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

TL;DR

This study introduces an optical–mid-infrared color evolution approach to identify and characterize novae using WISE data. A dedicated pipeline extracts time-domain W1/W2 photometry, applying variability, sampling, and spatial criteria to recover optically confirmed novae (41 objects) and identify nova-like candidates from ~1,900 targets. The authors leverage the V−W1 color, focusing on the first 60 days post-peak to avoid dust effects, and find a strong correlation between peak color and post-peak decline, as well as a link between the V and W1 peaks that traces the mass-loss timescale during eruption. They demonstrate that non-novae occupy distinct regions in the V−W1 color–time space, provide physical interpretations based on ejecta expansion and cooling, and estimate a Galactic nova rate of approximately $40$--$50$ novae per year, underscoring the value of infrared time-domain surveys for a more complete census of nova activity.

Abstract

We present a novel approach for characterizing nova candidates by exploiting the infrared capabilities of the Wide-field Infrared Survey Explorer (WISE) catalog. We developed a pipeline to identify novae based on well-defined infrared criteria, and leveraging this pipeline, we successfully identified 41 optically confirmed novae in the WISE catalog. In particular, we focus on the color difference between the optical V band and the WISE 3.4 microns W1 band as a diagnostic. We compared their infrared light curves with their optical counterparts. We identified a strong correlation from which we proposed a color difference model that can be used for further identification and characterization of novae. Our analysis validates the mass-loss timescale theory, which predicts that systems with lower accretion rates accumulate larger envelopes and produce more massive ejecta. We also confirm models' prediction that the early color evolution of novae is governed by ejecta expansion and cooling. From our sample statistics, we infer a Galactic nova rate of approximately 40 to 50 novae per year, consistent with modern and infrared-corrected estimates. The resultant model from this work paves the way for future large-scale investigations of nova candidates.

Figures (11)

• Figure 1: $V-W1$ color difference model applied to our identified samples of known novae. Individual data points are shown in red (WISE W1 band) and blue (optical V band), capturing the temporal evolution of each emission component. The green curve represents the computed ($V-W1$) color difference, which serves as a diagnostic of the nova’s emission characteristics.
• Figure 2: Continued: $V-W1$ color difference model applied to our identified samples of known novae. Individual data points are shown in red (WISE W1 band) and blue (optical V band), capturing the temporal evolution of each emission component. The green curve represents the computed ($V-W1$) color difference, which serves as a diagnostic of the nova’s emission characteristics.
• Figure 3: Novae from our pipeline without suitable overlap between V and W1 for computing a $V-W1$ color difference. Individual data points are shown in red (WISE W1 band) and blue (optical V band), capturing the temporal evolution of each emission component.
• Figure 4: Continued: Novae from our pipeline without suitable overlap between V and W1 for computing a $V-W1$ color difference. Individual data points are shown in red (WISE W1 band) and blue (optical V band), capturing the temporal evolution of each emission component.
• Figure 5: $V-W1$ color evolution as a function of normalized time (in days) for the entire sample of nova candidates. Each line corresponds to an individual nova, with distinct colors assigned to differentiate between objects. The time axis has been normalized relative to each nova’s eruption time to facilitate direct comparison of their early color evolution.