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Astron. Astrophys. 341, 98-109 (1999)

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The ionizing cluster of 30 Doradus

I. Internal reddening from NTT photometry and multi-object spectroscopy *

F. Selman 1, J. Melnick 1, G. Bosch 2 and R. Terlevich 2

1 European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
2 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

Received 8 April 1998 / Accepted 7 September 1998


UBV profile fitting photometry is presented for 1469 stars within [FORMULA] of the center of the ionizing cluster of 30 Doradus (NGC 2070). A value of [FORMULA] is found for the extinction parameter S = E(U-B)/E(B-V), constant over almost the whole area covered by this research, with some evidence for local variations. Two reddening components can be identified: a smooth and moderate one that increases towards R136, and a clumpy one varying widely across the face of the cluster. The total-to-selective extinction parameter, [FORMULA], is found to be in the range of 3.0 to 3.7, consistent with previous determinations. A new visualization tool, the colour-magnitude stereogram, is introduced and used to argue that: (1) the observations imply mass segregation in a dust filled cluster; (2) that there has been continuous dust formation near the cluster core up to the present; and (3) that an insidious systematic error has plagued previous determinations of IMF slopes. A method to obtain an unbiased estimate of the slope is discussed.

Key words: stars: early-type – stars: luminosity function, mass function – ISM: dust, extinction – Galaxy: open clusters and associations: general – galaxies: Magellanic Clouds

* Based on observations collected with the NTT ESO telescope. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr/pub/cats/J/A+A/341/98 ( or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/341/98

Send offprint requests to: fselman@ESO.org

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© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998