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

• Published in: Astronomy and astrophysics (Berlin) 2010-02, Vol.510, p.A95
• Main Authors: Testor, G., Lemaire, J. L., Heydari-Malayeri, M., Kristensen, L. E., Diana, S., Field, D.
• Format: Article
• Language: English
• Subjects: Astrophysics; circumstellar matter; Clusters; dust; extinction; HII regions; Imaging; ISM: individual: N88A; Magellanic Clouds; Physics; Sheet molding compounds; Shells; Spatial resolution; Spectroscopy; Stars; stars: formation
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/200911786

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$\arcsec$, 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. $J-K$ 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$\arcsec$ (~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 $H-K$ ≥ 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$\arcsec$ 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$\arcsec$ east of this star, a heavily embedded core is detected in the L'-band. This core with L' ~ 14 mag and $L'-K$ ≥ 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$\arcsec$ (~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.