Disk Mass Limits and Lifetimes of Externally Illuminated Young Stellar Objects Embedded in the Orion Nebula

by

John Bally (1), Leonardo Testi (2), Anneila Sargent (2), and John Carlstrom (3)

(1) Department of Astrophysical and Planetary Sciences and Center for Astrophysics and Space Astronomy, University of Colorado, Campus Box 389, Boulder, CO 80309-0389

(2) Division of Physics, Mathematics and Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125

(3) Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637

Abstract:

We present 1.3 millimeter wavelength interferometric observations of two fields containing 6 externally illuminated young stellar objects embedded within the Orion Nebula that have been observed with Hubble Space Telescope. We derive upper bounds on the dust mass from the absence of continuum emission and upper bounds on the gas mass from the lack of CO emission. These limits imply circumstellar disk masses less than 0.015Msun for the observed sources and upper bounds on the column density of 13CO of N(13CO) < 1.5x10^15 cm^-2. Comparison with lower bounds on the dust content derived from the visibility of the circumstellar material in silhouette against the background nebular light and the extinction towards the embedded central star implies that 13CO is at least an order of magnitude less abundant in these circumstellar environments than in normal molecular clouds. The non-detection statistics are combined with estimates of UV radiation-induced mass loss rates to derive an upper bound on the UV irradiation time for these young stellar objects. The young stellar objects in the Orion Nebula that are still surrounded by circumstellar material have been exposed to external UV radiation for less than 10^5 years and possibly for as little as 10^4 years.


Mantained by: Leonardo Testi

lt@arcetri.astro.it