Field Binary OB Stars: Multifaceted Diagnostics of Star Formation

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The most massive stars are of vital interest to understanding how stars are formed, and how they affect their host galaxy throughout their life, especially in their inevitable explosive end. We normally expect high-mass stars to form in clusters with lower-mass stars. However, about 25% of high-mass stars are found not in clusters but in apparent isolation (known as "field" stars). This project will quantify the properties of massive field stars and determine the relative contributions to the field of stars that were ejected from clusters vs those formed in isolation. These findings will set critical observational constraints on theories of star formation, which are broadly relevant to understanding our environment within our host galaxy, including planet formation. The project will exploit new instrumentation on the 6.5-m Magellan telescope. The project will involve both undergraduate and graduate students. They will incorporate their data sets into simple activities that can be utilized in undergraduate introductory astronomy courses. The PI is involved in several curricular innovation and outreach activities, including partnerships with the UM Special Collections Library, the historic UM Detroit Observatory, and UM Museum of Natural History. These promote broader science education among undergraduates and the public, and build synergistic ties on campus. The team will carry out a spectroscopic monitoring survey of the field OB star population in the Small Magellanic Cloud using the Michigan/Magellan Fiber System (M2FS), a multi-object, echelle spectrometer. Their goals are to (1) Identify field star binaries and obtain the distributions of orbital parameters, including period, mass ratio, and eccentricity. 2) Accurately determine the radial velocity distribution and constrain models of runaway ejection mechanisms. Constrain the relative contribution to the field of runaways vs stars that formed in situ. (3) Determine whether field stars that formed in situ are indeed slow rotators. (4) Identify any trends in Oe/Be star properties with binarity and v sin i while also providing high-quality monitoring of the Balmer emission.