Hubble Space Telescope NICMOS Observations of the Embedded Cluster in NGC 2024: Constraints on the Initial Mass Function and Binary Fraction

We present an analysis of NICMOS observations of the embedded cluster associated with NGC 2024. An analysis of the cluster color-magnitude diagram (CMD) using the models of D'Antona & Mazzitelli and Baraffe et al. (published in 1997 and 1998, respectively) indicates that the ratio of intermediate-mass (1.0–10.0 M⊙) to low-mass (0.1–1.0 M⊙) stars is consistent with the stellar initial mass function (IMF) for the field. In addition to the CMD analysis, we present results on the multiplicity of stars in the region. Three companions (in a sample of 95 potential primaries) were found, with angular separations between 04 and 10, translating to a projected linear separation of 184–460 AU for an estimated distance of 460 pc. The completeness of binary detections is assessed using recovery fractions calculated by a series of tests using artificially generated companions to potential primaries in the data frames. We find that the binary fraction in NGC 2024 is consistent with that of Duquennoy & Mayor (published in 1991) for solar neighborhood stars over the range of separations and companion masses appropriate for our survey.

[1]  Elizabeth A. Lada,et al.  A 2.2 micron survey in the L1630 molecular cloud , 1991 .

[2]  J. Elias,et al.  Bolometric luminosities and infrared properties of carbon stars in the Magellanic Clouds and the galaxy. , 1981 .

[3]  Glenn E. Miller,et al.  The Initial mass function and stellar birthrate in the solar neighborhood , 1979 .

[4]  J. Carlstrom,et al.  Star Formation in the NGC 2024 Molecular Ridge , 1996 .

[5]  A. Boss,et al.  Protostars and Planets VI , 2000 .

[6]  Andrea Richichi,et al.  Binary Stars in the Orion Trapezium Cluster Core , 1998 .

[7]  B. Shustov.  Protostars and Planets II , 1987 .

[8]  T. J. T. Moore,et al.  A Near-Infrared Reflection Nebula Associated with NGC 2024 FIR 4 , 1995 .

[9]  The formation of a bound star cluster: from the orion nebula cluster to the pleiades , 2000, astro-ph/0009470.

[10]  L. Close,et al.  Near-Infrared Adaptive Optics Imaging of the Embedded Cluster NGC 2024 , 2002, astro-ph/0210053.

[11]  Stefano Casertano,et al.  The 1997 HST Calibration Workshop, with a new generation of instruments : proceedings of a workshop held at the Space Telescope Science Institute, Baltimore, Maryland, September 22-24, 1997 , 1997 .

[12]  C. Lada,et al.  A Near-Infrared L-Band Survey of the Young Embedded Cluster NGC 2024 , 2000, astro-ph/0006219.

[13]  J. Najita,et al.  From Stars to Superplanets: The Low-Mass Initial Mass Function in the Young Cluster IC 348 , 2000, astro-ph/0005290.

[14]  P. Kroupa.  On the variation of the initial mass function , 2000, astro-ph/0009005.

[15]  J. Lunine,et al.  Protostars and planets III , 1993 .

[16]  G. Neugebauer,et al.  The multiplicity of T Tauri stars in the star forming regions Taurus-Auriga and Ophiuchus-Scorpius: A 2.2 micron speckle imaging survey , 1993 .

[17]  Laird M. Close,et al.  Adaptive Optics Imaging of the Orion Trapezium Cluster , 1999 .

[18]  The initial mass function of low-mass stars and brown dwarfs in young clusters , 2000, astro-ph/0004386.

[19]  M. Skrutskie,et al.  in Protostars and Planets III , 1993 .

[20]  A Preliminary Study of the Orion Nebula Cluster Structure and Dynamics , 1998 .

[21]  R. Koehler.  Multiplicity of X-Ray-selected T Tauri Stars in Chamaeleon , 2001, astro-ph/0109103.

[22]  D. Padgett,et al.  Hubble Space Telescope WFPC2 Observations of the Binary Fraction among Pre-Main-Sequence Cluster Stars in Orion , 1997 .

[23]  M. Rieke,et al.  Properties of Low-Mass Objects in NGC 2024 , 1996 .

[24]  Daniel Durand,et al.  Astronomical Data Analysis Software and Systems XI , 2009 .

[25]  R. Padman,et al.  Submillimetre continuum images of the NGC 2024 star-forming ridge , 1998 .

[26]  Donald W. McCarthy,et al.  The Multiplicity of Pre-Main-Sequence Stars in Southern Star-forming Regions , 1997 .

[27]  M. Meyer,et al.  Intrinsic near-infrared excesses of T tauri stars: Understanding the classical T tauri star locus , 1997 .

[28]  C. Chandler,et al.  Near-infrared observations of NGC 2024: identification of a 2-µm source within a dense core , 1989 .

[29]  F. Adams,et al.  Modes of Multiple Star Formation , 2001, astro-ph/0102039.

[30]  Italo Mazzitelli,et al.  New pre-main-sequence tracks for M less than or equal to 2.5 solar mass as tests of opacities and convecti on model , 1994 .