Discovery of Multiple High-Velocity Narrow Circumstellar NaI D Lines in Nova V1280 Sco

Abstract

We discovered multiple high-velocity (ranging from $-$900 to $-$650 km s$^{-1}$) and narrow (FWHM $\sim$ 15 km s$^{-1}$) absorption components corresponding to both the D2 and the D1 lines of Na I on a high-dispersion spectrum of V1280 Sco, observed on 2009 May 9 (UT), 814 d after the V band maximum. Subsequent observations carried out on 2009 June and July confirmed at least 11 distinct absorption components in both systems. Some components had deepened during the two-month period while their HWHMs and wavelengths remained nearly constant. We suggest that these high-velocity components originated in cool clumpy gas clouds moving on the line-of-sight, produced during interactions between pre-existing cool circumstellar gas and high-velocity gas ejected in the nova explosion. The optical region spectrum of V1280 Sco in 2009 is dominated by the continuum radiation, and exhibits no forbidden line characterizing the nebular phase of typical novae. Permitted Fe II lines show doubly peaked emission profiles, and some strong Fe II lines are accompanied by a blue-shifted ($\sim -$ 255 km s$^{-1}$) absorption component. However, no high-velocity and narrow components corresponding to those of Na I could be detected in Fe II lines nor in the Balmer lines. The 255 km s$^{-1}$ low-velocity absorption component most probably originates in the wind from the nova.