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

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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 ISOPHOT C200 camera aboard ISO has been used to observe the extended far infrared (FIR) emission from the Coma cluster of galaxies. Two scans with 48 0 length across the cluster, each at 120m and 185m, were obtained at cross- ing position angles. The proles of the surface brightness ratio I120m=I185m along the two scans are quite similar in show- ing an enhanced 120 m emission within the central region of 10 0 (0.4 Mpc) diameter. This flux excess is interpreted as thermal emission from intracluster dust with a temperature slightly higher than the galactic foreground cirrus. A conserva- tive value for the excess surface brightness at 120 mi s0.1 MJy/sr, corresponding to a total net flux of 0.7 Jy. Depend- ing on the dust opacity and temperature, a total dust mass of 6:210 7 M < MD < 1:610 9 M is inferred. The detected excess emission represents the rst direct evidence from FIR observation for intracluster dust in a galaxy cluster. Since dust is destroyed effectively by the hot intracluster medium, the dust detected may result from galaxy stripping during the ongoing merging process in Coma. FIR emission from intracluster dust thusmightbeusedasatooltosearchfornon-equilibriumgalaxy clusters.

http://aa.springer.de/papers/8329001/2300055.pdf

Far-infrared emission of intracluster dust in the Coma galaxy cluster.

A dry ice cooled 15-cm ir telescope was used on board the balloon-borne gondola THISBE for absolute surface photometry of the Milky Way, the zodiacal light, and the airglow in the PbS wavelength region The mechanical, optical, electronical, and thermal design of the instrument is described The efficiency of the baffle system for suppression of stray light from earth and balloon is discussed in detail Recent airglow measurements are presented

Balloon-borne infrared telescope for absolute surface photometry of the night sky.

HERSCHELs 3.5 m primary mirror will be passively cooled to T ~ 80 K in the L2 orbit. In order to reduce the effects of the remaining high thermal background on the sensitive far in frared detectors (60..210 µm), a focal plane chopper is a vital element in the entrance optics of the imaging and spectroscopic instrument PACS. A gold coated 32 × 26 mm 2 plane mirror, suspended by two flexural pivots and driven by a linear motor, allows for precise square wave chopping with up to 9° throw at a frequency 10 Hz with a position ac curacy of 1 arcmin. The power required at T ~ 4 K is about 1 mW. The chopper has undergone an extensive qualification programme, including 650 million cold chop throws, 15 cold-warm-cold thermal cycles, 3-axis 26 G-vibration at T~4 K etc. Five models were built and thoroughly tested; the flight model of the chopper is now integrated into the flight model of PACS, ready for the HERSCHEL/PLANCK launch in 2008 by an ARIANE5 rocket and the following 5-year mission.

The cold focal plane chopper of HERSCHEL's PACS instrument

We examine two positions, ON1 and ON2, within the Ophiuchus cloud LDN 1688 using observations made with the ISOPHOT instrument aboard the ISO satellite. The data include mid-IR spectra (~6-12{\mu}m) and several photometric bands up to 200{\mu}m. The data probe the emission from molecular PAH-type species, transiently-heated Very Small Grains (VSGs), and large classical dust grains. We compare the observations to earlier studies, especially those carried out towards an isolated translucent cloud in Chamaeleon (Paper I). The spectra towards the two LDN 1688 positions are very similar to each other, in spite of position ON1 having a larger column density and probably being subjected to a stronger radiation field. The ratios of the mid-IR features are similar to those found in other diffuse and translucent clouds. Compared to paper I, the 7.7/11.3{\mu}m band ratios are lower, ~2.0, at both LDN 1688 positions. A continuum is detected in the ~10{\mu}m region. This is stronger towards the position ON1 but still lower than on any of the sightlines in Paper I. The far-infrared opacities are higher than for diffuse medium. The value of the position ON2, {\tau}200/N(H) = 3.9 x 10^{-25} cm^2/H, is twice the value found for ON1. The radiation field of LDN 1688 is dominated by the two embedded B type double stars, {\rho} Oph AB and HD 147889, with an additional contribution from the Upper Sco OB association. The strong heating is reflected in the high colour temperature, ~24 K, of the large grain emission. Radiative transfer modelling confirms a high level of the radiation field and points to an increased abundance of PAH grains. However, when the hardening of the radiation field caused by the local B-stars is taken into account, the observations can be fitted with almost no change to the standard dust models. However, all the examined models underestimate the level of the mid-IR continuum.

Observations of 6–200 μm emission of the Ophiuchus cloud LDN 1688

A stressed Ge:Ga infrared detector was tested in various operating conditions. Background-limited performance was demonstrated at photon backgrounds down to less than 10 to the 8th photon/s sq cm. The optimal operational parameters were determined.

Dietrich Lemke

Papers

Far-infrared emission of intracluster dust in the Coma galaxy cluster.

Balloon-borne infrared telescope for absolute surface photometry of the night sky.

The cold focal plane chopper of HERSCHEL's PACS instrument

Observations of 6–200 μm emission of the Ophiuchus cloud LDN 1688

Stressed Ge:Ga infrared detectors: performance and operational parameters