SEGUE-2 Limits on Metal-Rich Old-Population Hypervelocity Stars In the
  Galactic Halo
  We present new limits on the ejection of metal-rich old-population
hypervelocity stars from the Galactic center (GC) as probed by the SEGUE-2
survey. Our limits are a factor of 3-10 more stringent than previously
reported, depending on stellar type. Compared to the known population of B-star
ejectees, there can be no more than 30 times more metal-rich old-population F/G
stars ejected from the GC. Because B stars comprise a tiny fraction of a normal
stellar population, this places significant limits on a combination of the GC
mass function and the ejection mechanism for hypervelocity stars. In the
presence of a normal GC mass function, our results require an ejection
mechanism that is about 5.5 times more efficient at ejecting B-stars compared
to low-mass F/G stars.
