Work

Light curve spectral energy distribution fitting of 13 carbon-rich Mira variable stars in the Small Magellanic Cloud

Year: 2026

Type: article

Abstract: Context. Carbon-rich Mira variables are highly dynamic stars characterized by large-amplitude radial pulsations and intense mass-loss. The standard spectral energy distribution (SED) fitting often relies on time-averaged observations, which flatten the intrinsic variability and provide only an approximation of the stellar and circumstellar parameters. Aims. We aim to overcome the limitations of static SED modeling by dynamically tracing the physical parameters of a selected sample of 13 carbon-rich Mira variables in the Small Magellanic Cloud (SMC) throughout their entire pulsation cycle. Methods. We combined time-series photometry from Gaia , WISE, VMC, 2MASS, and OGLE to reconstruct simultaneous multiband light curves. We extract independent SEDs at 14 distinct phases across the pulsation cycle and model them using the ATHENA-C grid. Results. Our phase-resolved approach allows us to coherently trace the cyclic variations of effective temperature ( T eff ), optical depth ( τ 0.55 ), and bolometric luminosity. We found peak-to-peak T eff variations ranging from ∼100 K to over 1000 K. A strong anti-correlation between τ 0.55 and bolometric luminosity is observed, consistent with the dust condensation zone being pushed outward at maximum brightness, thereby making the star’s circumstellar environment optically thinner. Additionally, we recovered the classical period-luminosity relation and derived the amplitude of the radius variation, along with the radial expansion velocities, which we find to be consistent with independent measurements. Conclusions. The phase-resolved SED fitting reveals the true dynamic ranges of atmospheric and circumstellar parameters, which traditional static fits fail to capture. Although the determination of these parameters is limited by the coarse sampling of the hydrostatic model grid and the gaps in parameter space where converged models are unavailable, explicitly accounting for time-dependent behavior provides a much more physically realistic picture of the interplay between stellar pulsation and dust formation. This highlights the importance of time-resolved methodologies for studying high-amplitude variables.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202662509