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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