An investigation of Nova Persei (1901) and its environment

Abstract

The nature of the ambient medium about the classical nova GK Persei (Nova Persei 1901) has been investigated using IRAS far-infrared and optical observations, coupled with detailed modelling of the optical light echoes. Measurements of the time-dependent expansion of the nova ejecta show that significant deceleration is occurring in the SW quadrant, otherwise the expansion appears fairly uniform at a velocity of around 1200 km s. Interaction with the surrounding medium is the likely cause of this deceleration.
Analysis of IRAS 12-100pm raw data reveals that GK Per is centrally positioned on a saddle point between the two emission peaks of an isothermal (T = 22 ± 1K) bipolar nebulosity. The cloud has a total dust mass of between 0.058 and 0.078 MQ, and is possibly distributed in the form of a toroid about the nova.
Results from an analysis of the optical extinction using Strömgren uvby and 11$ photometry of 106 stars in a 1 square degree region about the nova show that, at the nova distance (470 pc), Ày = 0.85 ± 0.20, with an upper limit of Av = 0.4
placed on the local extinction due to the IRAS and light echo nebulosities. Around 30 archival plates of GK Per were scanned by PDS and computer processed to enhance the appearance of optical light echoes visible in 1901 and 1902. Further analysis performed resulted in the first surface calibration of a GK Per light echo plate. On August 23, 1901, the brightest nebular regions were found to have a B-band surface brightness of 3.4 x 10 -21 W c7rC2 prn 1 arcseC2 (23.2 mag arcsec 2 ).
Results from simple light echo models show that the brighter nebular regions probably originate in a dust plane which has a closest approach to the nova of 1.4 pc and is inclined at 32(±3)°. to the line of sight to the nova. A more detailed model was formulated which used numerical integration to calculate the time-dependent nebular surface brightness. Comparison of model and calibration results suggests that a plane of light echo material would have a thickness of 0.15 pc and a grain number density of 2.1 x 10 nC3 .
This work has helped to further elucidate the cause of some of the rare features associated with CK Per, and also to achieve a better understanding of the nova environment. It paves the way for future work to further clarify the possible links between the nova and its ambient medium.