WR Stars in the Giant HII Region NGC 4236III

Summary

We present long-slit optical and near-infrared spectroscopy of the giant HII region NGC 4236III. We have found broad emission lines at 4686 Å attributed to WR stars. We have derived the physical conditions and chemical composition of the nebula.

Introduction

HII regions are one of the most useful tools to study the properties of massive stars as well as the physical conditions and chemical composition of the interstellar medium. One of the target of the GEFE programme is the giant HII region NGC 4236III located in the outskirts of the SBd galaxy NGC 4236. The object was observed with the 4.2-m WHT telescope in La Palma, using the blue and the red arms of the ISIS spectrograph and an EEV CCD in each arm. The dispersion was 1.4 Åpix⁻¹, and the spatial sampling 0.33 arcsec pix⁻¹.

Results

The emission of the region is extended over 15 arcsec. Three different spectra were extracted (A, B, C). These spectra are typical of high-excitation HII regions. In B (Figure la), where most of the continuum emission is concentrated, we have detected a broad emission bump at 4686 Å which is attributed to WR stars.

The distribution of the emission lines Hα, [OIII], [OII], [NII] and [SIII] are quite similar; they show a maximum at 1.5 arcsec to the North of the peak of the continuum distribution.