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On the Distance Measurements in the Thin Milky Way Disk

Krełowski J., Strobel A., Galazutdinov G. A., Musaev F., Bondar A.

Acta Astronomica

2018

Vol. 68, No. 3

285--300

We present a test how far the direct, trigonometric parallax measurements and those, based on interstellar CaII H and K lines lead to distances to OB stars similar to those, based on spectrophotometrically determined ones. For this we use relatively nearby objects where the extinction effects are negligible. A test is based on observations of interstellar CaII H and K lines, that determine distances, in spectra of bright, nearby objects, free of extinction effects. For these objects one can find also trigonometric parallaxes. CaII H and K lines are weak in spectra of nearby stars and thus measurable only in high S/N ratio spectra. Such spectra being at our disposal also allow us to check the spectral classification of our targets and thus to comment the observed differences between distances acquired using different methods. Using four methods, we determined distances to nearly fifty B0-5 type stars, practically free of any extinction effects. We demonstrate that direct, astrometric, CaII H and K and spectrophotometric distances agree reasonably well in the absence of substantial interstellar extinction and when spectral classification is reliable. Apparently the absolute magnitude calibration, provided by Schmidt-Kaler, appears to be correct.