ИСТИНА

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 Hipparcos proper motions, combined with 51 young open clusters (log t ≤ 7.5) with Hipparcos-based proper motions (Rastorguev et al., 1999), mean radial velocities (Rastorguev et al., 1999), and photometric distances based on ZAMS fitting (Dambis, 1999) is used to infer the following Galactic rotation-curve solution : vector of solar motion (u O = 5.5±1.2, v O = 11.2 ± 1.2, w O = 7.7 ± 0.7) km s−1; rotation-curve parameters ΩO = 29.3 ± 1.0 km s−1 kpc−1, ΩO = −4.78 ± 0.21 km s−1 kpc−2, and Ω”O = +1.07 ± 0.21 km s−1 kpc−3), and velocity ellipsoid semiaxes σu = 13.0 ± 1.0 km s−1, σv = 10.9 ± 0.8 km s−1, and σw = 5.8 ± 0.7 km s−1.