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 \(\mu\)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 \(\mu\)m has been found to depend on the star’s brightness. We show that the CO \(\lambda 2.29\) \(\mu\)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: \(4.8\times 10^{-10}\) and \(2.5\times 10^{-10}\) W m\({}^{-2}\), respectively. For the distance to T Dra of 944 pc they correspond to the star’s luminosity at maximum brightness \(L_{\textrm{max}}\approx 13\,300\;L_{\odot}\) and at minimum brightness \(L_{\textrm{min}}\approx 6900\;L_{\odot}\). We have modeled the radiative transfer in the circumstellar envelope of T Dra and estimated the parameters of the star and the envelope: \(T_{\textrm{eff}}=2400\) K, \(R_{*}=670R_{\odot}\), \(R_{\textrm{in}}=5{-}6\) AU, \(R_{\textrm{out}}\sim 50\,000\) AU, \(\tau_{V}=3.5\), \(M_{\textrm{dust}}=4{-}8\times 10^{-5}\;M_{\odot}\), and \(dM/dt\sim 1.5\times 10^{-6}\) \(M_{\odot}\) yr\({}^{-1}\).