The Peculiar Variable FG Sagittae
Abstract
The brightening of FG Sge from mpg = 13 6 in 1894 to B = 9 6 in 1965 is examined in terms of the continuous outflow of matter from a hot, subluminous star. FG Sge is centered in an apparently normal planetary nebula of 18" radius, but this envelope predates the present activity. Coudé spectrograms are available for the years 1960-1967, while information from low-dispersion plates begins in 1955 Over this period, the spectral type has changed progressively from B4 I to A5 Ta, the colors (1960-1965) have altered in the same sense, and strong P Cygni-like emission fringes at the Balmer lines have faded out The high-luminosity spectrum is interpreted as being due to gas lying above a false photosphere which itself is rising very slowly in the rapidly outflowing material, at approximately 26 stellar radii (in 1965) above the invisible central star. There has also been some variation in radial velocity and spectral char- acteristics that may be linked with the erratic UBV fluctuations observed at Sonneberg The observa- tional data are discussed on the assumption that FG Sge is in process of producing another planetary nebula as it did once before, about 3000 years ago
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1968
- DOI:
- 10.1086/149676
- Bibcode:
- 1968ApJ...153..397H