DY Persei,the coolest metal-poor R CrB carbon star

We have derived the atmospheric parameters of the R CrB carbon star DY Per. The spectrum of DY Per near its maximum brightness was obtained using the 2.6-m ZTSh telescope of the Crimean Astrophysical Observatory, and has a resolution of about 1.74 Å per pixel. We compare the absolute observed and theoretical spectral energy distributions (SEDs) of DY Per for λλ 430–730 nm for the first time. The model atmospheres were computed using a code written by Ya.V. Pavlenko in the classical approximation, taking into account the main opacity sources in carbon-star atmospheres. The theoretical SEDs were computed using the list of atomic lines from the VALD database and the molecular line lists from CD-ROM No. 18 of Kurucz’s database. The estimated by spectral synthesis effective temperature of DY Per is in the range of 2900–3100 K, if we assume log g = 0. We find a metal deficiency in the atmosphere of DY Per. Quantitative estimates of the overall metallicity, carbon and nitrogen abundances, and the H/He ratio are somewhat uncertain: ?2 ≤ Fe/H] ≤ ?0.5, 0.65 ≤ C/Fe] ≤ 1.35, 0.0 ≤ N/Fe] ≤ 0.8, 1/9 ≤ H/He ≤ 9/1. These high H/He values do not quite agree with qualitative observational estimates made by other authors. Our results confirm that DY Per is a unique stellar object. This is the coolest and possibly the most metal-poor of all known R CrB stars. We conclude that the large deficiencies of metals and hydrogen lead to C/Fe] values in the atmosphere of DY Per characteristic of R CrB stars.