Aims. This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods. The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480−1250 GHz with SIS mixers and the 1410−1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s −1 . Results. After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations.
Aims. In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described. Methods. The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources. Results. The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies.
Abstract. -The Far Infrared (FIR) properties of galaxies which are members of compact groups bear relevant information on the dynamical status and the physical properties of these structures. All studies published so far have been undermined by the poor sensitivity and spatial resolution of the IRAS-PSC and IRAS Sky Survey data. We used the HIRAS software available at the IRAS server at the Laboratory for Space Research in Groningen to fully exploit the redundancy of the IRAS data and to approach the theoretical diffraction limit of IRAS. Among the 97 groups which were observed by IRAS, 62 were detected in at least one band, while reliable upper limits were derived for all the others. Among the detected groups, 49 were fully or partially resolved, i.e. it was possible to discriminate which member or members emit most of the FIR light. At 60 µm, for instance, 87 individual sources were detected in 62 groups. In order to ease the comparison with data obtained at other wavelengths -and in particular in the X and radio domains -we give co-added and HIRAS maps for all the detected groups.
We present new optical observations of the nearby barred spiral galaxy Dwingeloo 1 (Dwl) obtained with the Isaac Newton, William Herschel and Wise telescopes. Dwl lies at Galactic coordinates (I = 138 ~ 52, b =-0 ~ 11) and it is heavily obscured by dust and gas in the Milky Way. We infer that Dwl is of morphological type SBb or SBc (T = 4), has an inclination i ~ 50°, a position angle PA ~ 110°, and a recession velocity relative to the Milky Way V Mw =256 ± 9 km S-1. The measured total apparent magnitudes of Dwl are V=14.0±0.5, R=12.2±0.2 and 1= 10.7 ±0.2. The extinction estimate towards Dwl is highly uncertain. The extinction in the B band, derived from Galactic H I column density measurements, is AB ~ 5.8. Estimated from Galactic 100-llm emission, the extinction is AB~4.3, while the reddened colours of Dwl yield an estimate of AB ~ 10.4. Assuming AB = 5.8, Tully-Fisher relations in the I and R bands lead to a distance estimate for Dwl of D ~ 300 km S-1. However, for the derived range of extinction estimates 4.3;;;:;AB;S1O.4, the distance varies from 100 to 500 km s-1. We also report the detection of numerous H II regions associated with Dwl, and present data from the Infrared Astronomical Satellite (IRAS) archive.
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