KELT-9 b, the hottest known exoplanet, with
T
eq
~ 4400 K, is the archetype of a new planet class known as ultra-hot Jupiters. These exoplanets are presumed to have an atmosphere dominated by neutral ...and ionized atomic species. In particular, H
α
and H
β
Balmer lines have been detected in the KELT-9 b upper atmosphere, suggesting that hydrogen is filling the planetary Roche lobe and escaping from the planet. In this work, we detected
δ
Scuti-type stellar pulsation (with a period
P
puls
= 7.54 ± 0.12 h) and studied the Rossiter-McLaughlin effect (finding a spin-orbit angle
λ
= −85.01° ± 0.23°) prior to focussing on the Balmer lines (H
α
to H
ζ
) in the optical transmission spectrum of KELT-9 b. Our HARPS-N data show significant absorption for H
α
to H
δ
. The precise line shapes of the H
α
, H
β
, and H
γ
absorptions allow us to put constraints on the thermospheric temperature. Moreover, the mass loss rate, and the excited hydrogen population of KELT-9 b are also constrained, thanks to a retrieval analysis performed with a new atmospheric model. We retrieved a thermospheric temperature of
T
= 13 200
−720
+800
K and a mass loss rate of
Ṁ
= 10
12.8±0.3
g s
−1
when the atmosphere was assumed to be in hydrodynamical expansion and in local thermodynamic equilibrium (LTE). Since the thermospheres of hot Jupiters are not expected to be in LTE, we explored atmospheric structures with non-Boltzmann equilibrium for the population of the excited hydrogen. We do not find strong statistical evidence in favor of a departure from LTE. However, our non-LTE scenario suggests that a departure from the Boltzmann equilibrium may not be sufficient to explain the retrieved low number densities of the excited hydrogen. In non-LTE, Saha equilibrium departure via photo-ionization, is also likely to be necessary to explain the data.
Context.
The atmosphere of exoplanets has been studied extensively in recent years, making use of numerical models to retrieve chemical composition, dynamical circulation, or temperature from the ...data. One of the best observational probes in transmission is the sodium doublet thanks to its extensive cross-section. However, modelling the shape of planetary sodium lines has proven to be challenging. Models with different assumptions regarding the atmosphere have been employed to fit the lines in the literature, yet statistically-sound, direct comparisons of different models are needed to paint a clear picture.
Aims.
We aim to compare different wind and temperature patterns, as well as to provide a tool to distinguish them based on their best fit for the sodium transmission spectrum of the hot Jupiter HD 189733b. We parametrise different possible wind patterns that have already been tested the in literature and introduce the new option of an upwards-driven vertical wind.
Methods.
We construct a forward model where the wind speed, wind geometry, and temperature are injected into the calculation of the transmission spectrum. We embed this forward model in a nested sampling retrieval code to rank the models via their Bayesian evidence.
Results.
We retrieve a best-fit to the HD 189733b data for vertical upward winds |
v
ver
(mean)| = 40 ± 4 km s
−1
at altitudes above 10
−6
bar. With the current data from HARPS, we cannot distinguish wind patterns for higher-pressure atmospheric layers.
Conclusions.
We show that vertical upwards winds in the upper atmosphere provide a possible explanation for the broad sodium signature in hot Jupiters. We highlight other influences on the width of the doublet and we explore strong magnetic fields acting on the lower atmosphere as one possible origin of the retrieved wind speed.
Context.
Despite swift progress in the characterisation of exoplanet atmospheres in composition and structure, the study of atmospheric dynamics has not progressed at the same speed. While ...theoretical models have been developed to describe the lower layers of the atmosphere, and independently, the exosphere, little is known about the intermediate layers up to the thermosphere.
Aims.
We aim to provide a clearer picture of atmospheric dynamics for the class of ultra-hot Jupiters, which are highly irradiated gas giants, based on the example of WASP-76 b.
Methods.
We jointly analysed two datasets that were obtained with the HARPS and ESPRESSO spectrographs to interpret the resolved planetary sodium doublet. We then applied the MERC code, which retrieves wind patterns, speeds, and temperature profiles on the line shape of the sodium doublet. An updated version of MERC, with added planetary rotation, also provides the possibility of modelling the latitude dependence of the wind patterns.
Results.
We retrieve the highest Bayesian evidence for an isothermal atmosphere, interpreted as a mean temperature of 3389 ± 227 K, a uniform day- to nightside wind of 5.5
−2.0
+1.4
km s
−1
in the lower atmosphere with a vertical wind in the upper atmosphere of 22.7
−4.1
+4.9
km s
−1
, switching atmospheric wind patterns at 10
−3
bar above the reference surface pressure (10 bar).
Conclusions.
Our results for WASP-76 b are compatible with previous studies of the lower atmospheric dynamics of WASP-76 b and other ultra-hot Jupiters. They highlight the need for vertical winds in the intermediate atmosphere above the layers probed by global circulation model studies to explain the line broadening of the sodium doublet in this planet. This work demonstrates the capability of exploiting the resolved spectral line shapes to observationally constrain possible wind patterns in exoplanet atmospheres. This is an invaluable input to more sophisticated 3D atmospheric models in the future.
Comparisons of the alignment of exoplanets with a common host star and each other can be used to distinguish among concurrent evolution scenarios for the star and the planets. However, multi-planet ...systems usually host mini-Neptunes and super-Earths, whose sizes make orbital architecture measurements challenging. We introduce the Rossiter-McLaughlin effect Revolutions (RMR) technique, which can access the spin-orbit angle of small exoplanets by exploiting the full extent of information contained in spectral transit time series. We validated the technique through its application to published HARPS-N data of the mini-Neptune HD 3167c (
P
= 29.8 days), refining its high sky-projected spin-orbit angle (−108.9
−5.5
+5.4°
), and we applied it to new ESPRESSO observations of the super-Earth HD 3167 b (
P
= 0.96 days), revealing an aligned orbit (−6.6
−7.9
+6.6°
). Surprisingly different variations in the contrast of the stellar lines occulted by the two planets can be reconciled by assuming a latitudinal dependence of the stellar line shape. In this scenario, a joint fit to both datasets constrains the inclination of the star (111.6
−3.3
+3.1°
) and the 3D spin-orbit angles of HD 3167b (29.5
−9.4
+7.2°
) and HD 3167c (107.7
−4.9
+5.1°
). The projected spin-orbit angles do not depend on the model for the line contrast variations, and so, with a mutual inclination of 102.3
−8.0
+7.4°
, we can conclude that the two planets are on perpendicular orbits. This could be explained by HD 3167b being strongly coupled to the star and retaining its primordial alignment, whereas HD 3167c would have been brought to a nearly polar orbit via secular gravitational interactions with an outer companion. Follow-up observations of the system and simulations of its dynamical evolution are required to search for this companion and explore the likelihood of this scenario. HD 3167 b (
R
= 1.7
R
Earth
) is the smallest exoplanet with a confirmed spectroscopic Rossiter-McLaughlin signal. The RMR technique opens the way to determining the orbital architectures of the super-Earth and Earth-sized planet populations.
ABSTRACT
In this paper, we present high-resolution spectroscopic transit observations from ESPRESSO of the super-Neptune WASP-166 b. In addition to spectroscopic ESPRESSO data, we analyse photometric ...data from TESS of six WASP-166 b transits along with simultaneous NGTS observations of the ESPRESSO runs. These observations were used to fit for the planetary parameters as well as assessing the level of stellar activity (e.g. spot crossings, flares) present during the ESPRESSO observations. We utilize the reloaded Rossiter McLaughlin (RRM) technique to spatially resolve the stellar surface, characterizing the centre-to-limb convection-induced variations, and to refine the star–planet obliquity. We find WASP-166 b has a projected obliquity of $\lambda = -15.52^{+2.85}_{-2.76}\, ^{\circ }$ and vsin (i) = 4.97 ± 0.09 km s−1 which is consistent with the literature. We were able to characterize centre-to-limb convective variations as a result of granulation on the surface of the star on the order of a few km s−1 for the first time. We modelled the centre-to-limb convective variations using a linear, quadratic, and cubic model with the cubic being preferred. In addition, by modelling the differential rotation and centre-to-limb convective variations simultaneously, we were able to retrieve a potential antisolar differential rotational shear (α ∼ −0.5) and stellar inclination (i* either 42.03$^{+9.13}_{-9.60}\, ^{\circ }$ or 133.64$^{+8.42}_{-7.98}\, ^{\circ }$ if the star is pointing towards or away from us). Finally, we investigate how the shape of the cross-correlation functions change as a function of limb angle and compare our results to magnetohydrodynamic simulations.
ABSTRACT We present high spectral resolution observations of the hot Jupiter WASP-94 A b using the HARPS instrument on ESO’s 3.6-m telescope in La Silla, Chile. We probed for Na absorption in its ...atmosphere as well as constrained the previously reported misaligned retrograde orbit using the Rossiter–McLaughlin effect. Additionally, we undertook a combined atmospheric retrieval analysis with previously published low-resolution data. We confirm the retrograde orbit as well as constrain the orbital misalignment with our measurement of a projected spin-orbit obliquity of λ = 123.0 ± 3.0°. We find a tentative detection of Na absorption in the atmosphere of WASP-94 A b, independent of the treatment of the Rossiter–McLaughlin effect in our analysis (3.6σ and 4.4σ). We combine our HARPS high-resolution data with low-resolution data from the literature and find that while the posterior distribution of the Na abundance results in a tighter constraint than using a single data set, the detection significance does not improve (3.2σ), which we attribute to degeneracies between the low- and high-resolution data.
ABSTRACT
With high-resolution spectroscopy, we can study exoplanet atmospheres and learn about their chemical composition, temperature profiles, and presence of clouds and winds, mainly in hot, giant ...planets. State-of-the-art instrumentation is pushing these studies towards smaller exoplanets. Of special interest are the few planets in the ‘Neptune desert’, a lack of Neptune-sized planets in close orbits around their hosts. Here, we assess the presence of water in one such planet, the bloated super-Neptune WASP-166 b, which orbits an F9-type star in a short orbit of 5.4 d. Despite its close-in orbit, WASP-166 b preserved its atmosphere, making it a benchmark target for exoplanet atmosphere studies in the desert. We analyse two transits observed in the visible with ESPRESSO. We clean the spectra from the Earth’s telluric absorption via principal component analysis, which is crucial to the search for water in exoplanets. We use a cross-correlation-to-likelihood mapping to simultaneously estimate limits on the abundance of water and the altitude of a cloud layer, which points towards a low water abundance and/or high clouds. We tentatively detect a water signal blue-shifted ∼5 $\mathrm{km\, s^{-1}}$ from the planetary rest frame. Injection and retrieval of model spectra show that a solar-composition, cloud-free atmosphere would be detected at high significance. This is only possible in the visible due to the capabilities of ESPRESSO and the collecting power of the VLT. This work provides further insight on the Neptune desert planet WASP-166 b, which will be observed with JWST.
Multiband photometric transit observations or low-resolution spectroscopy (spectro-photometry) are normally used to retrieve the broadband transmission spectra of transiting exoplanets in order to ...assess the chemical composition of their atmospheres. In this paper we present an alternative approach for recovering the broadband transmission spectra using chromatic Doppler tomography based on physical modeling through the
SOAP
tool: CHOCOLATE (CHrOmatiC line prOfiLe tomogrAphy TEchnique). To validate the method and examine its performance, we use observational data recently obtained with the ESPRESSO instrument to retrieve the transmission spectra of the archetypal hot Jupiter HD 209458b. Our findings indicate that the recovered transmission spectrum is in good agreement with the results presented in previous studies, which used different methodologies to extract the spectrum, achieving similar precision. We explored several atmospheric models and inferred from spectral retrieval that a model containing H
2
O and NH
3
is the preferred scenario. The CHOCOLATE methodology is particularly interesting for future studies of exoplanets around young and active stars or moderate to fast rotating stars, considering
SOAP
’s ability to model stellar active regions and the fact that the rotational broadening of spectral lines favors its application. Furthermore, CHOCOLATE will allow the broad transmission spectrum of a planet to be retrieved using high-S/N, high-resolution spectroscopy with the next generation of extremely large telescopes, where low-resolution spectroscopy will not always be accessible.
ABSTRACT
High spectral resolution transmission spectroscopy is a powerful tool to characterize exoplanet atmospheres. Especially for hot Jupiters, this technique is highly relevant, due to their ...high-altitude absorption, e.g. from resonant sodium (Na i) and potassium (K i) lines. We resolve the atmospheric K i absorption on HD189733b with the aim to compare the resolved K i line and previously obtained high-resolution Na i-D line observations with synthetic transmission spectra. The line profiles suggest atmospheric processes leading to a line broadening of the order of ∼10 km/s for the Na i-D lines and only a few km/s for the K i line. The investigation hints that either the atmosphere of HD189733b lacks a significant amount of K i or the alkali lines probe different atmospheric regions with different temperature, which could explain the differences we see in the resolved absorption lines.
ABSTRACT
The hot Neptune desert, a distinct lack of highly irradiated planets in the size range of Neptune, remains one of the most intriguing results of exoplanet population studies. A deeper ...understanding of the atmosphere of exoplanets sitting at the edge or even within the Neptune desert will allow us to better understand if planetary formation or evolution processes are at the origin of the desert. A detection of sodium in WASP-166 b was presented previously with tentative line broadening at the $3.4\, \sigma$ with the HARPS spectrograph. We update this result with two transits observed with the ESPRESSO spectrograph, confirming the detection in each night and the broadened character of the line. This result marks the first confirmed resolved sodium detection within the Neptune desert. In this work, we additionally highlight the importance of treating low-SNR spectral regions particularly where absorption lines of stellar sodium and planetary sodium overlap at mid transit – an important caveat for future observations of the system.
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