Unveiling the infrared excess of SIPS J2045-6332 II: SPHEREx spectral decomposition supports a young unresolved binary interpretation

SIPS J2045−6332 is an unusual low-mass object previously identified by its significant infrared excess and possible signatures of youth and unresolved multiplicity. Earlier studies suggested that the object is relatively young and may host a mid-L companion based on infrared spectroscopy, broadband photometry, and spectral energy distribution (SED) analysis. Here, we reassess the nature of the system using low-resolution spectroscopy from the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx). We perform spectral decomposition over 0.75–5 μm using single-template and binary-template fitting with field-gravity and intermediate-gravity (β) templates spanning spectral types M8–L4. The statistical significance of the fits is evaluated using reduced χ2 values and a baseline distribution constructed from reference single objects. Binary-template models consistently outperform single-template models, with the strongest improvements obtained for the intermediate-gravity templates. The preferred solution, an L0β + L1β combination (χ ²_ν =10.72), provides the best match to the observed combined-light spectrum, although M9β + L1β and M9β + L2β give comparably good fits, supporting the interpretation of a young unresolved binary. Using bolometric luminosities derived from gravity-dependent bolometric corrections (log Lbol/L⊙ = −3.42 ± 0.08 and −3.85 ± 0.09) together with the Sonora evolutionary models, we estimate component masses of ≈0.015 and ≈0.011 M⊙ at 25 Myr and ≳ 0.043–0.046 and ≈0.038–0.043 M⊙ at 200–250 Myr for the primary and secondary, respectively (the primary values are lower limits). The mass ratio is q ≲ 0.7 and q ≲ 0.9, respectively, indicating a companion of comparable but not necessarily equal mass. These results independently reinforce previous interpretations that SIPS J2045−6332 is a relatively young unresolved binary system and demonstrate the capability of SPHEREx low-resolution spectroscopy to identify and characterise young low-mass binaries through spectral decomposition.