HST Planetary Camera Photometry of the Trapezium Cluster

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Session 49 -- Associations and Clusters
Display presentation, Wednesday, 9:20-6:30, Pauley Room

[49.02] HST Planetary Camera Photometry of the Trapezium Cluster

J. Stauffer, C. Prosser and L. Hartmann (SAO), D. Soderblom (STScI), B. F. Jones (UCSC), M. Werner (JPL), M. J. McCaughrean (MPIA Heidelberg)

Herbig and Terndrup (1986 - ApJ 307 609) showed that the Trapezium cluster in Orion is by far the densest known star-forming region in the Galaxy (excluding the galactic center). We present the results from V and I images of 11 fields in the Trapezium cluster obtained with the Planetary Camera of the Hubble Space Telescope. In the approximately thirteen square arcminute region covered by these images, we have identified 326 stars, including approximately 35 new visual binaries with separations from $\sim$\ 1 arcsecond ($\sim$\ 440 AU) down to $\sim$\ 0.06 arcseconds ($\sim$\ 26 AU). Three stars with physically associated nebulosity on small scales are present near $\Theta$$^1$\ Ori, including one such object previously discovered by O'Dell et al. The photometry has enabled the identification of Trapezium cluster members down to at least V $\sim$\ 22, roughly five magnitudes fainter than the best published ground based study. We have compared the location of these stars in a color-magnitude diagram to new theoretical isochrones derived by F. Swenson. If the faintest stars are not preferentially heavily reddened, they should have masses of order 0.15 solar masses. Our data suggest that star formation in the Trapezium did not take place over an extended period - $\geq$80\% of the stars lie above the 10$^6$\ year isochrone. Furthermore, the high and low mass stars have the same inferred ages, thus providing no evidence for ``bimodal star formation", at least in this particular cluster.

This research was supported by STScI grant GO2595.01-87A.

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