A three-dimensional view of the remnant of Nova Persei 1901 (GK Per)

TL;DR

This study provides a detailed 3D kinematic analysis of GK Per's optical ejecta, revealing a mostly radial, expanding shell with modest deceleration, uniform expansion, and a decreasing flux, challenging previous interaction-based models.

Contribution

It offers the first comprehensive 3D kinematic view of GK Per's ejecta, combining proper motions and Doppler shifts to refine understanding of its expansion and evolution.

Findings

Ejecta form a thick shell with velocities between 600 and 1000 km/s.

Knots have experienced only modest deceleration over a century.

The nebula's flux decreases linearly at 2.6% per year, with asymmetric fading.

Abstract

We present a kinematical study of the optical ejecta of GK Per. It is based on proper motions measurements of 282 knots from ~20 images spanning 25 years. Doppler-shifts are also computed for 217 knots. The combination of proper motions and radial velocities allows a unique 3-D view of the ejecta to be obtained. The main results are: (1) the outflow is a thick shell in which knots expand with a significant range of velocities, mostly between 600 and 1000 km/s; (2) kinematical ages indicate that knots have suffered only a modest deceleration since their ejection a century ago; (3) no evidence for anisotropy in the expansion rate is found; (4) velocity vectors are generally aligned along the radial direction but a symmetric pattern of non-radial velocities is also observed at specific directions; (5) the total Halpha+[NII] flux has been linearly decreasing at a rate of 2.6 % per year in the last decade. The Eastern nebular side is fading at a slower rate than the Western one. Some of the knots displayed a rapid change of brightness during the 2004-2011 period. Over a longer timescale, a progressive circularization and homogenization of the nebula is taking place; (6) a kinematic distance of 400+-30 pc is determined. These results raise some problems to the previous interpretations of the evolution of GK Per. In particular, the idea of a strong interaction of the outflow with the surrounding medium in the Southwest quadrant is not supported by our data.