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Astron. Astrophys. 349, 169-176 (1999)

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Circumstellar matter around M-giants in symbiotic binaries: SY Muscae and RW Hydrae *

T. Dumm 1, W. Schmutz 1,2, H. Schild 1 and H. Nussbaumer 1

1 Institute of Astronomy, ETH-Zentrum, CH-8092 Zürich, Switzerland
2 PMOD/WRC, CH-7260 Davos-Dorf, Switzerland

Received 28 May 1999 / Accepted 19 July 1999


For the eclipsing symbiotic binary system SY Mus we present evidence for an asymmetric density distribution around the M-giant. We obtain this result from an improved orbital solution. We determine a revised orbital period of [FORMULA] d from UV eclipse observations and a re-analysis of the visual light curve. Based on new radial velocity observations, we measure the epoch of mid-eclipse accurately to within [FORMULA] days, or [FORMULA] of the period. At ingress the eclipse curve is steeper and closer to mid-eclipse than at egress. From measured column densities of neutral hydrogen during egress we conclude that the mass loss rate of the M-giant is of the order of [FORMULA].

The eclipse of the UV light in SY Mus and RW Hya can be partially explained by Rayleigh scattering but there is also an additional source of opacity. HST high resolution UV observations of RW Hya during egress reveal that this additional flux attenuation is due to blanketing by numerous absorption lines, predominantly Fe II . Line blanketing is an important effect that has to be taken into account to explain the eclipse of SY Mus and of other symbiotic binaries.

Key words: stars: circumstellar matter – stars: binaries: symbiotic – stars: late-type – stars: mass-loss – stars: individual: SY Mus – stars: individual: RW Hya

* Based on observations made with IUE, HST and at the European Southern Observatory at La Silla (Chile). ESO observations were granted for the proposals 47.7-081, 48.7-083, 49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083, 54.E-061, 55.E-446, 56.E-526 57.D-684, 58.D-248, 59.D-700, 60.D-714. The visual brightness estimates were done by the RASNZ.

Send offprint requests to: T. Dumm

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999