N88: The physical properties of a compact star-forming region and its neighbourhood in the SMC

II. H and H₂ near infrared emission

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: 6 April 2004
Accepted: 14 December 2004

Abstract

This paper, the second in a series of papers on the conspicuous compact HII region N88A in the Small Magellanic Cloud, emphasizes the properties of the H₂ emission as well as of the surrounding stellar content of the entire Henize region N88. Using VJK photometry and stellar evolutionary models our analysis of N88 reveals a miscellaneous population of evolved stars of low and intermediate masses (1.2–8 ) in an age range of 40 Myr to 6 Gyr. The majority of these stars are found in the cluster HW 82 which also contains several main sequence stars. A_V in N88A is revisited using near-IR Pδ, Pγ and Pβ Paschen emission lines. Spectroscopic measurements of the H₂ emission in Z, J, H and K bands allow, in conjunction with measurements in the visible, a full spectral coverage from 0.37 μm to 2.45 μm. Long slit spectroscopy through N88 and the nebulosity to the east clearly distinguishes the ionization zone in N88 characterized by H I and He I emission with pure H₂ emission clearly delineated in the cloud nearby. The principal excitation mechanism for H₂ is through fluorescent excitation in a photodissociation region associated with N88A.