AAVSO: American Association of Variable Star Observers

APASS as a Tool for Calibrating the Cepheid Period-Luminosity Relation (Abstract)

Volume 44 number 1 (2016)

David Turner
St. Mary’s University, Department of Astronomy and Physics, 56 Shalimar Crescent, Dartmouth, NS B2W 4L8, Canada; turner@ap.smu.ca


(Abstract only) In a recent study of field reddenings for Cepheid variables (Turner 2015, Rev. Mex. Astron. Astrofis., submitted), the author noticed that the field of the classical Cepheid S Sge contained five B-type stars of well-defined reddening, E(B–V) = 0.10 ±0.01, implying a reddening of E(B–V) = 0.09 ±0.01 for S Sge. The stars also appeared to be constrained in distance in a color-magnitude diagram. Given the well-defined reddening for B-stars in the surrounding field, a search was made using the AAVSO Photometric All Sky Survey (APASS) of other potential B and A-type companions. A sizeable number of such stars appear to define a well-populated main sequence in the color-magnitude diagram for the field, with an implied distance of 646 ±17 parsecs and age of log t = 7.9. Presumably the stars represent the remains of a dissolved open cluster where S Sge was created. Additional searches for such cluster remains are possible with APASS for the fields of other distance scale calibrators with well-defined field reddenings.