A homogeneous analysis of archival and new low-resolution spectra of YZ Cancri

Zhibin Dai, Lihuan Yu, Jiao Li, Xuefei Chen, Zhanwen Han

First listed 2026-09-17 | Last updated 2026-09-16

Abstract

YZ Cancri is an SU UMa-type dwarf nova with sparse and heterogeneous optical spectroscopy. We present a homogeneous analysis of archival outburst-related spectra and seven new low-resolution quiescent spectra. We consistently characterize the Balmer, He I, Fe II, O I, and occasional He II and Bowen features, and assess which state-dependent differences are robustly supported. We applied a common continuum-normalization and line-measurement procedure, measuring equivalent widths, integrated line intensities, and selected profile parameters, and comparing line morphologies and intensity ratios between quiescent and outburst-related states. Because the spectra have modest and nonuniform resolving power and are not orbital-phase resolved, profile widths and centroid shifts are used only as relative diagnostics. Outburst-related spectra are dominated by broad Balmer absorption or composite profiles, whereas quiescent spectra show strong single-peaked Balmer and He I emission, recurrent Fe II λ5169, and weak O I λ7772 emission. He II λ4686 is detected in only two quiescent exposures, and the Bowen blend in one. The quiescent Balmer decrement is relatively flat, while the He I ratios show substantial exposure-to-exposure scatter. The measured Fe II ratios show no clear systematic departure from optically thin reference values, although blending limits their interpretation. These spectra establish an empirical state-dependent description of YZ Cnc and provide a reference dataset for future phase-resolved, higher-resolution spectroscopy.

Short digest

Dai et al. homogenize three calibrated archival outburst-related spectra and seven new BFOSC quiescent exposures of the SU UMa dwarf nova YZ Cnc, applying a common continuum and line-measurement procedure across Balmer, He I, Fe II, O I, He II, and Bowen features. The central state contrast is clear: outburst-related spectra show broad Balmer absorption or composite profiles, while quiescence is characterized by strong single-peaked Balmer and He I emission, recurrent Fe II λ5169, and weak O I λ7772; He II λ4686 and the Bowen blend appear only intermittently. The line-ratio analysis finds a relatively flat quiescent Balmer decrement, variable He I ratios, and no compelling Fe II departure from optically thin expectations, yielding a useful empirical reference for future phase-resolved, higher-resolution mapping of the line-forming gas despite the present spectra's limited resolution and phase coverage.

Key figures to inspect

• Figure 1. This archival-spectrum overview establishes the heterogeneous outburst-related and qualitative comparison material, making the broad Balmer absorption and composite-profile states visually explicit before the homogeneous measurements are introduced.
• Figure 2. The BFOSC quiescent sequence is the key observational evidence for persistent single-peaked Balmer and He I emission, recurrent Fe II and O I, and the exposure-limited appearances of He II λ4686 and the Bowen blend.
• Figure 3. This is the conclusion-driving diagnostic figure: it directly compares quiescent Balmer, He I, and Fe II ratios, showing the flat Balmer decrement, substantial He I scatter, and Fe II ratios without a clear systematic offset from optically thin reference values.