Herschel was launched on 14 May 2009, and is now an operational ESA space observatory o ering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55 671 m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.

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Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments on ESA's far infrared and submil- limetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 × 25 pixels, each, and two filled silicon bolometer arrays with 16 × 32 and 32 × 64 pixels, respectively, to perform integral-field spectroscopy and imaging photom- etry in the 60−210 μm wavelength regime. In photometry mode, it simultaneously images two bands, 60−85 μ mo r 85−125 μ ma nd 125−210 μm, over a field of view of ∼1.75 � × 3.5 � , with close to Nyquist beam sampling in each band. In spectroscopy mode, it images afi eld of 47 �� × 47 �� , resolved into 5 × 5 pixels, with an instantaneous spectral coverage of ∼ 1500 km s −1 and a spectral resolution of ∼175 km s −1 . We summarise the design of the instrument, describe observing modes, calibration, and data analysis methods, and present our current assessment of the in-orbit performance of the instrument based on the performance verification tests. PACS is fully operational, and the achieved performance is close to or better than the pre-launch predictions.

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The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory

We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star-formation rates are discussed, and updated prescriptions for calculating star-formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.

Star Formation in the Milky Way and Nearby Galaxies

The Spectral and Photometric Imaging REceiver (SPIRE), is the Herschel Space Observatory`s submillimetre camera and spectrometer It contains a three-band imaging photometer operating at 250, 350 and 500 mu m, and an imaging Fourier-transform spectrometer (FTS) which covers simultaneously its whole operating range of 194-671 mu m (447-1550 GHz) The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 03 K The photometer has a field of view of 4' x 8', observed simultaneously in the three spectral bands Its main operating mode is scan-mapping, whereby the field of view is scanned across the sky to achieve full spatial sampling and to cover large areas if desired The spectrometer has an approximately circular field of view with a diameter of 26' The spectral resolution can be adjusted between 12 and 25 GHz by changing the stroke length of the FTS scan mirror Its main operating mode involves a fixed telescope pointing with multiple scans of the FTS mirror to acquire spectral data For extended source measurements, multiple position offsets are implemented by means of an internal beam steering mirror to achieve the desired spatial sampling and by rastering of the telescope pointing to map areas larger than the field of view The SPIRE instrument consists of a cold focal plane unit located inside the Herschel cryostat and warm electronics units, located on the spacecraft Service Module, for instrument control and data handling Science data are transmitted to Earth with no on-board data compression, and processed by automatic pipelines to produce calibrated science products The in-flight performance of the instrument matches or exceeds predictions based on pre-launch testing and modelling: the photometer sensitivity is comparable to or slightly better than estimated pre-launch, and the spectrometer sensitivity is also better by a factor of 15-2

/pdf/the-herschel-spire-instrument-and-its-in-flight-performance-3wv4kydzfn.pdf

The Herschel-SPIRE instrument and its in-flight performance

▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical lum...

https://www.ifa.hawaii.edu/users/reipurth/reviews/draine.pdf

Interstellar dust grains

The Herschel Space Observatory is a passively cooled 3.5 m telescope (Tmirror < 90 K) scheduled for launch in 2007. One of its three scientific instruments is PACS (Photoconductor Array Camera and Spectrometer) which will carry out astronomical observations in the wavelength range of 57 μm to 210 μm with unprecedented sensitivity and spatial resolution. PACS has two cameras for imaging spectroscopy in two wavelength bands from 57 μm to 130 μm and 130 μm to 210 μm. Both cameras are built up from 25 linear arrays, each with 16 detector pixels consisting of Gallium doped Germanium crystals. By stressing these crystals with a bolt­spring mechanism, the desired cut­-off wavelengths of ~ 127 μm and ~ 205 μm can be reached. The detectors are operated at temperatures of ~ 2 K and read out by cryogenic readout electronics (CRE), featuring pre­amplifiers and multiplexers. Test facilities have been designed and built up at MPIA, Heidelberg, and MPE, Garching, in order to characterize and calibrate the spectrometer cameras before integration into the instrument. Both test facilities have a cryostat cooled by superfluid liquid helium. While the MPE facility uses an internal cold black body to illuminate the camera, the facility at MPIA makes use of an external black body and cold attenuation filters. Tests of the qualification models of the spectrometer cameras show that the detector responsivity is ~ 8 A/W and ~ 40 A/W for the low and high stressed detectors respectively, surpassing the requirements. The NEP is currently limited by CRE readout noise and will be improved with the new generation of FM CREs. Ionizing irradiation significantly increases the detector responsivity, which might make it necessary to operate them with a lower bias voltage. On the other hand, radiation effects can be reliably cured by a combination of bias boosts and infrared flashes.

Characterization of high- and low-stressed Ge:Ga array cameras for Herschel's PACS instrument

Spectrum of the zodiacal light in the middle UV.

The Photodetector Array Camera and Spectrometer (PACS) is one of three science instruments on board the 
Herschel space observatory to be launched in 2008. It will perform imaging photometry and spectroscopy in 
the wavelength range from 57 μm to 210 μm. The integral field spectrometer contains two 25 x 16 pixel cameras 
of Gallium doped Germanium crystals (Ge:Ga). By stressing these crystals, cutoff wavelengths of 127 μm 
(low-stressed, 200 N) and 205 μm (high-stressed, 800 N) are reached. The characterization of these detectors 
(responsivity, noise equivalent power (NEP), dark current,...) is carried out at the Max-Planck-Institutes for Astronomy 
(MPIA, Heidelberg) and Extraterrestrial Physics (MPE, Garching). Both test facilities allow simulation 
of the in-flight operational conditions of the arrays and provide accurate IR fluxes by means of external/internal 
black bodies and calibrated cold attenuation filters. A radioactive 137Cs source is used at MPIA to simulate the 
steady cosmic radiation impact on the photoconductor arrays in order to study the radiation induced changes 
in responsivity, noise, and the transient behavior. The goal is to determine the optimal operating parameters 
(temperature, bias, integration time,..) for the operation at the L2 orbit, the best curing method, curing frequency 
and calibration procedure for high photometric accuracy. The "lessons learned" on operating, curing, 
deglitching and calibrating stressed Ge:Ga detectors during the ISO mission are applied as well as the relevant 
reports from IRAS and Spitzer.

Laboratory simulation of cosmic radiation effects on stressed Ge:Ga detectors at L2 and curing

The spectrum of the unidentified infrared (UIR) emission bands between 5.9 and 11.7 [micro]m has been observed for the first time in the disk of an external galaxy. We have used the low-resolution spectrometer of the ISOPHOT instrument aboard ISO. The UIR bands at 6.2, 7.7 and 11.3 [micro]m have absolute intensities which are similar to the values observed for the diffuse emission of our own Galaxy. The UIR bands between 5.9 and 11.7 [micro]m contribute ~9% of the total IR radiation of NGC 891. The intensity ratios and band widths in the NGC 891 disk emissions are similar to the diffuse emission of the Milky Way, pointing to a common carrier for the UIR bands in the two galaxies. However, there are some notable variations of the band ratios along the major axis of the galaxy.

Detection of widely distributed UIR band emission in the disk of NGC 891

We present infrared spectra covering the wavelength ranges 3.1-5.0 m and 5.8-11.6 m for 9 young stars located in the Chamaeleon I dark cloud. The spectra were taken with the spectrophotometer of ISO (ISOPHOT-S). The spectra of three stars which illuminate reflection nebulae are dominated by the series of strong emission features generally ascribed to polycyclic aromatic hydrocarbons. Three or possibly four stars classified as T Tauri stars show the 10 m silicate band in emis- sion, whereas another object, T42, shows the silicate band in absorption and could b eaTT austar with a disk seen edge-on. The last source, Cha IRN, is a deeply embedded young stellar object. Its spectrum is characterized by deep absorption bands due to various interstellar ices, but shows a very weak silicate band only.

http://aa.springer.de/papers/9346001/2300205.pdf

Dietrich Lemke

Papers

Characterization of high- and low-stressed Ge:Ga array cameras for Herschel's PACS instrument

Spectrum of the zodiacal light in the middle UV.

Laboratory simulation of cosmic radiation effects on stressed Ge:Ga detectors at L2 and curing

Detection of widely distributed UIR band emission in the disk of NGC 891

Infrared spectra of young stars in Chamaeleon