Analysis of the spectral energy distribution of the peculiar carbon giant TU gem

The TU Gem star has long been known as a peculiar carbon giant of the Galaxy halo, but its classification as a CH star is still debated. We estimated the TU Gem atmosphere parameters through modeling its spectrum and comparision one with the spectra of the star observed in two wide spectral ranges (λλ 400–720 nm and λλ 900–2440 nm). The low-dispersion optical TU Gem spectrum obtained by Barnbaum et al. (2006) (R ～ 600) and the infrared spectrum presented by Tanaka et al. (2007) (R ～ 2600) were used in the analysis. The model atmospheres were calculated using the SAM12 software (Pavlenko, 2003). Since the metallicity (Fe/H]) value could not be determined conclusively based on our spectral data, only the TU Gem effective temperature T _eff (that depends weakly on metallicity) was defined with certainty (T _eff = 3000 ± 100 K). We determined the C/O, C/Fe], and N/Fe] values for the ?2.0 ≤ Fe/H] ≤ 0.0 range with a step of ΔFe/H] = 0.5. Our estimate of C/Fe] (0.63–0.67 at Fe/H] = ?1.0) is higher than the corresponding estimate (C/Fe] = 0.21 at Fe/H] = ?1.1) given in (Kipper et al., 1996), while the estimates for N/Fe] at the stated metallicities agree with each other: N/Fe] = +1.0. This brings TU Gem closer to CH stars, but a detailed analysis of the chemical composition of the TU Gem atmosphere is required to reach a definite conclusion.