EDP Sciences
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Volume 434, Number 2, May I 2005
Page(s) 497 - 506
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041041

A&A 434, 497-506 (2005)
DOI: 10.1051/0004-6361:20041041

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

II. H and H $\mathsf{_2}$ near infrared emission
G. Testor1, J. L. Lemaire2, D. Field3 and G. Callejo2

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)

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 $M_\odot$) 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. $A_{\rm V}$ in N88A is revisited using near-IR P$\delta$, P$\gamma$ and P$\beta$ 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 $\mu$m to 2.45 $\mu$m. 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.

Key words: Magellanic Clouds -- stars: formation -- circumstellar matter -- ISM: molecules -- infrared: stars -- stars: evolution

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