Search for gas from the disintegrating rocky exoplanet K2-22b. (arXiv:1906.08795v1 [astro-ph.EP])

Search for gas from the disintegrating rocky exoplanet K2-22b. (arXiv:1906.08795v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ridden_Harper_A/0/1/0/all/0/1">A. R. Ridden-Harper</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Snellen_I/0/1/0/all/0/1">I. A. G. Snellen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Keller_C/0/1/0/all/0/1">C. U. Keller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Molliere_P/0/1/0/all/0/1">P. Molli&#xe8;re</a>

[Abridged] Aims. We searched for circumplanetary sodium and ionized calcium
gas around the disintegrating rocky exoplanet K2-22 b to constrain its gas-loss
and sublimation processes.

Methods. We observed four transits of K2-22 b with X-shooter on ESO’s Very
Large Telescope to obtain time-series of intermediate-resolution (R $sim$
11400) spectra. Our analysis focused on the two sodium D lines (588.995 nm and
589.592 nm) and the Ca$^{+}$ triplet (849.802 nm, 854.209 nm and 866.214 nm).
Planet-related absorption is searched for in the velocity rest frame of the
planet, which changes from $pm$66 kms$^{-1}$ during the transit.

Results. Since K2-22 b exhibits highly variable transit depths, we analyzed
the individual nights and their average. By injecting signals we reached
5$sigma$ upper-limits on the individual nights that ranged from 11% – 13% and
1.7% – 2.0% for the tail’s sodium and ionized calcium absorption, respectively.
Night 1 was contaminated by its companion star so we considered weighted
averages with and without Night 1 and quote conservative 5$sigma$ limits
without Night 1 of 9% and 1.4%, respectively. Assuming their mass fractions to
be similar to those in the Earth’s crust, these limits correspond to scenarios
in which 0.04% and 35% of the transiting dust is sublimated and observed as
absorbing gas. However, this assumes the gas to be co-moving with the planet.
We show that for the high irradiation environment of K2-22 b, sodium and
ionized calcium could be quickly accelerated to 100s of km s$^{-1}$ due to
radiation pressure and entrainment by the stellar wind, making them much more
difficult to detect. No evidence for such possibly broad and blue-shifted
signals are seen in our data.

Conclusions. Future observations aimed at observing circumplanetary gas
should take into account the possible broad and blue-shifted velocity field of
atomic and ionized species.

[Abridged] Aims. We searched for circumplanetary sodium and ionized calcium
gas around the disintegrating rocky exoplanet K2-22 b to constrain its gas-loss
and sublimation processes.

Methods. We observed four transits of K2-22 b with X-shooter on ESO’s Very
Large Telescope to obtain time-series of intermediate-resolution (R $sim$
11400) spectra. Our analysis focused on the two sodium D lines (588.995 nm and
589.592 nm) and the Ca$^{+}$ triplet (849.802 nm, 854.209 nm and 866.214 nm).
Planet-related absorption is searched for in the velocity rest frame of the
planet, which changes from $pm$66 kms$^{-1}$ during the transit.

Results. Since K2-22 b exhibits highly variable transit depths, we analyzed
the individual nights and their average. By injecting signals we reached
5$sigma$ upper-limits on the individual nights that ranged from 11% – 13% and
1.7% – 2.0% for the tail’s sodium and ionized calcium absorption, respectively.
Night 1 was contaminated by its companion star so we considered weighted
averages with and without Night 1 and quote conservative 5$sigma$ limits
without Night 1 of 9% and 1.4%, respectively. Assuming their mass fractions to
be similar to those in the Earth’s crust, these limits correspond to scenarios
in which 0.04% and 35% of the transiting dust is sublimated and observed as
absorbing gas. However, this assumes the gas to be co-moving with the planet.
We show that for the high irradiation environment of K2-22 b, sodium and
ionized calcium could be quickly accelerated to 100s of km s$^{-1}$ due to
radiation pressure and entrainment by the stellar wind, making them much more
difficult to detect. No evidence for such possibly broad and blue-shifted
signals are seen in our data.

Conclusions. Future observations aimed at observing circumplanetary gas
should take into account the possible broad and blue-shifted velocity field of
atomic and ionized species.

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