Long-term spectral variations of V Sagittae: Two spectroscopic states with red- or blue-shifted emission wings of H i and He ii.

This article focuses on the long-term spectroscopic monitoring of the peculiar variable star V Sagittae (V Sge) over three decades, revealing notable changes in its emission line profiles and radial velocity behaviors. The study finds that the radial velocities of the wings of hydrogen (H i) and helium (He ii) emission lines exhibited red-shifted sinusoidal variations related to the orbital motion of the hot primary white dwarf until 2005, after which alternating red- and blue-shifted states appeared, each lasting several years. Analysis of emission line widths, particularly He ii 5412 and the carbon (C iv) doublet at 5805 Å, suggests a thermal-equilibrium-like condition with nearly equal kinetic energy in helium and carbon ions, indicating an absence of large-scale mass outflows in recent years. The findings support models of V Sge as a close binary with a white dwarf primary and an accretion disk, though some observed spectral features challenge existing interpretations of emission line origins.