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The companion to the central star of Abell 35

  • A. A. Gatti (a1), J. E. Drew (a1), S. Lumsden (a2), T. Marsh (a3), C. Moran (a3) and P. Stetson (a4)...

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Close binary systems may undergo the “Common Envelope” (CE) phase when the primary star expands on the red giant branch or the asymptotic giant branch. Filling its Roche Lobe, the primary transfers mass to the companion driving it out of thermal equilibrium and causing it to expand as well. The giant core and the companion star become surrounded by a CE. When sufficient energy is deposited in the circumstellar material this will be ejected and the binary orbit will shrink further (see review by Iben 1995). Planetary nebulae (PNe) with short-period binary nuclei are considered the most probable post-CE candidates. Abell 35, Lotr 1 and Lotr 5 (the Abell 35-like objects) are the only three PNe with binary nuclei known to contain a very hot UV-bright primary and a chromospherically active, rapidly rotating, G-K companion that dominates the optical spectrum. The origin of these unusual systems is unclear and hence presents a challenge to theories of binary star evolution. Identified in 1966 by Abell, Abell 35 is possibly the largest PN known (D=1.6 pc at a distance of 360 pc, Jacoby 1981) and also the oldest (the kinematical age is 185.000 years from the small expansion velocity of 4.2 km/s, Bohuski 1974). The bright giant star BD −22° 3467 (mv = 9.6mag) lies off-center within the nebula. A white dwarf was detected at the same location in 1988 in IUE spectra obtained by Grewing and Bianchi. BD − 22° 3467 has a vsin i of 90 km/s (Vilhu et al. 1991), variable Hα and Ca II emission lines associated with chromospheric activity, and a variable light curve (P=0.76 days, Jasniewicz and Acker 1988) probably produced by the rotation of the giant star. All attempts to determine the orbital period have failed, raising doubts as to whether the nucleus of Abell 35 is a close binary at all. In pursuit of this point, we have started a radial velocity study of the giant companion.

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References

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Abell, G. O., ApJ., 144, 259 (1966).
Bohuski, T. J. and Smith, M. G., ApJ., 193: 197203 (1974).
Grewing, M., Bianchi, L., ESA SP-281, Vol 2, p. 177 (1988).
Iben, I., Physics Reports, 2509, 194 (1995).
Jacoby, G. H., ApJ., 244, 903911 (1981).
Jasniewicz, G. and Acker, A., A&A, 189, L7L9 (1988).
Vilhu, O., Gustafsson, B., Walter, F. M., A&A, 241, 167175, (1991).

The companion to the central star of Abell 35

  • A. A. Gatti (a1), J. E. Drew (a1), S. Lumsden (a2), T. Marsh (a3), C. Moran (a3) and P. Stetson (a4)...

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