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Title:
AG Pegasi - A multishell radio source
Authors:
Kenny, H. T.; Taylor, A. R.; Seaquist, E. R.
Affiliation:
AA(Calgary, University, Canada), AB(Calgary, University, Canada), AC(Toronto, University, Canada)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 366, Jan. 10, 1991, p. 549-559. (ApJ Homepage)
Publication Date:
01/1991
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
RADIO SOURCES (ASTRONOMY), STELLAR ENVELOPES, SYMBIOTIC STARS, RADIO ASTRONOMY, STELLAR MODELS, VERY LARGE ARRAY (VLA)
Astronomy Keywords:
stars: circumstellar shells stars: individual (AG Pegasi) stars: radio radiation, stars: symbiotic
DOI:
10.1086/169590
Bibliographic Code:
1991ApJ...366..549K

Abstract

AG Pegasi is one of about 30 symbiotic stars that have been detected as radio sources. It is a symbiotic nova system that has taken longer than 100 yr to return to quiescence after a major outburst (ca. 1850). We present here radio continuum observations of the system made at nine epochs over a period of 3 yr. These observations include data at four frequencies (1.5, 5, 15, 22 GHz) and from all configurations of the Very Large Array (VLA).

The observations reveal that circumstellar gas exists in four distinct radio features: an unresolved central source of diameter less than 0".1, an inner nebular shell with diameter of 2".00±+ 0".06 and mass of 4 × 10-5 Msun, and an intermediate nebula with diameter of ˜20" and mass of ˜10-4 to 10-5 Msun, an intermediate nebula with diameter of ˜1' and a mass of 10-5 to 10-4 Msun. The outer nebulosity is thought to be the remnant of the 1850 outburst. The intermediate nebula appears to represent the preeruption mass loss from the system's M3 giant.

Comparison of very high resolution observations, 2.7 yr apart, show that the inner nebular shell is expanding at 60±15 km s-1. It is detached from the central unresolved object and is brightening with time. This nebula may arise from an interaction between preeruption mass loss and a fast diffuse wind which is at present emanating from the compact companion of the M3 giant.

The flux of the central unresolved object is found to be variable with time and appears to be periodic in phase with the photometric light curve of the system.

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