Journal Article

Time variability in simulated ultracompact and hypercompact H <span class="smallCaps">ii</span> regions

Roberto Galván-Madrid, Thomas Peters, Eric R. Keto, Mordecai-Mark Mac Low, Robi Banerjee and Ralf S. Klessen

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 2, pages 1033-1044
Published in print September 2011 | ISSN: 0035-8711
Published online September 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19101.x
Time variability in simulated ultracompact and hypercompact H ii regions

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Ultracompact and hypercompact H ii regions appear when a star with a mass larger than about 15 M starts to ionize its own environment. Recent observations of time variability in these objects are one of the pieces of evidence that suggest that at least some of them harbour stars that are still accreting from an infalling neutral accretion flow that becomes ionized in its innermost part. We present an analysis of the properties of the H ii regions formed in the three-dimensional radiation-hydrodynamic simulations presented by Peters et al. as a function of time. Flickering of the H ii regions is a natural outcome of this model. The radio-continuum fluxes of the simulated H ii regions as well as their flux and size variations are in agreement with the available observations. From the simulations, we estimate that a small but non-negligible fraction (∼10 per cent) of observed H ii regions should have detectable flux variations (larger than 10 per cent) on time-scales of ∼10 yr, with positive variations being more likely to happen than negative variations. A novel result of these simulations is that negative flux changes do happen, in contrast to the simple expectation of ever growing H ii regions. We also explore the temporal correlations between properties that are directly observed (flux and size) and other quantities like density and ionization rates.

Keywords: stars: formation; stars: massive; H ii regions

Journal Article.  7374 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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