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 300, 403-414 (1995)
Abstract
We present diffraction-limited speckle masking observations of the
central object HD 97950 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
6.3x6.3" (about 0.2x0.2pc) field of view. Four different filters were
used for the selection of distinct spectral regions comprising Hα
emission, the main Wolf-Rayet and Of-type emission lines, and two
continuum bands. The angular resolutions of the four reconstructed
images are 0.080" (RG695 filter), 0.075" (658nm), 0.079" (545nm), and
0.174" (471nm). 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 3.2Myr 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 of HD 97950 has a fairly steep slope of
x=1.59, in contrast 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 1000Msun_, corresponding to
a mass density of ~10^5^Msun_/pc^3^. Thus, HD 97950 is even more
compact than R136a, the core of the giant HII region 30 Dor in the LMC.