2024PASJ...76.1002I

The spectral variation in the optical region of a peculiar variable star V Sagittae was monitored in the recent three decades. The main aim of this article is to report several interesting phenomena discovered in the monitoring; we briefly discuss interpretations of them. Emission lines of H I and He II were decomposed into narrow components and wide wings. The radial velocities of the wings were related to the orbital motion of the hot primary, but did not reflect it directly. Widely red-shifted sinusoidal variations according to the orbital period were detected in 1993-2005 (e.g., $K = 195$ km s$^{-1}$ and $\gamma = +252$ km s$^{-1}$ for He II 4686). Sporadic blue-shifts were also observed. The mode of the radial velocity variation drastically changed between 2005 and 2007. Red-shifted sinusoidal variations ($K = 224$ km s$^{-1}$ and $\gamma = +260$ km s$^{-1}$ idem) or blue-shifted ones ($K =206$ km s$^{-1}$ and $\gamma = -289$ km s$^{-1}$ idem) appeared alternately in 2007-2019. One red- or blue-shift state lasted several years. The radial velocities of O III 5592 and the doublet C IV 5805 exhibited sinusoidal variations without large red- or blue-shifts (e.g., $K =215$ km s$^{-1}$ and $\gamma = -18$ km s$^{-1}$ for C IV 5805). The widths of emission lines He II 5412 and C IV in the doublet 5805 suggest that helium and carbon ions contained nearly the same kinetic energy, because the former line was wider than the latter by a factor of about $\surd {3}$ on most spectra. It is probable that there was no large-scale mass motion in such a thermal-equilibrium-like condition. The C IV lines and He II 5412 had roughly same widths, like the spectra of Wolf-Rayet stars, only three times in 2007-2019 on which there were likely large-scale mass outflows.