ﻻ يوجد ملخص باللغة العربية
We present FOS observations of O III] 1666 A and C III] 1909 A emission in H II regions in dwarf irregular galaxies to measure C/O abundance ratios in those galaxies. We observe a continuous increase in C/O with increasing O/H over the range -4.7 < log(O/H) < -3.6. One interpretation is that the most metal-poor galaxies are the youngest and dominated by the products of early enrichment by massive stars, while more metal-rich galaxies show increasing, delayed contributions of C from intermediate mass stars. However, recent evolution models for massive stars including mass loss suggest that the yield of C relative to O may increase with metallicity; new chemical evolution models for the solar neighborhood which account for this predict a C/O abundance evolution similar to that observed in the metal-poor galaxies. The C/N ratio increases steadily with O/H in the irregular galaxies, but is much smaller in solar neighborhood stars and H II regions. This may indicate that the bulk of N production is decoupled from that of C in the Galaxy.
We report the results of a time-resolved eclipse mapping of the dwarf nova IP Pegasi during the decline of its May 1993 outburst from HST/FOS fast spectroscopy covering 3 eclipses in the ultraviolet spectral range.
Minor mergers have been proposed as the driving mechanism for the size growth of quiescent galaxies with decreasing redshift. The process whereby large star-forming galaxies quench and join the quiescent population at the large size end has also been
This paper joins a series compiling consistent emission line measurements of large AGN spectral databases, useful for reliable statistical studies of emission line properties. It is preceded by emission line measurements of 993 spectra from the Large
We present new measurements of the abundances of carbon and oxygen derived from high-excitation C I and O I absorption lines in metal-poor halo stars, with the aim of clarifying the main sources of these two elements in the early stages of the chemic
We investigate in detail the white dwarf cooling sequence of the globular cluster Messier 4. In particular we study the influence of various systematic uncertainties, both observational and theoretical, on the determination of the cluster age from th