Lithium and chromospherically active single giants

Nine chromospherically active single K giants were identified from surveys of chromospherically active stars. The stars have v sin i's ranging from 6 to 46 km/sec. Such large velocities are not explained by scenarios of main sequence to giant star evolution. Fluxes of the ultraviolet emission lines of these stars are substantially less than those of FK Comae. Many of these giants have a moderate or strong lithium line strongly suggesting that these stars recently evolved from rapidly rotating A or early F stars as is suggested by their space motions. Thus, they are not spun down FK Com stars. The characteristics of these stars are such that they may be confused with pre-main sequence stars. The primary difference may be that the post main sequence stars have strong H alpha absorption lines while the pre-main sequence stars appear to have a weak H alpha absorption line or possibly H alpha in emission above the continuum

Astrometric mass ratios for three spectroscopic binaries

The orbits of five single-lined spectroscopic binaries have recently been determined. We now use astrometric measurements that were collected with the Hipparcos satellite to constrain the systems' mass ratios and secondary masses. The barycentric astrometric orbits of three binary systems, HD 140667, HD 158222, and HD 217924, are fully determined and precise estimates of their mass ratios are obtained. Follow-up of these systems with infrared spectroscopy could yield model-independent dynamical masses for all components.Comment: 4 pages, 4 figures. Research note accepted for publication in Astronomy and Astrophysic

Secondaries Of Eclipsing Binaries. IV. The Triple System Lambda-Tauri

NSF AST 81-16409, AST 79-22014Astronom

Absolute Properties of the Eclipsing Binary Star V501 Herculis

V501 Her is a well detached G3 eclipsing binary star with a period of 8.597687 days for which we have determined very accurate light and radial-velocity curves by using robotic telescopes. Results of these data indicate that the component stars have masses of 1.269 +/- 0.004 and 1.211 +/- 0.003 solar masses, radii of 2.001 +/- 0.003 and 1.511 +/- 0.003 solar radii, and temperatures of 5683 +/- 100K and 5720 +/- 100K, respectively. Comparison with the Yonsei-Yale series of evolutionary models results in good agreement at an age of about 5.1 Gyr for a somewhat metal rich composition. Those models indicate that the more massive, larger, slightly cooler star is just beyond core hydrogen exhaustion while the less massive, smaller, slightly hotter star has not quite reached core hydrogen exhaustion. The orbit is not yet circularized, and the components are rotating at or near their pseudosynchronous velocities. The distance to the system is 420 +/- 30 pc

New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. III. HD 82191, Omega Draconis, And 108 Herculis

We have determined improved spectroscopic orbits for three double-lined binaries, HD 82191 (Am), omega Dra (F5 V), and 108 Her (Am), using radial velocities from the 2.1 m telescope at McDonald Observatory, the coude feed telescope at Kitt Peak National Observatory, and 2 m telescope at Fairborn Observatory. The orbital periods range from 5.28 to 9.01 days, and all three systems have circular orbits. The new orbital dimensions (a(1) sin i and a(2) sin i) and minimum masses (m(1) sin(3) i and m(2) sin(3) i) have accuracies of 0.2% or better. Our improved results confirm the large minimum masses of HD 82191 and also agree with the values previously found for. Dra. However, for the components of 108 Her our minimum masses are about 20% larger than the previous best values. We conclude that both components of HD 82191 as well as the primary of 108 Her are Am stars. However, the A9 secondary of 108 Her has normal abundances. We estimate spectral types of F4 dwarf and G0 dwarf for the components of. Dra. The primaries of the three binaries are synchronously rotating as is the secondary of 108 Her. The secondaries of HD 82191 and omega Dra are possibly synchronously rotating.NASA NCC5-511NSF HRD-9706268Astronom

New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. VIII. HR 1528, HR 6993, 2 Sagittae, And 18 Vulpeculae

Improved orbital elements for four A-star double-lined spectroscopic binaries have been determined with numerous new radial velocities. Three of the four systems, HR 1528, 2 Sge, and 18 Vul, have moderately short orbital periods of 7.05, 7.39, and 9.31 days, respectively, and also have circular or nearly circular orbits. Only HR 6993 with a period of 14.68 days has a significantly eccentric orbit. The close visual companion of 2 Sge has been detected spectroscopically, and its velocity measured. The orbital dimensions (a(1) sin i and a(2) sin i) and minimum masses (m(1) sin(3) i and m(2) sin(3) i) of the short-period binary components all have accuracies of 0.5% or better. We determine basic properties of the individual stars and compare them with solar-abundance evolutionary tracks to estimate their masses. Half of the eight components may be synchronously or pseudosynchronously rotating.NASANSFTennessee State UniversityState of Tennessee through its Centers of ExcellenceAstronom

HD 207651: A Composite Spectrum Triple System

From numerous radial velocities obtained at KPNO and Fairborn Observatory, we have determined the orbital elements of the composite spectrum triple system HD 207651. This system consists of a broad-lined A8 V star and an unseen M dwarf companion in a 1.470739 days orbit. Variations of the center-of-mass velocity of this short-period system and velocity variations of a narrow-lined F7: V star have an orbital period of 724.1 days or 1.98 yr and an eccentricity of 0.39. The revised Hipparcos parallax, corresponding to a distance of 255 pc, appears to be too small to yield consistent properties. Instead, we adopt a distance of 150 pc

Rotational Velocities of Late-Type Stars

A calibration based on the results of Gray has been used to determine projected rotational velocities for 133 bright stars with spectral types of F, G, or K, most of which appear in {The Bright Star Catalogue}. The vast majority have {v} sin {i} ≤q 10 km s-1 and, thus, are slow rotators. With the new calibration, projected rotational velocities have been determined for a sample of 111 late-type stars, most of which are chromospherically active. Some of the stars have had their rotational velocities measured for the first time

Chromospherically Active Stars. IV. HD 178450=V478 LYR: an Early-Type BY Draconis Type Binary

The variable star HD 178450 = V478 Lyr is a chromospherically active G8 V single-lined spectroscopic binary with a period of 2.130514 days. This star has strong ultraviolet emission features and a filled-in Hα absorption line which is variable in strength. It is classified as an early-type BY Draconis system and is similar in many respects to the BY Dra star HD 175742 = V775 Her. The unseen secondary of HD 178450 has a mass of about 0.3 M_sun; and is probably an M2-M3 dwarf. The inclination of the system is 67°±12°. The lithium abundance of the G8 dwarf results in an age for the system that is somewhat less than that of the Hyades cluster. The system is relatively nearby, with an estimated distance of 26 pc, or a parallax of 0arcsec.039