Zodiacal exoplanets in time – X. The orbit and atmosphere of the young ‘neptune desert’-dwelling planet K2-100b

Gaidos, Eric; Hirano, Teruyuki; Mann, Andrew W.; Owens, Dylan A.; Berger, Travis A.; France, Kevin; Vanderburg, Andrew; Harakawa, Hiroki; Hodapp, Klaus W.; Ishizuka, Masato; Jacobson, Shane; Konishi, Mihoko; Kotani, Takayuki; Kudo, Tomoyuki; Kurokawa, Takashi; Kuzuhara, Masayuki; Nishikawa, Jun; Omiya, Masashi; Serizawa, Takuma; Tamura, Motohide; Ueda, Akitoshi

doi:10.1093/mnras/staa918

Cited by 39 publications

(21 citation statements)

References 109 publications

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“…In addition to the spectral shape and intensity of the XUV stellar irradiation (see, e.g. Oklopčić 2019), high H/He ratios could help to explain the non-detection of the He(2 3 S) in some highly irradiated exoplanets, such as GJ 1214 b and GJ 9827 d (as suggested by Kasper et al 2020) as well as K2-100b (Gaidos et al 2020).…”

Section: Retrieved Temperatures Mass-loss Rates and H/he Compositionmentioning

confidence: 99%

Modelling the He I triplet absorption at 10 830 Å in the atmospheres of HD 189733 b and GJ 3470 b

Lampón

López‐Puertas

Sanz-Forcada

et al. 2021

A&A

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Characterising the atmospheres of exoplanets is key to understanding their nature and provides hints about their formation and evolution. High resolution measurements of the helium triplet absorption of highly irradiated planets have been recently reported, which provide a new means of studying their atmospheric escape. In this work we study the escape of the upper atmospheres of HD 189733 b and GJ 3470 b by analysing high resolution He I triplet absorption measurements and using a 1D hydrodynamic spherically symmetric model coupled with a non-local thermodynamic model for the He I triplet state. We also use the H density derived from Lyα observations to further constrain their temperatures, mass-loss rates, and H/He ratios. We have significantly improved our knowledge of the upper atmospheres of these planets. While HD 189733 b has a rather compressed atmosphere and small gas radial velocities, GJ 3470 b, on the other hand with a gravitational potential ten times smaller, exhibits a very extended atmosphere and large radial outflow velocities. Hence, although GJ 3470 b is much less irradiated in the X-ray and extreme ultraviolet radiation, and its upper atmosphere is much cooler, it evaporates at a comparable rate. In particular, we find that the upper atmosphere of HD 189733 b is compact and hot, with a maximum temperature of 12 400−300+400 K, with a very low mean molecular mass (H/He = (99.2/0.8) ± 0.1), which is almost fully ionised above 1.1 RP, and with a mass-loss rate of (1.1 ± 0.1) × 1011 g s−1. In contrast, the upper atmosphere of GJ 3470 b is highly extended and relatively cold, with a maximum temperature of 5100 ± 900 K, also with a very low mean molecular mass (H/He = (98.5/1.5)−1.5+1.0), which is not strongly ionised, and with a mass-loss rate of (1.9 ± 1.1) × 1011 g s−1. Furthermore, our results suggest that upper atmospheres of giant planets undergoing hydrodynamic escape tend to have a very low mean molecular mass (H/He ≳ 97/3).

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Section: Retrieved Temperatures Mass-loss Rates and H/he Compositionmentioning

confidence: 99%

Modelling the He I triplet absorption at 10 830 Å in the atmospheres of HD 189733 b and GJ 3470 b

Lampón

López‐Puertas

Sanz-Forcada

et al. 2021

A&A

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“…Our observations target the 10833 Å He triplet feature, which has recently emerged as a way to probe the escaping atmospheres of larger planets (Allart et al 2018(Allart et al , 2019Kreidberg & Oklopčić 2018;Mansfield et al 2018;Nortmann et al 2018;Salz et al 2018;Spake et al 2018;Alonso-Floriano et al 2019;dos Santos et al 2020;Gaidos et al 2020;Kirk et al 2020;Ninan et al 2020;Palle et al 2020;Vissapragada et al 2020). The He triplet feature arises from a metastable transition.…”

Section: Introductionmentioning

confidence: 99%

Nondetection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets

Kasper

Bean

Oklopčić

et al. 2020

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We present a search for helium in the upper atmospheres of three sub-Neptune-sized planets to investigate the origins of these ubiquitous objects. The detection of helium for a low-density planet would be strong evidence for the presence of a primary atmosphere accreted from the protoplanetary nebula because large amounts of helium are not expected in the secondary atmospheres of rocky planets. We used Keck+NIRSPEC to obtain high-resolution transit spectroscopy of the planets GJ 1214b, GJ 9827d, and HD 97658b around the 10833 Å He triplet feature. We did not detect helium absorption for any of the planets despite achieving a high level of sensitivity. We used the nondetections to set limits on the planets' thermosphere temperatures and atmospheric loss rates by comparing grids of 1D models to the data. We also performed coupled interior structure and atmospheric loss calculations, which suggest that the bulk atmospheres (winds) of the planets would be at most modestly enhanced (depleted) in helium relative to their primordial composition. Our lack of detections of the helium triplet for GJ 1214b and GJ 9827d is highly inconsistent with the predictions of models for the present-day mass loss on these planets. Higher signal-to-noise data would be needed to detect the helium feature predicted for HD 97658b. We identify uncertainties in the extreme-ultraviolet fluxes of the host stars and the lack of detailed mass-loss models specifically for cool and metal-enhanced atmospheres as the main limitations to the interpretation of our results. Ultimately, our results suggest that the upper atmospheres of sub-Neptune planets are fundamentally different from those of gas giant planets.

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“…Studies of individual young systems can also be powerful, providing new insight into topics such as haze and cloud formation in young systems (e.g., Gao & Zhang 2020;Thao et al 2020), photoevaporation and atmospheric escape (e.g., Gaidos et al 2020;K. Rockcliffe et al 2020, in preparation), and exoplanet migration (e.g., David et al 2016b;Mann et al 2016b).…”

Section: Introductionmentioning

confidence: 99%

TESS Hunt for Young and Maturing Exoplanets (THYME). III. A Two-planet System in the 400 Myr Ursa Major Group

Mann

Johnson

Vanderburg

et al. 2020

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Exoplanets can evolve significantly between birth and maturity, as their atmospheres, orbits, and structures are shaped by their environment. Young planets (<1 Gyr) offer an opportunity to probe the critical early stages of this evolution, where planets evolve the fastest. However, most of the known young planets orbit prohibitively faint stars. We present the discovery of two planets transiting HD 63433 (TOI 1726, TIC 130181866), a young Sun-like ( =  M 0.99 0.03 * ) star. Through kinematics, lithium abundance, and rotation, we confirm that HD 63433 is a member of the Ursa Major moving group (τ=414±23 Myr). Based on the TESS light curve and updated stellar parameters, we estimate that the planet radii are 2.15±0.10 R ⊕ and 2.67±0.12 R ⊕ , the orbital periods are 7.11

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Zodiacal exoplanets in time – X. The orbit and atmosphere of the young ‘neptune desert’-dwelling planet K2-100b

Cited by 39 publications

References 109 publications

Modelling the He I triplet absorption at 10 830 Å in the atmospheres of HD 189733 b and GJ 3470 b

Modelling the He I triplet absorption at 10 830 Å in the atmospheres of HD 189733 b and GJ 3470 b

Nondetection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets

TESS Hunt for Young and Maturing Exoplanets (THYME). III. A Two-planet System in the 400 Myr Ursa Major Group

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