Time-resolved photometry of the nova remnants DM Gem, CP Lac, GI Mon, V400 Per, CT Ser and XX Tau^*

¹ Department of Physics, University of Warwick, Coventry CV4 7AL, UK e-mail: Pablo.Rodriguez-Gil@warwick.ac.uk
² Instituto de Astrofísica de Canarias, Vía Láctea, s/n, La Laguna, 38205 Santa Cruz de Tenerife, Spain
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
⁴ Physics Department, University College, Cork, Ireland

Received: 16 April 2004
Accepted: 7 October 2004

Abstract

We present the first results of a photometric survey of poorly studied nova remnants in the Northern Hemisphere. The main results are as follows: DM Gem shows a modulation at 0.123 d (probably linked to the orbit) and rapid variations at ∼22 min. A moderate resolution spectrum taken at the time of the photometric observations shows intense He ii λ4686 and Bowen emission, characteristic of an intermediate polar or a SW Sex star. Variability at 0.127 d and intense flickering (or quasi-periodic oscillations) are the main features of the light curve of CP Lac. A 0.1-mag dip lasting for ∼45 min is observed in GI Mon, which could be an eclipse. A clear modulation (probably related to the orbital motion) either at 0.179 d or 0.152 d is observed in the B-band light curve of V400 Per. The results for CT Ser point to an orbital period close to 0.16 d. Intense flickering is also characteristic of this old nova. Finally, XX Tau shows a possible periodic signal near 0.14 d and displays fast variability at ∼24 min. Its brightness seems to be modulated at ∼5 d. We relate this long periodicity to the motion of an eccentric/tilted accretion disc in the binary.