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Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) : IV. A spectral inventory of atoms and molecules in the high-resolution transmission spectrum of WASP-121 b

Hoeijmakers, H. J. LU ; Seidel, J. V. ; Pino, L. ; Kitzmann, D. ; Sindel, J. P. ; Ehrenreich, D. ; Oza, A. V. ; Bourrier, V. ; Allart, R. and Gebek, A. , et al. (2020) In Astronomy and Astrophysics 641.
Abstract

Context. WASP-121 b is a hot Jupiter that was recently found to possess rich emission (day side) and transmission (limb) spectra, suggestive of the presence of a multitude of chemical species in the atmosphere. Aims. We survey the transmission spectrum of WASP-121 b for line-absorption by metals and molecules at high spectral resolution and elaborate on existing interpretations of the optical transmission spectrum observed with the Hubble Space Telescope (HST). Methods. We applied the cross-correlation technique and direct differential spectroscopy to search for sodium and other neutral and ionised atoms, TiO, VO, and SH in high-resolution transit spectra obtained with the HARPS spectrograph. We injected models assuming chemical and... (More)

Context. WASP-121 b is a hot Jupiter that was recently found to possess rich emission (day side) and transmission (limb) spectra, suggestive of the presence of a multitude of chemical species in the atmosphere. Aims. We survey the transmission spectrum of WASP-121 b for line-absorption by metals and molecules at high spectral resolution and elaborate on existing interpretations of the optical transmission spectrum observed with the Hubble Space Telescope (HST). Methods. We applied the cross-correlation technique and direct differential spectroscopy to search for sodium and other neutral and ionised atoms, TiO, VO, and SH in high-resolution transit spectra obtained with the HARPS spectrograph. We injected models assuming chemical and hydrostatic equilibrium with a varying temperature and composition to enable model comparison, and employed two bootstrap methods to test the robustness of our detections. Results. We detect neutral Mg, Na, Ca, Cr, Fe, Ni, and V, which we predict exists in equilibrium with a significant quantity of VO, supporting earlier observations by HST/WFC3. Non-detections of Ti and TiO support the hypothesis that Ti is depleted via a cold-trap mechanism, as has been proposed in the literature. Atomic line depths are under-predicted by hydrostatic models by a factor of 1.5 to 8, confirming recent findings that the atmosphere is extended. We predict the existence of significant concentrations of gas-phase TiO2, VO2, and TiS, which could be important absorbers at optical and near-IR wavelengths in hot Jupiter atmospheres. However, accurate line-list data are not currently available for them. We find no evidence for absorption by SH and find that inflated atomic lines can plausibly explain the slope of the transmission spectrum observed in the near-ultraviolet with HST. The Na I D lines are significantly broadened (FWHM ∼50 to 70 km s-1) and show a difference in their respective depths of ~15 scale heights, which is not expected from isothermal hydrostatic theory. If this asymmetry is of astrophysical origin, it may indicate that Na I forms an optically thin envelope, reminiscent of the Na I cloud surrounding Jupiter, or that it is hydrodynamically outflowing.

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Contribution to journal
publication status
published
subject
keywords
Planets and satellites: atmospheres, Planets and satellites: gaseous planets, Techniques: spectroscopic
in
Astronomy and Astrophysics
volume
641
article number
A123
publisher
EDP Sciences
external identifiers
  • scopus:85092008820
ISSN
0004-6361
DOI
10.1051/0004-6361/202038365
language
English
LU publication?
yes
id
08a45df1-f33d-4dd2-841b-346653032d08
date added to LUP
2020-11-03 11:36:16
date last changed
2024-04-17 18:18:50
@article{08a45df1-f33d-4dd2-841b-346653032d08,
  abstract     = {{<p>Context. WASP-121 b is a hot Jupiter that was recently found to possess rich emission (day side) and transmission (limb) spectra, suggestive of the presence of a multitude of chemical species in the atmosphere. Aims. We survey the transmission spectrum of WASP-121 b for line-absorption by metals and molecules at high spectral resolution and elaborate on existing interpretations of the optical transmission spectrum observed with the Hubble Space Telescope (HST). Methods. We applied the cross-correlation technique and direct differential spectroscopy to search for sodium and other neutral and ionised atoms, TiO, VO, and SH in high-resolution transit spectra obtained with the HARPS spectrograph. We injected models assuming chemical and hydrostatic equilibrium with a varying temperature and composition to enable model comparison, and employed two bootstrap methods to test the robustness of our detections. Results. We detect neutral Mg, Na, Ca, Cr, Fe, Ni, and V, which we predict exists in equilibrium with a significant quantity of VO, supporting earlier observations by HST/WFC3. Non-detections of Ti and TiO support the hypothesis that Ti is depleted via a cold-trap mechanism, as has been proposed in the literature. Atomic line depths are under-predicted by hydrostatic models by a factor of 1.5 to 8, confirming recent findings that the atmosphere is extended. We predict the existence of significant concentrations of gas-phase TiO2, VO2, and TiS, which could be important absorbers at optical and near-IR wavelengths in hot Jupiter atmospheres. However, accurate line-list data are not currently available for them. We find no evidence for absorption by SH and find that inflated atomic lines can plausibly explain the slope of the transmission spectrum observed in the near-ultraviolet with HST. The Na I D lines are significantly broadened (FWHM ∼50 to 70 km s-1) and show a difference in their respective depths of ~15 scale heights, which is not expected from isothermal hydrostatic theory. If this asymmetry is of astrophysical origin, it may indicate that Na I forms an optically thin envelope, reminiscent of the Na I cloud surrounding Jupiter, or that it is hydrodynamically outflowing.</p>}},
  author       = {{Hoeijmakers, H. J. and Seidel, J. V. and Pino, L. and Kitzmann, D. and Sindel, J. P. and Ehrenreich, D. and Oza, A. V. and Bourrier, V. and Allart, R. and Gebek, A. and Lovis, C. and Yurchenko, S. N. and Astudillo-Defru, N. and Bayliss, D. and Cegla, H. and Lavie, B. and Lendl, M. and Melo, C. and Murgas, F. and Nascimbeni, V. and Pepe, F. and Ségransan, D. and Udry, S. and Wyttenbach, A. and Heng, K.}},
  issn         = {{0004-6361}},
  keywords     = {{Planets and satellites: atmospheres; Planets and satellites: gaseous planets; Techniques: spectroscopic}},
  language     = {{eng}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) : IV. A spectral inventory of atoms and molecules in the high-resolution transmission spectrum of WASP-121 b}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202038365}},
  doi          = {{10.1051/0004-6361/202038365}},
  volume       = {{641}},
  year         = {{2020}},
}