Richard M. Williamon

LONG-TERM PHOTOMETRIC ANALYSIS OF THE ACTIVE W UMa-TYPE SYSTEM TU BOOTIS

We present multicolor light curves for the W UMa-type eclipsing binary TU Boo for two epochs separated by 22 years. An analysis of the O – C diagram indicates the earlier observations took place right in the middle of a major period change, thus allowing for a unique study on mass transfer and period changes in this W UMa-type system. We compute model fits to our light curves, along with the only other published set, using the Wilson-Devinney program, and find temporally correlated changes in the size of the secondary component with anomalies in the O – C diagram. We investigate the cause of these changes and find support for the existence of rapid, large-scale mass transfer between the components. We postulate that this interaction allows them to maintain nearly equal surface temperatures despite having achieved only marginal contact. We also find support for the evolutionary scenario in which TU Boo has undergone a mass ratio reversal in the past, due to large-scale mass transfer so that what is presently the secondary component of TU Boo is in an advanced evolutionary state, oversized due to a helium-enriched core, with a total system age of ≥10 Gyr.

SUDDEN CHANGES IN THE PERIOD OF RT ANDROMEDAE

Photoelectrically determined times of primary and secondary minimum are presented for the eclipsing binary RT And. These times of primary minima, when combined with other published minima, indicate that the system has undergone two sudden decreases in period since its discovery in 1901. The possibility of smaller amplitude, sporadic period jumps is also indicated. Key words: eclipsing binary - photometry - period changes

Orbital Solutions and Absolute Elements of the Eclipsing Binary EE Aquarii

EE Aqr is a 7.9 mag Algol variable with a 12 hr orbital period. The Wilson-Devinney program is used to simultaneously solve 11 previously published light curves together with two existing radial velocity curves. The resulting masses are M 1 = 2.24 ± 0.13 M ☉ and M 2 = 0.72 ± 0.04 M ☉, and the radii are R 1 = 1.76 ± 0.03 R ☉ and R 2 = 1.10 ± 0.02 R ☉. The system has the lower-mass component completely filling its Roche lobe. Its distance from Hipparcos observations is 112 ± 10 pc. An improved ephemeris is derived, and no deviations in the period over time were seen. Light and velocity curve parameters, orbital elements, and absolute dimensions are presented, plus a comparison is made with previous solutions.

ORBITAL SOLUTIONS AND ABSOLUTE ELEMENTS OF THE ECLIPSING BINARY AY CAMELOPARDALIS

New differential UBV photoelectric photometry for the eclipsing binary AY Cam is presented. The Wilson-Devinney program is used to simultaneously solve the three light curves together with previously published radial velocities. We determine absolute dimensions and estimate the age of the system. AY Cam is a detached binary consisting of two stars on the main sequence but evolved beyond their respective main-sequence life midpoints. As expected, the more massive star is the most evolved and about 145 K cooler than its less massive companion. We determine color indexes for the two stars and estimate color excesses.

Orbital Solutions and Absolute Elements of the Eclipsing Binary MY Cygni

YY Cet is a 10.5 mag semidetached variable with a 19 hr orbital period. The Wilson-Devinney program is used to simultaneously solve two new sets of UBV light curves together with preexisting photometry and single-line radial velocity measurements . The system has the lower-mass component completely filling its Roche lobe. The resulting masses are M1 = 1.78 ± 0.19 M⊙ and M2 = 0.92 ± 0.10 M⊙, and the radii are R1 = 2.08 ± 0.08 R⊙ and R2 = 1.62 ± 0.06 R⊙. Its computed distance is 534 ± 28 pc. Light- and velocity-curve parameters, orbital elements, and absolute dimensions are presented. A study of published TOM observations indicates that the period changed around 1999.

Orbital Solutions and Absolute Elements of the Short-Period Eclipsing Binary ES Librae

We have obtained new differential UBV photoelectric photometry and radial velocities of both components of the short-period eclipsing binary ES Lib. The system has a circular orbit with a period of 0.883040928 days and is seen at an inclination of 70.1°. With the Wilson-Devinney analysis program, we obtained a simultaneous solution of our photometric and spectroscopic observations that resulted in masses of M1 = 2.30 ± 0.03 M⊙ and M2 = 0.97 ± 0.01 M⊙ and the equal-volume radii of R1 = 2.69 ± 0.02 R⊙ and R2 = 1.83 ± 0.01 R⊙ for the primary and secondary, respectively. The secondary is oversized and overluminous for its mass. The effective temperatures of the primary and secondary are 8500 K (fixed) and 5774 ± 57 K, respectively. Despite the very large temperature difference, our photometric and spectroscopic data indicate that ES Lib is not semidetached but rather require it to be in an overcontact state, where both components exceed their critical Roche lobes. Given its nonthermal equilibrium state, if the overcontact solution correctly characterizes the system, the change from being semidetached to overcontact may have occurred recently. While the asymmetry of the light curves can be modeled well with a large, hot starspot or a large, cool one on the secondary component, we prefer the latter interpretation because cool spots are a typical feature on many contact binaries.

Orbital Solutions and Absolute Elements of the Massive Algol Binary ET Tauri

We acquired differential UBV photoelectric photometry and radial velocities of the relatively bright, understudied, massive Algol binary ET Tau and utilized the Wilson-Devinney (WD) analysis program to obtain a simultaneous solution of these observations. To improve the orbital ephemeris, the V measurements from the ASAS program were also analyzed. Because of the very rapid rotation of the significantly more massive and hotter component (B2/3 spectral class), only radial velocities of the secondary component, which has a ~B7 spectral class, could be measured. We derive masses of and and equal-volume radii of and for the primary and secondary, respectively. The secondary is filling its Roche lobe, so the system is semi-detached. The effective temperature of the secondary was held fixed at 15,000 K, and the primarys temperature was found to be K. The system, which has a period of 5.996883 ± 0.000002 days, is assumed to have a circular orbit and is seen at an inclination of .

Orbital Solutions and Absolute Elements of the W UMa Binary MW Pavonis

We present differential UBV photoelectric photometry obtained by Williamon of the short-period A-type W UMa binary MW Pav. With the Wilson-Devinney analysis program, we obtained a simultaneous solution of these observations with the UBV photometry of Lapasset, the V measurements by the ASAS program, and the double-lined radial velocity measurements of Rucinski and Duerbeck. Our solution indicates that MW Pav is in an overcontact state, where both components exceed their critical Roche lobes. We derive masses of M1 = 1.514 ± 0.063 M⊙ and M2 = 0.327 ± 0.014 M⊙, and equal-volume radii of R1 = 2.412 ± 0.034 R⊙ and R2 = 1.277 ± 0.019 R⊙ for the primary and secondary, respectively. The system is assumed to have a circular orbit and is seen at an inclination of 86.39° ± 0.63°. The effective temperature of the primary was held fixed at 6900 K, whereas the secondarys temperature was found to be 6969 ± 10 K. The asymmetry of the light curves requires a large, single star spot on the smaller, less massive secondary component. A consistent base solution, with different spot characteristics for the Williamon, Lapasset, and ASAS data, was found. The modeled spot varied little during the 40-year range of photometric observations. The combined solution utilized a third light component and found that the period is changing at a rate of dP/dt = (6.50 ± 0.19) × 10-10.

The Eclipsing Binary RU Eridani

RU Eri is a near-contact eclipsing binary (V ≈ 9.24 magV) with a 0.632-day orbital period. The Wilson-Devinney program is used to simultaneously solve new UBVUBV light curves obtained between 1973 and 1981 at the Fernbank Science Center Observatory, together with existing single-lined radial velocity measurements. Light and velocity solution parameters, orbital elements, and absolute dimensions are presented. We find the more massive component to fill its Roche lobe completely, while the less massive star nearly fills its limiting lobe (98% by radius), making RU Eri a near-contact or broken-contact system. Thermal contact between the two stars is also broken, as indicated by the large temperature difference between the two components (≈1800 K). We present masses and radii for the two stars for a range of adopted masses for the primary component. The absolute dimensions imply a distance greater than 190 pc. New ephemerides are computed from published eclipse timings, including 13 new minima determined from our observations.

Photoelectric observations of mutual eclipses and occultations of the Galilean satellites in 1973

Four mutual occultations and three mutual eclipses of the Galilean satellites were observed from Fernbank Science Center Observatory between July and December 1973. The observed midtime and duration of each event as well as the magnitude loss in yellow light is presented. Cause for small discrepancies between the observations and predictions are discussed.