HII Regions in hydrostatic balance between gas pressure, radiation pressure and gravity

We study the solutions of a modified version of the isothermal Lane-Emden equation, which incorporates the effect of the (owtwards directed) radiation pressure resulting from photoionizations. These solutions are relevant for HII regions around a cluster with over ≈500 O stars, which can photoionize gas out to ≈ 200 √10 cm-3n0 pc (where no is the central gas density), where the effects of the self-gravity and the radiation pressure become important. We find that the solutions have a transition from a "gravity dominated" regime (in which the solutions converge at large radii to the non-singular, isothermal sphere solution) to a "radiation pressure dominated" regime (in which the density diverges at a finite radius) for central HII region densities above n crit = 100 cm-3. We argue that the high central density, radiation pressure dominated solutions will not occur in most astrophysically relevant situations, because of the absence of a possible confining environment with a high enough pressure.

Bibliographic Details

Main Authors:	Raga,A. G., Cantó,J., Mellema,G., Rodríguez-González,A., Esquivel,A.
Format:	Digital revista
Language:	English
Published:	Universidad Nacional Autónoma de México, Instituto de Astronomía 2015
Online Access:	http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0185-11012015000100003
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