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UBC Theses and Dissertations

A recalibration of the Hγ luminosity relation with high signal-to-noise Reticon spectra Millward, Christopher Gordon


40 Å/mm high signal-to-noise Reticon spectra of 71 O, B, and early A-type stars in 8 open clusters and OB associations along with 37 zero point stars (early A-type stars with reliable trigonometric parallaxes, eclipsing binaries, and visual binaries) have been used to recalibrate the W(Hγ)-absolute magnitude relation. The new empirical calibration for luminosity classes III-V is presented. The calibration has a mean probable dispersion of ±0.28 mag. No spectral type corrections are necessary. The new main sequence calibration averages 0.1 mag. fainter than the Balona & Crampton (1974) calibration. Close agreement with the Petrie (1965) calibration is found for spectral types BO-7. However, the present relation is up to 0.8 mag. brighter than Petrie's 0 star calibration and 0.7 mag. brighter than the A star calibration. The Blaauw (1963) calibration averages 0.4 mag. fainter than the present one over the spectral range 09-B2. The effect of evolution and high V sin i on the relation are investigated. The derived distance modulus of NGC 2244, 11.00±0.27 mag., is in close agreement with other determined values and an explanation as to why Petrie obtained an anomalously low value (9.7±0.1 mag.) is given. Rotational velocities are determined for most stars as well as the central depths of selected lines.

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