A problem in distance-determination for Mira variables with an appendix on OB-star distances

Abstract

Difficulties in accepting the results on the kinematics of distant Mira variables obtained by Smak and Preston (1965) and in paper II, are outlined. It is shown that proper allowance for statistical bias in the distance determinations together with an allowance for the different definition of maximum magnitude, as used in these two investigations and in the statistical parallax work, removes the difficulties. It appears that the values of the Oort constant ( A) for Mira variables do not contradict the predictions of ellipsoidal theory. It is estimated that a considerable number of the stars in paper II must lie in the vicinity of the galactic centre, where large rotational effects are found. The present investigation strengthens the previous conclusion that the velocity dispersion, radial from the galactic centre, is independent of the galactocentric distance for Miras of a given period. It is shown that the absolute magnitudes of the Miras derived from statistical parallaxes are in substantial agreement with those derived from clusters and visual binaries including a new determination from the companion to U Men. Statistical effects in the distance determinations for OB-type stars are discussed in the appendix in order to bring out differences between the treatment necessary in this case and in that of the Miras.