Evolution of the dusty nova QY Mus from eruption to quiescence

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 (Formula presented) 123 d post-outburst and reaching a maximum optical depth of (Formula presented). We classify QY Mus as a slow nova with (Formula presented)  d, and derive an absolute magnitude of (Formula presented) using the magnitude versus rate of decline relation. The spectroscopic evolution, traced from 94 to 1348 d, 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 (Formula presented) 233 d, marked by the emergence of [O iii] emission. Photoionization modelling using cloudy of 41 emission lines on day 590 yields a central source temperature of (Formula presented)  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 (Formula presented) 502 d indicate the presence of cool dust at (Formula presented) 400 K. Using a Gaia-based colour–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.