1 Keele University
2 ESA, Vilspa
3 Liverpool John Moores University
4 University of Calgary
5 Laboratory for Space Research
6 University College London
GK Per is an old nova which erupted in 1901. In the 97 years since that time, it has been the subject of considerable study, not least because of its remarkable circumstellar environment. At an estimated distance of 500 pc, this environment extends north-west to south-east over 5 pc. Studies at mm wavelengths show CO emission, and at cm wavelengths small-scale nonthermal emission is found south-west of the nova. The object was observed by IRAS at 12, 25, 60, and 100 micron, imaging the nebula and suggesting it consisted of 23 K 'crystalline' dust. A diffuse 100 K dust component may also be present close to the nova.
We observed the GK Per environment with ISO PHT-C at 120 and 180 micron.
The structure found in previous HIRAS images is confirmed, but we find
that the flux density continues to rise to longer wavelengths, suggesting
that the dust is cooler than previously thought. If the emission is
modelled in terms of dust with emissivity
,
it
can be expected that the beta index will be in the range 0 to 2. However,
comparison of flux densities from ISO and IRAS suggest a number of
unexpected discrepancies, which open up a number of possiblities:
1) The dust has cooled (unlikely as the main source of heating is the IS radiation field);
2) The nature of the dust has changed;
3) The emission is not from dust at all.
ISO LWS data will allow us to distinguish these cases. We are in the process of getting a more complete map of the CO emission in order to correlate it with the IR emission, and continuum mapping (with SCUBA on the JCMT) of the extended emission to help tie down the tail of the flux distribution.