Evolutionary status of the active star PZ Mon

• Published in: Monthly notices of the Royal Astronomical Society 2015-01, Vol.446 (1), p.56-64
• Main Authors: Pakhomov, Yu. V., Chugai, N. N., Bondar’, N. I., Gorynya, N. A., Semenko, E. A.
• Format: Article
• Language: English
• Subjects: Carbon; Dwarf stars; Emission; Evolutionary; Gravity; Luminosity; Nitrogen; Orbitals; Photometry; Stars; Stellar atmospheres; Symbols; X-ray astronomy
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stu2034

We use original spectra and available photometric data to recover the parameters of the stellar atmosphere of PZ Mon, formerly referred to as an active red dwarf. The derived effective temperature T eff = 4700 K and gravity log g = 2.8 suggest that PZ Mon is a K2III giant. Stellar atmosphere parameters (T eff and log g), along with evolutionary tracks, are used to estimate a stellar mass of ≈1.5 M⊙ and a radius of ≈7.7 R⊙. The angular radius derived by the infrared flux method, when combined with the linear radius, suggests a distance of 250 ± 70 pc, a factor of 2.5 smaller than that suggested by the Hipparcos parallax. The red giant status of PZ Mon is confirmed by its carbon and nitrogen abundance. The spectrum reveals pronounced He i 5876-Å absorption and Hα emission, indicating a robust chromosphere. The International Ultraviolet Explorer (IUE) spectrum is found to contain a transition-layer emission line of C iv 1550 Å. The C iv and X-ray luminosities are typical of RS CVn stars. The extended set of available photometric data confirms a period of 34.14 d, presumably related to stellar rotation. We found variations of radial velocity with amplitude of ≈8 km s−1, which could be caused by orbital motion.