The metallicity and carbon-to-oxygen ratio of the ultrahot Jupiter WASP-76b from Gemini-S/IGRINS
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Published version
Author(s)
Type
Journal Article
Abstract
Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their
formation and evolution. Recently, high-resolution cross-correlation analysis has emerged as a method of precisely
constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b
observed between 1.4 and 2.4 μm with the high-resolution Immersion GRating INfrared Spectrometer on the
Gemini-S telescope. We detected the presence of H2O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and
3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three
species retrieved a volatile metallicity of ⎡⎣ ⎤⎦ = - +
-
+ 0.70 C O
H 0.93
1.27, consistent with the stellar value, and a supersolar
carbon-to-oxygen ratio of C/O = -
+ 0.80 0.11
0.07. We also ran a chemically self-consistent grid retrieval, which agreed
with the free retrieval within 1σ but favored a slightly more substellar metallicity and solar C/O ratio
(⎡⎣ ⎤⎦ = - +
-
+ 0.74 C O
H 0.17
0.23 and C/O = -
+ 0.59 0.14
0.13). A variety of formation pathways may explain the composition of
WASP-76b. Additionally, we found systemic (Vsys) and Keplerian (Kp) velocity offsets which were broadly
consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshifted
Vsys for H2O. Future observations to measure the phase-dependent velocity offsets and limb differences at high
resolution on WASP-76b will be necessary to understand the H2O velocity shift. Finally, we find that the
population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios.
More results from high-resolution observations or JWST will serve to further elucidate any population-level trends.
formation and evolution. Recently, high-resolution cross-correlation analysis has emerged as a method of precisely
constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b
observed between 1.4 and 2.4 μm with the high-resolution Immersion GRating INfrared Spectrometer on the
Gemini-S telescope. We detected the presence of H2O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and
3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three
species retrieved a volatile metallicity of ⎡⎣ ⎤⎦ = - +
-
+ 0.70 C O
H 0.93
1.27, consistent with the stellar value, and a supersolar
carbon-to-oxygen ratio of C/O = -
+ 0.80 0.11
0.07. We also ran a chemically self-consistent grid retrieval, which agreed
with the free retrieval within 1σ but favored a slightly more substellar metallicity and solar C/O ratio
(⎡⎣ ⎤⎦ = - +
-
+ 0.74 C O
H 0.17
0.23 and C/O = -
+ 0.59 0.14
0.13). A variety of formation pathways may explain the composition of
WASP-76b. Additionally, we found systemic (Vsys) and Keplerian (Kp) velocity offsets which were broadly
consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshifted
Vsys for H2O. Future observations to measure the phase-dependent velocity offsets and limb differences at high
resolution on WASP-76b will be necessary to understand the H2O velocity shift. Finally, we find that the
population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios.
More results from high-resolution observations or JWST will serve to further elucidate any population-level trends.
Date Issued
2024-07-01
Date Acceptance
2024-05-09
Citation
The Astronomical Journal, 2024, 168 (1)
ISSN
0004-6256
Publisher
IOP Publishing
Journal / Book Title
The Astronomical Journal
Volume
168
Issue
1
Copyright Statement
© 2024. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
License URL
Identifier
https://iopscience.iop.org/article/10.3847/1538-3881/ad4a5f
Subjects
ABSORPTION
Astronomy & Astrophysics
ATMOSPHERE
CROSS-CORRELATION SIGNAL
EXOPLANET FORMATION
HOT JUPITERS
Physical Sciences
PLANET FORMATION
RETRIEVAL
Science & Technology
SPECTROSCOPY
SUBSOLAR METALLICITY
SUN-LIKE STARS
Publication Status
Published
Article Number
14
Date Publish Online
2024-06-18