Stellar heating causes atmospheres of close-in exoplanets to expand and escape. These extended atmospheres are difficult to observe because their main spectral signature-neutral hydrogen at ...ultraviolet wavelengths-is strongly absorbed by interstellar medium. We report the detection of the near-infrared triplet of neutral helium in the transiting warm Neptune-mass exoplanet HAT-P-11b using ground-based, high-resolution observations. The helium feature is repeatable over two independent transits, with an average absorption depth of 1.08 ± 0.05%. Interpreting absorption spectra with 3D simulations of the planet's upper atmosphere suggests it extends beyond 5 planetary radii, with a large scale height and a helium mass loss rate ≲ 3×10
g‧s
A net blue-shift of the absorption might be explained by high-altitude winds flowing at 3 km‧s
from day to night-side.
Context. Ground-based telescopes equipped with state-of-the-art spectrographs are able to obtain high-resolution transmission and emission spectra of exoplanets that probe the structure and ...composition of their atmospheres. Various atomic and molecular species, such as Na, CO, H2O have been already detected in a number of hot Jupiters. Molecular species have been observed only in the near-infrared while atomic species have been observed in the visible. In particular, the detection and abundance determination of water vapor bring important constraints to the planet formation process. Aims. We aim to search for water vapor in the atmosphere of the exoplanet HD 189733b using a high-resolution transmission spectrum in the visible obtained with HARPS. Methods. We used the atmospheric transmission code Molecfit to correct for telluric absorption features. Then we computed the high-resolution transmission spectrum of the planet using three transit datasets. We finally searched for water vapor absorption in the water band around 6500 Å using a cross-correlation technique that combines the signal of 600–900 individual lines. Results. Telluric features are corrected to the noise level. We place a 5-σ upper limit of 100 ppm on the strength of the 6500 Å water vapor band. The 1-σ precision of 20 ppm on the transmission spectrum demonstrates that space-like sensitivity can be achieved from the ground, even for a molecule that is a strong telluric absorber. Conclusions. This approach opens new possibilites for the detection of various atomic and molecular species with future instruments such as ESPRESSO at the VLT. Extrapolating from our results, we show that only one transit with ESPRESSO would be sufficient to detect water vapor on HD 189733b-like hot Jupiter with a cloud-free atmosphere. Upcoming near-IR spectrographs will be even more efficient and sensitive to a wider range of molecular species. Moreover, the detection of the same molecular species in different bands (e.g., visible and IR) is key to constrain the structure and composition of the atmosphere, such as the presence of Rayleigh scattering or aerosols (cloud and/or hazes).
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.
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.
GJ 3470b is a warm Neptune transiting an M-dwarf star at the edge of the evaporation desert. It offers the possibility of investigating how low-mass, close-in exoplanets evolve under the irradiation ...from their host stars. We observed three transits of GJ 3470b in the Lyman-α line with the Hubble Space Telescope (HST) as part of the Panchromatic Comparative Exoplanet Treasury (PanCET) program. Absorption signatures are detected with similar properties in all three independent epochs, with absorption depths of 35 ± 7% in the blue wing of the line, and 23 ± 5% in the red wing. The repeatability of these signatures, their phasing with the planet transit, and the radial velocity of the absorbing gas allow us to conclude that there is an extended upper atmosphere of neutral hydrogen around GJ 3470b. We determine from our observations the stellar radiation pressure and XUV irradiation from GJ 3470 and use them to perform numerical simulations of the upper atmosphere of GJ 3470b with the EVaporating Exoplanets (EVE) code. The unusual redshifted signature can be explained by the damping wings of dense layers of neutral hydrogen that extend beyond the Roche lobe and are elongated in the direction of the planet motion. This structure could correspond to a shocked layer of planetary material formed by the collision of the expanding thermosphere with the wind of the star. The blueshifted signature is well explained by neutral hydrogen atoms escaping at rates of about 1010 g s−1 that are blown away from the star by its strong radiation pressure and are quickly photoionized, resulting in a smaller exosphere than that of the warm Neptune GJ 436b. The stronger escape from GJ 3470b, however, may have led to the loss of about 4–35% of its current mass over its ~2 Gyr lifetime.
WASP-52b is a low-density hot Jupiter orbiting a moderately active K2V star. Previous low-resolution studies have revealed a cloudy atmosphere and found atomic Na above the cloud deck. Here we report ...on the detection of excess absorption at the Na doublet, the H
α
line, and the K D
1
line. We derived a high-resolution transmission spectrum based on three transits of WASP-52b, observed with the ultra-stable, high-resolution spectrograph ESPRESSO at the Very Large Telescope array. We measured a line contrast of 1.09 ± 0.16% for Na D
1
, 1.31 ± 0.13% for Na D
2
, 0.86 ± 0.13% for H
α
, and 0.46 ± 0.13% for K D
1
, with a line FWHM range of 11–22 km s
−1
. We also found that the velocity shift of these detected lines during the transit is consistent with the planet’s orbital motion, thus confirming their planetary origin. We did not observe any significant net blueshift or redshift that could be attributed to planetary winds. We used activity indicator lines as control but found no excess absorption. However, we did notice signatures arising from the Center-to-Limb variation (CLV) and the Rossiter-McLaughlin (RM) effect at these control lines. This highlights the importance of the CLV + RM correction in correctly deriving the transmission spectrum, which, if not corrected, could resemble or cancel out planetary absorption in certain cases. WASP-52b is the second non-ultra-hot Jupiter to show excess H
α
absorption after HD 189733b. Future observations targeting non-ultra-hot Jupiters that show H
α
could help reveal the relation between stellar activity and the heating processes in the planetary upper atmosphere.
Context. Probing the evaporation of exoplanet atmospheres is key to understanding the formation and evolution of exoplanetary systems. The main tracer of evaporation in the UV is the Lyman-α ...transition, which can reveal extended exospheres of neutral hydrogen. Recently, the near-infrared (NIR) metastable helium triplet (10 833 Å) revealed extended thermospheres in several exoplanets. This opens a new window into evaporation. Aims. We aim at spectrally resolving the first helium absorption signature detected in the warm Saturn WASP-107b with the Wide Filed Camera 3 on board the Hubble Space Telescope (HST/WFC3). Methods. We obtained one transit of WASP-107b with CARMENES installed on the 3.5 m telescope at the Calar Alto observatory. Results. We detect an excess helium absorption signature of 5.54 ± 0.27% (20σ) in the planet rest frame during the transit. The detection is in agreement with the previous detection achieved with HST/WFC3. The signature shows an excess absorption in the blue part of the lines, suggesting that He I atoms are escaping from the atmosphere of WASP-107b. We interpret the time-series absorption spectra using the 3D EVE code. Our observations can be explained by combining an extended thermosphere that fills half of the Roche lobe and a large exospheric tail sustained by an escape rate of metastable helium of about 106 g s−1. In this scenario, however, the upper atmosphere needs to be subjected to a reduced photoionisation and radiation pressure from the star for the model to match the observations. Conclusions. We confirm the presence of helium in the atmosphere of WASP-107b at high confidence. The helium feature is detected from space and from the ground. The ground-based high-resolution signal brings detailed information about the spatial and dynamical structure of the upper atmosphere, and simulations suggest that the He I signature of WASP-107b probes both its thermosphere and exosphere, establishing this signature as a robust probe of exoplanetary upper atmospheres. Surveys with NIR high-resolution spectrographs (e.g. CARMENES, the Spectromètre infrarouge (SPIRou), or the Near-Infrared Planet Searcher (NIRPS)) will deliver a statistical understanding of exoplanet thermospheres and exospheres through the helium triplet.
Context.
Ultra-hot Jupiters are excellent laboratories for the study of exoplanetary atmospheres. WASP-121b is one of the most studied; many recent analyses of its atmosphere report interesting ...features at different wavelength ranges.
Aims.
In this paper we analyze one transit of WASP-121b acquired with the high-resolution spectrograph ESPRESSO at VLT in one-telescope mode, and one partial transit taken during the commissioning of the instrument in four-telescope mode.
Methods.
We take advantage of the very high S/N data and of the extreme stability of the spectrograph to investigate the anomalous in-transit radial velocity curve and study the transmission spectrum of the planet. We pay particular attention to the removal of instrumental effects, and stellar and telluric contamination. The transmission spectrum is investigated through single-line absorption and cross-correlation with theoretical model templates.
Results.
By analyzing the in-transit radial velocities we were able to infer the presence of the atmospheric Rossiter–McLaughlin effect. We measured the height of the planetary atmospheric layer that correlates with the stellar mask (mainly Fe) to be 1.052 ± 0.015
R
p
and we also confirmed the blueshift of the planetary atmosphere. By examining the planetary absorption signal on the stellar cross-correlation functions we confirmed the presence of a temporal variation of its blueshift during transit, which could be investigated spectrum-by-spectrum thanks to the quality of our ESPRESSO data. We detected significant absorption in the transmission spectrum for Na, H, K, Li, Ca
II
, and Mg, and we certified their planetary nature by using the 2D tomographic technique. Particularly remarkable is the detection of Li, with a line contrast of ~0.2% detected at the 6
σ
level. With the cross-correlation technique we confirmed the presence of Fe
I
, Fe
II
, Cr
I
, and V
I
. H
α
and Ca
II
are present up to very high altitudes in the atmosphere (~1.44
R
p
and ~2
R
p
, respectively), and also extend beyond the transit-equivalent Roche lobe radius of the planet. These layers of the atmosphere have a large line broadening that is not compatible with being caused by the tidally locked rotation of the planet alone, and could arise from vertical winds or high-altitude jets in the evaporating atmosphere.
Context.
Proxima Centauri is the closest star to the Sun. This small, low-mass, mid M dwarf is known to host an Earth-mass exoplanet with an orbital period of 11.2 days within the habitable zone, as ...well as a long-period planet candidate with an orbital period of close to 5 yr.
Aims.
We report on the analysis of a large set of observations taken with the ESPRESSO spectrograph at the VLT aimed at a thorough evaluation of the presence of a third low-mass planetary companion, which started emerging during a previous campaign.
Methods.
Radial velocities (RVs) were calculated using both a cross-correlation function (CCF) and a template matching approach. The RV analysis includes a component to model Proxima’s activity using a Gaussian process (GP). We use the CCF’s full width at half maximum to help constrain the GP, and we study other simultaneous observables as activity indicators in order to assess the nature of any potential RV signals.
Results.
We detect a signal at 5.12 ± 0.04 days with a semi-amplitude of 39 ± 7 cm s
−1
. The analysis of subsets of the ESPRESSO data, the activity indicators, and chromatic RVs suggest that this signal is not caused by stellar variability but instead by a planetary companion with a minimum mass of 0.26 ± 0.05
M
⊕
(about twice the mass of Mars) orbiting at 0.029 au from the star. The orbital eccentricity is well constrained and compatible with a circular orbit.
In recent years, the advent of a new generation of radial velocity instruments has allowed us to detect planets with increasingly lower mass and to break the one Earth-mass barrier. Here we report a ...new milestone in this context by announcing the detection of the lowest-mass planet measured so far using radial velocities: L 98-59 b, a rocky planet with half the mass of Venus. It is part of a system composed of three known transiting terrestrial planets (planets b–d). We announce the discovery of a fourth nontransiting planet with a minimum mass of 3.06 −0.37 +0.33 M ⊕ and an orbital period of 12.796 −0.019 +0.020 days and report indications for the presence of a fifth nontransiting terrestrial planet. With a minimum mass of 2.46 −0.82 +0.66 M ⊕ and an orbital period 23.15 −0.17 +0.60 days, this planet, if confirmed, would sit in the middle of the habitable zone of the L 98-59 system. L 98-59 is a bright M dwarf located 10.6ṗc away. Positioned at the border of the continuous viewing zone of the James Webb Space Telescope, this system is destined to become a corner stone for comparative exoplanetology of terrestrial planets. The three transiting planets have transmission spectrum metrics ranging from 49 to 255, which undoubtedly makes them prime targets for an atmospheric characterization with the James Webb Space Telescope, the Hubble Space Telescope, Ariel, or ground-based facilities such as NIRPS or ESPRESSO. With an equilibrium temperature ranging from 416 to 627 K, they offer a unique opportunity to study the diversity of warm terrestrial planets without the unknowns associated with different host stars. L 98-59 b and c have densities of 3.6 −1.5 +1.4 and 4.57 −0.85 +0.77 g cm −3 , respectively, and have very similar bulk compositions with a small iron core that represents only 12 to 14% of the total mass, and a small amount of water. However, with a density of 2.95 −0.51 +0.79 g cm −3 and despite a similar core mass fraction, up to 30% of the mass of L 98-59 d might be water.
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