Astron. Astrophys. 345, 521-530 (1999)

BVRI photometry of the star-forming region NGC 2264: the initial mass function and star-forming rate ^*

E. Flaccomio ¹, G. Micela ², S. Sciortino ², F. Favata ³, C. Corbally ⁴ and A. Tomaney <sup>5

1</sup> Dipartimento di Scienze Fisiche ed Astronomiche - Università di Palermo
² Osservatorio Astronomico di Palermo G.S. Vaiana, Palazzo dei Normanni, I-90134 Palermo, Italy
³ Astrophysics Division - Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
⁴ Vatican Observatory Research Group, University of Arizona, Tucson, AZ 85721, USA
⁵ Department of Astronomy, Columbia University, New York, NY, USA

Received 1 September 1998 / Accepted 29 January 1999

Abstract

The pre-main sequence (PMS) population in the mass range between and in southern part of the star-forming region NGC 2264 has been studied, determining both the Initial Mass Function in the region as well as the star-formation rates for different mass ranges. The sample is a composite one, derived through the union of samples obtained through different techniques and each suffering from different biases: previously known PMS stars in the region from the literature, photometrically-selected T Tauri candidates (from our own photometric data, discussed in detail in the present paper) and X-ray selected PMS candidates (discussed in detail in a companion paper) have been joined to form a sample which we show to be statistically complete (i.e. free from the biases which affect each of the parent samples) down to (while being incomplete at lower masses). Individual masses and ages have been derived by placing the individual stars on evolutionary tracks, allowing us to derive both the IMF and the star formation rate.

The Initial Mass Function thus derived for NGC 2264 shows evidence for a bimodal distribution of masses, with a break in the IMF at around 1 .

Key words: Galaxy: open clusters and associations: individual: NGC 2264 stars: pre-main sequence stars: late-type stars: formation

* Based on observations with the VATT: the Alice P. Lennon Telescope and the Thomas J. Bannan Astrophysics Facility. Table 3 is available in electronic form at CDS via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/345/521

Send offprint requests to: Ettore Flaccomio (ettoref@oapa.astropa.unipa.it)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
  • 2.1. Instrumentation and observations
  • 2.2. Data reduction and photometry
• 3. Results
  • 3.1. Color-color diagrams
  • 3.2. The membership catalog
  • 3.3. The H-R diagram
  • 3.4. Dynamical Evolution and Mass Segregation
  • 3.5. The Initial Mass Function in NGC 2264
  • 3.6. Star formation history
• 4. Summary and Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999
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