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Metastable Helium Reveals an Extended Atmosphere for the Gas Giant HAT-P-18b

Paragas, Kimberly and Vissapragada, Shreyas and Knutson, Heather A. and Oklopčić, Antonija and Chachan, Yayaati and Greklek-McKeon, Michael and Dai, Fei and Tinyanont, Samaporn and Vasisht, Gautam (2021) Metastable Helium Reveals an Extended Atmosphere for the Gas Giant HAT-P-18b. Astrophysical Journal Letters, 909 (1). Art. No. L10. ISSN 2041-8205. doi:10.3847/2041-8213/abe706.

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The metastable helium line at 1083 nm can be used to probe the extended upper atmospheres of close-in exoplanets and thus provide insight into their atmospheric mass loss, which is likely to be significant in sculpting their population. We used an ultra-narrow band filter centered on this line to observe two transits of the low-density gas giant HAT-P-18b, using the 200'' Hale Telescope at Palomar Observatory, and report the detection of its extended upper atmosphere. We constrain the excess absorption to be 0.46% ± 0.12% in our 0.635 nm bandpass, exceeding the transit depth from the Transiting Exoplanet Survey Satellite (TESS) by 3.9σ. If we fit this signal with a 1D Parker wind model, we find that it corresponds to an atmospheric mass loss rate between 8.3^(+2.8)_(−1.9) ×10⁻⁵ M_J Gyr⁻¹ and 2.63^(+0.46)_(−0.64)×10⁻³ M_J Gyr⁻¹ for thermosphere temperatures ranging from 4000 K to 13,000 K, respectively. With a J magnitude of 10.8, this is the faintest system for which such a measurement has been made to date, demonstrating the effectiveness of this approach for surveying mass loss on a diverse sample of close-in gas giant planets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Vissapragada, Shreyas0000-0003-2527-1475
Knutson, Heather A.0000-0002-0822-3095
Oklopčić, Antonija0000-0002-9584-6476
Chachan, Yayaati0000-0003-1728-8269
Greklek-McKeon, Michael0000-0002-0371-1647
Dai, Fei0000-0002-8958-0683
Tinyanont, Samaporn0000-0002-1481-4676
Vasisht, Gautam0000-0002-1871-6264
Additional Information:© 2021 The American Astronomical Society. Received 2020 December 22; revised 2021 February 12; accepted 2021 February 16; published 2021 March 3. We are thankful to the Palomar staff, especially Kajse Peffer, Paul Nied, Joel Pearman, Carolyn Heffner, and Kevin Rykoski for their support. K.P. acknowledges support from the Summer Undergraduate Research Fellowship (SURF) at the California Institute of Technology and the NASA CT Space Grant. S.V. is supported by an NSF Graduate Research Fellowship and the Paul & Daisy Soros Fellowship for New Americans. H.A.K. acknowledges support from NSF CAREER grant 1555095.
Funding AgencyGrant Number
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Paul and Daisy Soros FellowshipUNSPECIFIED
Subject Keywords:Exoplanet atmospheres; Narrow band photometry; Transits; Exoplanets; Extrasolar gaseous giant planets; Extrasolar gaseous planets
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Narrow band photometry (1088); Transits (1711); Exoplanets (498); Extrasolar gaseous giant planets (509); Extrasolar gaseous planets (2172)
Record Number:CaltechAUTHORS:20210305-083505302
Persistent URL:
Official Citation:Kimberly Paragas et al 2021 ApJL 909 L10
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108326
Deposited By: Tony Diaz
Deposited On:08 Mar 2021 22:49
Last Modified:16 Nov 2021 19:11

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