Optical and Near-infrared High-resolution Spectroscopic Observations of Nova V2659 Cyg: Structure of Nova Ejecta and Origin of Two-distinct Velocity Systems

Abstract

Two distinct absorption-line systems distinguished by radial velocities have often been observed in the optical high-resolution spectra of classical novae during their early decline phase. The origin of these absorption-line systems is under debates. We present optical high-resolution spectroscopic observations spectra of nova V2659 Cyg and discuss about the temporal evolution of those absorption-line systems observed in this nova during its early decline phase. The observed temporal evolution of absorption-line profiles with relatively higher velocities (the high-velocity component) can be explained qualitatively by the clumpy ejecta and movement of the ionization fronts in the ejecta with time. Conversely, the low-velocity component may originate in the cool region compressed by the shock caused by collision between the fast nova wind and the slow expanding, equatorially focused dense ejecta. We also present high-resolution spectra of V2659 Cyg during its nebular phase in optical and near-infrared wavelength regions. Emission lines detected during the nebular phase also showed two velocity components, suggesting that the velocity structure of the ejecta during the nebular phase is similar to that during the early decline phase. The double-horned profiles of emission lines with low velocities imply a ring-like distribution of materials with lower velocities. The observations during both the early-decline phase and the nebular phase support the multiple ejection of ejecta at a nova explosion, with different velocities.