Spectral appearance of the planetary-surface accretion shock: Global spectra and hydrogen-line profiles and fluxes. (arXiv:2011.06608v2 [astro-ph.EP] UPDATED)

Spectral appearance of the planetary-surface accretion shock: Global spectra and hydrogen-line profiles and fluxes. (arXiv:2011.06608v2 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Aoyama_Y/0/1/0/all/0/1">Yuhiko Aoyama</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marleau_G/0/1/0/all/0/1">Gabriel-Dominique Marleau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mordasini_C/0/1/0/all/0/1">Christoph Mordasini</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ikoma_M/0/1/0/all/0/1">Masahiro Ikoma</a>

Hydrogen-line emission from an accretion shock has recently been observed at
planetary-mass objects. Previous work predicted the shock spectrum and
luminosity for a shock on the circumplanetary disc. We extend this to the
planet-surface shock. We calculate the global spectral energy distribution
(SED) of accreting planets by combining our model emission spectra with
photospheric SEDs, and predict the line-integrated flux for several hydrogen
lines, especially H alpha, but also H beta, Pa alpha, Pa beta, Pa gamma, Br
alpha, and Br gamma. We apply our non-equilibrium emission model to the surface
accretion shock for a wide range of accretion rates Mdot and masses M_p. Fits
to formation calculations provide radii and effective temperatures. Extinction
by the surrounding material is neglected, which is arguably often relevant. We
find that the line luminosity increases monotonically with Mdot and M_p,
depending mostly on Mdot and weakly on M_p for the relevant range of
parameters. The Lyman, Balmer, and Paschen continua can exceed the photosphere.
The H b line is fainter by 0 to 1 dex than H alpha, whereas other lines are
weaker (by 1 to 3 dex). Shocks on the planet or the CPD surface are
distinguishable at very high spectral resolution, but the planet surface shock
likely dominates if both are present. Applied to recent non-detections of H
alpha, our models imply looser constraints on the Mdot of putative
large-separation planets than from stellar extrapolations. These hydrogen-line
luminosity predictions are useful for interpreting (non-)detections of
accreting planets.

Hydrogen-line emission from an accretion shock has recently been observed at
planetary-mass objects. Previous work predicted the shock spectrum and
luminosity for a shock on the circumplanetary disc. We extend this to the
planet-surface shock. We calculate the global spectral energy distribution
(SED) of accreting planets by combining our model emission spectra with
photospheric SEDs, and predict the line-integrated flux for several hydrogen
lines, especially H alpha, but also H beta, Pa alpha, Pa beta, Pa gamma, Br
alpha, and Br gamma. We apply our non-equilibrium emission model to the surface
accretion shock for a wide range of accretion rates Mdot and masses M_p. Fits
to formation calculations provide radii and effective temperatures. Extinction
by the surrounding material is neglected, which is arguably often relevant. We
find that the line luminosity increases monotonically with Mdot and M_p,
depending mostly on Mdot and weakly on M_p for the relevant range of
parameters. The Lyman, Balmer, and Paschen continua can exceed the photosphere.
The H b line is fainter by 0 to 1 dex than H alpha, whereas other lines are
weaker (by 1 to 3 dex). Shocks on the planet or the CPD surface are
distinguishable at very high spectral resolution, but the planet surface shock
likely dominates if both are present. Applied to recent non-detections of H
alpha, our models imply looser constraints on the Mdot of putative
large-separation planets than from stellar extrapolations. These hydrogen-line
luminosity predictions are useful for interpreting (non-)detections of
accreting planets.

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