Planetary atmospheric escape and disk formation around WDJ0914+1914

The spectrum of the white dwarf WD,J091405.30+191412.25 displays the absorption and double-peaked emission lines of the volatiles hydrogen, oxygen, and sulfur. This unique characteristic has been interpreted as evidence of this white dwarf accreting mass from a circumstellar disk that had formed from atmospheric material evaporating off a close-in Neptune-like or super-puff mass planet. Thus far, however, the orbital separation of the planet and its mass-loss rate have only been estimated using simple analytical approximations. In this work, we tested the outlined scenario by determining the mass-loss rate of the irradiated planet through hydrodynamical simulations and by studying in detail the formation and evolution of the disk, as well as the resulting mass accretion rates onto the white dwarf. We used 3D radiative-hydrodynamic simulations of a pure hydrogen atmosphere under the influence of extreme UV (XUV) radiation from the white dwarf to determine the mass loss rates for Neptune-like and super-puff planets at different orbital separations. The escaping material was assumed to feed a circumstellar disk, whose viscous evolution was then modeled using 1D radial disk calculations to determine the resulting accretion rates in each case. For the explored cases, the planetary mass loss rates span a narrow range of ∼ (1.8 -4.0) g s 12 -1 . This material forms a disk around the star that stabilizes in łesssim 10^5 years, as a result of the balance between continuous mass injection from the evaporating planet and viscous mass loss onto the central star. The accretion rates at this stage are on the order of a few times 10^ 9 –10^10 g s -1 , in agreement with previous observational estimates. Our simulations suggest that the disk extends beyond the planet position, in contrast to the size derived from observations. We conclude that a planet with a gaseous envelope at a distance of sim15 R_⊙ will indeed suffer from photoevaporation and that the material escaping the planet will form a gaseous disk around WD,J0914+1914, most likely extending beyond the location of the planet. Our results confirm the possibility that the observed spectral features of WD,J0914+1914 can be explained by an evaporating gas-rich planet.