V4633 Sgr – a probable second asynchronous polar classical nova |
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| Authors: | Y M Lipkin E M Leibowitz |
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| Institution: | Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE;Astrophysics Group, School of Physical and Geographical Sciences, Keele University, Keele ST5 5BG |
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| Abstract: | Photometric observations of V4633 Sgr (Nova Sagittarii 1998) during 1998–2005 reveal the presence of a stable photometric periodicity at P 1= 180.8 min which is probably the orbital period of the underlying binary system. A second period was present in the light curve of the object for 6 yr. Shortly after the nova eruption it was measured as P 2= 185.6 min . It has decreased monotonically in the following few years reaching the value P 2= 183.9 min in 2003. In 2004 it was no longer detectable. We suggest that the second periodicity is the spin of the magnetic white dwarf of this system that rotates nearly synchronously with the orbital revolution. According to our interpretation, the post-eruption evolution of Nova V4633 Sgr follows a track similar to the one taken by V1500 Cyg (Nova Cygni 1975) after that nova eruption, on a somewhat longer time-scale. The asynchronism is probably the result of the nova outburst that led to a considerable expansion of the white dwarf's photosphere. The increase in the moment of inertia of the star was associated with a corresponding decrease in its spin rate. Our observations have followed the spinning-up of the white dwarf resulting from the contraction of its outer envelope as the star is slowly returning to its pre-outburst state. It is thus the second known asynchronous polar classical nova. |
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| Keywords: | circumstellar matter novae cataclysmic variables |
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