Other
Scientific paper
May 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.3704j&link_type=abstract
American Astronomical Society, 182nd AAS Meeting, #37.04; Bulletin of the American Astronomical Society, Vol. 25, p.854
Other
Scientific paper
Newly formed stars produce sufficient Lyman continuum luminosity phi to significantly alter the structure and evolution of the accretion disk surrounding them. In the absence of a stellar wind, a nearly static, photoionized, 10(4) K, disk atmosphere, with a scale height that increases with r(3/2) , forms inside the gravitational radius r_g ~ 10(14) (M_* / M_&sun;) cm where M_* is the mass of the central star. This ionized atmosphere is maintained by both the direct radiation from the central star and the diffuse field produced in the disk atmosphere by the significant fraction of hydrogen recombinations directly to the ground state. Beyond r_g the material evaporated from the disk is capable of escaping from the system and produces an ionized disk wind. The mass-loss due to this disk wind peaks at r_g. The inclusion of a stellar wind into the basic picture reduces the height of the inner disk atmosphere and introduces a new scale radius r_w where the thermal pressure of the material evaporated from the disk balances the ram pressure in the wind. In this case the mass-loss due to the disk wind peaks at r_w and is enhanced over the no-wind case. The photoevaporation of disks around newly formed stars has significance to both the UCHII problem and the dispersal of solar-type nebulae. High mass stars are intrinsically hot and thus yield sufficient Lyman luminosity to create disk mass-loss rates of order 2 times 10(-5) phi_ {49}(1/2) M_&sun; yr(-1) , where phi_ {49} = phi /(10(49) Lyman continuum photons s(-1) ) even without a stellar wind. This wind which will last for ~ 10(5) yrs if the disk mass is M_d ~ 0.3 M_*, yields sizes, emission measures and ages consistent with observations of UCHIIs. On the other end of the stellar scale, many newly formed low-mass stars are known to have enhanced extreme ultraviolet luminosity suggested to be due to boundary layer accretion. Assuming that the sun had such an enhanced Lyman luminosity phi ~ 10(41) s(-1) , for ~ 3times 10(7) yrs it is possible to remove all of the gas beyond the orbit of Saturn, r_g for the sun, associated with the minimum solar nebula. This process also has implications for the formation of the giant planets.
Hollenbach David
Johnstone Dorothy
Shu Frank H.
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