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

Free access article

Issue		A&A Volume 407, Number 3, September I 2003


Page(s)		905 - 912
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20030974

A&A 407, 905-912 (2003)
DOI: 10.1051/0004-6361:20030974

I. Excitation and abundances

G. Testor¹, J. L. Lemaire² and D. Field³

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

(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 $\mu$ m. The NIR observations identified a region emitting in H ₂, 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 $\mu$ m/2.11 $\mu$ m 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.

Key words: galaxies: Magellanic Clouds -- ISM: individual objects: N88A (SMC) -- ISM: HII regions -- ISM: abundances -- infrared: ISM -- stars: early-type

Offprint request: G. Testor, testor@obspm.fr
and L. Lemaire, lemaire@obspm.fr

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