The physical properties of the compact star forming region N88A and its neighbourhood in the SMC^*

I. Excitation and abundances

¹ LUTH, UMR 8102 du CNRS, Observatoire de Paris, 92195 Meudon, France e-mail: gerard.testor@obspm.fr
² LERMA, UMR 8112 du CNRS, Observatoire de Paris, 92195 Meudon, France and Université de Cergy-Pontoise, 95031 Cergy Cedex, France e-mail: jean-louis.lemaire@obspm.fr
³ Department of Physics and Astronomy, Århus University, 8000 Århus C, Denmark e-mail: dfield@phys.au.dk

Corresponding authors: G. Testor, testor@obspm.fr and L. Lemaire, lemaire@obspm.fr

Received: 1 April 2003
Accepted: 12 June 2003

Abstract

We present optical, near-infrared (NIR) images and spectra of the compact, dusty and complex HII region N88A in the SMC. The data were obtained mainly in the visible with the Boller & Chivens (B&C) spectrograph at the ESO 1.5 m telescope and recently with the infrared spectrometer and array camera (ISAAC) at the VLT, around 2 μm. The NIR observations identified a region emitting in H₂, both in and around the two major components of N88. Using long-slit spectra obtained in the 3600–10 100 Å wavelength range we have re-determined the key physical parameters of electron temperature and densities. The spectral type of the complex exciting source of N88A
has been classified as an O6-O8 V, using He and H lines in the visible and NIR, with the HeI 1.7 μm/2.11 μm line ratio in the K band spectrum, suggesting that N88A is effectively ionized by a source of type <O7 V. However, from reddening correction and the temperature determined by photoionization model calculations, the ionizing source should also contain a very early type O star. A comparison with a recent photometric study shows that the V magnitude of the exciting source of N88A has previously been overestimated. The chemical abundances of He, O, N, Ne, S, and Ar, from emission-line intensities, are also derived. Abundancies are consistent with the average abundances for SMC HII regions.