Ionizational Boundedness of HII Regions and Lifetimes of O Stars in HII Regions

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Session 43 -- HII Regions and Star Formation in Spirals
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[43.06] Ionizational Boundedness of HII Regions and Lifetimes of O Stars in HII Regions

Kanan Patel (McMaster University)

Observations suggesting O stars spend a considerable fraction of their lifetimes outside of bright HII regions have important implications for a number of issues in star formation and the interstellar medium: from understanding the evolution of the molecular interstellar medium in galaxies to calculations of galactic star formation rates from H$\alpha$ flux. In particular, calculations of global star formation rates rely heavily on the assumption that the galaxy is radiationally bounded, an assumption that is not certain to be valid if significant numbers of and/or an appreciable fractional lifetime of O stars are spent outside of HII regions or in the \lq \lq field". We have attempted to answer the question of whether a galaxy or individual regions of the galaxy are radiationally bounded as well as estimated the lifetime of a typical O star that is spent ionizing the surrounding interstellar medium by studying the OB associations and HII regions in two morphologically distinct Local Group galaxies, M33 (Sb) and NGC 6822 (dIrr). Our results are based on the analysis of data consisting of H$\alpha $ images (for the HII regions), UBV photometry (for the OB stars) as well as optical spectra (for accurate O star masses) combined with theoretical models for the ionizing flux due to OB stars.

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