Ronald G. Samec

CN Andromedae: A Broken-Contact Binary?

We solve new UBV light curves of the eclipsing binary CN Andromedae simultaneously with radial velocities by the method of differential corrections. We find it semidetached with the more massive star filling its limiting lobe and the less massive star very close to lobe-filling. Our solutions of earlier light curves have the same configuration. Within the uncertainties, the system may be in a broken or a marginal contact stage as it undergoes thermal relaxation oscillations. The light curves are strongly affected by a large dark spot at high latitude on the more massive star and by a bright substellar spot on the companion. Spot locations and temperatures do not differ significantly from epoch to epoch. Based on single star evolutionary models, the primarys mass (1.299 ± 0.045 M⊙) and radius (1.425 ± 0.016 R⊙) are consistent with those of a star of age 2.9 × 109 yr that will leave the main sequence in another 2.0 × 109 yr. The orbital period has decreased during the past 50 yr according to traditional eclipse timings and also according to our generalized light and velocity solutions that include a reference epoch T0 and a rate of period change dP/dt. We find dP/dt = -0.01951 ± 0.00054 s yr-1, which is consistent with mass transfer from the more to the less massive star of 1.4 × 10-7 M⊙ yr-1, assuming no mass is lost from the system. Reliable absolute dimensions are determined.

THE PHYSICAL NATURE AND ORBITAL BEHAVIOR OF V523 CASSIOPEIAE

V523 Cassiopeiae is a dwarf contact binary with one of the shortest orbital periods among the nondegenerate systems. Its orbital history is marked by large period changes. The photometrically determined mass ratios have historically been inconsistent with those calculated from radial velocity curves. In 1998 we acquired high-precision and standardized Johnson-Cousins UBV light curves. Our simultaneous BV light curve/radial velocity curve solutions provided good fits to both the light curves and the radial velocity curves using standard gravity darkening coefficients with a mass ratio of ~0.5. Seven precision mean epochs of minimum light were determined from these observations. We combine these with all available published times of minimum light, along with 50 times of low light found from a search of the archival Harvard plate stacks in the interval 1901–1942 to give us 567 eclipse timings. Our period study covers nearly 160,000 orbits, or ~102 yr. We find a high-amplitude sinusoidal variation with a period of 101 ± 7 yr, overlaid on a strong continuous period increase. The quadratic term is common in contact binaries, but a sinusoidal one is not. This suggests a hierarchical three-star system. Assuming that this is the case and that the inclination from our orbital solution for the close pair is the same as the larger orbit, we obtain a mass for the third star of 0.41 M⊙. This is similar to the masses of the stars that comprise the contact binary. If this scenario is correct, V523 Cas consists of a trio of late K and early M-type dwarfs having a total mass of ~1.6 M⊙. We show that high-resolution imaging can confirm this suggestion.

BVRcIc Observations and Analyses of the Dwarf Detached Binary V1043 Cassiopeia and a Comment on Precontact W Uma's

Complete Bessel BVR{sub c}I{sub c} light curves of V1043 Cassiopeia [2MASS J00371195+5301324, Mis V1292, USNO-A2.0 1425-00875743, {alpha}(2000) = 00{sup h}37{sup m}11.{sup s}95, {delta}(2000) = +53 Degree-Sign 0132.5] are analyzed. The system is a member of the small group of pre-contact W UMa binaries (PCWBs). Its light curve has the appearance of an Algol (EA) light curve, however it is made up of dwarf solar type components in a detached mode with a period of only 0.6616 days. The analysis includes a period study, an improved ephemeris, a mass ratio search, and a simultaneous BVR{sub c}I{sub c} Wilson-Devinney solution. We document about 20 other PCWBs given in the literature. Several have RS CVn-like properties.

UBVRc Ic Analysis of the Recently Discovered Totally Eclipsing Extreme Mass Ratio Binary V1853 Orionis, and a Statistical Look at 25 Other Extreme Mass Ratio Solar-type Contact Binaries

We present precision CCD light curves, a period study, photometrically derived standard magnitudes, and a five-color simultaneous Wilson code solution of the totally eclipsing, yet shallow amplitude (Av ~ 0.4 mag) eclipsing, binary V1853 Orionis. It is determined to be an extreme mass ratio, q = 0.20, W-type W UMa overcontact binary. From our standard star observations, we find that the variable is a late-type F spectral-type dwarf, with a secondary component of about 0.24 solar masses (stellar type M5V). Its long eclipse duration (41 minutes) as compared to its period, 0.383 days, attests to the small relative size of the secondary. Furthermore, it has reached a Roche lobe fill-out of ~50% of its outer critical lobe as it approaches its final stages of binary star evolution, that of a fast spinning single star. Finally, a summary of about 25 extreme mass ratio solar-type binaries is given.

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.

BVRcIc Observations and Analyses on V2421 Cygni, a Precontact W UMa Binary

We present the first precision BVRI light curves, synthetic light curve solutions, and a period study for the high amplitude solar type binary, V2421 Cygni. The light curves have the appearance of an Algol (EA) type; however, it is made up of dwarf solar type components in a detached mode with a period of only 0.6331 days with an amplitude of about a full magnitude, i.e., it is a precontact W UMa binary. Flare-like disruptions occur in the light curves following the primary and secondary eclipses possibly due to the line-of-sight track of a gas stream. An associated stream spot and splash spot cause bright equatorial spots on the stellar surface of the primary star. The more massive star is the gainer, making this system a classic, albeit dwarf, Algol.

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).

BVRI Photometric Analysis and 73 year Period Study of the Totally Eclipsing Binary, DK Andromedae

DK And is a Sonneberg variable, first classified as an RR Lyrae type-C. It was reclassified in 2006 as a totally eclipsing W Ursae Majoris variable with a period of 0.49 d. We present complete BVRI are light curves, a period study, and a simultaneous BVRI light-curve solution. The period study, covering some 73 years, reveals a 4-sigma-level quadratic ephemeris. Our light curves shows a time of constant light in the secondary eclipse of 28 minutes making this a totally eclipsing, A-type W UMa system. The depths of eclipses are only about 0.5 mag in V due to the fairly extreme fill-out. The light curve solution reveals a component temperature difference of ~300 K, fairly high for such variables, and an inclination of 82.5°. Although the variable is near F2V type, it shows definite dark spot activity (31° radius spot). High fill-out binarity evidently induces the convective envelopes responsible for this activity.

UBVRI Photometric Study of the Totally Eclipsing Very Short Period W Ursae Majoris Binary GSC 2765-0348

ABSTRACT.GSC 2765-0348 is a very short period (Pxa0=xa00.2835xa0dP=0.2835u2009u2009d), solar type, G4V contact binary. Complete BVRIBVRI and partial UU light curves covering the secondary eclipse are presented, along with a period study, surface temperature determination, and a simultaneous UBVRIUBVRI light-curve solution. Our light curves show low-level ripples, surface activity, and asymmetries due to magnetic activity. Light curve amplitudes vary from 0.4–0.6xa0mag (VV) in the primary and secondary eclipses. The difference in adjacent maxima varies from ∼3–5%∼3–5%. Modeled results include two spot regions, one hot and one cool, both at equatorial positions of the primary, more massive component. A firm 34% fill-out and a small mass ratio of 0.31 is also determined. A total eclipse of 33xa0minutes is found to occur in the secondary eclipse, making GSC 2765-0348 a WW-type (less massive star is hotter), W UMa variable.

Photometric Analysis and 60-Year Period Study of the Detached but Near-Contact System VV Virginis

VV Vir is a near-contact but detached mid-G-type eclipsing binary with an asymmetrical light curve due to a weak but regular mass exchange. The binary is apparently approaching contact and has a stream impact spot on the secondary component that is responsible for a quadratically decreasing period. Our period study included more than 140 minima observed over the past 60 years. We explore other possible near-contact configurations for this binary.