Observing Atmospheric Escape in Sub-Jovian Worlds with JWST

Santos, Leonardo A. dos; Alam, Munazza K.; Espinoza, N.; Vissapragada, Shreyas

doi:10.3847/1538-3881/accf10

Cited by 7 publications

(1 citation statement)

References 78 publications

(100 reference statements)

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“…Evidently, they are the most helium-detected class of planets (see Figure 6). On the other hand, atmospheres of smaller, high-density planets are difficult to detect as they might not have accumulated sufficient primordial atmosphere and might require the James Webb Space Telescope to capture the escape (Santos et al 2023). Alternatively, they might have already lost them through atmospheric escape.…”

Section: Planetary Parametersmentioning

confidence: 99%

Helium in Exoplanet Exospheres: Orbital and Stellar Influences

Krishnamurthy,

Cowan

2024

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Searches for helium in the exospheres of exoplanets via the metastable near-infrared triplet have yielded 17 detections and 40 nondetections. We performed a comprehensive reanalysis of published studies to investigate the influence of stellar X-ray and extreme-ultraviolet (XUV) flux and orbital parameters on the detectability of helium in exoplanetary atmospheres. We identified a distinct “orbital sweet spot” for helium detection, 0.03 to 0.08 au from the host star, where the majority of detections occurred. This sweet spot is influenced by the stellar luminosity and planet size. Notably, a lower ratio of XUV flux to mid-UV flux is preferred for planets compared to nondetections. We also found that helium detections occur for planets around stars with effective temperatures of 4400–6500 K (i.e., spectral type K and G stars), with a sharp gap between 5400 and 6000 K, where no detections occur. We also report an upper-limit efficiency of 6% for energy-limited atmospheric escape from our analysis. Additionally, our analysis of the cumulative XUV flux versus escape velocity shows planets with helium detections above the “cosmic shoreline,” where atmospheres are not thought to be present, suggesting the shoreline needs revision. The unexpected trends revealed in our meta-analysis can contribute to a better understanding of star–planet interaction and exosphere evolution.

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Section: Planetary Parametersmentioning

confidence: 99%

Helium in Exoplanet Exospheres: Orbital and Stellar Influences

Krishnamurthy,

Cowan

2024

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The Rossiter-McLaughlin effect and exoplanet transits: A delicate association at medium and low spectral resolution

Carteret,

Bourrier,

Dethier

2024

A&A

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The characterization of exoplanetary atmospheres via transit spectroscopy is based on the comparison between the stellar spectrum filtered through the atmosphere and the unadulterated spectrum from the occulted stellar region. The disk-integrated spectrum is often used as a proxy for the occulted spectrum, yet they differ along the transit chord depending on stellar type and rotational velocity. This is refereed to as the Rossiter-McLaughlin (RM) effect, which is known to bias transmission spectra at high spectral resolution when calculated with the disk-integrated stellar spectrum. Recently, it was shown that the first claimed atmospheric signal from an exoplanet cannot arise from absorption in the core of the sodium doublet, because the features observed at high resolution are well reproduced by the RM effect. However, it remains unclear as to whether the detection made at medium spectral resolution with the HST arises from the smoothed RM signature or from the wings of the planetary absorption line. More generally, the impact of the RM effect at medium and low spectral resolution remains poorly explored. To address this question, we simulated realistic transmission spectra in a variety of systems using the EVaporating Exoplanets code. We find that the RM effect should not bias broadband atmospheric features, such as hazes or molecular absorption, measured with the JWST/NIRSPEC (prism mode) at low resolution. However, absorption signatures from metastable helium or sodium measured at medium resolution with the JWST/NIRSPEC (G140H mode) or HST/STIS can be biased, especially for planets on misaligned orbits across fast rotators. In contrast, we show that the Na signature originally reported in HD209458b, an aligned system, cannot be explained by the RM effect, supporting a planetary origin. Contamination by the RM effect should therefore be accounted for when interpreting high- and medium-resolution transmission spectra of exoplanets.

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The open-source sunbather code: Modeling escaping planetary atmospheres and their transit spectra

Linssen,

Shih,

MacLeod

et al. 2024

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Atmospheric escape is thought to significantly influence the evolution of exoplanets, especially sub-Jupiter planets on short orbital periods. Theoretical models predict that hydrodynamic escape could erode the atmospheres of such gaseous planets, leaving only a rocky core. Deriving atmospheric mass-loss rates from observations is necessary to check these predictions. One of the ways to obtain mass-loss-rate estimates is to fit transit spectra of the 10830 Å helium or UV metal lines with Parker wind models. We aim to provide the community with a tool that enables this type of analysis, and present sunbather an open-source Python code that can be used to model escaping exoplanet atmospheres and their transit spectra. sunbather incorporates the Parker wind code p-winds and the photoionization code Cloudy with the ability to calculate any currently known spectral tracer, using an arbitrary atmospheric composition. With sunbather we investigate how the atmospheric structure of a generic hot-Neptune planet depends on metallicity. We find that the mass-loss rate drops by roughly one order of magnitude as we increase the metallicity from solar to 50 times solar. Line cooling by metal species is already important for a solar composition, and is even more so at higher metallicity. We then demonstrate how sunbather can be used to interpret observations of spectral lines that form in the upper atmosphere. We fit the observed helium spectrum of the mini-Neptune TOI-2134 b and show how, even for helium data, the inferred mass-loss rate can change by a factor of up to three, depending on the assumed metallicity.

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Observing Atmospheric Escape in Sub-Jovian Worlds with JWST

Cited by 7 publications

References 78 publications

Helium in Exoplanet Exospheres: Orbital and Stellar Influences

Helium in Exoplanet Exospheres: Orbital and Stellar Influences

The Rossiter-McLaughlin effect and exoplanet transits: A delicate association at medium and low spectral resolution

The open-source sunbather code: Modeling escaping planetary atmospheres and their transit spectra

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