Engineering topics

Tinsley, B. M.

Publications and source records attributed to Tinsley, B. M..

7 records

NASA NTRS1980

The ultraviolet continua of the nuclei of M31 and M81

Ultraviolet measurements of the central 2.5 arcmin of M31 and M81 made with the ANS satellite are reported. A library of standard-star observations is also included for comparison. In agreement with OAO 2 results, it is found that both galaxies exhibit a significant UV excess as compared to expectations for a pure, old metal-rich stellar population including just the main sequence and giant branch. Model calculations show that the excess UV light could be produced either by young stars or by commonly occurring hot stars in an old stellar population. At the present time, several lines of evidence slightly favor old stars. An ultraviolet excess of similar magnitude seems to be common to all early-type galaxies yet observed in the UV and thus may significantly affect the appearance of redshifted galaxies.

Wu, C.-C.↗

NASA NTRS1979

Galactic evolution with the space telescope

Some aspects of research on galactic evolution with the Space Telescope (ST) are discussed. Viewpoints are provided from which ST (and related ground based) studies can be planned.

Tinsley, B. M.↗

NASA NTRS1978

On the origin and evolution of isotopes of carbon, nitrogen, and oxygen

Calculations of CNO processing in stellar envelopes, based on theoretical nucleosynthesis rather than empirical abundances in evolving stars, are presented and used in two models for the chemical evolution of the solar neighborhood. Seven stable isotopes are considered: C-12, C-13, N-14, N-15, O-16, O-17, and O-18. The two models ('infall' and 'initial-burst') represent extremes of types consistent with general constraints and include theoretical estimates of other nucleosynthesis sites and yields for CNO isotopes. The results obtained are found to predict that all CNO isotopes are produced mainly by stars with lifetimes much less than the age of the Galaxy (even at the present time when low-mass stars have the greatest death rate), so that isotopic ratios evolve very slowly after the first few billion years. Consequences of these slow changes are that the isotopic ratios cannot be employed to test between alternative hypotheses and that galactic evolution does not seem to be able to account for the apparent difference between the C-13/C-12 ratio in the solar system and in molecular clouds. The predicted envelope processing is shown to lead to approximately the solar-system values for the C-13/C-12 and O-17/O-16 abundance ratios but to a N-14/C-12 ratio that is too small by at least a factor of 2.

Dearborn, D.↗

NASA NTRS1974

Possible influence of comets on the chemical evolution of the galaxy

It has been suggested by Cameron (1973) that a cloud of comets containing a mass of condensable elements, comparable to the mass of such elements in the sun, formed on the outskirts of the solar system. If the formation of such comet clouds is a general feature of star formation, they constitute a significant sink of elements heavier than helium. It is shown here that this process provides a possible explanation for the very slow rate at which the mean metal abundance of disk stars has increased during the lifetime of the Galaxy.

Tinsley, B. M.↗

NASA NTRS1973

Star formation and evolution in spiral galaxies.

Evolutionary models for regions of M31 and M33 and the solar neighborhood are based on a stellar birthrate suggested by the dynamics of spiral structure: we assume that stars are formed very efficiently until the gas content reaches equilibrium at its present value, which takes about 1 b.y.; thereafter, the birthrate just equals the rate at which gas enters the system from stellar mass-loss or infall of intergalactic matter. Each model represents an average around a cylindrical-shell-shaped region, which is homogeneous and closed except for possible infall. The disk and spiral-arm populations only are considered. Each star is followed in the H-R diagram from the main sequence to death as an invisible remnant. Integrated magnitudes, colors, mass-to-light ratio (M/L), gas content, helium and metal abundance (Z), are computed in steps of 1 b.y.

Quirk, W. J.↗

NASA NTRS1972

Possibility that the far ultraviolet excess in M31 is due to main sequence stars

The far ultraviolet excess in the central region of M31, observed by OAO-2, could be due to young main sequence stars. More than enough such stars are present in the model for the M31 inner disk population derived by Tinsley and Spinrad (1971) to match line- and color-indices at longer wavelengths. If the far ultraviolet radiation of typical galaxies arises from young stars, the theoretical ultraviolet background is enhanced greatly by evolutionary effects. For evolution at the rate of Tinsley and Spinrad's model for M31, or of Arnett's (1971) linear model for our galaxy, the enhancement is a factor 2.5 to 14, depending on the Hubble constant and the spectrum at wavelengths below 1700 A.

Tinsley, B. M.↗

NASA NTRS1969

Distribution of redshifts of quasars.

Quasars red shifts distribution interpreted as due to cosmological and gravitational red shifts distribution, noting analysis error

Patterson, T. N. L.↗