No escaping helium from 55 Cnc e. (arXiv:2012.02198v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_M/0/1/0/all/0/1">Michael Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Knutson_H/0/1/0/all/0/1">Heather A. Knutson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_L/0/1/0/all/0/1">Lile Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dai_F/0/1/0/all/0/1">Fei Dai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oklopcic_A/0/1/0/all/0/1">Antonija Oklopcic</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hu_R/0/1/0/all/0/1">Renyu Hu</a>
We search for escaping helium from the hot super Earth 55 Cnc e by taking
high-resolution spectra of the 1083 nm line during two transits using
Keck/NIRSPEC. We detect no helium absorption down to a 90% upper limit of 250
ppm in excess absorption or 0.27 milli-Angstrom in equivalent width. This
corresponds to a mass loss rate of less than $sim10^9$ g/s, although the
precise constraint is heavily dependent on model assumptions. This rate is
notably below that predicted by both the 1D hydrodynamical simulations of Salz
et al 2016 and our own 2.5D models, even for implausibly thin hydrogen/helium
atmospheres with surface pressures of less than 100 microbar. We consider both
hydrogen- and helium-dominated atmospheric compositions, and find similar
bounds on the mass loss rate in both scenarios. Together with the non-detection
of Lyman $alpha$ absorption by Ehrenreich et al 2012, our helium non-detection
indicates that 55 Cnc e either never accreted a primordial atmosphere in the
first place, or lost its primordial atmosphere shortly after the dissipation of
the gas disk.
We search for escaping helium from the hot super Earth 55 Cnc e by taking
high-resolution spectra of the 1083 nm line during two transits using
Keck/NIRSPEC. We detect no helium absorption down to a 90% upper limit of 250
ppm in excess absorption or 0.27 milli-Angstrom in equivalent width. This
corresponds to a mass loss rate of less than $sim10^9$ g/s, although the
precise constraint is heavily dependent on model assumptions. This rate is
notably below that predicted by both the 1D hydrodynamical simulations of Salz
et al 2016 and our own 2.5D models, even for implausibly thin hydrogen/helium
atmospheres with surface pressures of less than 100 microbar. We consider both
hydrogen- and helium-dominated atmospheric compositions, and find similar
bounds on the mass loss rate in both scenarios. Together with the non-detection
of Lyman $alpha$ absorption by Ehrenreich et al 2012, our helium non-detection
indicates that 55 Cnc e either never accreted a primordial atmosphere in the
first place, or lost its primordial atmosphere shortly after the dissipation of
the gas disk.
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