SUPERBUBBLES Theodore R. Gull Laboratory for Astronomy and Solar Physics NASA/Goddard Space Flight Center Frederick C. Bruhweiler Computer Sciences Corporation Minas Kafatos George Mason University Sabatino Sofia Laboratory for Astronomy and Solar Physics NASA/Goddard Space Flight Center ABSTRACT Individual massive stars with W_l__ <-6 have huge stellar winds that create interstellar bubbles. Stars masses greater than 8M O (4M8?) are considered supernova progenitors. These massive stars are numerous in OB associations where few supernova remnants are detected. Model calculations describing the evolution of an association show: i) that la[ge, hot cavities are formed by pushing the ambient gas into neutral shells; 2) that the shell radii change with galactocentric radius, 3) that only thirty percent of the interstellar medium is in the form of supercavities and 4) that a consequence is that only a small fraction of supernovae form supernova remnants. These results have strong bearing on interpretation of interstellar studies being done by IUE and by HEAO-B. INTRODUCTION The previous talk (ref. i) described the observable interstellar bubble being driven by an 0 star, HD148937. Other talks (ref. 2,3) discussed IUE observations of supernova remnants which presumably had massive stars as progenitors. We know that O and B stars form as associations throughout the galactic plane. If individual stars can dramatically alter the inter- stellar medium, we are led to wonder what an OB association would do. The model calculations discussed here described the bulk properties of how the surrounding interstellar medium is changed as an OB association evolved. The resultant structure of the interstellar medium,an be studied by IUE and HEAO-B and indeed such studies are underway at present. THE BASIS FOR CONSIDERING SUPERBUBBLES Our interest in the structure of the interstellar medium has been whetted by a recent emission line survey of the Milky Way (ref. 4). It presents a photographic record of nearby dust clouds and ionized hydrogen regions with a rough excitation classification being possible by singly- ionized sulfur imagery and by doubly-ionized oxygen imagery. Several new supernova remnants (ref. 5, 6) were discovered from this data. Many inter- stellar bubbles in the form of bowshocks (ref. 7), arcs and shells (ref. 8 and 9) were newly detected. However, ionization structure around OB 679 https://ntrs.nasa.gov/search.jsp?R=19810017433 2020-03-21T12:06:00+00:00Z