July 11-15, 2011
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Observations of Boron Abundances in Rapidly Rotating Early-B Stars

Charles Proffitt (STScI/CSC)

Daniel Lennon STScI/ESA

We discuss new HST/STIS observations of the B III resonance doublet in 26 early-B stars with projected rotational velocities between 50 and 220 km/s and compare the measured boron abundances with predictions of stellar evolution models that include rotationally induced mixing. Our results suggest that some stars show significantly less mixing than predicted by the models. When combined with previous results for stars with low projected rotational velocities (below 50 km/s) the distribution of [B/H] with V sin(i) bears a strong resemblance to that for nitrogen, the so-called Hunter diagram (Hunter et al 2008). Especially surprising is the apparent detection of substantial boron in two Be stars that are believed to be very rapid rotators viewed at small inclination angles for which the true rotational velocities are at 75 - 80% of the breakup limit.
(to be confirmed by the SOC)