1 Introduction

Starbursts play an important role in the formation and evolution of galaxies ([Ellis 1997]), and the IMF is the key parameter in starburst models ([Stasinska & Leitherer 1996]; [Elmegreen 1997]). One of the few starburst clusters that can be studied in detail (either from the ground or space) is the central cluster of the 30 Doradus giant HII region, which, in fact, has been called the Rosetta Stone for young stellar evolution by [Walborn (1991)].

This paper is the second of a series devoted to the determination of the IMF of the ionising cluster of 30 Doradus. This a-priory simple task is made extremely complex by a number of factors including stellar crowding, strong and variable internal extinction within the cluster, overlapping of stellar ages, and degeneracy of the relation between mass and photometric indices for the most massive stars.

In Paper I of this series ([Selman et~al. 1999]) we combined accurate UBV photometry with spectral classifications in order to determine the extinction law of the dust, and map the distribution of reddening within the cluster. We also introduced a new technique to compare photometry with models in clusters with strong and variable internal extinction.

In this paper (Paper II of the series) we present spectral types for 175 stars in 30 Dor, of which 105 have not been published, obtained with the NTT multi-slit spectrograph. These types were used in Paper I for the study of the extinction law, and will be used in the study of the IMF in Paper III of the series (in preparation). Spectroscopy is critical for the study of the high-mass end of the IMF because it is impossible to determine masses for earliest O-type stars using only photometry ([Massey 1985]; [Massey 1998]). In addition to spectral types, the spectroscopy has also been used to determine the radial velocities of the stars. These data will be used in Paper IV of this series (in preparation) to investigate in depth the intriguing possibility of mass segregation in this extremely young cluster which was briefly discussed in Paper I, and which is also discussed in the present paper.

Section 2 describes the spectroscopic observations, Sect. 3 outlines the procedures followed for extracting the spectra, and Sect. 4 shows and discusses the spectral classification itself. The spatial distribution analysis of stars according to their spectral types is presented in Sect. 5.