Research on Orion

(IMF updated as of 11/99)

I have worked on an analysis of the stellar population and star-forming history of the Orion Nebula Cluster (ONC), located in the Ori OBIc/d region of the Orion Molecular Cloud Complex. The ONC harbors the namesake Trapezium stars, and is *the* densest of nearby star-forming regions by a factor of 3-10. Despite its scientific and popular fame (they've even made a movie!) , the stellar population of the ONC remains largely unexplored, due in large part to the strength and extreme spatial variability of the optical nebulosity. Past work included a synthesis of near-infrared photometry, optical photometry, and optical spectroscopy for several thousand stars located within about 2.5pc of the Trapezium stars. More recently we have worked on deeper near-infrared photometry in the inner 5.1 x 5.1 arcmin^2 of the cluster and pushed our mass function measurements down to 0.02 Msun. Interestingly, this has led us to a revision of the mass function results presented earlier (see above .gif) and this URL for details.

A related study has been of the infrared variability exhibited by stars located within the spatial boundaries of these previous stellar population studies and extending out to 0.8 x 6 degrees^2. Those results have be found here.

I have collected (stolen??) the following set of images on the region:

• molecular data from the FCRAO chemistry survey (centered near BN/KL)
• interferometric molecular data from BIMA (centered on BN/KL)
• interferometric data from the VLA

• 8-20u images from the MSX satellite (Kraemer et al. ApJ 2003)
• 12u, 25u, 60u, and 100u data from the IRAS postage stamps
• 37u data from Stacey's work with the KWIC camera
• 10u and 20u data from Hayward's work with the SpectroCam-10 camera

• 1.2,1.6,2.2u color image from the 2MASS survey (~5" FWHM)
• 2.2u data from the 2MASS prototype camera (~5" FWHM)
• 2.2u data from the NOAO SQIID camera (~3.5" FWHM)
• 2.2u data from the UMass NICMASS camera (2" FWHM)
• 2.2u data from McCaughrean's work with the MAGIC camera (0.7" FWHM)
• 1.6 and 2.2u data from Keck/NIRC (0.5-0.9" FWHM)
• near-infrared data on the BN region from HST-NICMOS
• near-infrared data from Subaru
• near-infrared H2 data from Subaru
• near-infrared data from the VLT (McCaughrean et al.)

• optical emission-line data from O'Dell and Wen's work with HST-WFPC2
• a compilation of star-disk systems by Bally etal
• the silhouette disks from McCaughrean and O'Dell
• the core of the Trapezium also from Bally etal
• red optical image of mine from the KPNO 0.9m showing the area of the cluster covered in the HR diagram (see above .gif).
• wider field (3 x 3 deg^2) spatial distribution of I-band sources also from the KPNO 0.9m

• x-ray data from Gagne's work with ROSAT
• x-ray data from Chandra
• schematic of the Ori OBI stellar subgroups, from Warren & Hesser (1977)

• finally, i don't quite understand what is going on in this one

And here is some science (or at least how things appeared in my 1997,1998 series of papers on the ONC):

• the distribution of spectral types compared to other regions of low-mass star formation
• the HR diagram and an expanded view at the low-mass end with either CM convection or MLT convection
  (these figures use the theoretical pre-main sequence evolutionary predictions of D'Antona/Mazzitelli at the low-mass end, Swenson et al. at intermediate masses, and Ezer/Cameron at high masses.)
• the measured initial mass function as published in Hillenbrand (1997) -- see revision below, however!
• the low-mass mass distribution as a function of limiting magnitude
  (i claim the survey is representative of the stellar population
  down to I=17.5 mag, which corresponds to 0.1Msun
  for a cluster age of 1Myr assuming a mean extincton of Av=2 mag)
• the low-mass mass distribution as a function of projected cluster radius

• the ONC mass function now updated for new theoretical models (D'Antona/Mazzitelli), new transformations between theoretical and observational quantities, and new data which extend our measurements down to 0.02 Msun. This will be published in Hillenbrand & Carpenter (2000). Here is a three-panel comparison of results along the way.

• an optical-infrared color-color diagram
• an infrared color-color diagram
• variation of the infrared excess fraction with projected cluster radius via the V-I vs I-K diagram and the J-H vs H-K diagram
• an infrared color-magnitude diagram

See my publications page for some ONC-related papers including the data tables.

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