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J/ApJ/448/179                  HST photometry in R136 (Hunter+ 1995)
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The intermediate stellar mass population in R136 determined from Hubble Space
Telescope planetary camera 2 images
     Hunter D.A., Shaya E.J., Holtzman J.A., Light R.M., Oneil Jr. E.J., 
     Lynds, R.
    <Astrophys. J. 448, 179 (1995)>
    =1995ApJ...448..179H
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ADC_Keywords: Magellanic Clouds ; Photometry ; Clusters, open
Keywords: Hertzsprung-Russell diagram - Magellanic Clouds -
          open clusters and associations: individual (R136) - stars: evolution -
          stars: luminosity function, mass function

Abstract:
    We have analyzed Hubble Space Telescope (HST) images of the compact,
    luminous star cluster R136 in the LMC that were taken with the
    refurbished HST and new Wide Field/Planetary Camera. These images
    allow us to examine the stellar population in a region of unusually
    intense star formation at a scale of 0.01pc. We have detected stars to
    23.5 in F555W and have quantified the stellar population to an M_555.0
    of 0.9 or a mass of 2.8M_{sun}_. Comparisons of HR diagrams with
    isochrones that were constructed for the HST flight filter system from
    theoretical stellar evolutionary tracks reveal massive stars, a main
    sequence to at least 2.8M_{sun}_, and stars with M_555.0>=0.5 still on
    pre-main sequence tracks. The average stellar population is fit with a
    3-4Myr isochrone. Contrary to expectations from star formation models,
    however, the formation period for the massive stars and lower mass
    stars appear to largely overlap. We have measured the IMF for stars
    2.8-15M_{sun}_ in three annuli from 0.5-4.7pc from the center of the
    cluster. The slopes of the IMF in all three annuli are the same within
    the uncertainties, thus, showing no evidence for mass segregation
    beyond 0.5pc. Furthermore, the combined IMF slope, -1.22+/-0.06, is
    close to a normal Salpeter IMF. The lower mass limit must be lower
    than the limits of our measurements: <=2.8M_{sun}_ beyond 0.5pc and
    <=7M_{sun}_ within 0.1pc. This is contrary to some predictions that
    the lower mass limit could be as high as 10M_{sun}_ in regions of
    intense massive star formation. Integrated properties of R136 are
    consistent with its being comparable to a rather small globular
    cluster when such clusters were the same age as R136. From the surface
    brightness profile, an upper limit for core radius of 0.02pc is set.
    Within a radius of 0.4pc we estimate that there have been roughly 20
    crossing times and relaxation should be well along. Within 0.5pc
    crowding prevents us from detecting the intermediate mass population,
    but there is a hint of an excess of stars brighter than M_555.0=-5 and
    of a deficit in the highest mass stars between 0.6pc and 1.2pc. This
    would be consistent with dynamical segregation.

Objects:
    ----------------------------------------------------------
       RA   (2000)   DE      Designation(s)
    ----------------------------------------------------------
    05 38 42.8   -69 06 03   R 136 = RMC 136 = HD 38268
    ----------------------------------------------------------

File Summary:
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 FileName    Lrecl    Records    Explanations
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ReadMe          80          .    This file
table2.dat      98       3623    The photometry
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Byte-by-byte Description of file: table2.dat
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   Bytes Format  Units  Label          Explanations
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   1-  6  I6     ---    Star           Star identification number
   8- 13  F6.1   pix    Xpos          *X pixel coordinate
  15- 20  F6.1   pix    Ypos          *Y pixel coordinate
  22- 27  F6.2   mag    F336W          []?=100.00 F336W magnitude
  29- 34  F6.2   mag  e_F336W          []?=100.00 F336W magnitude uncertainty
  36- 41  F6.2   mag    F555W          []?=100.00 F555W magnitude
  43- 48  F6.2   mag  e_F555W          []?=100.00 F555W magnitude uncertainty
  50- 55  F6.2   mag    F814W          []?=100.00 F814W magnitude
  57- 62  F6.2   mag  e_F814W          []?=100.00 F814W magnitude uncertainty
  64- 71  F8.2   mag    F336W-F555W    []?=100.00 F336W-F555W color
  73- 80  F8.2   mag  e_F336W-F555W    []?=100.00 F336W-F555W color uncertainty
  82- 89  F8.2   mag    F555W-F814W    []?=100.00 F555W-F814W color
  91- 98  F8.2   mag  e_F555W-F814W    []?=100.00 F555W-F814W color uncertainty
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Note on Xpos, Ypos:
  The X,Y coordinates are those in the short exposure F555W image, and
  the coordinate system is indicated in Figure 2 of the printed paper.
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Origin: AAS CD-ROM series, Volume 5, 1995           Lee Brotzman [ADS] 10-Oct-95
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(End)                                                         [CDS]  29-Jan-1996