High-resolution confirmation of an extended helium atmosphere around WASP-107b. (arXiv:1901.08073v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Allart_R/0/1/0/all/0/1">R. Allart</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bourrier_V/0/1/0/all/0/1">V. Bourrier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lovis_C/0/1/0/all/0/1">C. Lovis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ehrenreich_D/0/1/0/all/0/1">D. Ehrenreich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aceituno_J/0/1/0/all/0/1">J. Aceituno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guijarro_A/0/1/0/all/0/1">A. Guijarro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pepe_F/0/1/0/all/0/1">F. Pepe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sing_D/0/1/0/all/0/1">D. K. Sing</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Spake_J/0/1/0/all/0/1">J.J. Spake</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wyttenbach_A/0/1/0/all/0/1">A. Wyttenbach</a>
Probing the evaporation of exoplanet atmospheres is key to understanding the
formation and evolution of exoplanetary systems. The main tracer of evaporation
in the UV is the Lyman-alpha transition, which can reveal extended exospheres.
Recently, NIR metastable helium triplet (1.08 microns) revealed extended
thermospheres in several exoplanets, opening a new window into evaporation. We
aim at spectrally resolving the first helium absorption signature detected in
WASP-107b with HST/WFC3. We obtained one transit of WASP-107b with the
high-resolution spectrograph CARMENES. We detect an excess helium absorption
signature of 5.54+/-0.27 % in the planet rest frame during the transit. The
detection is in agreement with the previous detection done with WFC3. The
signature shows an excess absorption in the blue part of the lines suggesting
that HeI atoms are escaping from the atmosphere of WASP-107b. We interpret the
time-series absorption spectra using the 3D EVE code. Our observations can be
explained by combining an extended thermosphere filling half the Roche lobe and
a large exospheric tail sustained by an escape rate of metastable helium on the
order of 10^6 g/s. In this scenario, however, the upper atmosphere needs to be
subjected to a reduced photoionisation and radiation pressure from the star for
the model to match the observations. The helium feature is detected from space
and the ground. The ground-based high-resolution signal brings detailed
information about the spatial and dynamical structure of the upper atmosphere,
and simulations suggest that the HeI signature of WASP-107b probes both its
thermosphere and exosphere establishing this signature as a robust probe of
exoplanetary upper atmospheres. Surveys with NIR high-resolution spectrographs
(e.g. CARMENES, SPIRou or NIRPS) will deliver a statistical understanding of
exoplanet thermospheres and exospheres via the helium triplet.
Probing the evaporation of exoplanet atmospheres is key to understanding the
formation and evolution of exoplanetary systems. The main tracer of evaporation
in the UV is the Lyman-alpha transition, which can reveal extended exospheres.
Recently, NIR metastable helium triplet (1.08 microns) revealed extended
thermospheres in several exoplanets, opening a new window into evaporation. We
aim at spectrally resolving the first helium absorption signature detected in
WASP-107b with HST/WFC3. We obtained one transit of WASP-107b with the
high-resolution spectrograph CARMENES. We detect an excess helium absorption
signature of 5.54+/-0.27 % in the planet rest frame during the transit. The
detection is in agreement with the previous detection done with WFC3. The
signature shows an excess absorption in the blue part of the lines suggesting
that HeI atoms are escaping from the atmosphere of WASP-107b. We interpret the
time-series absorption spectra using the 3D EVE code. Our observations can be
explained by combining an extended thermosphere filling half the Roche lobe and
a large exospheric tail sustained by an escape rate of metastable helium on the
order of 10^6 g/s. In this scenario, however, the upper atmosphere needs to be
subjected to a reduced photoionisation and radiation pressure from the star for
the model to match the observations. The helium feature is detected from space
and the ground. The ground-based high-resolution signal brings detailed
information about the spatial and dynamical structure of the upper atmosphere,
and simulations suggest that the HeI signature of WASP-107b probes both its
thermosphere and exosphere establishing this signature as a robust probe of
exoplanetary upper atmospheres. Surveys with NIR high-resolution spectrographs
(e.g. CARMENES, SPIRou or NIRPS) will deliver a statistical understanding of
exoplanet thermospheres and exospheres via the helium triplet.
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