Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...474..741j&link_type=abstract
Astrophysical Journal v.474, p.741
Astronomy and Astrophysics
Astronomy
72
Ism: Dust, Extinction, Ism: Clouds, Ism: Individual Name: Red Rectangle, Radio Continuum: Ism, Stars: Agb And Post-Agb
Scientific paper
We report VLA observations at 3.6 cm, 2 cm, and 1.3 cm of the Red Rectangle and H alpha spectroscopy of HD 44179, the central binary star in the nebulosity. Emission is detected at all three radio wavelengths, and the source is resolved at 2 cm and 1.3 cm. Convolved to the same beam, the radio spectrum of the inner 0."76 x 0."49 is characteristic of thermal emission from ionized gas which becomes optically thin near 2 cm. The diameter of the bulk of the ionized gas producing this radio emission is between 1.3 x 1014 cm (~10 AU) and 2 x 1015 cm (~100 AU); in this region we estimate that 106 cm-3 <= ne <= 4 x 106 cm-3. The H alpha profile has both a wide (200 km s-1 full-width zero-intensity) plateau which is probably associated with a small circumstellar region (<1013 cm or ~1 AU) and a spike (FWHM ~ 20 km s-1) which we suggest is produced in the extended ionized gas (>=1014 cm) detected at radio wavelengths. We also detect low surface brightness radio emission at 2 cm and 1.3 cm, but not at 3.6 cm, that is extended well beyond 1" from the source. This extended radio emission has a spectral index between 1.3 cm and 3.6 cm greater than 3.2 and is therefore produced by grains. Our VLA data also indicate that the previously observed millimeter continuum flux cannot result from ionized gas and therefore is emitted by dust. Although uncertain, it is possible that the centimeter and millimeter wavelength continuum arise from the same dust, in which case there is probably little frequency variation in the emissivity of the dust between 1.3 cm and 0.13 cm. We propose that there is an orbiting, long-lived gravitationallly bound disk of dust grains with radii >=0.02 cm.
Balm Simon P.
Jura Michael
Turner Jonathan
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