Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...525l.113j&link_type=abstract
The Astrophysical Journal, Volume 525, Issue 2, pp. 113-L116.
Astronomy and Astrophysics
Astronomy
34
Stars: Circumstellar Matter, Stars: Mass Loss, Stars: Winds, Outflows
Scientific paper
We have used the Keck I telescope to resolve at three mid-IR wavelengths the emission from HD 179821 (=RAFGL 2343), a G-type supergiant of perhaps 30 M_solar with a detached dust shell. The shell is very approximately circular in shape with an inner diameter of ~3.3", corresponding to 3.0x10^17 cm. We estimate that the star was losing ~4x10^-4 M_solar yr^-1 until about 1800 yr ago, when the mass loss slowed dramatically. During the past ~10^4 yr, the star has lost ~10% of its initial mass. The star lies about 0.35" off center and is closer to the brighter, northern hemisphere of the nebula, which can be explained if the outflow velocity V_∞ deviates by +20% from the average in the southern hemisphere and -20% from the average in the northern hemisphere. The mass-loss rate M(θ) may have been inversely correlated with the outflow velocity so that the momentum outflow p was isotropic during the mass-loss phase. It also seems that M_totalV_∞ was within a factor of 2 of L_*/c, where L_* is the current luminosity of the star; the mass loss may have been driven by radiation pressure. These results may help characterize the asymmetric circumstellar winds into which supernova explosions propagate.
Jura Michael
Werner Michael W.
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