Daryl W. Willmarth

The Quadruple Gravitational Lens PG 1115+080: Time Delays and Models

Optical photometry is presented for the quadruple gravitational lens PG 1115+080. A preliminary reduction of data taken from 1995 November to 1996 June gives component C leading component B by 23.7 ? 3.4 days and components A1 and A2 by 9.4 days. A range of models has been fitted to the image positions, none of which gives an adequate fit. The best-fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km s-1 Mpc-1 for ? = 1, with an observational uncertainty of 14%, as computed from the B - C time delay measurement. Taking the lensing galaxy to have an approximately E5 isothermal mass distribution yields H0 = 64 km s-1 Mpc-1, while taking the galaxy to be a point mass gives H0 = 84 km s-1 Mpc-1. The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned Hubble Space Telescope observations.

BINARIES IN THE PRAESEPE AND COMA STAR CLUSTERS AND THEIR IMPLICATIONS FOR BINARY EVOLUTION

This completes a study of the evolution of binary systems in five open clusters of various ages. Among 21 stars observed in Praesepe, eight are found or confirmed to be spectroscopic binaries and orbital elements are derived, while one more shows long-term binary motion. Among 18 stars observed in the Coma Berenices cluster, five are found or confirmed to be spectroscopic binaries and orbital elements are derived, while a sixth has tentative elements. Among five clusters studied we searched for three expected evolutionary effects, namely an increase with age in the mass ratios, a decrease with age of the binary periods, and an increase in binary frequencies. We find that there is a progression (at the 3 σ level) from no binaries out of 10 with mass ratios greater than 0.5 in the youngest cluster (combined with the published results for NGC 6193) to 25% such stars in the intermediate-age clusters to 43% such stars in these two oldest clusters. There is no evidence for an increase in short-period binaries with age. And there is slight evidence (at the 1 σ level) for an increase with age from 15% to 28% in the fraction of large-amplitude binaries. These results are mostly consistent with the idea that most binaries are formed or modified in three-body interactions, and successive generations of formation and disruptions tend to form binaries with larger mass ratios. However, part of the initial generation of binaries is probably primordial.

A Survey for Enhanced Lithium in 261 Globular Cluster Giants

A survey of 261 giants in the globular clusters M3, M13, M15, and M92 carried out with the Hydra multiobject spectrograph on the WIYN 3.5 m telescope has identified no stars with Li I 6707 A resonance lines stronger than 20 mA. The limiting equivalent widths of the lithium line provide upper limits of log (Li) < +0.0 at Teff = 4500 K and log (Li) < +1.0 at Teff = 5000 K. The absence of lithium-rich stars in the sample suggests that the percentage of giants exhibiting enhanced lithium abundances in globular clusters is low.

New precision orbits of bright double-lined spectroscopic binaries. IX. HD 54371, HR 2692, and 16 ursa majoris

With extensive sets of new radial velocities we have determined orbital elements for three previously known spectroscopic binaries, HD 54371, HR 2692, and 16 UMa. All three systems have had the lines of their secondaries detected for the first time. The orbital periods range from 16.24 to 113.23 days, and the three binaries have modestly or moderately eccentric orbits. The secondary to primary mass ratios range from 0.50 to 0.64. The orbital dimensions (a{sub 1} sin i and a{sub 2} sin i) and minimum masses (m{sub 1} sin{sup 3} i and m{sub 2} sin{sup 3} i) of the binary components all have accuracies of ⩽1%. With our spectroscopic results and the Hipparcos data, we also have determined astrometric orbits for two of the three systems, HR 2692 and 16 UMa. The primaries of HD 54371 and 16 UMa are solar-type stars, and their secondaries are likely K or M dwarfs. The primary of HR 2692 is a late-type subgiant and its secondary is a G or K dwarf. The primaries of both HR 2692 and 16 UMa may be pseudosynchronously rotating, while that of HD 54371 is rotating faster than its pseudosynchronous velocity.

WIYN queue: theory meets reality

During the past two years NOAO has conducted a queue observing experiment with the 3.5m WIYN telescope on Kitt Peak, Arizona. The WIYN telescope is ideally suited to queue-scheduled operation in terms of its performance and its instrument complement. The queue scheduling experiment on WIYN was designed to test a number of beliefs and hypotheses about gains in efficiency and scientific effectiveness due to queue scheduling. In addition, the experiment was a test of our implementation strategy and management of community expectations. The queue is run according to a set of rules that guide decisions about which observation to do next. In practice, scientific rank, suitability of current conditions, and the desire to complete programs all enter into these decisions. As predicted by Monte Carlo simulations, the queue increases the overall efficiency of the telescope, particularly for observations requiring rare conditions. Together with this improvement for typical programs, the queue enables synoptic, target-of-opportunity, and short programs that could not be scheduled classically. Despite this success, a number of sociological issues determine the communitys perception of the WIYN queue.

A SPECTROSCOPIC BINARY GIANT IN THE GALACTIC CLUSTER NGC 752

Orbital elements are reported for the spectroscopic binary H110 (HD 11811), a giant star in the intermediate-age galactic cluster NGC 752. The center-of-mass velocity of the star is consistent with its membership in the cluster. Light from a mid-F dwarf companion can account for the unusual position of the star to the blue of the helium-burning clump.

SPECTROSCOPIC ORBITAL ELEMENTS FOR A DOUBLE-LINED BINARY IN NGC 752.

Orbital elements for a double-lined spectroscopic binary in the intermediate-age galactic cluster NGC 752 are reported. The binary is located just above the cluster main-sequence turnoff, and is a confirmed proper-motion and radial-velocity member. The equal amplitudes of the primary and the secondary velocity curves indicate that the stars have equal masses.