Abstract
Canada-France-Hawaii-Telescope adaptive optics bonnette images through narrowband filters in the K band are presented for the Arches cluster. Continuum fluxes, line fluxes, and equivalent widths are derived from high angular resolution images, some nearly diffraction limited, for the well-known massive stars in the Arches cluster. Images were obtained in the lines He I 2.06 μm, H I Brγ (2.17 μm), and He II 2.19 μm, as well as continuum positions at 2.03, 2.14, and 2.26 μm. In addition, fluxes are presented for H I Pα (1.87 μm) and a nearby continuum position (1.90 μm) from Hubble Space Telescope archival dataBased on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.. The 2 μm and Pα data reveal two new emission-line stars and three fainter candidate emission-line objects. Indications for a spectral change of one object between earlier observations in 1992–1993 and our data from 1999 are found. The ratio of He II 2.19 μm to Brγ emission exhibits a narrow distribution among the stars, suggesting a narrow evolutionary spread centered predominantly on spectral types O4 If or Wolf-Rayet stars of the WN7 subtype. From the approximate spectral types of the identified emission-line stars and comparisons with evolutionary models we infer a cluster age between ∼2 and 4.5 Myr.
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