High resolution optical spectra of the dormant LBV star P Cyg

Abstract

High resolution optical spectra (R = 60 000) of the LBV star P Cyg beyond outburst were obtained on the 6-meter BTA telescope in the wavelength range 477-780 nm. We perform a detailed identification of different types lines (photospheric absorptions, permitted and forbidden emissions, components of lines with P Cyg type profiles), and studied the variability of their profiles and radial velocities. The average radial velocity from positions of forbidden emissions ([NII] 5754.64, [FeII] 5261.62, [FeII] 7155.14 and [NiII] 7377.83 \r{A}) is accepted as the system velocity Vsys=$-34\pm1.4$ km/s. About a dozen photospheric absorptions of CNO triad ions and SiIII are found, their stable position, Vr(abs)=$-73.8$ km/s, shifted relative to at $-40$ km/s, indicates that these absorbtions are formed in the pseudophotosphere region. The high-excitation emissions ([OI] 5577, 6300, 6363 \r{A}, [OIII] 4959 and 5007 \r{A}, as well as HeII 4686 \r{A}) are absent in the spectra. The radial velocity Vr(DIBs)=$-11.8$ km/s according to the position of numerous DIBs is consistent with the position of the interstellar components of the D-lines NaI and KI forming in the galactic Perseus arm. A color excess E(B-V)=0.34+/-0.03 mag and interstellar absorption Av=1.09 mag were determined by measurements of equivalent widths of nine DIBs.