Analysis of the spectral energy distributions of four cool R CrB stars near the brightness maximum

• Published in: Astronomy reports 2013-10, Vol.57 (10), p.734-750
• Main Authors: Yakovina, L. A., Rosenbush, A. E., Pavlenko, Ya. V., Kaminsky, B. M.
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics; Atmosphere; Luminosity; Nitrogen; Observations and Techniques; Opacity; Physics; Physics and Astronomy; Stars; Stars & galaxies
• ISSN: 1063-7729; 1562-6881
• DOI: 10.1134/S1063772913100077

The effective temperatures T eff and carbon and nitrogen abundances in the atmospheres of the cool R CrB stars ES Aql, SV Sge, Z UMi, and NSV 11154 have been determined by modeling their spectral energy distributions in the optical and near-infrared. The hydrogen-deficient model atmospheres were computed using the SAM12 code in the classical approximation, taking into account sources of opacity characteristic of the atmospheres of R CrB stars. The influence of the hydrogen deficiency on theoretical stellar spectra is analyzed. The resulting effective-temperature estimates for ES Aql, SV Sge, Z UMi, and NSV 11154 are in the range T eff = 4600–5200 K. The carbon abundances log n (C) in the atmospheres of ES Aql, SV Sge, and Z UMi are 8.9–10.1, corresponding to [C/Fe] values typical of the atmospheres of R CrB stars. The nitrogen abundances are lower than those determined in other studies, and differ considerably from star to star. The mean [N/Fe] value for these three stars is ≈1.5 dex lowthan the mean [N/Fe] for known warm R CrB stars. Abnormally high estimates were obtained for the atmosphere of NSV 11154: log n (C) = 10.8 and log n (N) = 10.0. The approximate log g estimates agree with the conclusion from photometric observations that cool R CrB stars have lower luminosities than hotter R CrB stars.