Speckle masking observations of HD 97950 with 75 MAS resolution: evolution of the stellar core of the starburst cluster NGC 3603

K.H. Hofmann, W. Seggewiss, and G. Weigelt

Astronomy and Astrophysics, Vol.300, p.403


We present diffraction-limited speckle masking observations of the central object HD97950 in the giant HII region and starburst cluster NGC 3603. In the reconstructed images 28 stellar components with V magnitudes in the range from 11.40 to 15.85 were detected in the 6".3 × 6".3 (∼0.2 pc × 0.2pc) field of view. Four different filters were used for the selection of distinct spectral regions comprising Hα emission, the main Wolf-Rayet and of Of-type emission lines, and two continuum bands. The angular resolutions of the four reconstructed images are 0".080 (RG 695 filter), 0".075 (658 nm), 0".079 (545 nm), and 0".174 (471 nm). Two WN stars and two further stars with mild WN-type characteristics were found. A colour-magnitude diagram has been constructed. Isochrone fits taken from the new grids of stellar models from Schaller et al. (1992), yield a cluster age of about 3.2 Myr which is in accordance with the time-scale of Wolf-Rayet star evolution and places NGC 3603 in the Carina nebula phase of young stellar aggregates. The initial mass function IMF f HD 97950 has a fairly steep slope of x = 1.59, in constrast to other Local Group giant HII regions and to starburst galaxies. HD 97950 has, compared to the cores of extragalactic HII regions, a similar, but high number ratio of WN to OB-type stars, indicating an instantaneous burst of star formation. HD 97950 hosts OB-type stars with a total mass of about 1000 M, corresponding to a mass density of ∼ 105 M pc-3. Thus, HD97950 is even more compact than R 136a, the core of the giant HII region 30 Dor in the LMC.

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