UBVRI photometry of 225 AM stars

Abstract

UBVRI photometry of 225 Am stars taken from Mendoza's (1974) catalog is presented. The results are compared with those obtained by Feinstein (1974) for 21 of the stars and with the values of Johnson et al. (1966). It is assumed that in the first approximation the (V-I) color index of an unreddened Am star is equal to that of a normal main-sequence star; a standard main sequence is defined for A and early F stars, and the five-color photometry is analyzed by means of plots of U-V vs. V-I, B-V vs. V-I, and V-R vs. V-I. Mean color deficiencies of Am stars are examined, and it is suggested that an unreddened star located below the main-sequence A0-F2 line in the (V-I, U-V) plane is a photometric Am star. It is concluded that: (1) photometric Am stars have color deficiencies (as a function of V-I) which, on the average, are 0.07 mag in (U-V) color index and 0.025 mag in (B-V) color index; (2) Am stars with V-R less than 0.25 mag may also have a color deficiency of about 0.01 mag; (3) Am stars with V-R greater than 0.3 mag may have a color excess of approximately 0.01 mag; and (4) Am stars with V-R between 0.25 and 0.3 mag may have normal colors.