Bibcode
Vilchez, J. M.; Pagel, B. E. J.; Diaz, Angeles I.; Terlevich, Elena; Edmunds, M. G.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 235, Dec. 1, 1988, p. 633-653.
Advertised on:
12
1988
Citations
280
Refereed citations
238
Description
The abundance gradient in M 33 is studied on the basis of IPCS and CCD
data on emission lines in selected H II regions, using O II, O III, S
II, and S III in the wavelength range 3700-9600 A to refine the oxygen
abundances in the inner parts as well as to study the behavior of S/O.
Spatially resolved observations in each H II region permit the
ionization structure to be studied and enable ionization parameters and
stellar effective temperatures to be separately determined. The main
results are: (1) the hardness of the ionizing radiation and the
ionization parameter increase outwards (with diminishing abundances)
along the galactic radius; (2) the O/H gradient is steep in the inner
regions, but much flatter in the outer regions; (3) N/O is constant over
most of the visible disk, but lower in an outer H II region; and (4) the
S/H gradient is shallower than the O/H gradient exemplifying what
appears to be a universal trend for S/O to decrease with O/H in H II
regions. This latter trend is rather unexpected from the viewpoint of
nucleosynthesis theory.