| Description |
Debris discs are belts of dust particles created from collisions of
planetesimals (comets and asteroids) in extrasolar planetary systems.
The prototype disc around Vega was discovered ~25 years ago by IRAS,
and ~20 discs have been imaged to date, primarily by HST, SCUBA and
Spitzer. Despite the relatively low numbers, debris discs are seen to
be extraordinarily diverse in character, including systems with vast
populations of comets or with perturbations by planets at tens of AU
from the host star. Due to this low number, however, our knowledge of
debris discs is incomplete; there has been no unbiased survey
specifically designed to image a large number of discs. Spitzer
greatly improved our understanding of the disc-rich A stars but the
number of detections is still low for solar-analogue FGK stars and
especially the numerous M stars. For Herschel, we therefore propose
the DEBRIS (``Disc Emission via a Bias-free Reconnaissance in the
Infrared/Submillimetre) Key Project which will probe 450 nearby A-M
stellar systems for debris and measure Solar System dust levels in
debris discs for the first time. The large sample is statistically
robust and without bias, providing a rich legacy for debris disc and
exo-planet science. This deep, flux-limited survey will obtain PACS
100/160 images of all 450 systems (472 fields due to wide binaries),
and it will be possible to resolve discs toward each one with the
PACS high resolution. DEBRIS includes SPIRE imaging in systems where
debris is detected with PACS (a rate of 50% is expected). The key
science questions are: (a) which kinds of stars have debris and why?
(b) what are the sizes, temperatures and masses of the debris discs?
(c) what is the relation of resolved disc structures to the
exo-planets? and (d) is our Kuiper Belt common or unusual? The
Herschel DEBRIS Key Project will answer these questions using
Herschels high sensitivity, spectral coverage and resolution. Our
team includes world experts in debris discs and exo-planet science
from 8 countries. |
