The Radiation Environment of Exoplanet Atmospheres

Linsky, Jeffrey L.

doi:10.3390/challe5020351

Cited by 10 publications

(2 citation statements)

References 81 publications

(110 reference statements)

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“…To compare the laboratory UV doses to the radiation from an exoplanet host star, we use the UV spectra of GJ876, an M dwarf observed by the International Ultraviolet Explorer (Linsky 2014). In this study, the spectral flux is rescaled to the distance of its habitable zone (0.21 au).…”

Section: Vuv Irradiation Of Tholinsmentioning

confidence: 99%

Organic Aerosols in Anoxic and Oxic Atmospheres of Earth-like Exoplanets: VUV-MIR Spectroscopy of CHON Tholins

Gavilan

Carrasco

Hoffmann

et al. 2018

ApJ

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Organic hazes can drastically impact the characterization and detection of exoplanet atmospheres. We explore the effects of the transition from an anoxic to oxic atmosphere on the molecular structure of organic aerosols, by producing aerosols in N 2 :CO 2 :CH 4 -rich plasmas with increasing CO 2 /CH 4 gas ratios. We performed a spectroscopic study on the resulting aerosol analogs, CHON-rich tholins, from the vacuum-ultraviolet (VUV) to the mid-infrared (MIR), i.e., the 0.13-10 μm range. VUV spectroscopy revealed the presence of π-π * and n-π * transitions in the 200-500 nm range in all samples. These are attributed to electronic transitions in amine groups. As the CO 2 /CH 4 ratio increases, new bands emerge that can be attributed to electronic transitions in hydroxyl and carboxyl functional groups. MIR spectroscopy showed that the molecular structure of oxidized aerosols is dominated by the CO 2 /CH 4 ratio. Band deconvolution revealed the oxygenation of the organic matrix via the formation of oxygenated functional groups, including amide, hydroxyl, and carbonyl groups. For the most oxidized aerosols, absorption is greatest in the 0.13-0.3 μm and 6-10 μm regions. Some of the oxidized samples were further irradiated with VUV photons, resulting in the formation of π-π * bands in the 200-250 nm region and a decrease in the band intensities below 200 nm, attributed to amine and nitrile losses. We discuss how oxidized aerosols could provide a detectable (bio-)signature in exoplanet atmospheres.

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Section: Vuv Irradiation Of Tholinsmentioning

confidence: 99%

Organic Aerosols in Anoxic and Oxic Atmospheres of Earth-like Exoplanets: VUV-MIR Spectroscopy of CHON Tholins

Gavilan

Carrasco

Hoffmann

et al. 2018

ApJ

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“…Therefore, stellar emission lines close to the blue side of the ionization edge will undergo significant absorption by the ISM before they reach our telescopes. The solar EUV spectrum, which we can observe without strong absorption, shows some moderately strong EUV emission lines in that wavelength range, namely NeVII465 and SiXII499 (see for example Del Zanna & Mason (2018); Linsky (2014)). In the solar spectrum the SiXII499 line is of roughly comparable strength to the stronger iron lines in the vicinity of HeII304, and NeVII465 line is inbetween the iron lines and the HeII304 line in intensity (Del Zanna & Mason 2018).…”

Section: The Influence Of Ism Absorption On the Observed Spectramentioning

confidence: 69%

Helium absorption in exoplanet atmospheres is connected to stellar coronal abundances

Poppenhaeger

2022

Preprint

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Transit observations in the helium triplet around 10830 Angstrom are a successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionisation and recombination of helium in the exoplanetary atmosphere. This ionisation is caused by stellar photons at extreme ultra-violet (EUV) wavelengths; however, no currently active telescopes can observe this part of the stellar spectrum. The relevant part of the stellar EUV spectrum consists of individual emission lines, many of them being formed by iron at coronal temperatures. The stellar iron abundance in the corona is often observed to be depleted for high-activity low-mass stars due to the first ionisation potential (FIP) effect. I show that stars with high versus low coronal iron abundances follow different scaling laws that tie together their X-ray emission and the narrow-band EUV flux that causes helium ionisation. I also show that the stellar iron to oxygen abundance ratio in the corona can be measured reasonably well from X-ray CCD spectra, yielding similar results to high-resolution X-ray observations. Taking coronal iron abundance into account, the currently observed large scatter in the relationship of EUV irradiation with exoplanetary helium transit depths can be reduced, improving the target selection criteria for exoplanet transmission spectroscopy. In particular, previously puzzling non-detections of helium for Neptunic exoplanets are now in line with expectations from the revised scaling laws.

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Panchromatic Spectra of Exoplanet Host Stars

Linsky

2019

Lecture Notes in Physics

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The Radiation Environment of Exoplanet Atmospheres

Cited by 10 publications

References 81 publications

Organic Aerosols in Anoxic and Oxic Atmospheres of Earth-like Exoplanets: VUV-MIR Spectroscopy of CHON Tholins

Organic Aerosols in Anoxic and Oxic Atmospheres of Earth-like Exoplanets: VUV-MIR Spectroscopy of CHON Tholins

Helium absorption in exoplanet atmospheres is connected to stellar coronal abundances

Panchromatic Spectra of Exoplanet Host Stars

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