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

TL;DR

This study analyzes optical observations of two dwarf novae, revealing their orbital periods, eclipse behaviors, and spectral features, and suggests they are similar to U Gem-type systems with dynamic accretion discs.

Contribution

First detailed optical analysis of CRTS J080846.2+313106 and V416 Dra, including discovery of a new orbital period for CRTS J080846.2+313106 and insights into their accretion disc behavior.

Findings

CRTS J080846.2+313106 has an orbital period of 4.9116 hours.

V416 Dra shows increased disc size during outbursts.

Both systems exhibit spectral features typical of U Gem-type dwarf novae.

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. CRTS J080846.2+313106 has been found to vary with a period of 4.9116$\pm$0.0003 h, which was not found in earlier studies and is provisionally suggested as the orbital period of the system. In both long-period systems, the observed dominant signal at 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, the investigation of accretion disc eclipse in V416 Dra implies 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. 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 both systems look remarkably similar, and seem to resemble the characteristics of U Gem-type dwarf novae.