What is PACS?
is an imaging photometer and integral field line spectrometer
for wavelengths up to ~210 µm. It has recently been redesigned
to employ in total four detector arrays, two bolometer arrays
for photometry, and two Ge:Ga detector arrays for spectroscopy.
PACS has three photometric bands with R~2. The
short wavelength `blue' array covers the 60-90 and 90-130 µm
bands, while the `red' array covers the 130-210 µm band.
In photometric mode one of the `blue' bands and the `red' band
are observed simultaneously. The bolometer arrays fully sample
a field of view of 1.75x3.5 arcmin,
and provide a point source detection limit of ~3 mJy (5 sigma,
1 hour). An internal He3 sorption cooler will provide the 300
mK environment needed by the bolometers.
For spectroscopy PACS covers 57-210 µm
in three contiguous bands, providing a velocity resolution in
the range 150-200 km/s and an instantaneous coverage of ~1500
km/s. The two Ge:Ga arrays are appropriately stressed and operated
at slightly different temperatures - cooled by being `strapped'
to the liquid helium - in order to optimise sensitivity for their
respective wavelength coverage. The point source detection limit
is ~3x10^-18 W/m^2.