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Astron. Astrophys. 339, 385-397 (1998)


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The distribution of stars in three regions in the northeastern part of the Large Magellanic Cloud *

B.E. Westerlund 1, K. Lundgren 1, B. Pettersson 1 and E. Koziej 2

1 Astronomical Observatory, Uppsala University, Box 515, S-75120 Uppsala, Sweden
2 Kasprowicska 22, Torun, Poland

Received 24 November 1997 / Accepted 20 July 1998

Abstract

B,V-CCD photometry has been obtained for stars in two fields in the NE part of the Large Magellanic Cloud (LMC) and photographic photometry, and a calibrating CCD sequence, for a third field. The colour-magnitude diagrams (CMDs) and luminosity functions (LFs) for main sequence (MS) and red giant (RG) stars in the fields are established. The red giant clumps (RGCs) are found to be bimodal and to contain stars from one old population, [FORMULA] 10 Gyr, and one younger, [FORMULA] 0.3-4 Gyr old. Analyses of published data for a number of LMC fields reveal similar compositions of their RGCs. These epochs of star formation are common to most of the studied LMC fields; only those in or close to now active star-forming regions contain a considerably younger population. Comparisons with recent HST results for main-sequence stars permit the identification of star formation events [FORMULA] 1 and 2 Gyr ago.

The data are used to estimate the masses of Population II and the intermediate-age Population I to [FORMULA] and [FORMULA], respectively, meaning that the burst(s) of star formation which occurred between 4 and 0.3 Gyr ago were about 3 to 4 times as productive as the original star production in the LMC.

Key words: Hertzsprung-Russel(HR) diagram – stars: luminosity function, mass function – galaxies: evolution – Magellanic Clouds – galaxies: stellar content

* Based on Observations carried out at the European Southern Observatory, La Silla, Chile

© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998

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