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J/ApJ/540/236       KH photometry of Orion Nebula Cluster   (Hillenbrand+, 2000)
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Constraints on the stellar/substellar mass function in the inner
Orion Nebula Cluster.
      Hillenbrand L.A., Carpenter J.M.
     <Astrophys. J. 540, 236 (2000)>
     =2000ApJ...540..236H
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ADC_Keywords: Clusters, open ; Photometry, infrared
Keywords: circumstellar matter -
          open clusters and associations: individual (Orion Nebula Cluster) -
          stars: luminosity function, mass function - stars: pre-main-sequence

Abstract:
    We present the results of a 0.5"-0.9" FWHM imaging survey at
    K (2.2{mu}m) and H (1.6{mu}m) covering ~ 5.1'x5.1' centered on
    {theta}^1^C Ori, the most massive star in the Orion Nebula Cluster
    (ONC). At the age and distance of this cluster, and in the absence of
    extinction, the hydrogen-burning limit (0.08M_{sun}_) occurs at
    K~13.5mag, while an object of mass 0.02M_{sun}_ has K~16.2mag. Our
    photometry is complete for source detection at the 7{sigma} level to
    K~17.5mag and thus is sensitive to objects as low-mass as 0.02M_{sun}_
    seen through visual extinction values as high as 10mag. We use the
    observed magnitudes, colors, and star counts to constrain the shape of
    the inner ONC stellar mass function across the hydrogen-burning limit.
    After determining the stellar age and near-infrared excess properties
    of the optically visible stars in this same inner ONC region, we
    present a new technique that incorporates these distributions when
    extracting the mass function from the observed density of stars in the
    K-(H-K) diagram. We find that our data are inconsistent with a mass
    function that rises across the stellar/substellar boundary. Instead,
    we find that the most likely form of the inner ONC mass function is
    one that rises to a peak around 0.15M_{sun}_, and then declines across
    the hydrogen-burning limit with slope N(log M){prop.to}M^0.57^. We
    emphasize that our conclusions apply to the inner 0.71pc x 0.71pc of
    the ONC only; they may not apply to the ONC as a whole where some
    evidence for general mass segregation has been found.

File Summary:
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 FileName  Lrecl  Records  Explanations
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ReadMe        80        .  This file
table1.dat    92      777  Keck/NIRC photometry and astrometry for the inner ONC
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See also:


Byte-by-byte Description of file: table1.dat
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   Bytes Format Units   Label     Explanations
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   1-  3  I3    ---     [HC2000]  Orion Nebula Cluster Identification number (1)
       6  I1    h       RAh       Right Ascension (J2000) (2)
   8-  9  I2    min     RAm       Right Ascension (J2000) (2)
  11- 15  F5.2  s       RAs       Right Ascension (J2000) (2)
      17  A1    ---     DE-       Declination (J2000) (2)
      18  I1    deg     DEd       Declination (J2000) (2)
  20- 21  I2    arcmin  DEm       Declination (J2000) (2)
  23- 26  F4.1  arcsec  DEs       Declination (J2000) (2)
      28  A1    ---   l_Kmag      Limit on Kmag
  29- 34  F6.3  mag     Kmag      ? The 2.2{mu}m magnitude from Keck/NIRC
      37  A1    ---   l_Hmag      Limit on Hmag
  38- 43  F6.3  mag     Hmag      ? The 1.6{mu}m magnitude from Keck/NIRC
  45- 50  F6.3  mag   e_Kmag      ? IRAF/PHOT errors in Kmag; intended for
                                     relative comparison only
  52- 57  F6.3  mag   e_Hmag      ? IRAF/PHOT errors in Hmag; intended for
                                     relative comparison only
  59- 69  A11   ---     OptID     Optical identification (3)
  71- 90  A20   ---     AltID     Alternative IR identification (4)
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Note (1): Object 187 is missing as this source is no longer believed real.
Note (2): Coordinates referenced to the ACT catalog; note that this 
    astrometry is offset by +1.5" in right ascension and -0.3" in
    declination from that reported in Hillenbrand (1997, Cat. J/AJ/113/1733>)
Note (3): Identification numbers as listed in
    Hillenbrand (1997, Cat. <J/AJ/113/1733>), NNNNa ([H97b] NNNNa in Simbad)
    or from O'Dell & Wong (1996, Cat. J/AJ/111/846>), OW-NNN-NNN 
      ([OW94] NNN-NNN in Simbad)
Note (4): Identification numbers:
   MS-NN: TCC NNN in Simbad, McCaughrean & Stauffer (1994AJ....108.1382M)
  LBLS-a: LBLS a in Simbad, Lonsdale et al. (1982AJ.....87.1819L)
    IRcN: [RLK73] IRc N in Simbad, Downes et al. (1981ApJ...244..869D)
          and Rieke, Low, & Kleinmann (1973ApJ...186L...7R)
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History:
    From ApJ electronic version
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(End)                   Greg Schwartz [AAS], Patricia Bauer [CDS]    05-Dec-2000