PLASKETTS STAR (HD-47129) - STILL MORE CURIOUS

The properties of the components of Plaskett's Star (HD 47129) have be en the subject of a continuing controversy for over seven decades. In a recent paper, Bagnuolo, Gies, & Wiggs analyzed a set of 17 UV spectr a of this object from IUE archives. A tomography algorithm was used to produce the individual spectra of the two components. The physical pr operties of the stars were estimated including the mass ratio (q = 1.1 8), the UV intensity ratio (r(UV) = 0.53), the interpolated MK types ( O7.3 I and O6.2 I, respectively), and the rotational velocities (v sin i approximate to 88 km s(-1) and 310 km s(-1), respectively). These p roperties of the primary and secondary of HD 47129 were questioned by Underhill based on visual spectra. We now present reconstructions of t he component spectra in four visual wavebands with data obtained using the CHARA 1 m Multiple Telescope Telescope (MTT). Data were taken at nine epochs well distributed in orbital phase about the 14.4 day perio d and separated with a tomography algorithm. An analysis produces resu lts consistent with those of Bagnuolo, Gies, & Wiggs. Specifically, we find that the secondary is roughly 1-1.5 subclasses earlier than the primary (O7 vs. O8.5 from He II lambda 4542:He I lambda 4471 ratio. Th e intensity ratio in the visual is about 0.5 (primary brighter). The m ass ratio appears to be similar to that estimated from the UV lines (q = 1.18). The primary lines are sharp and are compatible with a relati vely low rotational velocity from the primary: v sin i = 105 km s(-1). The secondary lines appear to be rotationally broadened, and we estim ate that v sin i = 370 km s(-1) for this star. We suggest that the mai n reason for the discrepancy between our interpretation and Underhill' s is abundance differences in the stars. Specifically, the primary app ears to be depleted in C and O and enriched in N. We briefly discuss t he implications for the evolutionary history of this interesting binar y.