Unveiling the nature of two dwarf novae: CRTS J080846.2+313106 and V416 Dra

¹ Institute of Astrophysics, Pontificia Universidad Católica de Chile, Av. Vicuña MacKenna 4860, 7820436 Santiago, Chile
² Indian Institute of Astrophysics, Koramangala, Bangalore 560 034, India
³ Millennium Institute of Astrophysics, Nuncio Monseñor Sótero Sanz 100, Providencia, Santiago, Chile
⁴ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁵ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263001, India
⁷ Instituto de Astrofísica, Universidad Andres Bello, Fernandez Concha 700, Las Condes, Santiago RM, Chile
⁸ Department of Sciences, Amrita School of Physical Sciences, Amrita Vishwa Vidyapeetham, Coimbatore, TamilNadu 641112, India

Received: 18 October 2023
Accepted: 7 July 2024

Abstract

We present the analysis of optical photometric and spectroscopic observations of two non-magnetic cataclysmic variables, namely CRTS J080846.2+313106 and V416 Dra. We find CRTS J080846.2+313106 to vary with a period of 4.9116 ± 0.0003 h, which was not found in earlier studies and which we provisionally suggest is the orbital period of the system. In both long-period systems, the observed dominant signal at the second harmonic of the orbital frequency and the orbital modulation during quiescence are suggestive of ellipsoidal variation from changing aspects of the secondary, with an additional contribution from the accretion stream or hotspot. However, during the outburst, the hotspot itself is overwhelmed by the increased brightness, which is possibly associated with the accretion disc. The mid-eclipse phase for V416 Dra occurs earlier and the width of the eclipse is greater during outbursts compared to quiescence, suggesting an increased accretion disc radius during outbursts. Furthermore, from our investigation of the accretion disc eclipse in V416 Dra, we find that a total disc eclipse is possible during quiescence, whereas the disc seems to be partially obscured during outbursts, which further signifies that the disc may grow in size as the outburst progresses. The optical spectra of CRTS J080846.2+313106 and V416 Dra are typical of dwarf novae during quiescence, and they both show a significant contribution from the M2-4V secondary. The light curve patterns, orbital periods, and spectra observed in the two systems look remarkably similar, and seem to resemble the characteristics of U Gem-type dwarf novae.