Study of the Carbon Star T Draconis

We present the results of the infrared photometric observations in the JHKLM bands and infrared spectroscopic observations in the range 1–2.5 μ m for the carbon Mira star T Dra performed from 2019 to 2023. An analysis of the photometric observations shows the presence of both pulsational brightness fluctuations with an amplitude falling from 1.2^m in the J band to 0.84^m in the L and M bands and a linear trend in the mean brightness with a value of 0.0007^m/d in the J band. In the infrared spectrum of T Dra we have identified the absorption bands of C _2 H _2 , HCN, CN, CO, and C _2 molecules. The depth of the absorption band at 1.53 μ m has been found to depend on the star’s brightness. We show that the CO λ 2.29 μ m bands have a high contrast, suggesting their formation not in the stellar atmosphere but in the circumstellar dust envelope. We present the spectral energy distribution of T Dra in a wide spectral range from which the bolometric fluxes at maximum and minimum brightness have been estimated: 4.8× 10^-10 and 2.5× 10^-10 W m ^-2 , respectively. For the distance to T Dra of 944 pc they correspond to the star’s luminosity at maximum brightness L_max≈ 13 300 L_⊙ and at minimum brightness L_min≈ 6900 L_⊙ . We have modeled the radiative transfer in the circumstellar envelope of T Dra and estimated the parameters of the star and the envelope: T_eff=2400 K, R_*=670R_⊙ , R_in=5-6 AU, R_out∼ 50 000 AU, τ_V=3.5 , M_dust=4-8× 10^-5 M_⊙ , and dM/dt∼ 1.5× 10^-6 M_⊙ yr ^-1 .