Issue |
A&A
Volume 439, Number 2, August IV 2005
|
|
---|---|---|
Page(s) | L23 - L26 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:200500150 | |
Published online | 29 July 2005 |
Letter to the Editor
The diffuse nature of Strömgren spheres
Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: ritzerveld@strw.leidenuniv.nl
Received:
8
June
2005
Accepted:
3
July
2005
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
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.