Spectropolarimetry of the symbiotic nova HM Sge

Citation
Hm. Schmid et al., Spectropolarimetry of the symbiotic nova HM Sge, ASTRON ASTR, 355(1), 2000, pp. 261-270
Citations number
49
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMY AND ASTROPHYSICS
ISSN journal
00046361 → ACNP
Volume
355
Issue
1
Year of publication
2000
Pages
261 - 270
Database
ISI
SICI code
0004-6361(200003)355:1<261:SOTSNH>2.0.ZU;2-V
Abstract
We present the first spectropolarimetric observations of the symbiotic nova HM Sge. We first note that marked spectral changes occurred: in the near I R the spectrum of the Mira in the system has clearly appeared. The nebular emission line spectrum remains largely unchanged but we detect for the firs t time the Raman line at lambda 6825. These changes indicate that the dust content in HM Sge is rapidly decreasing and chat the dust obscuration perio d which began in 1985 has come to an end. In terms of polarization we find that the red giant spectrum is intrinsical ly polarized at the 0.5 % level and the polarization signal is structured a cross the TiO absorption bands. The Raman scattered O VI line at lambda 682 5 shows a polarization of 3.4 % at an angle of 33 degrees. The behaviour of the polarization angle across the Raman line strongly indicates that an ax isymmetric O VI-H I scattering geometry prevails. The distribution of the n eutral hydrogen in the inner binary system does not seem to be strongly per turbed by binary motion. We conclude that the present binary axis is orient ated at a position angle of similar to 123 degrees. The deduced orientation of the binary axis of HM Sge is parallel or perpend icular to distinct geometric features of the surrounding nebulosity. This i ndicates that the orientation of the binary system is of prime importance f or the understanding of the nebular structure.