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J. Song (Space Telescope Science Institute), M. Robberto (ESA-Space Telescope Science Institute), S. V. W. Beckwith, R. B. Makidon (Space Telescope Science Institute), N. Panagia (ESA-Space Telescope Science Institute)
We have observed the core of the Orion Nebula in the U- and B-bands using the Wide Field Planetary Camera 2 onboard the Hubble Space Telescope. We obtained photometry for 91 stars in the U-band (F336W) and 71 stars in the B-band (F439W), and searched the archive of WFPC2 images for V-band (F547M) and I-band (F791W) photometry. Our primary sample is made of 12 sources having complete WFPC2 UBVI photometry and known spectral type. We locate each star on the HR diagram considering both the standard ISM reddening law with RV=3.1 and the ``anomalous'' reddening law with RV=5.5 more appropriate for the Orion Nebula, together with two different bolometric corrections. We find that the RV=5.5 reddening law provides the smallest scatter in age and a HR diagram nicely compatible with the Palla and Stahler model. With the possible exception of one source, all sources show excess luminosity in the U-band, that we attribute to accretion. The known correlation between the U-band excess and the total accretion luminosity, recalibrated to our photometric system, allows to estimate the accretion rates, all within the range 10-7 - 10-10 M\odotyr-1. Within our sample, the mass accretion rates appear to decrease with the stellar age.
The author(s) of this abstract have provided an email address for comments about the abstract: robberto@stsci.edu
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.