet's atmosphere at >8 σ, which could contribute to (or even fully explain) the temperature inversion in the stratosphere. However, using standard cross-correlation methods, it is difficult to extract physical parameters such as temperature and abundances. Recent pioneering efforts have sought to develop likelihood 'mappings' that can be used to directly fit models to high-resolution datasets. We introduce a new framework that directly computes the likelihood of the model fit to the data, and can be used to explore the posterior distribution of parameterised model atmospheres via MCMC techniques. Our method also recovers the physical extent of the atmosphere, as well as account for time-and wavelength-dependent uncertainties. We measure a temperature of 3710 +490 −510 K, indicating a higher temperature in the upper atmosphere when compared to low-resolution observations. We also show that the Fe i signal is physically separated from the exospheric Fe ii. However, the temperature measurements are highly degenerate with aerosol properties; detection of additional species, using more sophisticated atmospheric models, or combining these methods with low-resolution spectra should help break these degeneracies.

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“…Snellen et al 2008;Redfield et al 2008), and the technique is rapidly growing in popularity (e.g. Cauley et al 2016;Casasayas-Barris et al 2017;Wyttenbach et al 2017;Khalafinejad et al 2017;Yan & Henning 2018). While insensitive to continuum features in the planet, and necessarily sacrificing signal-to-noise to observe at high resolution, this technique is arguably less sensitive to instrumental systematics, making it well suited to confirming features discovered at low-resolution.…”

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confidence: 99%

“…Here, we present results of observations of the exoplanet WASP-31b at high-resolution, using the UV-Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) (Dekker et al 2000), which has been previously shown to be sensitive to signatures of exoplanet atmospheres (e.g. Snellen 2004;Czesla et al 2015;Khalafinejad et al 2017). WASP-31b is an inflated hot-Jupiter discovered by Anderson et al (2011), with a mass and radius of ≈ 0.48 M J and 1.55 R J , respectively.…”

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confidence: 99%

Revisiting the potassium feature of WASP-31b at high resolution

Gibson

Mooij

Evans

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The analysis and interpretation of exoplanet spectra from time-series observations remains a significant challenge to our current understanding of exoplanet atmospheres, due to the complexities in understanding instrumental systematics. Previous observations of the hot Jupiter WASP-31b using transmission spectroscopy at low-resolution have presented conflicting results. Hubble Space Telescope (HST) observations detected a strong potassium feature at high significance (4.2σ), which subsequent ground-based spectro-photometry with the Very Large Telescope (VLT) failed to reproduce. Here, we present high-resolution observations (R>80,000) of WASP-31b with the UVES spectrograph, in an effort to resolve this discrepancy. We perform a comprehensive search for potassium using differential transit light curves, and integration over the planet's radial velocity. Our observations do not detect K absorption at the level previously reported with HST, consistent with the VLT observations. We measure a differential light curve depth ∆F = 0.00031 ± 0.00036 using 40Å bins centred on the planet's K feature, and set an upper limit on the core line depth of ∆F ≤ 0.007 (3σ) at a few times the resolution limit (≈ 0.24Å). These results demonstrate that there are still significant limitations to our understanding of instrumental systematics even with our most stable space-based instrumentation, and that care must be taken when extracting narrow band signatures from low-resolution data. Confirming exoplanet features using alternative instruments and methodologies should be a priority, and confronting the limitations of systematics is essential to our future understanding of exoplanet atmospheres.

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Exoplanetary atmospheric sodium revealed by orbital motion

Cited by 57 publications

References 60 publications

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

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

Detection of Fe i in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy

Revisiting the potassium feature of WASP-31b at high resolution

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