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J/ApJS/71/25        NGC 1866 CCD photometry (Brocato+ 1989)
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CCD photometry of the Large Magellanic cloud cluster NGC 1866: observational
results
    Brocato E., Buonanno R., Castellani V., Walker A.R.
   <Astrophys. J. Suppl. Ser. 71, 25 (1989)>
   =1989ApJS...71...25B      (SIMBAD/NED BibCode)
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ADC_Keywords: Clusters, globular ; Photometry, CCD
Keywords: clusters: globular - galaxies: Magellanic Clouds - photometry -
          stars: evolution

Description:
    The first part of this paper is devoted to a new CCD investigation of
    stars in the field of the LMC cluster NGC 1866. Two main frames have
    been analyzed, one covering the cluster's central region and the other
    covering an area about 10' from the cluster's center, and data has
    been collected for 2207 objects. On this basis, a C-M diagram has been
    derived, which shows a well-developed blue sequence reaching a
    limiting magnitude of about V=21mag together with the already known
    sequence of the cluster's He-burning giants. A new feature in our data
    is represented by the evidence for a second group of less luminous
    giants clumping around V=19mag, which we interpret as field He-burning
    giants. The second part of the paper is devoted to a comparison of
    these data with theoretical calculations. On the basis of new
    evolutionary tracks we find that the composition Y=0.28, Z=0.02
    already used by Becker and Mathews (1983ApJ...270..155B) offers an
    adequate fitting of the observed range in color spanned by cluster He
    giants. Theoretical isochrones for this composition have been produced
    and are compared with the observed distribution of cluster stars. A
    good agreement with the observed C-M diagram is achieved for a cluster
    age of the order of t=100Myr, whereas field stars appear to be
    significantly older, with ages of about 500 Myr or more. The
    distribution of cluster stars is studied, and both the luminosity
    function of the blue sequence (BS) and number of He giants relative to
    BS stars are examined. We find that both these cluster characteristics
    can be reproduced with a Salpeter slope for the initial mass function,
    overcoming previous difficulties raised by suggestions of a serious
    disagreement between theory and observations in this cluster. The
    Appendix reports data for the evolutionary models and for the
    corresponding isochrones, covering both the H- and He-burning phases

Objects:
    ----------------------------------------------------------
        RA  (2000)  DE    Designation(s)
    ----------------------------------------------------------
     05 13 39   -65 27.9  NGC 1866
    ----------------------------------------------------------

File Summary:
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  FileName      Lrecl  Records   Explanations
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ReadMe             80        .   This file
table3             28     2207   Magnitude, colors, and local positions of
                                  program stars
table4             33      113   Distribution of star masses along selected
                                  isochrones for the labeled values of cluster
                                  ages in Myr (Y=0.28, Z=0.02).
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Byte-by-byte Description of file: table3
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   Bytes Format Units   Label     Explanations
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   1-  4  I4    ---     Star      [1/2207]+ Star number
   6- 10  F5.2  mag     Vmag      V magnitude
  12- 16  F5.2  mag     B-V       B-V color index
  18- 21  I4    pix     Xpos      X position
  24- 27  I4    pix     Ypos      Y position
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Byte-by-byte Description of file: table4
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   Bytes Format Units    Label     Explanations
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   1-  3  I3    Myr      Age       Cluster age
   5-  9  F5.3 [solMass] logM      Mass
  11- 15  F5.3 [solLum]  logL      Luminosity
  17- 21  F5.3 [K]       logTeff   Effective temperature
  23- 27  F5.2  mag      Mv        Absolute V magnitude
  29- 33  F5.2  mag      (B-V)0    Absolute B-V colour index
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History: Prepared via OCR at CDS.
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(End)                           James Marcout, Patricia Bauer [CDS]  07-Nov-1996