The GTC exoplanet transit spectroscopy survey

Murgas, F.; Chen, G.; Πάλλη, Ε.; Nortmann, L.; Nowak, G.

doi:10.1051/0004-6361/201834063

Cited by 14 publications

(10 citation statements)

References 72 publications

(79 reference statements)

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“…Our new STIS observations indicate that HAT-P-11b has a relatively featureless transmission spectrum at optical wavelengths with a hint of increasing transit depth with decreasing wavelength (scattering slope). This is in agreement with recently reported measurements obtained from ground-based observations (Murgas et al 2019). As mentioned above, a careful accounting for the effects of unocculted spots produces a much flatter optical transmission spectrum than the uncorrected version.…”

Section: Wavelength-dependent Light Curvessupporting

confidence: 94%

A Hubble PanCET Study of HAT-P-11b: A Cloudy Neptune with a Low Atmospheric Metallicity

Chachan

Knutson

Gao

et al. 2019

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We present the first comprehensive look at the 0.35−5 µm transmission spectrum of the warm (∼ 800 K) Neptune HAT-P-11b derived from thirteen individual transits observed using the Hubble and Spitzer Space Telescopes. Along with the previously published molecular absorption feature in the 1.1−1.7 µm bandpass, we detect a distinct absorption feature at 1.15 µm and a weak feature at 0.95 µm, indicating the presence of water and/or methane with a combined significance of 4.4 σ. We find that this planet's nearly flat optical transmission spectrum and attenuated near-infrared molecular absorption features are best-matched by models incorporating a high-altitude cloud layer. Atmospheric retrievals using the combined 0.35−1.7 µm HST transmission spectrum yield strong constraints on atmospheric cloudtop pressure and metallicity, but we are unable to match the relatively shallow Spitzer transit depths without under-predicting the strength of the near-infrared molecular absorption bands. HAT-P-11b's HST transmission spectrum is well-matched by predictions from our microphysical cloud models. Both forward models and retrievals indicate that HAT-P-11b most likely has a relatively low atmospheric metallicity (< 4.6 Z and < 86 Z at the 2σ and 3σ levels respectively), in contrast to the expected trend based on the solar system planets. Our work also demonstrates that the wide wavelength coverage provided by the addition of the HST STIS data is critical for making these inferences.

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Section: Wavelength-dependent Light Curvessupporting

confidence: 94%

A Hubble PanCET Study of HAT-P-11b: A Cloudy Neptune with a Low Atmospheric Metallicity

Chachan

Knutson

Gao

et al. 2019

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“…A combination of stellar features, such as spots and faculae, can explain the slope we detect with the GTC, which would make the transmission spectrum of WASP-69b similar to that of the Neptune-sized planet HAT-P-11b. In one GTC observation, HAT-P-11b presented a Rayleigh-like feature, which was attributed to spots, in contrast to the flat transmission spectrum observed on another occasion with the same instrument (Murgas et al 2019). However, unlike HAT-P-11b, for WASP-69b there are no reported cases of spot regions big enough to be detected as spot-crossing events in the follow-up observations made in the discovery paper by Anderson et al (2014), although there is evidence of stellar modulation due to spots in their long trend light curves.…”

Section: Stellar Spots and Faculaementioning

confidence: 84%

“…The results of the best fitting spot and faculae coverage model that is able to reproduce our observed transmission spectrum are presented in Table 3, and Fig surface versus faculae is ∆T phot−facu = −72 K. The filling factors for the spots and faculae are δ spot = 0.55 +0.30 −0.27 and δ facu = 0.15 +0.46 −0.13 , respectively. As mentioned in Murgas et al (2019) and references therein, spot coverage on the order of 40-50% for active K dwarfs are not rare; however, the correlation plot of the fit shows that the filling factors of the spots and faculae are not well constrained and are degenerate with the temperature of their respective features.…”

Section: Stellar Spots and Faculaementioning

confidence: 86%

“…As mentioned in Murgas et al (2019), the measured planetto-star radius ratio centered around the Na I doublet can be affected by unocculted stellar spots (for a more detailed discussion, see Rackham et al 2019). In Fig .…”

Section: Exploring the Na I Doublet Region For Planetary Absorptionmentioning

confidence: 98%

“…(2) We explore this scenario by fitting the transmission spectra using a grid of PHOENIX stellar spectra (Husser et al 2013) with different temperatures (ranging from 2700 to 7000 K) but with the same metallicity and log g as WASP-69 (taken from Anderson et al 2014) to model the temperature of the star, the spots, and the faculae. As described in Murgas et al (2019), an MCMC fitting was done using emcee (Foreman-Mackey et al 2013); we used 80 chains and a two-step iteration procedure (7500 iterations as the burn-in phase and 25 000 iterations as the main MCMC run). The type of prior and range of values used for each parameter is presented in Table 3.…”

Section: Stellar Spots and Faculaementioning

confidence: 99%

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The GTC exoplanet transit spectroscopy survey

Murgas

Chen

Nortmann

et al. 2020

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Context. One of the main atmospheric features in exoplanet atmospheres, detectable both from ground- and space-based facilities, is Rayleigh scattering. In hydrogen-dominated planetary atmospheres, Rayleigh scattering causes the measured planetary radius to increase toward blue wavelengths in the optical range. Aims. We aim to detect and improve our understanding of several features in the optical range observable in planetary atmospheres. We focus on studying transiting exoplanets that present a wide range of orbital periods, masses, radii, and irradiation from their host star. Methods. We obtained a spectrophotometric time series of one transit of the Saturn-mass planet WASP-69b using the OSIRIS instrument at the Gran Telescopio Canarias. From the data we constructed 19 spectroscopic transit light curves representing 20 nm wide wavelength bins spanning from 515 to 905 nm. We derived the transit depth for each curve individually by fitting an analytical model together with a Gaussian process to account for systematic noise in the light curves. Results. We find that the transit depth increases toward bluer wavelengths, indicative of a larger effective planet radius. Our results are consistent with space-based measurements obtained in the near infrared using the Hubble Space Telescope, which show a compatible slope of the transmission spectrum. We discuss the origin of the detected slope and argue between two possible scenarios: a Rayleigh scattering detection originating in the planet’s atmosphere or a stellar activity induced signal from the host star.

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