An optical--mid-infrared color evolution tool for nova identification using WISE data

Novae are key tracers of accretion processes and contribute to the chemical and dynamical evolution of the Galaxy. However, optical surveys miss a significant fraction of nova eruptions due to interstellar extinction, particularly toward the Galactic plane. We present two contributions. First, we developed an infrared-based pipeline to identify nova candidates from WISE data using infrared variability criteria, validated against 62 optically confirmed novae, and identified 54 additional candidates that lacked optical classification. This infrared-selected sample suggests that extinction causes optical surveys to miss a significant fraction of Galactic nova eruptions, with the WISE color distribution indicating a possible incompleteness of ∼30%. Second, we introduce the extinction-corrected $(V-W1)_0$ color evolution as a photometric diagnostic of nova ejecta expansion and cooling timescales, enabling nova type classification and follow-up prioritization from infrared data alone. We found a strong correlation between the $(V-W1)_0$ peak color and the optical-to-W1 peak time delay (Pearson r = 0.90, p < 0.01) that is consistent with the delay that traces the duration of the mass-loss phase, and a further correlation between peak color and the rate of color decline over the first 60 days after the $(V-W1)_0$ peak. Together, these diagnostics can determine nova types from purely photometric infrared data and separate novae from contaminants. Infrared time-domain surveys provide a powerful complementary tool to optical searches and are essential for obtaining a more complete census of Galactic novae and improving estimates of the Galactic nova rate.