The Influence of Stellar Contamination on the Interpretation of Near-infrared Transmission Spectra of Sub-Neptune Worlds around M-dwarfs

Iyer, Aishwarya R.; Line, Michael R.

doi:10.3847/1538-4357/ab612e

Cited by 32 publications

(29 citation statements)

References 98 publications

(150 reference statements)

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“…The transmission spectrum of LHS 1140 b also has a marginally significant (2.65σ), noninverted water feature, but this too is consistent with expectations for stellar contamination (Edwards et al 2021). For planets around the coolest stars, H2O contamination from an imhomogeneous photosphere may be the norm and should be taken into account in the analysis of the spectra (Iyer & Line 2020).…”

Section: Planets With M-dwarf Host Starssupporting

confidence: 74%

Atmospheres of Rocky Exoplanets

Wordsworth,

Kreidberg

2021

Preprint

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Rocky planets are common around other stars, but their atmospheric properties remain largely unconstrained. Thanks to a wealth of recent planet discoveries and upcoming advances in observing capability, we are poised to characterize the atmospheres of dozens of rocky exoplanets in this decade. Theoretical understanding of rocky exoplanet atmospheres has advanced considerably in the last few years, yielding testable predictions of their evolution, chemistry, dynamics and even possible biosignatures. Here we review key progress in this field to date and discuss future objectives. Our major conclusions are:• Many rocky planets may form with initial H2 -He envelopes that are later lost to space, likely due to a combination of stellar UV/Xray irradiation and internal heating. • After the early stages of evolution, a wide diversity of atmospheric compositions is expected, due to variations in host star flux, atmospheric escape rates, interior exchange and other factors. • Observations have ruled out the presence of hydrogen-dominated atmospheres on several nearby rocky exoplanets, and the presence of any thick atmosphere on one target. More detailed atmospheric characterization of these planets and others will become possible in the near future. • Exoplanet biosphere searches are an exciting future goal. However, reliable detections for a representative sample of planets will require further advances in observing capability and improvements in our understanding of abiotic planetary processes.

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Section: Planets With M-dwarf Host Starssupporting

confidence: 74%

Atmospheres of Rocky Exoplanets

Wordsworth,

Kreidberg

2021

Preprint

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“…Transmission spectroscopy is useful and effective in detecting atmospheric compositions of hot Jupiters, and even hot sub-Neptunes and super-Earths (Sing et al, 2011;Nikolov et al, 2014;Wakeford and Sing, 2015;Benneke et al, 2019;Iyer and Line, 2020;Mikal-Evans et al, 2020). However, the present telescopes are not able to resolve the atmospheric spectra of habitable terrestrial planets that are smaller in size and cooler in temperature.…”

Section: Introductionmentioning

confidence: 91%

Asymmetry and Variability in the Transmission Spectra of Tidally Locked Habitable Planets

Song

Yang

2021

Front. Astron. Space Sci.

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Spatial heterogeneity and temporal variability are general features in planetary weather and climate, due to the effects of planetary rotation, uneven stellar flux distribution, fluid motion instability, etc. In this study, we investigate the asymmetry and variability in the transmission spectra of 1:1 spin–orbit tidally locked (or called synchronously rotating) planets around low-mass stars. We find that for rapidly rotating planets, the transit atmospheric thickness of the evening terminator (east of the substellar region) is significantly larger than that of the morning terminator (west of the substellar region). The asymmetry is mainly related to the spatial heterogeneity in ice clouds, as the contributions of liquid clouds and water vapor are smaller. The underlying mechanism is that there are always more ice clouds on the evening terminator, due to the combined effect of coupled Rossby–Kelvin waves and equatorial superrotation that advect vapor and clouds to the east, especially at high levels of the atmosphere. For slowly rotating planets, the asymmetry reverses (the morning terminator has a larger transmission depth than the evening terminator), but the magnitude is small or even negligible. For both rapidly and slowly rotating planets, there is strong variability in the transmission spectra. The asymmetry signal is nearly impossible to be observed by the James Webb Space Telescope (JWST), because the magnitude of the asymmetry (about 10 ppm) is smaller than the instrumental noise and the high variability further increases the challenge.

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“…Consequently, a lesser degree of heterogeneity is still consistent with our transmission spectrum (e.g., ΔT ≈ 300 K temperature contrast with ≈7% coverage fraction lies within 1σ). A promising avenue for future work would be to better constrain the degree of stellar heterogeneity WASP-79 exhibits via out-of-transit stellar decomposition (e.g., Wakeford et al 2019;Iyer & Line 2020).…”

Section: Faculae Characteristicsmentioning

confidence: 99%

HST PanCET Program: A Complete Near-UV to Infrared Transmission Spectrum for the Hot Jupiter WASP-79b

Rathcke

Macdonald

Barstow

et al. 2021

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We present a new optical transmission spectrum of the hot Jupiter WASP-79b. We observed three transits with the STIS instrument mounted on the Hubble Space Telescope (HST), spanning 0.3-1.0 μm. Combining these transits with previous observations, we construct a complete 0.3-5.0 μm transmission spectrum of WASP-79b. Both HST and ground-based observations show decreasing transit depths toward blue wavelengths, contrary to expectations from Rayleigh scattering or hazes. We infer atmospheric and stellar properties from the full near-UV to infrared transmission spectrum of WASP-79b using three independent retrieval codes, all of which yield consistent results. Our retrievals confirm previous detections of H 2 O (at 4.0σ confidence) while providing moderate evidence of H − bound-free opacity (3.3σ) and strong evidence of stellar contamination from unocculted faculae (4.7σ). The retrieved H 2 O abundance (∼1%) suggests a superstellar atmospheric metallicity, though stellar or substellar abundances remain consistent with present observations (O/H = 0.3-34× stellar). All three retrieval codes obtain a precise H − abundance constraint: log( -X H ) ≈ −8.0 ± 0.7. The potential presence of H − suggests that James Webb Space Telescope observations may be sensitive to ionic chemistry in the atmosphere of WASP-79b. The inferred faculae are ∼500 K hotter than the stellar photosphere, covering ∼15% of the stellar surface. Our analysis underscores the importance of observing UV-optical transmission spectra in order to disentangle the influence of unocculted stellar heterogeneities from planetary transmission spectra.

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The Influence of Stellar Contamination on the Interpretation of Near-infrared Transmission Spectra of Sub-Neptune Worlds around M-dwarfs

Cited by 32 publications

References 98 publications

Atmospheres of Rocky Exoplanets

Atmospheres of Rocky Exoplanets

Asymmetry and Variability in the Transmission Spectra of Tidally Locked Habitable Planets

HST PanCET Program: A Complete Near-UV to Infrared Transmission Spectrum for the Hot Jupiter WASP-79b

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