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Science Instruments
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The telescope focuses light onto three instruments:
PACS
and
SPIRE,
which each contain a photometer and low-to-medium resolution
spectrometer,
and HIFI,
an extremely high-resolution heterodyne spectrometer.
They are designed for deep, wideband photometry (with high spatial resolution thanks
to Herschel's large 3.5 meter mirror) and full spectral coverage, making Herschel
the first space facility to completely cover the far infrared and submillimeter range.
Together,
PACS
and
SPIRE
are capable of detecting light from 57-670 microns in wavelength.
HIFI
covers 480-1250 and 1410-1910 GHz (which corresponds to about 157-625 microns).
The three instruments are designed to complement each other.
SPIRE
and
PACS
have imaging spectrometers that provide spatial information, while
HIFI
resolves with very high spectral resolution, but only one beam on the sky at a time.
The emission lines of the main interstellar cooling agents are predominantly in the
PACS
range, but fall into the
SPIRE
wavelength range for very distant and hence highly redshifted objects. The combination
of both instruments provides the full range of information needed to determine SEDs
(spectral energy distributions - the total amount of power radiated by cosmic objects,
measured in watts), photometric redshifts, total luminosity, and accurate positions.
SPIRE
and
PACS
have both conducted deep surveys with their photometers to find galaxies from the early
Universe, and follow up with spectroscopic studies of the most interesting objects.
Keeping Cool
Observing light in that range means that Herschel detects subtle "heat" emission
from very cold objects, such as vast clouds of interstellar dust. The spacecraft has
to keep its instruments cold because their electronics work only at frigid temperatures,
and to prevent the instruments' own infrared radiation from drowning out the faint
signals they're trying to detect.
So the instruments are housed in a cryostat filled with more than 2,000 liters of
superfluid helium. Based on technology developed for the Infrared Space Observatory
(ISO), it keeps the instruments at a temperature of less than -271° Celsius,
which is less then three degrees above absolute zero. The bolometers aboard
PACS
and
SPIRE
are chilled even further, to -273.3° Celsius, just a few tenths of a degree
above absolute zero.
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