RATIO OF TOTAL TO SELECTIVE EXTINCTION AND DISTANCE TO GALACTIC CENTRE

A method for determining R, the ratio of total to selective extinction, is discussed. It is shown that reliable distances, expressed as a fraction of the distance ρ0 to the galactic centre, can be calculated from radial velocities and a model for the differential rotation of the Galaxy when care is taken to select suitable stars. A measure of the total extinction can be derived when the apparent distance modulus is known. From the slope of a graph of this extinction against colour excess for many stars, an average value of R is determined; the intercept gives ρ0. In this paper R =AV/EB-V on the UBV colour system. From a total of 180 OB stars, Cepheids and galactic clusters R is found to be 3.3-0.5+0.7 and ρ0 lies in the range 8-10 kpc. © 1971 Royal Astronomical Society. Provided by the NASA Astrophysics Data System.