Evolution of the M31 disk population

An evolutionary model for the M31 inner disk population is described, which at age 12 billion years agrees closely with the narrow-band colors and line indices recently measured by Spinradet al. (1971), and with the broad-band colors from 0.36 to 3.4 . Assuming that gE galaxies have the same stellar population as the M31 inner disk, this model is used to derive evolutionary effects in cosmology. Interpretation of the magnitude-redshift relation is substantially affected, since the evolutionary correction to V magnitudes at redshift 0.2 may be 0.09 mag. if H₀=100 km s^–1 Mpc^–1, or 0.25 mag. ifH ₀=50. Changes in some line strengths may be observable at redshift 0.46, showing the younger stellar population at earlier times. Our results differ from estimates by other authors, also based on the assumption that the gE and disk populations are identical, that the photometry of Spinradet al. (1971) precludes a significant rate of evolution. One reason for the difference is that our model has an unexpectedly shallow luminosity function just below the main sequence turnoff; another reason is that authors in the past have used the change in absolute V magnitude as the evolutionary correction, whereas the appropriate quantity is the change in absolute magnitude at theemitted wavelengths, and evolution is more rapid at these shorter wavelengths.     

The detection of the 5577.3å line of [OI] in comets

The spectral synthesis of C ₂ Swan band sequence V = – 1 indicates the intensity of the forbidden green oxygen line of 5577.3 to be about 3 to 5% of the 6300 line. Therefore, it appears that the green line should be observable in high-resolution spectra of a bright comet. Festou and Feldman suggest red/green >/ 10 means a water parent origin.     

Comet Sugano-Saigusa-Fujikawa (1983V)--a small, puzzling comet

Spectroscopic and infrared observations of Comet Sugano-Saigusa-Fujikawa (1983V) were obtained during its close approach to the Earth on 11-14 June 1983. The [O I] production rates of 1.8 +/- 0.9 x 10(26) atoms/s observed on 12.3 June and 7 +/- 3.5 x 10(26) atoms/s on 13.4 June lead to derived water-production rates of 3 x 10(27) mol/s on 12 June and 1.1 x 10(28) mol/s on 13 June. The abundances of the minor species NH2, CN, C2, and C3 are unusually low relative to [O I]. The upper limit to the average nuclear radius from our infrared and visual photometry on 12-13 June (assuming that the entire signal came from the nucleus) is approximately 370 m. The dust/gas mass ratio was <0.01 on June 12 and <0.005 on June 13.