Photoevaporation from Inner Protoplanetary Disks Confronted with Observations

Kavli Affiliate: Lile Wang

| First 5 Authors: Yiren Lin, Lile Wang, Min Fang, Ahmad Nemer, Jeremy Goodman

| Summary:

The decades-long explorations on the dispersal of protoplanetary disks
involve many debates about photoevaporation versus magnetized wind launching
mechanisms. This letter argues that the observed winds originating from the
inner disk ($Rlesssim 0.3$ AU) cannot be explained by the photoevaporative
mechanism. Energy conservation requires the presumed photoevaporative winds to
be heated to $gtrsim 10^5$ K when launched from inner disks. However, due to
efficient thermal accommodation with dust grains and cooling processes at high
densities, X-ray irradiation at energies above 1 keV cannot efficiently launch
winds in the first place because of its high penetration. Some studies claiming
X-ray wind launching have oversimplified the thermochemical couplings.
Furthermore, heating the gas to escape velocity will over-ionize it,
suppressing the species responsible for observed forbidden lines (e.g., [OI] 6300 $r{A}$ ). Confirmed by semi-analytic integrations of thermochemical fluid
structures, such high ionizations contradict the observed emission of neutral
and singly-ionized atoms from the winds originating from the inner disks.

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