VLT/NACO near-infrared imaging and spectroscopy of N88A in the SMC^*,**

G. Testor¹, J. L. Lemaire^1,2, M. Heydari-Malayeri¹, L. E. Kristensen³, S. Diana² and D. Field⁴

¹ LERMA, UMR 8112 du CNRS, Observatoire de Paris, 92195 Meudon, France e-mail: gerard.testor@obspm.fr
² Université de Cergy-Pontoise, 95031 Cergy Cedex, France
³ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁴ Department of Physics and Astronomy, Århus University, 8000 Århus C, Denmark

Received: 4 February 2009
Accepted: 24 November 2009

Abstract

Aims. We present near-infrared imaging and spectroscopic high spatial resolution observations of the SMC region N88 containing the bright, excited, extincted and compact H II region N88A of the size of about 1 pc.

Methods. To investigate its stellar content and reddening, N88 was observed using spectroscopy and imagery in the JHKs- and L'-band at a spatial resolution of ~0.1-0.3, using the VLT UT4 equipped with the NAOS adaptive optics system. In an attempt to establish if the origin of the infra-red (IR) excess is due to bright nebulosity, circumstellar material and/or local dust, we used Ks vs.  color-magnitude (CM) and JHK color-color (CC) diagrams, as well as L' imagery.

Results. Our IR-data reveal in the N88 area an IR-excess fraction of ≥30 per cent of the detected stars as well as an unprecedently detailed morphology of N88A. It consists of an embedded cluster of ~3.5 (~1 pc) in diameter of at least thirteen resolved stars superposed with an unusual bright continuum centered on a very bright star. The four brightest stars in this cluster lie red-ward of  ≥ 0.45 mag and could be classified as young stellar object (YSO) candidates. Four other probable YSO candidates are also detected in N88 along a north-south bow-shaped thin H₂ filament at ~7 east of the young central bright star. This star, which we assume to be the main exciting source, could also be complex. At 0.2 east of this star, a heavily embedded core is detected in the L'-band. This core with L' ~ 14 mag and  ≥ 4.5 mag could be a massive class I protostar candidate. The 2.12 μm H₂ image of N88A resembles a shell of a diameter of ~3 (~0.9 pc) centered on the bright star. This shell consists of three bright components, of which the brightest one superposes the ionization front. The line ratios of H₂ 2-1 S(1) and 1-0 S(0) relative to 1-0 S(1), as well as the presence of high v lines, are indicative of photodissociation regions, rather than shocks.