Variation in the Near-Infrared Surface Brightness Distribution of the Bipolar Nebula OH 231.8+4.2
Abstract
Near-infrared images of the bipolar nebula OH 231.8 + 4.2 obtained over a 3 yr period suggest that its surface brightness distribution varies with time. We present a model in which the variations are explained by the differences in travel times for photons scattered off dust grains at various positions along the polar axis of the nebula. This formulation allows us to determine the brightness fluctuations and heliocentric distance (d) of the embedded source and the inclination of the nebula (i). To explain the observed variations, the central star must possess a 2.2-micron amplitude of about 2 mag - larger than determined previously from aperture photometry and consistent with the classification of the central star as a Mira variable, rather than as a supergiant. We estimated d of about 1300 pc, and i of greater than about 35 deg with the south lobe further away. Comparison with published 2.2-micron photometry suggests that the nebula is brighter at maximum and shows a larger variation in integrated surface brightness than measured about 10 yr ago. These results demonstrate the potential utility of long-term monitoring, via near-IR imaging, of reflection nebulae around variable stars.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1992
- DOI:
- 10.1086/171880
- Bibcode:
- 1992ApJ...398..552K
- Keywords:
-
- Brightness Distribution;
- Infrared Imagery;
- Mira Variables;
- Reflection Nebulae;
- Light Curve;
- Stellar Models;
- Stellar Spectrophotometry;
- Astrophysics;
- STARS: CIRCUMSTELLAR MATTER;
- ISM: INDIVIDUAL ALPHANUMERIC: OH 231.8;
- 4.2;
- ISM: STRUCTURE;
- MASERS;
- STARS: VARIABLES: OTHER MISCELLANEOUS