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Astron. Astrophys. 332, 575-585 (1998)

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The fine structure of the Pleiades luminosity function and pre-main sequence evolution

A.N. Belikov 1, S. Hirte 2, H. Meusinger 3, A.E. Piskunov 1 and E. Schilbach 2

1 Institute of Astronomy of the Russian Acad. Sci., 48 Pyatnitskaya St., Moscow 109017, Russia (abelikov@inasan.rssi.ru; piskunov@inasan.rssi.ru)
2 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany (shirte@aip.de; eschilbach@aip.de)
3 Thüringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany (meus@tls-tautenburg.de)

Received 22 September 1997 / Accepted 27 November 1997

Abstract

The luminosity function (LF) of the Pleiades cluster stars was constructed for the study of the LF fine structure related to pre-MS stellar evolution. Theoretical luminosity functions based on present-day pre-MS and MS stellar models were constructed and compared with observations. We tested both power- and log-normal laws describing the cluster star IMF. Both single star formation burst- and age spread-models were examined. The agreement between the observed Pleiades CMD with the new HIPPARCOS distance and the theoretical ZAMS for a normal metallicity is excellent when the model positions in the HRD are corrected to the helium abundance Y=0.34. The corresponding age of the cluster is [FORMULA]. Three features (dips) were found in the observed cluster LF in a magnitude range [FORMULA] - [FORMULA]. Two of them (at [FORMULA] and [FORMULA]) are assumed to be field LF features: Wielen and Kroupa dips. Theoretical models fail to reproduce them. We attributed the third (brightest) detail (the dip at [FORMULA]) to the pre-MS evolution of Pleiades stars. The observed Pleiades LF corresponds in its brighter part to the standard Population I IMF. The log-normal IMF fits the observations much better than a simple power-law IMF. The brightest LF feature could be reproduced in the theoretical LF if a substantial age spread of order of several tens of Myrs is supposed to exist among the Pleiades stars.

Key words: open clusters and associations: individual: Pleiades – stars: luminosity function, mass function – stars: pre-main sequence

Send offprint requests to: E. Schilbach

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© European Southern Observatory (ESO) 1998

Online publication: March 23, 1998
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