Archival light curves from the Bamberg Sky Patrol: CF Octantis, 1964-76

Abstract

We use the archive of the Bamberg Sky Patrol to obtain light curves of the active K subgiant CF Octantis (HD 196818) for the interval 1964–76. Digitized images of the field near CF Oct were obtained with a flat-bed scanner. Aperture photometry was performed of photo-positives of these images. Using a transformation to second order in plate magnitude, and first order in B−V, for nine field stars for each plate, the B magnitudes of CF Oct were obtained for just over 350 plates. The estimated precision of an individual determination of the B magnitude of CF Oct is 0.05 mag. Analysis of the resulting data reveals the known 20 d rotational variation of this star, and shows the evolution of the light curves from year to year. We obtain light curves with good phase coverage for 1964 to 1969 inclusive, partial light curves for 1970 and 1976, and a few data points from 1971. The amplitude of variation ranges from ∼0.2 to ∼0.4 mag. There is evidence that the characteristic rotation period of the star in the 1960s was slightly less than that measured from photoelectric photometry in the 1980s.