Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aj....119.3026r&link_type=abstract
The Astronomical Journal, Volume 119, Issue 6, pp. 3026-3043.
Astronomy and Astrophysics
Astronomy
46
Stars: Pre-Main-Sequence
Scientific paper
We present an optical study of four 45'×45' fields centered ~0.5d east, west, north, and south of the Orion Nebula Cluster center. We have measured V and IC photometry for ~5000 stars, and U photometry for ~1600 of these. We have obtained spectral classifications for ~300 of the stars with UVIC photometry plus an additional ~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 ~230 active accretion disk candidates and estimate the accretion disk fraction at >~40%. We use the magnitude of the ultraviolet excess to infer disk accretion rates. The mass accretion rate (M) 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 Msolar. Although complicated selection effects are likely to affect the overall trends with mass and age, we are sensitive to, but do not see, high M-values associated with the older ages and lower masses in our sample. The mean value of M is ~10-8 Msolar yr-1, with a range of more than 1 order of magnitude at all ages and masses. We find an age and age spread for our sample of 106.0+/-0.4 yr with no variation within or between our fields. Meaningful constraint of the mass distribution is precluded because of the completeness limits of our survey.
Adams Mark T.
Duncan Douglas K.
Hillenbrand Lynne A.
Makidon Russell
Patten Brian Michael
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