Herschel Space Observatory - PACS
The Photodetector Array Camera and Spectrometer (PACS) is one of the three
instruments aboard ESA's fourth cornerstone mission in the Horizon
2000+ project, the Herschel Space Observatory. Herschel is a space
telescope observing in the Far-InfraRed and sub-millimeter wavelength
The institute is one of the consortium members with a large
participation in the Instrument Control Centre (ICC).
The European Space
Agency's Herschel Space Observatory (formerly called Far InfraRed and
Submillimetre Telescope or FIRST) will be the first space observatory
covering the full far-infrared and submillimetre waveband.
The satellite consists of three instruments:
HIFI, the Heterodyne Instrument for the Far Infrared, a
high-resolution spectrograph that operates in the range of 480 to 1250
GHz in five bands and 1410 to 1910 GHz in two additional bands.
PACS, the Photodetector Array Camera and Spectrometer, a
bolometer array photometer and a photoconductor array imaging
spectrometer operating at a wavelenght range between 60 and 210
SPIRE, the Spectral and Photometric Imaging Receiver,
consisting of a 3-band imaging photometer and a Imaging Fourier
Transform Spectrometer and will operate at wavelengths between 200 and 670
Herschel will be launched on 14 May 2009 together with Planck, another ESA
scientific mission. Both satellites will separate shortly after launch
and will be operated independently.
The institute of Astronomy has a substantial participation in the PACS
instrument. The principle investigator of PACS is Albrecht Poglitsch
from the Max-Planck-Institut für Extraterrestrische Physik (MPE)
in Garching, Germany. Prof. Christoffel Waelkens is co-Principle
Investigator of PACS.
Prior to launch, the instrument control center team is executing
a suite of laboratory tests of the qualification models and the flight
model of the instrument. These tests encompass detailed performance
and calibration tests on instrument level, as well as integrated system
tests with the instrument mated on the satellite. The team in Leuven
is focusing on the testing of mechanisms and the spectrometer calibration.
Mechanism testing includes the verification of compliance to specifications
and control loop optimisation of the grating and filter wheels, and of the
Ge:Ga detector flashers and heaters. We design tests, define the measurements
in the uplink logic, execute the tests, analyse data and follow-up the results
with the engineering team.
The ground calibration of the instrument is crucial for the full calibration
and understanding of the instrument in space. For the spectrometer we take
care of the spectrophotometric calibration strategy, absolute radiometric
calibration, relative spectral response calibration, flatfield determination,
testing of observing modes, and characterisation of the Ge:Ga detector and
cryogenic readout (CRE) behaviour.
In parallel to the testing of the instrument in the laboratory, a lot of
work is devoted to the preparation of the launch and the in-orbit phase.
A first version of the observing modes of the instrument have been delivered
to ESA's Herschel Science Centre (HSC) to support the first round of
proposals for the key programmes.
For the in-orbit calibration, a detailed plan is being prepared for the initial
calibration during the commissioning and performance verification phases.
The Leuven team is leading the work on fiducial stellar flux calibrators for the
Herschel instruments and participates in the Herschel Calibration steering group.
The preparation of the in-orbit spectrophotometric calibration of the PACS
spectrometer is K.U.Leuven responsibility . Continuing our involvement in
proton irradiation tests of the photoconductors in the cyclotron of
Louvain-La-Neuve, we are working on the strategy for detector curing, and detection
and correction for response changes due to cosmic particle hits. The corresponding
data reduction pipeline steps are also developed in our group.
A substantial amount of work in Leuven is spent on the development of software
in the common Herschel software system. A large part of the system is operational
already, visible in the proposal submission functionality, and the data analysis
system used for the analysis of instrument level data. The focus is now shifting
to in-orbit operations functionality including the standard product generation
pipelines, data access, access to housekeeping telemetry of all satellite subsystems
and interactive data analysis tools for the observers. In these areas, our team
has a leading role. On a system level, we deliver key personnel in the data
processing system architecture group and the ground segment system engineering group.
Via a software development contract with ESA, we contribute to advanced data reduction
functionality in the extended Herschel Data processing system.
With the broad wavelength range of approximately 60 to 670 um,
Herschel will observe the so-called `Cold Universe'. Black bodies with
temperatures between 5 and 50 K, peak at these wavelengths. Also the
brightest molecular and atomic emission lines for gasses with
temperatures between 10 and a few hundred Kelvin are emitted in the
With its photometric mapping capabilities, Herschel offers the
possibility of unbiased surveys related to galaxy and star formation.
With the spectroscopic instruments, a characterisation of (newly detected)
objects will be possible.
Interesting results are to be expected in the field of Cosmology (i.e.
discovery of proto-galaxies, formation of Galaxies), interstellar medium
(spectroscopic studies of gas and dust) and star formation as well as in
the field of our solar system, through the study of comets and planets.
The institute is leading the guaranteed time Herschel Key
programme on the circumstellar environment in post-main-sequence objects,
and is responsible for important parts of the guaranteed time Key Programmes
on Stellar Disk Evolution; HIFISTARS: The physical and chemical properties of
circumstellar environments around evolved stars; Water and related chemistry
in the Solar system; Probing the origin of the stellar initial mass function
(a wide-field Herschel photometeric survey of nearby star-forming cloud
complexes), and the Open Time key programmes on Gas in Protoplanetary
systems (GASP); Dust, Ice and Gas in Time (DIGIT) and Hi-GAL: the
Herschel infrared Galactic Plane Survey.
Wim De Meester
Herschel information at the ESA Science portal
The PACS consortium pages
PACS information at MPE, Garching