Brian John Carrigan

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.

BVRCIC Photometry of V743 Sagittarii: An Active, Very Short Period, Total Eclipsing W Ursae Majoris System*

A complete photometric analysis of BVRI photometry for the very short period W Ursae Majoris binary V743 Sagittarii is presented. Four epochs of minimum light were determined from observations made during two primary and two secondary eclipses. Corrected values of four previous timings are also given. The period study yielded an improved ephemeris. However, a large (~60,000 orbit) gap in the data precluded any definitive period analysis at this time. Standard magnitudes are reported. The light curves reveal that V743 Sgr is a G8–K0 spectral type W-type W UMa system with a 22 minute time of constant light in the primary minimum. The light curves have a prominent asymmetry occurring in the maximum at phase 0.25. It is 6% higher than the maximum at phase 0.75 in V magnitude. Our simultaneous light-curve solution yielded a component temperature difference of ~350 K, a mass ratio of ~0.31, and a fill-out of ~10%. A large polar cool star spot was calculated. Apparently, the system has rapidly changing spot activity. This is indicated by a comparison of our previously published 1989 curves with the present 1991 curves, which show a shallower primary eclipse and a reversal in the sense of the asymmetry in the maxima (phase 0.75 higher).

HW Persei: An Eclipsing Binary at Critical Contact?

A complete photometric analysis for the eclipsing binary candidate HW Persei is presented. The UBV observations were taken at Lowell Observatory in 1996 January. Three epochs of minimum light were determined, and an improved linear ephemeris was calculated. The O - C residuals, spanning some 60 years, show no evidence of a period change. Standard magnitudes are given, and reddening estimates are made. The first published synthetic light curve solutions of HW Per reveal that it is near a state of critical contact, which we define as both components exactly filling their respective Roche lobes. The primary component is of A8 spectral type, and the secondary component is a K3–K4 spectral type. The nature of the model is discussed.