TY - JOUR
T1 - A Search for Water in a Super-Earth Atmosphere: High-resolution Optical Spectroscopy of 55Cancri e
AU - Esteves, Lisa J.
AU - de Mooij, Ernst J. W.
AU - Jayawardhana, Ray
AU - Watson, Chris
AU - de Kok, Remco
PY - 2017/5/31
Y1 - 2017/5/31
N2 - We present the analysis of high-resolution optical spectra of four
transits of 55Cnc e, a low-density super-Earth that orbits a nearby
Sun-like star in under 18 hr. The inferred bulk density of the planet
implies a substantial envelope, which, according to mass–radius
relationships, could be either a low-mass extended or a high-mass
compact atmosphere. Our observations investigate the latter scenario,
with water as the dominant species. We take advantage of the Doppler
cross-correlation technique, high-spectral resolution, and the large
wavelength coverage of our observations to search for the signature of
thousands of optical water absorption lines. Using our observations with
HDS on the Subaru telescope and ESPaDOnS on the
Canada–France–Hawaii Telescope, we are able to place a
3σ lower limit of 10 g mol‑1 on the
mean-molecular weight of 55Cnc e’s water-rich (volume mixing ratio
>10%), optically thin atmosphere, which corresponds to an atmospheric
scale-height of ∼80 km. Our study marks the first high-spectral
resolution search for water in a super-Earth atmosphere, and
demonstrates that it is possible to recover known water-vapor absorption
signals in a nearby super-Earth atmosphere, using high-resolution
transit spectroscopy with current ground-based instruments.
AB - We present the analysis of high-resolution optical spectra of four
transits of 55Cnc e, a low-density super-Earth that orbits a nearby
Sun-like star in under 18 hr. The inferred bulk density of the planet
implies a substantial envelope, which, according to mass–radius
relationships, could be either a low-mass extended or a high-mass
compact atmosphere. Our observations investigate the latter scenario,
with water as the dominant species. We take advantage of the Doppler
cross-correlation technique, high-spectral resolution, and the large
wavelength coverage of our observations to search for the signature of
thousands of optical water absorption lines. Using our observations with
HDS on the Subaru telescope and ESPaDOnS on the
Canada–France–Hawaii Telescope, we are able to place a
3σ lower limit of 10 g mol‑1 on the
mean-molecular weight of 55Cnc e’s water-rich (volume mixing ratio
>10%), optically thin atmosphere, which corresponds to an atmospheric
scale-height of ∼80 km. Our study marks the first high-spectral
resolution search for water in a super-Earth atmosphere, and
demonstrates that it is possible to recover known water-vapor absorption
signals in a nearby super-Earth atmosphere, using high-resolution
transit spectroscopy with current ground-based instruments.
KW - planets and satellites: atmospheres
KW - planets and satellites: terrestrial planets
U2 - 10.3847/1538-3881/aa7133
DO - 10.3847/1538-3881/aa7133
M3 - Article
SN - 0004-6256
VL - 153
SP - 268
JO - Astronomical Journal
JF - Astronomical Journal
IS - 6
ER -