2009A&A...503.1023F

A set of 55x10³ stars brighter than about B-magnitude 14 and having at least three observations are identified in the Sydney Observatory Galactic Survey, carried out over the years 1892-1932 along the galactic equator section l∈[275°,335°] with galactic latitude b∈[-7°,7°]. Short-term (30min) and long-term (decades) magnitude variations in the data set are analyzed. Evidence is sought for a correlation between short-term and long-term variabilities which would identify stars in a non-quiescent phase. We use a reduced proper motion diagram to classify the stars in our sample into probable dwarfs, giants and other types. The validity of the kinematical classification is checked using objective-prism spectroscopic classification for 10x10³ early-type stars. A search is made for statistical correlations between our variability indicators and physical and kinematical stellar properties. We find that suspected photospheric activity for giant and dwarf stellar candidates is correlated with the time to cross the galactic thin disk. We estimate a significant apparent B-magnitude variation of ±0.25 over the 40 years of photographic observations, and candidates for monitoring for possible photospheric activity at the present time are selected employing a statistical colour-diagram which uses the total proper motion component as a distance indicator. Follow up studies of our tentative findings are suggested. Toward this aim the derived data for the set of 55x10³ stars with variability information is archived as the variability Sample Catalogue. The data for a set of 2.4x10⁵ stars along the section of the galactic equator l∈[275°,335°], |b|≤7°, and a set of of 1.7x10⁵ stars along the section of the galactic meridian 330°±5°, b∈[-64°,-7°] is also archived as a quick-look facility for seeking long-term magnitude changes since the century-old photographic observations were obtained.