| Abstract | Cepheid variables have been found in the nearby Sm IV galaxy NGC 3109. Periods for 29 of the variables, determined from blue plates taken over a 4 yr interval with the duPont 2.5 m reflector at Las Campanas, range from 31 to 5 days. The period-luminosity relation is well defined, showing the intrinsic scatter in magnitude at a given period due to the width of the instability strip. As expected, the P-L relation has a shallower slope than that of the standard calibration, caused by observational selection bias near the plate limit. The apparent blue distance modulus is (m-M)_AB_=26.4, based on the P-L zero point adopted in the text. The brightest supergiants, found by blinking blue and yellow plates, have absolute magnitudes of M_B_(3)= -7.6 for the mean of the three brightest blue stars, and M_V_(3)= -7.7 for the corresponding mean of the three brightest red stars. The first ten brightest red supergiant candidates are variable, ensuring membership. These absolute magnitudes agree with the previous calibration of the brightest red and blue star luminosities as a function of the absolute magnitude of the parent galaxy. |
