Engineering topics

Eaton, Joel A.

Publications and source records attributed to Eaton, Joel A..

23 records · Page 2

NASA NTRS1988

The outer atmospheres of the coolest M giants - Ultraviolet spectra of Rho Persei, 2 Centauri, g Herculis, Theta Apodis, and R Lyrae

New IUE observations of five M giants cooler than most studied previously have been obtained in order to study the variation of chromospheric properties with effective temperature. The ultraviolet spectrum lines of one of these stars, Rho Persei, are identified. The properties of the spectra of of the five stars are examined in detail, including the line widths and turbulence, the radial velocities of groups of lines, the structure in the Mg II resonance lines, and the fluorescent lines. The physical properties of the M giants' chromospheres are considered, including the formation of Fe II, the electron density, the degree of ionization of iron, magnesium, silicon, and carbon, the hydrogen ionization and energy balance, and the creation and destruction of photons.

Eaton, Joel A.↗

NASA NTRS1988

The long-period semi-detached giant binary system 5 Ceti

The binary system 5 Ceti consists of a K3 III star at or near its Roche lobe and a small hot companion best studied in the satellite ultraviolet. The hot radiation source at the secondary star is immersed in the chromosphere of the K giant, and the slight enhancements of a few UV absorption lines at secondary minimum are used to estimate chromospheric column densities. The variability and flatness of the spectrum is evidence for considering the object a main-sequence star accreting mass by way of Roche-lobe overflow at the rate of 5 X 10 to the minus 7 solar masses/yr. Thus 5 Ceti may represent the elusive rapid stage of mass transfer in which matter is lost from the shrinking Roche lobe of the more massive star. The Fe II UV spectrum in interacting binaries is also discussed.

Eaton, Joel A.↗

NASA NTRS1986

Synthetic spectra of cool stars for the wavelength range 2550-3200 A

In order to interpret the ultraviolet spectra of cool stars obtained with IUE and to determine the physical conditions in their outer atmospheres, synthetic IUE spectra of stars cooler than the Sun, mainly the Sun and the metal-deficient, carbon-rich CH stars were calculated. Results are encouraging. Synthetic spectra for the Sun over the range 2550 to 3300 A give roughly the observed level of overall emission and relative strengths or various absorption features (Fe II, Mg II, Mg I, and Fe I) although they still require extra sources of continuous opacity longward of 2650 A. Spectra of the CH stars have roughly the correct shape in the ultraviolet continuum for the expected effective temperature, although these models are problematic in that the electron density, hence H(-) opacity, is directly proportional to the Mg-Si-Fe density and the ratio of line to continuum opacity is only slightly affected by changing metallicity.

Eaton, Joel A.↗

NASA NTRS1986

The outer atmospheres of cool M giants: High-dispersion ultraviolet spectra of Rho Per, 2 Cen, and g Her

Long duration IUE spectra were obtained to extend coverage of cool giants studied in the ultraviolet at high dispersion to M6. The chromospheric spectra of the three stars, which consist of a profusion of Fe II lines and a few lines of Mg II, Mg I, Al II, C II, C I, Cr II, and Fe I, are remarkably similar, both among themselves and with respect to stars of earlier spectral type. These lines present a picture of a warm chromosphere that is static in the average but may be far from uniform in density and ionization. The Mg II emission lines of 2 Cen show 2 unresolved absorption components, the shorter at the velocity of the local interstellar medium. The longer is blueshifted from the star by 12 to 18 km/sec and must be one of very few observed shell lines uncontaminated by interstellar absorption.

Eaton, Joel A.↗

NASA NTRS1986

Implications of the light curve of the A-type W UMa binary V566 Ophiuchi

Broadband (2585-3200-A) IUE photometric observations of V566 Oph obtained in three 8-h shifts on July 17-19, 1984 are reported and solved simultaneously with the ground-based optical observations of Bookmyer (1976). The observed light curves are fit to theoretical Roche-model light curves using the computer program described by Eaton (1986). The data and solutions are presented in tables and graphs, and the modifications required to match the solutions to data for 1965 (Bookmyer, 1969) and 1957 (Binnendjik, 1959) are considered. The lower-than-expected darkening observed is attributed to a reduced common-radiative-envelope temperature gradient, probably a result of circulation related to energy transfer between the components of V566 Oph.

Eaton, Joel A.↗