TY - JOUR
T1 - Detection of Fe I in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy
AU - Gibson, Neale P.
AU - Merritt, Stephanie
AU - Nugroho, Stevanus K.
AU - Cubillos, Patricio E.
AU - de Mooij, Ernst J. W.
AU - Mikal-Evans, Thomas
AU - Fossati, Luca
AU - Lothringer, Joshua
AU - Nikolov, Nikolay
AU - Sing, David K.
AU - Spake, Jessica J.
AU - Watson, Chris A.
AU - Wilson, Jamie
PY - 2020/4/1
Y1 - 2020/4/1
N2 - High-resolution Doppler-resolved spectroscopy has opened up a new window
into the atmospheres of both transiting and non-transiting exoplanets.
Here, we present VLT/UVES observations of a transit of WASP-121b, an
`ultra-hot' Jupiter previously found to exhibit a temperature inversion
and detections of multiple species at optical wavelengths. We present
initial results using the blue arm of UVES (≈3700-5000 Å),
recovering a clear signal of neutral Fe in the planet's atmosphere at
>8 σ, which could contribute to (or even fully explain) the
temperature inversion in the stratosphere. However, using standard
cross-correlation methods, it is difficult to extract physical
parameters such as temperature and abundances. Recent pioneering efforts
have sought to develop likelihood `mappings' that can be used to
directly fit models to high-resolution data sets. We introduce a new
framework that directly computes the likelihood of the model fit to the
data, and can be used to explore the posterior distribution of
parametrised model atmospheres via MCMC techniques. Our method also
recovers the physical extent of the atmosphere, as well as account for
time- and wavelength-dependent uncertainties. We measure a temperature
of 3710^{+490}_{-510} K, indicating a higher temperature in the upper
atmosphere when compared to low-resolution observations. We also show
that the Fe I signal is physically separated from the exospheric Fe II.
However, the temperature measurements are highly degenerate with aerosol
properties; detection of additional species, using more sophisticated
atmospheric models, or combining these methods with low-resolution
spectra should help break these degeneracies.
AB - High-resolution Doppler-resolved spectroscopy has opened up a new window
into the atmospheres of both transiting and non-transiting exoplanets.
Here, we present VLT/UVES observations of a transit of WASP-121b, an
`ultra-hot' Jupiter previously found to exhibit a temperature inversion
and detections of multiple species at optical wavelengths. We present
initial results using the blue arm of UVES (≈3700-5000 Å),
recovering a clear signal of neutral Fe in the planet's atmosphere at
>8 σ, which could contribute to (or even fully explain) the
temperature inversion in the stratosphere. However, using standard
cross-correlation methods, it is difficult to extract physical
parameters such as temperature and abundances. Recent pioneering efforts
have sought to develop likelihood `mappings' that can be used to
directly fit models to high-resolution data sets. We introduce a new
framework that directly computes the likelihood of the model fit to the
data, and can be used to explore the posterior distribution of
parametrised model atmospheres via MCMC techniques. Our method also
recovers the physical extent of the atmosphere, as well as account for
time- and wavelength-dependent uncertainties. We measure a temperature
of 3710^{+490}_{-510} K, indicating a higher temperature in the upper
atmosphere when compared to low-resolution observations. We also show
that the Fe I signal is physically separated from the exospheric Fe II.
However, the temperature measurements are highly degenerate with aerosol
properties; detection of additional species, using more sophisticated
atmospheric models, or combining these methods with low-resolution
spectra should help break these degeneracies.
KW - methods: data analysis
KW - techniques: spectroscopic
KW - stars: individual (WASP-121)
KW - planetary systems
U2 - 10.1093/mnras/staa228
DO - 10.1093/mnras/staa228
M3 - Article
VL - 493
SP - 2215
EP - 2228
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -