this proposal requests an upgrade from priority 3 for mbarlow.prop_1. vega-excess systems are main sequence stars with ir excesses due to the presence of circumstellar dust discs. they were discovered using iras and it is found that the majority do not exhibit detectable ir excesses until 25 um or greater. much of their emission is there- fore unobservable from the ground and we must use satellite observations to characterise full spectral energy distributions (seds) and determine the parameters of the discs and grains. walker and wolstencroft (1988) identified a list of about 20 such systems using iras measurements. about half of these sources are to be observed in the iso guaranteed time programme. to extend these observations and to improve the sampling of stellar spectral types, we have produced a new catalogue of vega-excess candidates by cross- correlating sources in the iras faint source survey catalogue and the michigan catalogue of 2-d spectral types. some 58 sources satisfy our selection criteria. iso launch constraints reduce this number to 27 observable objects. we propose to obtain 4.85- to 200-micron continuum seds of the dust grains in each of our targets. these data will be analysed as part of our on-going theoretical modelling of optically thin discs, complemented by our ground-based optical, ir and mm/sub-mm observations. vega-excess discs may be remnants of proto-planetary discs. iso observations therefore offer a valuable opportunity to probe environments similar to that in which our solar system might have been created.
Instrument
PHT03 , PHT22
Temporal Coverage
1997-04-22T07:12:58Z/1997-11-16T01:21:34Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the world's first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
