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 spectrum of the unidentiﬁed infrared (UIR)emission bands between 5.8 and 11.6  m has been observedfor the ﬁrst time for the diffuse emission of the galactic diskwhere the interstellar radiation ﬁeld (ISRF) is quite low. TheUIR bands at 6.2, 7.7, 8.6, and 11.3  m have absolute inten-sities which are  1/10th of the values observed in planetaryand reﬂection nebulae. However, the intensity ratios and bandwidths are similar, pointing to a common carrier for the UIRbands over a large range of different environmental parametersin the ISM. This mid-IR emission from a low-ISRF mediumandthe absenceofanydetectablecontinuumemission at 10  min the diffuse galactic spectra go against any signiﬁcant con-tribution from grains at equilibrium temperature or emissionduring temperature spikes of very small silicate grains; it sup-ports the identiﬁcation of the UIR bands as being due to thePAH molecules.Key words: interstellar medium: dust – infrared: ISM: bands –Galaxy: general1. IntroductionThefamilyoftheso-calledunidentiﬁedinfraredemissionbands(UIR), centered at 3.3, 6.2, 7.7, 8.6, and 11.3

Spectrophotometry of uir bands in the diffuse emission of the galactic disk

Using ISOPHOT maps at 100 and 200um and raster scans at 100, 120, 150 and 200um we have detected four unresolved far-infrared sources in the high latitude molecular cloud L183. Two of the sources are identified with 1.3mm continuum sources found by Ward-Thompson et al. and are located near the temperature minimum and the coincident column density maximum of dust distribution. For these two sources, the ISO observations have enabled us to derive temperatures (about 8.3 K) and masses (about 1.4 and 2.4 solar masses). They are found to have masses greater than or comparable to their virial masses and are thus expected to undergo gravitational collapse. We classify them as pre-protostellar sources. The two new sources are good candidates for pre-protostellar sources or protostars within L183.

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Far infrared observations of pre-protostellar sources in Lynds 183

Extrinsic photodetectors with implanted low ohmic contacts are used in ISOPHOT, which is one of the four focal plane instruments of the Infrared Space Observatory (ISO). If operated under the low temperature and low background conditions of ISO, such detectors show a highly nonlinear transient response to step changes of infrared illumination. For the Si:Ga detector arrays in PHT-S, the spectrometer in ISOPHOT, we are able to describe accurately the nonlinear photoresponse by a simple analytical function of time. Based on the theory, fundamental detector constants characterizing the dynamic behavior of such detectors can be extracted from experimental data. This allows the prediction of the steady state signals of short time measurements that have not stabilized after an illumination change. Results are presented on the dynamic effects of step-like flux changes and on the observed nonstationary injection of carriers due to temperature variations of the detector. The optimization of the in-orbit observation strategy is discussed using theory and experimental results.

Transient response of ISOPHOT Si:Ga infrared photodetectors: experimental results and application of the theory of nonstationary processes

Using the ISOPHOT Serendipity Survey (ISOSS) at 170um a sample of galactic star-forming regions exhibiting very cold dust temperatures ( 100 M_sun) has been established. We characterise the star-forming content of five regions that were selected as potential sites for early stage high-mass star formation using SCUBA (JCMT) and Spitzer observations. In every region we identify one to four submillimeter clumps with projected sizes between 0.1 and 0.4 pc. The dust temperatures range from 11.6 to 21.3 K and the estimated clump masses are 2 to 166 M_sun. Towards the majority of submillimeter peaks we find point sources in the near- to mid-infrared. Most are interpreted as low-mass young stellar objects but we also detect very red sources. They probably represent very young and deeply embedded protostars that continue to accrete clump material and may reach higher masses. Several candidate intermediate-mass proto- or pre-main-sequence stars embedded in the clumps are identified. A subset of four clumps may be massive enough (> 100 M_sun) to form high-mass stars and accompanying clusters. The absence of stellar precursors with current masses in the high-mass regime leave the type of star formation occuring in the clumps unsettled. We confirm the presence of large fractions of cold material as derived from large-scale far-infrared measurements which dominates the emission of most clumps and suggests that the star-forming process will continue.

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An infrared-submillimeter study of star-forming regions selected by the ISOSS 170um survey

We present a multi-wavelength study of the star forming region ISOSS J 20298+3559, which was identified by a cross-correlation of cold compact sources from the 170 μ m ISOPHOT Serendipity Survey (ISOSS) database coinciding with objects detected by the MSX, 2MASS and IRAS infrared surveys. ISOSS J 20298+3559 is associated with a massive dark cloud complex ( M  ~ 760 $M_{\odot}$) and located in the Cygnus X giant molecular cloud. We derive a distance of 1800 pc on the basis of optical extinction data. The low average dust temperature ( T  ~ 16 K) and large mass ( M  ~ 120 $M_{\odot}$) of the dense inner part of the cloud, which has not been dispersed, indicates a recent begin of star formation. The youth of the region is supported by the early evolutionary stage of several pre- and protostellar objects discovered across the region: I) two candidate Class 0 objects with masses of 8 and 3.5 $M_{\odot}$, II) a gravitationally bound, cold ( T  ~ 12 K) and dense ( n (H 2 ) ~ 2 $\times$ 10 5  cm -3 ) cloud core with a mass of 50 $M_{\odot}$ and III) a Herbig B2 star with a mass of 6.5 $M_{\odot}$ and a bolometric luminosity of 2200 $L_{\odot}$, showing evidence for ongoing accretion and a stellar age of less than 40 000 years. The dereddened SED of the Herbig star is well reproduced by an accretion disc + star model. The externally-heated cold cloud core is a good candidate for a massive pre-protostellar object. The star formation efficiency in the central cloud region is about 14%.

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Dietrich Lemke

Papers

Spectrophotometry of uir bands in the diffuse emission of the galactic disk

Far infrared observations of pre-protostellar sources in Lynds 183

Transient response of ISOPHOT Si:Ga infrared photodetectors: experimental results and application of the theory of nonstationary processes

An infrared-submillimeter study of star-forming regions selected by the ISOSS 170um survey

A very young star forming region detected by the ISOPHOT Serendipity Survey