EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 439/2 Article
Free access article

Issue A&A
Volume 439, Number 2, August IV 2005
Page(s) L23 - L26
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500150



A&A 439, L23-L26 (2005)
DOI: 10.1051/0004-6361:200500150

Letter

The diffuse nature of Strömgren spheres

J. Ritzerveld

Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
    e-mail: ritzerveld@strw.leidenuniv.nl

(Received 8 June 2005 / Accepted 3 July 2005)

Abstract
In this Letter, we argue that the standard analytical derivations of properties of HII regions, such as the speed, shape and asymptotic position of ionisation fronts require a more precise treatment. These derivations use the on the spot approximation, which in effect ignores the diffuse component of the radiation field. We show that, in fact, HII regions are diffusion dominated. This has as a result that the morphology of inhomogeneous HII regions will be drastically different, because shadowing effects have a less profound impact on the apparent shape. Moreover, it will have influence on the propagation speed of ionisation fronts. We quantify our claims by analytically deriving the internal radiation structure of HII regions, taking diffusion fully into account for several different cosmologically relevant density distributions.


Key words: diffuse radiation -- HII regions -- radiative transfer




© ESO 2005


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.