Identification of V1017 Sgr as a cataclysmic variable binary system with unusually long period

CLASSICAL and dwarf novae are both binary star systems in which mass is transferred onto a white-dwarf primary from a red-dwarf secondary that overflows its Roche lobe. In classical novae, mass accumulates on the surface of the white dwarf and erupts in a thermonuclear outburst every ten thousand years or so, whereas dwarf novae show less intense and more frequent outbursts, on a timescale of months, due to brightening of an accretion disk. V1017 Sgr, the remnant of nova Sagitarii 1919, has shown out-bursts of both classical and dwarf nova type during this century. It has been described as a recurrent nova^1,2 or as a symbiotic star^2,3. Unlike most novae it has a more massive evolved secondary, of type G5 III (ref. 4), and its relation to other nova types has been obscure. Here I report a preliminary spectroscopic orbit determination which yields a period of 5.7 days. This is much longer than the typical periods of cataclysmic binaries, which are generally less than 0.5 day. I suggest that V1017 Sgr, along with a few other systems of unusually long period such as BV Cen and GK Per, may form a distinct class of cataclysmic variables, characterized by their larger, more evolved secondaries.