Jamison D. Gray

Analysis of UBV Photometry of the Near-Contact Binary AK Canis Minoris

As a part of our study of eccentric eclipsing binary candidates, we have obtained complete UBV photoelectric light curves of the neglected system AK Canis Minoris. The observations were taken at Lowell Observatory in 1994 February. Two new epochs of minimum light were determined from these observations. A period study, spanning 33 years, was undertaken, and both improved linear and quadratic ephemerides were obtained. The robust period decrease determined in the quadratic ephemeris may imply magnetic braking arising from the solar-type secondary component. UBV light curves formed from our precision observations are presented. The first synthetic light-curve solution of AK CMi is presented. Our analysis reveals that AK CMi is in a near-contact, semidetached configuration with an A3 spectral type primary component and a K2 secondary filling its Roche lobe. Contrary to earlier reports that AK CMi has a displaced secondary eclipse, our secondary eclipse occurs at phase 0.5.

ANALYSIS OF CCD PHOTOMETRY FOR THE VERY SHORT PERIOD ECLIPSING BINARY BM URSAE MAJORIS

CCD images of the fourteenth magnitude variable BM Ursae Majoris were taken in the spring of 1991. The observations were taken at Lowell Observatory. An RCA CCD camera system and a standard PMT were used. Four times of minimum light were determined and improved linear and quadratic ephemerides were calculated. A period study, spanning over a thirty year interval, shows that the system is undergoing a small but continuous period decrease of ~5 X 10-8 d/yr. This may be due to angular momentum loss (AML) caused by stellar winds. The V, R, I light curves formed from the present precision observations, show that BM UMa is a W-type W UMa system. The first synthetic light curve solution of BM UMa is also presented. This solution reveals that BM UMa is a contact binary consisting of two early K spectral type components with a fill out of ~20% and a mass ratio of ~0.5. A subtantial temperature difference of ~400 K was determined. Both unspotted and spotted models were calculated. The spotted model indicates the presence of a region of enhanced birghtness in the neck of the secondary component. This may be attributed to fluid dynamics of mass in transit rather than to magnetic activity.