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Astron. Astrophys. 322, 41-48 (1997)


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A sulphur abundance study of NGC 300 by an empirical calibration method *

T. Christensen 1, 2, L. Petersen 1 and P. Gammelgaard 1

1 Institut for Fysik og Astronomi, Aarhus Universitet, Ny Munkegade, DK-8000 Å rhus C, Denmark
2 Nordic Optical Telescope, Apartado 474, E-38700 Sta. Cruz de La Palma, Spain

Received 25 June 1996 / Accepted 24 October 1996

Abstract

We propose an empirical sulphur abundance determination method based on the strong sulphur emission lines, [S II ]   [FORMULA] 6716, 6731 and [S III ]   [FORMULA] 9069, 9531 in H II regions . From a compilation of literature data we have made a calibration of sulphur abundance versus ([S II ]  + [S III ])/ [FORMULA], similar to what has been widely used for the more easily observable iso-electronic element oxygen. This enables abundance determinations in extragalactic H II regions   without measurements of weak temperature sensitive lines for use in model calculations.

As a first application of the empirical calibration 15 spectra covering the wavelength range 3650-10000 Å  have been obtained of H II regions  at various galactocentric distances in the spiral galaxy NGC 300, by employing specially designed multiaperture slitmasks which allow simultaneous observations of several H II regions . Sulphur and oxygen abundances are determined and an oxygen gradient in agreement with previously published work is found as well as a somewhat steeper sulphur abundance gradient. This results in a slight decrease of log S/O with increasing radius.

The quite low values of S/O seem to confirm the trend demonstrated by Díaz et al. (1991) of a decrease in log S/O at high metallicities, but still more data are needed before any definite conclusions can be drawn. We find as expected that the radiation softness parameter [FORMULA] decreases with increasing radius and the slope is comparable to what is found for spiral galaxies of similar metallicity.

Key words: galaxies: abundances – galaxies: NGC 300 – galaxies: spiral – galaxies: ISM

* Based on observations obtained with the Danish 1.5-m telescope at ESO, La Silla, Chile

Send offprint requests to: tina@obs.aau.dk, larsp@obs.aau.dk

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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