A spectral survey of an ultra-hot Jupiter

Hoeijmakers, H. J. and Ehrenreich, D. and Kitzmann, D. and Allart, R. and Grimm, S. L. and Seidel, J. V. and Wyttenbach, A. and Pino, L. and Nielsen, L. D. and Fisher, C. and Rimmer, P. B. and Bourrier, V. and Cegla, H. M. and Lavie, B. and Lovis, C. and Patzer, A. B. C. and Stock, J. W. and Pepe, F. A. and Heng, Kevin (2019) A spectral survey of an ultra-hot Jupiter. Astronomy & Astrophysics, 627. A165. ISSN 0004-6361 DOI https://doi.org/10.1051/0004-6361/201935089

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Abstract

Context. KELT-9 b exemplifies a newly emerging class of short-period gaseous exoplanets that tend to orbit hot, early type stars – termed ultra-hot Jupiters. The severe stellar irradiation heats their atmospheres to temperatures of ~4000 K, similar to temperatures of photospheres of dwarf stars. Due to the absence of aerosols and complex molecular chemistry at such temperatures, these planets offer the potential of detailed chemical characterization through transit and day-side spectroscopy. Detailed studies of their chemical inventories may provide crucial constraints on their formation process(es) and evolution history. Aims. We aim to search the optical transmission spectrum of KELT-9 b for absorption lines by metals using the cross-correlation technique. Methods. We analysed two transit observations obtained with the HARPS-N spectrograph. We used an isothermal equilibrium chemistry model to predict the transmission spectrum for each of the neutral and singly ionized atoms with atomic numbers between three and 78. Of these, we identified the elements that are expected to have spectral lines in the visible wavelength range and used those as cross-correlation templates. Results. We detect (>5σ) absorption by Na I, Cr II, Sc II and Y II, and confirm previous detections of Mg I, Fe I, Fe II, and Ti II. In addition, we find evidence of Ca I, Cr I, Co I, and Sr II that will require further observations to verify. The detected absorption lines are significantly deeper than predicted by our model, suggesting that the material is transported to higher altitudes where the density is enhanced compared to a hydrostatic profile, and that the material is part of an extended or outflowing envelope. There appears to be no significant blue-shift of the absorption spectrum due to a net day-to-night side wind. In particular, the strong Fe II feature is shifted by 0.18 ± 0.27 km s−1, consistent with zero. Using the orbital velocity of the planet we derive revised masses and radii of the star and the planet: M* = 1.978 ± 0.023 M⊙, R* = 2.178 ± 0.011 R⊙, mp = 2.44 ± 0.70 MJ and Rp = 1.783 ± 0.009 RJ.

Item Type:	Article
Uncontrolled Keywords:	NILAREP; IA76
Subjects:	05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions:	05 - Petrology - Igneous, Metamorphic and Volcanic Studies 08 - Green Open Access
Journal or Publication Title:	Astronomy & Astrophysics
Volume:	627
Page Range:	A165
Identification Number:	https://doi.org/10.1051/0004-6361/201935089
Depositing User:	Sarah Humbert
Date Deposited:	10 Sep 2020 15:31
Last Modified:	10 Sep 2020 15:31
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4876

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