The Distance scale and the rotation curve of young supergiants and open clusters

Abstract

Abstract The Hipparcos trigonometric parallaxes of 188 blue (O-type and BO-A3 I-II) supergiants with published uvby and Hβ photometry are compared to the photomeric parallaxes of these stars based on the Mv absolute-magnitude calibration of Dambis (1990). The photometric distance scale is found to require only a minor correction −πHip = (1.03 ± 0.04)πPhot, i.e., r Hip = (0.97 ± 0.04)r Phot, which is corroborated by applying the statistical-parallax technique to a sample of 106 blue supergiants with published radial velocities and Hipparcos proper motions (r True = (0.98 ± 0.08)r Phot). The weighted mean distance-scale correction factor can thus be estimated at r True = (0.97 ± 0.03)r Phot, thereby constraining the LMC distance modulus to DM LMC = 18.36 ± 0.08 (standard error) ±0.07 (systematic error) and providing further evidence in favor of the so-called ‘short’ distance scale. An expanded sample consisting of 106 blue supergiants with corrected photometric distances, published radial velocities, and Hi...