Massive Stars as Cosmic Engines

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My research is directed to the determination of the properties of massive stars. Such stars have initial masses above 8 times solar. They eventually fuse elements in successively smaller shells in their cores right through to iron, leading to sudden collapse accompanied by explosion of matter outside the core in the form of a supernova (SN). Although rare, massive stars deliver back to their surroundings far more than their share of radiation and enriched nuclear material for most of their relatively short lifetimes, both from their strong winds and their final SN. This makes them major contributors to the ecology and energetics of the Universe. In this proposal, I will concentrate on the following specific GOALS : *** (1) Search for and quantify pulsation and rotation properties in luminous massive stars using the recently launched international array of nanosatellites, BRITE-Constellation - a Canadian-driven first in astronomy. Despite their small 30 mm telescopes, all of the five functioning car-battery size BRITE nanosats can obtain precision dual-band photometric time-series (1 mmag rms) of all stars in the sky down to 4-6th magnitude on an hourly basis for up to 6 months. First results from BRITE are already beginning to revolutionize what we know about the properties of massive stars.*** (2) Recent evidence has revealed that virtually all massive stars form in binaries. In the closer systems, gravitational tidal effects lead to Roche-lobe overflow (RLOF) from one star to the other, actively seen in only a handful of systems. I will carry out a more systematic test of RLOF by quantifying the rotation speeds of O companions in WR+O binaries: the closest systems should have spun-up O-stars from the RLOF process. This effective test will have repercussions in all of stellar astrophysics.*** (3) Resolve an outstanding fundamental puzzle: dust formation in the hostile radiation fields of hot-star winds. This will be approached in various ways, including zeroing in on the WC9d star WR112 with ALMA in the sub-mm range, and following the Rosetta stone colliding-wind and episodic dust-forming binary WR140 using the CHARA interferometer in the NIR K-band.*** (4) Continue to search for and quantify the fundamental properties of the most massive stars in the local Universe. This must be done using Kepler's laws in binaries as the only viable method with minimum assumptions. Masses over 100 solar have already been found for the first time in some cases, with more to be examined. Such information is needed to constrain star formation both locally and in the early Universe, where massive stars are believed to dominate.*** (5) Continue large-scale surveys to locate large numbers of cWR stars (direct descendants of massive H-burning main-sequence stars above 25 solar masses) as immediate progenitors of type Ib/c SNe. Such a direct link has never been made before, yet is required to make progress in understanding the most exotic stellar deaths.**