PHOTOEVAPORATION OF DISKS AROUND MASSIVE STARS AND APPLICATION TO ULTRACOMPACT H II REGIONS

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

450 Scopus Citations
View graph of relations

Author(s)

  • David HOLLENBACH
  • Doug JOHNSTONE
  • Susana LIZANO
  • Frank SHU

Detail(s)

Original languageEnglish
Pages (from-to)654-669
Journal / PublicationAstrophysical Journal
Volume428
Issue number2
Publication statusPublished - 20 Jun 1994
Externally publishedYes

Abstract

Young massive stars produce sufficient Lyman continuum photon luminosity Φi, to significantly affect the structure and evolution of the accretion disks surrounding them. A nearly static, ionized, isothermal 104 K atmosphere forms above the neutral disk for disk radii r < rg = 1015M1 cm, where M* = 10 M M1 is the stellar mass. For rrg the diffuse field created by hydrogen recombinations to the ground state in the photoionized gas above the disk produces a steady evaporation at the surface of the disk, and this H II gas flows freely out to the ISM (the "disk wind"). The detailed structure depends on the mass-loss rate w of the fast, ≳ 1000 km s-1, stellar wind from the massive star. A critical mass-loss rate cr is defined such that the ram pressure of the stellar wind equals the thermal pressure of the H II atmosphere at rg. In the weak stellar wind solution, w < cr, the diffuse photons from the atmosphere above rg produce a photoevaporative mass-loss rate from the disk at rrg of order 1 × 10-5Φ491/2M11/2 M yr-1, where Φi, = 1049Φ49 s-1. The resulting slow (10-50 km s-1) ionized outflow, which persists for ≳ 105 yr for disk masses Md ∼ 0.3M*, may explain the observational characteristics of unresolved, ultracompact H II regions. 
In the strong stellar wind solution, w, > cr, the ram pressure of the stellar wind blows down the atmosphere for r < rg and allows the stellar photons to penetrate to greater radii and smaller heights. A slow, ionized outflow produced mainly by diffuse photons is again created for r>rg; however, it is now dominated by the flow at rw (>rg), the radius at which the stellar wind ram pressure equals the thermal pressure in the evaporating flow. The mass-loss rate from the disk is of order 6 × 10-5 w-6 νw8Φ49-1/2 M⊙ yr-1, where w-6w/10-6 M⊙ yr-1 and νw8 = νw/1000 km s-1 is the stellar wind velocity. The resulting outflow, which also persists for ≳ 105 yr may explain many of the more extended (r ≳ 1016 cm) ultracompact H II regions. Both the weak-wind and the strong-wind models depend entirely on stellar parameters (Φi,M*w) and are independent of disk parameters as long as an extended (rrg), neutral disk exists. We compare both weak-wind and strong-wind model results to the observed radio free-free spectra and luminosities of ultracompact H II regions and to the interesting source MWC 349.

Research Area(s)

  • accretion, accretion disks, H II regions, radiative transfer, stars: mass loss

Citation Format(s)

PHOTOEVAPORATION OF DISKS AROUND MASSIVE STARS AND APPLICATION TO ULTRACOMPACT H II REGIONS. / HOLLENBACH, David; JOHNSTONE, Doug; LIZANO, Susana et al.

In: Astrophysical Journal, Vol. 428, No. 2, 20.06.1994, p. 654-669.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review