Showing papers by "Alan Fitzsimmons published in 1992"

A comparison of oxygen and nitrogen abundances in young clusters and associations and in the interstellar gas

Abstract: We have used previously published observations of main-sequence B-type stars lying in 11 young stellar clusters and associations to estimate non-LTE abundances of oxygen and nitrogen over galactocentric distances 6

Spectroscopy of D-Type Asteroids

Abstract: We have performed a spectroscopic survey of 19 D-type asteroids. Comparison with previous photometry shows excellent agreement. Although the majority have similar colors to cometary nuclei, no cometary emission bands were present in any of the spectra. Absorption bands sporadically appearing were apparently due to stellar objects, and no features inherent to the asteroids were observed.

Galactic abundance gradients from ob-type stars in young clusters and associations

Abstract: High-resolution spectra of main sequence B-type stars in young galactic clusters have been analysed using LTE and (where appropriate) non-LTE model atmosphere calculations. A re-analysis of the O II data from 11 clusters indicates that within 2 kpc of the sun there appears to be no obvious abundance gradient with respect to galactocentric distance. However, the cluster Dolidze 25 lying at R g = 13.5 kpc has been found to be oxygen deficient, implying that the abundance gradient may be non-linear. A comparison with studies of H II regions indicates that within the uncertainties the two methods yield consistent abundances. We are currently analysing clusters with 10 kpc ≤ Ry ≤ 12kpc and will shortly be obtaining data on clusters with R g ≤ 16kpc.