Abstract
With a temperature akin to an M dwarf, WASP-33b is among the hottest
Jupiters known, making it an ideal target for high-resolution optical
spectroscopy. By analyzing both transmission and emission spectra, we
aim to substantiate previous reports of atmospheric TiO and a thermal
inversion within the planet's atmosphere. We observed two transits and
six arcs of the phase curve with the Echelle SpectroPolarimetric Device
for the Observation of Stars (ESPaDOnS) on the Canada-France-Hawaii
Telescope and High Resolution Echelle Spectrometer (HIRES) on the Keck
telescope, which provide high spectral resolution and ample wavelength
coverage. We employ the Doppler cross-correlation technique to search
for the molecular signatures of TiO and H2O in these spectra,
using models based on the TiO line list of Plez. Though we cannot
exclude line-list-dependent effects, our data do not corroborate
previous indications of a thermal inversion. Instead we place a 3σ
upper limit of 10-9 on the volume mixing ratio of TiO for the
T-P profile we consider. While we are unable to constrain the volume
mixing ratio of water, our strongest constraint on TiO comes from
dayside emission spectra. This apparent absence of a stratosphere sits
in stark contrast to previous observations of WASP-33b as well as
theoretical predictions for the atmospheres of highly irradiated
planets. The discrepancy could be due to variances between line lists,
and we stress that detection limits are only as good as the line list
employed, and are only valid for the specific T-P profile considered due
to the strong degeneracy between lapse rate ( ${dT}/d\mathrm{log}P$ )
and molecular abundance.
Original language | English |
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Pages (from-to) | 93 |
Journal | Astronomical Journal |
Volume | 160 |
Issue number | 2 |
DOIs | |
Publication status | Published - 01 Aug 2020 |
Externally published | Yes |
Keywords
- Astronomy data analysis
- Exoplanet atmospheres
- High resolution spectroscopy
- Hot Jupiters
- Transmission spectroscopy
- Exoplanet atmospheric composition
- Exoplanets
- Extrasolar gas giants
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