Abstract We present a comprehensive study of the spectrophotometric evolution of the classical nova QY Mus from eruption to quiescence. The light curve shows a notable dust dip, classifying it as a D (137)-type nova, with dust formation beginning at ~123 days post-outburst and reaching a maximum optical depth of τ ~ 3.2. We classify QY Mus as a slow nova with t2 = 87 ± 6 days, and derive an absolute magnitude of MV = −6.55 ± 0.54 using the MMRD relation. The spectroscopic evolution, traced from 94 to 1348 days, shows prominent P-Cygni profiles in Balmer and Fe ii lines during the early decline, consistent with an Fe ii-type nova. The transition to the nebular phase occurs around ~233 days, marked by the emergence of O iii emission. Photoionization modeling using Cloudy of 41 emission lines on day 590 yields a central source temperature of (7.08 ± 0.20) × 105 K, with enhanced nitrogen and oxygen abundances and moderate neon enrichment, suggesting that QY Mus is not a neon nova. Mid-infrared WISE observations at ~502 days indicate the presence of cool dust at ~400 K. Using a Gaia-based color–magnitude diagram constructed in this work for 34 quiescent novae, we find that QY Mus occupies a region consistent with systems hosting main-sequence or subgiant secondaries; its orbital period further supports a subgiant companion. These results establish QY Mus as a slow, dust-forming nova with well-characterized evolution and a subgiant secondary.
Bisht et al. (Fri,) studied this question.