James R. Sowell

ICCD speckle observations of binary stars. IX: A duplicity survey of the Pleiades, Praesepe, and IC 4665 clusters

Multiplicity of stars within clusters is a well-studied phenomenon. However, recent survey work done on the Hyades by Mason et al. [AJ, 105, 220 (1993)] would seem to indicate that even in the most often studied clusters, there may be binaries yet undiscovered. In order to expand the sample of cluster binaries with potentially short-period visual orbits, a speckle survey of 45 Pleiades, 54 Praesepe, and 22 IC 4665 bright stars (V < 10) for possible multiplicity was conducted at the KPNO 4 m Mayall telescope between 1987 October and 1991 November. Of these, three new binaries have been discovered: one in the Pleiades where the new component may be spectroscopic, another in Praesepe which has been confirmed from examinations of archival observations and also has been resolved by occultation, and the third in IC 4665

ALL-SKY STROMGREN PHOTOMETRY OF SPECKLE BINARY STARS

All-sky Stromgren photometric observations were obtained for 303 speckle binaries. Most stars were in the range of V = 5 to 8. These data, when combined with ratios of intensities from the CHARA speckle photometry program, will allow the determination of photometric indices for the individual components of binary stars with separations as small as 0.05 arcsec. These photometric indices will complement the stellar masses from the speckle interferometry observations to provide a much improved mass-luminosity relationship.

Yellow evolved stars in open clusters

This paper describes a program in which Galactic cluster post-AGB candidates were first identified and then analyzed for cluster membership via radial velocities, monitored for possible photometric variations, examined for evidence of mass loss, and classified as completely as possible in terms of their basic stellar parameters. The intrinsically brightest supergiants are found in the youngest clusters. With increasing cluster age, the absolute luminosities attained by the supergiants decline. It appears that the evolutionary tracks of luminosity class II stars are more similar to those of class I than of class III. Only two superluminous giant star candidates are found in open clusters. 154 references.

H-R DIAGRAMS BASED ON THE HD STARS IN THE MICHIGAN SPECTRAL CATALOGUE AND THE HIPPARCOS CATALOG

The systematic, spectroscopic two-dimensional classification of the HD stars by N. H. is approximately three-quarters complete. Over 161,000 stars have been classified visually using 10° objective-prism plates (2 A resolution) taken at CTIO with the Michigan Curtis Schmidt telescope. The published portion of this large, homogeneous database, taken from volumes 1-5 of the Michigan Spectral Catalogue (declination -90° to +5°), has been used to create an H-R diagram. The Hipparcos parallax measurements provide a large homogenous database, too. H-R diagrams of the HD stars found in both catalogs are produced for distances to 20, 50, 100, and 200 pc.

Evolution of the starspots in V478 Lyrae from 1980 to 1988

Differential UBV photometry of V478 Lyrae from 1980 to 1988 is given and analyzed as 22 separate light curves, each spanning an average of a dozen rotation cycles. It is shown that spots on V478 Lyr appear to have lifetimes on the order of several months to a year. The amplitude of the light loss produced by a spot can change by a factor of 2 within 20 days. In the only four determinate cases, a spot came into existence at one of the two conjunctions, that is, in the middle of the hemisphere facing (or opposing) the companion star. This finding provides additional support for the picture of a four-sector longitudinal structure, aligned with the major axis of the binary, which determines where magnetically active regions develop. 12 refs.

Period Changes in Four Short-Period Spotted Binaries: UV Piscium, YY Geminorum, CG Cygni, and XY Ursae Majoris

Recently acquired times of minimum for three RS CVn systems and one BY Draconis binary, all with periods under a day, are presented. Times of minimum for UV Psc, YY Gem, CG Cyg, and XY UMa have been measured for decades. These observations have been collected, and the O-C curves for each system have been examined for period changes. The O-C curves for UV Psc and YY Gem showed a linear deviation, and improved periods have been computed. CG Cyg and XY UMa, though, appear to have experienced true changes in their periods. An additional 11.0 yr periodic variation has been found in the O-C data of XY UMa. The mechanism for the period variations remains uncertain.

The lithium abundances of the Capella giants

The abundance of lithium in each of the two giants which comprise the spectroscopic binary star Capella has been redetermined using digital, electronic spectra and modern analytical techniques. The abundance of lithium in the warm (G0) secondary star is log Li = 3.0, consistent with the value seen in young, unevolved stars and the interstellar medium. The abundance of lithium in the cooler (G8) primary star is log Li = 0.8, similar to what is found in other red giants of similar spectral type. The lithium abundance in the primary star is less than would be expected from classical predictions

CG Cygni: solutions of 1979 and 1980 light curves

Three new V light curves of CG Cyg, a short-period RS CVn binary, are presented. Fourier analysis showed the wave to be present still. The most striking feature of the light outside eclipse is the monotonic increase in the mean level by 15% since 1967. Solution of the rectified light curve yielded values of i = 81°.8, k = 1.00, and p0 = -0.44. These, combined with published spectroscopic elements, gave values of Rh = Rc = 0.80 Rsun;, Mh = Mc = 0.52 Msun;, and a = 3.13 Rsun;.

MM Herculis: An eclipsing binary of the RS CVn type

Differential photoelectric photometry inV, B, andU has been obtained for the eclipsing binary MM Her, a member of the RS Canum Venaticorum class. The light outside eclipse was Fourier-analyzed to study the wave. The migration and amplitude of the wave and the mean light level of the system now have been monitored from 1976 through 1980. The phase of wave minimum has decreased from 0.P80 to 0.P25, the wave amplitude has varied between 0.m06 and 0.m12, and the mean light level has fluctuated between 0.94 and 0.99. Observations within eclipse revealed that the eclipses are partial, not total as previously thought, and a new time of mid-eclipse was found to be JD (hel.)=2444 500.6665±0.d0008. The Russell model was used to solve the 1980 light curve. Elements of the rectified light curve werei=86.°35±0.°09,rh=0.070±0.002,rc=0.125±0.001,Lh(V)=0.585±0.008 andLh(B)=0.683±0.010. The geometric elements were forced on the pre-1980 light curves and found to be compatible. With these elements and previously obtained double-lined radial velocity curves, new absolute dimensions have been calculated: 1.18M⨀ and 1.58R⨀ for the hotter star and 1.27M⨀ and 2.83R⨀ for the cooler star. By plotting color indices on the color-color curve, spectral types of G2V and K21V were found, each uncertain by a couple of subclasses.

ABSOLUTE PROPERTIES OF THE HIGHLY ECCENTRIC, SOLAR-TYPE ECLIPSING BINARY HD 74057

We have obtained Str?mgren b and y differential photometric observations of the solar-type eclipsing binary HD 74057 plus follow-up high-resolution, red wavelength spectroscopic observations. The system has an orbital period of 31.2198 days, a high eccentricity of 0.47, and is seen almost exactly edge on with an inclination of 898. The two main-sequence G0 stars are nearly identical in all physical characteristics. We used the Wilson-Devinney program to obtain a simultaneous solution of our photometric and spectroscopic observations. The resulting masses of the components are M 1 = 1.138 ? 0.003 M ? and M 2 = 1.131 ? 0.003 M ?, and the radii are R 1 = 1.064 ? 0.002 R ? and R 2 = 1.049 ? 0.002 R ?. The effective temperatures are 5900?K (fixed) and 5843?K, and the iron abundance, [Fe/H], is estimated to be +0.07. A comparison with evolutionary tracks suggests that the system may be even more metal rich. The components rotate with periods of 8.4 days, significantly faster than the predicted pseudosynchronous period of 12.7 days. We see evidence that one or both components have cool spots. Both stars are close to the zero-age main sequence and are about 1.0?Gyr old.