A newly-identified emission-line region around P Cygni

TL;DR

This study reveals a new emission-line region around P Cygni, characterized by distinct velocity components, indicating a possible reverse shock in the stellar wind, based on high-resolution near-infrared spectroscopy.

Contribution

First detection of a distinct extended emission-line region around P Cygni with detailed velocity structure, suggesting a reverse shock in the stellar wind.

Findings

The [Fe II] emission lines show a two-peak velocity profile at ~220 km/s.

The ~220 km/s component is spatially extended to ~3 arcseconds from the star.

The region likely represents a reverse shock caused by stellar wind overtaking the outburst shell.

Abstract

We present a high-resolution ($R \simeq 20,000$) near-infrared (9,100-13,500 $\AA$) long-slit spectrum of P Cygni obtained with the newly commissioned WINERED spectrograph in Japan. In the obtained spectrum, we have found that the velocity profiles of the [Fe II] emission lines are resolved into two peaks at a velocity of $\simeq220$ km s$^{-1}$ with a moderate dip in between and with additional sub-peaks at $\simeq\pm100$~km~s$^{-1}$. The sub-peak component is confirmed with the long-slit echellogram to originate in the known shell with a radius of $\simeq10^{\prime\prime}$, which was originally created by the outburst in 1600 AD. On the other hand, the $\simeq220$ km s$^{-1}$ component, which dominates the [Fe II] flux from P Cygni, is found to be concentrated closer to the central star with an apparent spatial extent of $\simeq3^{\prime\prime}$. The extent is much larger than the compact ($<0^{\prime\prime}.1$) regions traced with hydrogen, helium, and metal permitted lines. The velocity, estimated mass, and dynamical time of the extended emission-line region suggest that the region is an outer part of the stellar wind region. We suggest that the newly-identified emission-line region may trace a reverse shock due to the stellar wind overtaking the outburst shell.