Circumstellar Disk Candidates Identified from Ultraviolet Excesses in the Orion Nebula Cluster Flanking Fields

We present an optical study of four 45' x 45' fields centered similar to 0.degrees 5 east, west, north, and south of the Orion Nebula Cluster center. We have measured V and I-C photometry for similar to 5000 stars, and U photometry for similar to 1600 of these. We have obtained spectral classifications for similar to 300 of the stars with UVIC photometry plus an additional similar to 200 stars located outside the area of our photometric survey. Dereddened photometry allows us to investigate the evidence for circumstellar accretion disks from excess emission at ultraviolet wavelengths, as well as the mass and age distributions of our sample. We find similar to 230 active accretion disk candidates and estimate the accretion disk fraction at greater than or equal to 40%. We use the magnitude of the ultraviolet excess to infer disk accretion rates. The mass accretion rate ((M) over bar) decreases slowly with age over the limited age range spanned by our data, 1-3 Myr, and increases slowly with mass over the limited mass range 0.2-1.2 M.. Although complicated selection effects are likely to affect the overall trends with mass and age, we are sensitive to, but do not see, high hi-values associated with the older ages and lower masses in our sample. The mean value of (M) over bar is similar to 10(-8) M. yr(-1), with a range of more than I order of magnitude at all ages and masses. We find an age and age spread for our sample of 10(6.0+/-0.4) y, with no variation within or between our fields. Meaningful constraint of the mass distribution is precluded because of the completeness limits of our survey.