Surface brightness profiles of dark nebulae: the Thumbprint nebula in Chamaeleon.
Abstract
The surface brightness profiles of a "bright dark nebula" (named by one of us, M. P. F., as the "Thumbprint Nebula," or TPN) in Chamaeleon have been observed by means of photographic photometry in four broad bandpasses. The surface brightness can be explained as the result of illumination by the general galactic star field, provided the single scattering albedo of the dust in the nebula a 0.7. The brightness distribution across the pronounced dark core of the nebula is characteristic of a density distribution p(r) r -2 and requires the presence of strongly forward throwing scattering particles with a phase function asymmetry of g = 0.7. The form of the density distribution has been confirmed by independent star counts in the outer portions of the nebula. The extinction through the opaque center of the cloud is found to be 17.5 mag at 4300 A. For a distance of 400 pc to the nebula we derive a central density of 3 >c 10-19 g cm -3 and a total mass of 9 M0. The physical properties of TPN make it appear that the nebula is in a state of gravitational contraction, but the range of observational uncertainties does not exclude the possibility of hydrostatic equilibrium. Subject heading: nebulae: general
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1976
- DOI:
- 10.1086/154654
- Bibcode:
- 1976ApJ...208..709F
- Keywords:
-
- Astronomical Models;
- Luminous Intensity;
- Nebulae;
- Radiative Transfer;
- Brightness;
- Density Distribution;
- Gravitational Collapse;
- Radiant Flux Density;
- Astrophysics