A photometric and spectroscopic study of the association LH 47 in the superbubble N 44 in the LMC ^*,**

¹ Sternwarte der Universität Bonn, Auf dem Hügel 71, D–53121 Bonn, Germany
² University of Illinois at Urbana-Champaign, Department of Astronomy, 1002 West Green Street, Urbana, IL 61801, U.S.A.

Send offprint request to: J.-M. Will

Received: 13 May 1996
Accepted: 10 October 1996

Abstract

The OB association LH 47 inside the superbubble N 44 in the Large Magellanic Cloud (LMC) is analyzed with CCD photometry. For the bright blue stars spectra in the optical and UV have been taken. The observed U, B, and V magnitudes and colours are converted to  and L. From isochrone fits to the colour magnitude diagram (CMD), we find an age of the association of about 5 to 6 Myr. The stellar population outside the shell is of similar age, so there is no direct evidence for sequential star formation. The slope of the luminosity function () agrees with what has been found for other young associations. We compare two methods to derive the slope of the initial mass function (IMF). First we count all stars along the main sequence in the BV CMD. Second we count the stars between stellar evolutionary tracks in the Hertzsprung-Russell diagram (HRD). Both methods give mainly the same result, i.e. and , respectively. The IMF of the stars outside the shell shows a slightly steeper slope than inside the shell. The slope of the IMF is very similar to values found for other associations and open clusters as well as in the solar neighborhood, thus supporting the idea of an universal shape of the IMF. LH 47 turns out to be a well behaved young association embedded in a molecular cloud.