Atmospheric escape is considered to be one of the main channels for evolution in sub-Jovian planets, particularly in their early lives. While there are several hypotheses proposed to explain escape ...in exoplanets, testing them with atmospheric observations remains a challenge. In this context, high-resolution transmission spectroscopy of transiting exoplanets for the metastable helium triplet (He 2
3
S) at 1083 nm has emerged as a reliable technique for observing and measuring escape. To aid in the prediction and interpretation of metastable He transmission spectroscopy observations, we developed the code
p-winds
. This is an open-source, fully documented, scalable Python implementation of the one-dimensional, purely H+He Parker wind model for upper atmospheres coupled with ionization balance, ray-tracing, and radiative transfer routines. We demonstrate an atmospheric retrieval by fitting
p-winds
models to the observed metastable He transmission spectrum of the warm Neptune HAT-P-11 b and take the variation in the in-transit absorption caused by transit geometry into account. For this planet, our best fit yields a total atmospheric escape rate of approximately 2.5 × 10
10
g s
−1
and an outflow temperature of 7200 K. The range of retrieved mass loss rates increases significantly when we let the H atom fraction be a free parameter, but its posterior distribution remains unconstrained by He observations alone. The stellar host limb darkening does not have a significant impact on the retrieved escape rate or outflow temperature for HAT-P-11 b. Based on the non-detection of escaping He for GJ 436 b, we are able to rule out total escape rates higher than 3.4 × 10
10
g s
−1
at 99.7% (3
σ
) confidence.
ABSTRACT
We present new observations of the transmission spectrum of the hot Jupiter WASP-6b both from the ground with the Very Large Telescope FOcal Reducer and Spectrograph (FORS2) from 0.45 to ...0.83 μm, and space with the Transiting Exoplanet Survey Satellite from 0.6 to 1.0 μm and the Hubble Space Telescope (HST) Wide Field Camera 3 from 1.12 to 1.65 μm. Archival data from the HST Space Telescope Imaging Spectrograph (STIS) and Spitzer are also re-analysed on a common Gaussian process framework, of which the STIS data show a good overall agreement with the overlapping FORS2 data. We also explore the effects of stellar heterogeneity on our observations and its resulting implications towards determining the atmospheric characteristics of WASP-6b. Independent of our assumptions for the level of stellar heterogeneity we detect Na i, K i, and H2O absorption features and constrain the elemental oxygen abundance to a value of O/H ≃ −0.9 ± 0.3 relative to solar. In contrast, we find that the stellar heterogeneity correction can have significant effects on the retrieved distributions of the Na/H and K/H abundances, primarily through its degeneracy with the sloping optical opacity of scattering haze species within the atmosphere. Our results also show that despite this presence of haze, WASP-6b remains a favourable object for future atmospheric characterization with upcoming missions such as the James Webb Space Telescope.
Abstract
Hydrodynamic atmospheric escape is considered an important process that shapes the evolution of sub-Jovian exoplanets, particularly those with short orbital periods. The metastable He line ...in the near-infrared at 1.083
μ
m is a reliable tracer of atmospheric escape in hot exoplanets, with the advantage of being observable from the ground. However, observing escaping He in sub-Jovian planets has remained challenging due to the systematic effects and telluric contamination present in ground-based data. With the successful launch and operations of JWST, we now have access to extremely stable high-precision near-infrared spectrographs in space. Here we predict the observability of metastable He with JWST in two representative and previously well-studied warm Neptunes, GJ 436 b (
T
eq
= 687 K,
R
p
= 0.37
R
J
) and GJ 1214 b (
T
eq
= 588 K,
R
p
= 0.25
R
J
). Our simulated JWST observations for GJ 436 b demonstrate that a single transit with NIRSpec/G140H is sensitive to mass-loss rates that are two orders of magnitude lower than what is detectable from the ground. Our exercise for GJ 1214 b show that the best configuration to observe the relatively weak outflows of warm Neptunes with JWST is with NIRSpec/G140H, and that NIRSpec/G140M and NIRISS/SOSS are less optimal. Since none of these instrument configurations can spectrally resolve the planetary absorption, we conclude that the 1D isothermal Parker-wind approximation may not be sufficient for interpreting such observations. More sophisticated models are critical for breaking the degeneracy between outflow temperature and mass-loss rate for JWST measurements of metastable He.
We present a 0.3−5 m transmission spectrum of the hot Jupiter HAT-P-32Ab observed with the Space Telescope Imaging Spectrograph and Wide Field Camera 3 instruments mounted on the Hubble Space ...Telescope, combined with Spitzer Infrared Array Camera photometry. The spectrum is composed of 51 spectrophotometric bins with widths ranging between 150 and 400 , measured to a median precision of 215 ppm. Comparisons of the observed transmission spectrum to a grid of 1D radiative-convective equilibrium models indicate the presence of clouds/hazes, consistent with previous transit observations and secondary eclipse measurements. To provide more robust constraints on the planet's atmospheric properties, we perform the first full optical to infrared retrieval analysis for this planet. The retrieved spectrum is consistent with a limb temperature of K, a thick cloud deck, enhanced Rayleigh scattering, and ∼10× solar H2O abundance. We find log(Z/Z ) = , and compare this measurement with the mass-metallicity relation derived for the solar system.
Abstract
We present new optical transmission spectra for two hot Jupiters: WASP-25b (
M
= 0.56
M
J
;
R
= 1.23
R
J
;
P
= 3.76 days) and WASP-124b (
M
= 0.58
M
J
;
R
= 1.34
R
J
;
P
= 3.37 days), with ...wavelength coverages of 4200–9100 Å and 4570–9940 Å, respectively. These spectra are from the ESO Faint Object Spectrograph and Camera (v.2) mounted on the New Technology Telescope and Inamori-Magellan Areal Camera & Spectrograph on Magellan Baade. No strong spectral features were found in either spectra, with the data probing 4 and 6 scale heights, respectively.
Exoretrievals
and
PLATON
retrievals favor stellar activity for WASP-25b, while the data for WASP-124b did not favor one model over another. For both planets the retrievals found a wide range in the depths where the atmosphere could be optically thick (∼0.4
μ
–0.2 bars for WASP-25b and 1.6
μ
–32 bars for WASP-124b) and recovered a temperature that is consistent with the planets’ equilibrium temperatures, but with wide uncertainties (up to ±430 K). For WASP-25b, the models also favor stellar spots that are ∼500–3000 K cooler than the surrounding photosphere. The fairly weak constraints on parameters are owing to the relatively low precision of the data, with an average precision of 840 and 1240 ppm per bin for WASP-25b and WASP-124b, respectively. However, some contribution might still be due to an inherent absence of absorption or scattering in the planets’ upper atmospheres, possibly because of aerosols. We attempt to fit the strength of the sodium signals to the aerosol–metallicity trend proposed by McGruder et al., and find WASP-25b and WASP-124b are consistent with the prediction, though their uncertainties are too large to confidently confirm the trend.
Abstract
Understanding planet formation requires robust population studies, which are designed to reveal trends in planet properties. In this work we aim to determine if and how different methods for ...selecting populations of exoplanets for atmospheric characterization with JWST could influence population-level inferences. We generate three hypothetical surveys of super-Earths/sub-Neptunes, with each survey designed to span a similar radius-insolation flux space. The survey samples are constructed based on three different selection criteria (evenly spaced by eye, binned, and a quantitative selection function). Using an injection-recovery technique, we test how robustly individual-planet atmospheric parameters and population-level parameters can be retrieved. We find that all three survey designs result in equally suitable targets for individual atmospheric characterization, but not equally suitable targets for constraining population parameters. Only samples constructed with a quantitative method or that are sufficiently evenly spaced-by-eye result in robust population parameter constraints. Furthermore, we find that the sample with the best targets for individual atmospheric study does not necessarily result in the best-constrained population parameters. The method of sample selection must be considered. We also find that there may be large variability in population-level results with a sample that is small enough to fit in a single JWST cycle (∼12 planets), suggesting that the most successful population-level analyses will be multicycle. Lastly, we infer that our exploration of sample selection is limited by the small number of transiting planets with measured masses around bright stars. Our results can guide future development of programs that aim to determine underlying trends in exoplanet-atmospheric properties, and, by extension, formation and evolution processes.
Abstract
We present the detection of neutral helium at 10833 Å in the atmosphere of WASP-52b and tentative evidence of helium in the atmosphere of the grazing WASP-177b, using high-resolution ...observations acquired with the NIRSPEC instrument on the Keck II telescope. We detect excess absorption by helium in WASP-52b’s atmosphere of 3.44% ± 0.31% (11
σ
), or equivalently 66 ± 5 atmospheric scale heights. This absorption is centered on the planet’s rest frame (Δ
v
= 0.00 ± 1.19 km s
−1
). We model the planet’s escape using a 1D Parker wind model and calculate its mass-loss rate to be ∼1.4 × 10
11
g s
−1
, or equivalently 0.5% of its mass per gigayear. For WASP-177b, we see evidence for redshifted (Δ
v
= 6.02 ± 1.88 km s
−1
) helium-like absorption of 1.28% ± 0.29% (equal to 23 ± 5 atmospheric scale heights). However, due to residual systematics in the transmission spectrum of similar amplitude, we do not interpret this as significant evidence for He absorption in the planet’s atmosphere. Using a 1D Parker wind model, we set a 3
σ
upper limit on WASP-177b’s escape rate of 7.9 × 10
10
g s
−1
. Our results, taken together with recent literature detections, suggest the tentative relation between XUV irradiation and He
i
absorption amplitude may be shallower than previously suggested. Our results highlight how metastable helium can advance our understanding of atmospheric loss and its role in shaping the exoplanet population.
We present an atmospheric transmission spectrum for the ultra-hot Jupiter WASP-121b, measured using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Across the 0.47-1 ...wavelength range, the data imply an atmospheric opacity comparable to-and in some spectroscopic channels exceeding-that previously measured at near-infrared wavelengths (1.15-1.65 ). Wavelength-dependent variations in the opacity rule out a gray cloud deck at a confidence level of 3.7 and may instead be explained by VO spectral bands. We find a cloud-free model assuming chemical equilibrium for a temperature of 1500 K and a metal enrichment of 10-30× solar matches these data well. Using a free-chemistry retrieval analysis, we estimate a VO abundance of dex. We find no evidence for TiO and place a 3 upper limit of −7.9 dex on its abundance, suggesting TiO may have condensed from the gas phase at the day-night limb. The opacity rises steeply at the shortest wavelengths, increasing by approximately five pressure scale heights from 0.47 to 0.3 in wavelength. If this feature is caused by Rayleigh scattering due to uniformly distributed aerosols, it would imply an unphysically high temperature of 6810 1530 K. One alternative explanation for the short-wavelength rise is absorption due to SH (mercapto radical), which has been predicted as an important product of non-equilibrium chemistry in hot Jupiter atmospheres. Irrespective of the identity of the NUV absorber, it likely captures a significant amount of incident stellar radiation at low pressures, thus playing a significant role in the overall energy budget, thermal structure, and circulation of the atmosphere.
ABSTRACT
We perform atmospheric retrievals on the full optical to infrared ($0.3\!-\!5 \, \mu \mathrm{m}$) transmission spectrum of the inflated hot Jupiter WASP-52b by combining HST/STIS, WFC3 IR, ...and Spitzer/IRAC observations. As WASP-52 is an active star that shows both out-of-transit photometric variability and star-spot crossings during transits, we account for the contribution of non-occulted active regions in the retrieval. We recover a 0.1–10× solar atmospheric composition, in agreement with core accretion predictions for giant planets, and no significant contribution of aerosols. We also obtain a <3000 K temperature for the star-spots, a measure which is likely affected by the models used to fit instrumental effects in the transits, and a 5 per cent star-spot fractional coverage, compatible with expectations for the host star’s spectral type. Such constraints on the planetary atmosphere and on the activity of its host star will inform future JWST GTO observations of this target.
Abstract
The search for rocky planet atmospheres with JWST has focused on planets transiting M dwarfs. Such planets have favorable planet-to-star size ratios, enhancing the amplitude of atmospheric ...features. Since the expected signal strength of atmospheric features is similar to the single-transit performance of JWST, multiple observations are required to confirm any detection. Here, we present two transit observations of the rocky planet GJ 1132 b with JWST NIRSpec G395H, covering 2.8–5.2
μ
m. Previous Hubble Space Telescope WFC3 observations of GJ 1132 b were inconclusive, with evidence reported for either an atmosphere or a featureless spectrum based on analyses of the same data set. Our JWST data exhibit substantial differences between the two visits. One transit is consistent with either an H
2
O-dominated atmosphere containing ∼1% CH
4
and trace N
2
O (
χ
ν
2
=
1.13
) or stellar contamination from unocculted starspots (
χ
ν
2
=
1.36
). However, the second transit is consistent with a featureless spectrum. Neither visit is consistent with a previous report of HCN. Atmospheric variability is unlikely to explain the scale of the observed differences between the visits. Similarly, our out-of-transit stellar spectra show no evidence of changing stellar inhomogeneity between the two visits—observed 8 days apart, only 6.5% of the stellar rotation rate. We further find no evidence of differing instrumental systematic effects between visits. The most plausible explanation is an unlucky random noise draw leading to two significantly discrepant transmission spectra. Our results highlight the importance of multivisit repeatability with JWST prior to claiming atmospheric detections for these small, enigmatic planets.
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