Time Variation in G24.78+0.08 A1: Evidence for an Accreting Hypercompact H II Region?

Over a timescale of a few years, an observed change in the optically thick radio continuum flux can indicate whether an unresolved H II region around a newly formed massive star is changing in size. In this Letter we report on a study of archival VLA observations of the hypercompact H II region G24....

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Bibliographic Details
Published in:The Astrophysical journal 2008-02, Vol.674 (1), p.L33-L36
Main Authors: Galván-Madrid, Roberto, Rodríguez, Luis F, Ho, Paul T. P, Keto, Eric
Format: Article
Language:English
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Summary:Over a timescale of a few years, an observed change in the optically thick radio continuum flux can indicate whether an unresolved H II region around a newly formed massive star is changing in size. In this Letter we report on a study of archival VLA observations of the hypercompact H II region G24.78+0.08 A1 that shows a decrease of similar to 45% in the 6 cm flux over a 5 yr period. Such a decrease indicates a contraction of similar to 25% in the ionized radius and could be caused by an increase in the ionized gas density if the size of the H II region is determined by a balance between photoionization and recombination. This finding is not compatible with continuous expansion of the H II region after the end of accretion onto the ionizing star, but is consistent with the hypothesis of gravitational trapping and ionized accretion flows if the mass accretion rate is not steady.
ISSN:1538-4357
0004-637X
1538-4357
DOI:10.1086/528957