Abstract
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.
Highlights
The Heterodyne Instrument for the Far-Infrared (HIFI, De Graauw et al 2010) is designed to be a very high spectral resolution receiver (R >∼ 106), with near-quantum limited performance for frequencies between 480 and 1910 GHz onboard the Herschel Space Observatory (Pilbratt et al 2010)
The HIFI instrument is based on the heterodyne technique, where the sky signal at a frequency νsky is mixed with an ultrastable internally generated local oscillator (LO) signal at frequency νLO
The focal plane chopper (FPC), a rotatable mirror that can change the orientation of the telescope beam on the sky, makes it possible to chop between an ON- and OFF- source sky position within 40 ms
Summary
The Heterodyne Instrument for the Far-Infrared (HIFI, De Graauw et al 2010) is designed to be a very high spectral resolution receiver (R >∼ 106), with near-quantum limited performance for frequencies between 480 and 1910 GHz onboard the Herschel Space Observatory (Pilbratt et al 2010). The near quantum-limited performance with an absolute calibration accuracy of 10% is needed for a detailed study of absorption lines and intercomparison of water lines in the same or different mixer bands. With the level of detail in the line profiles that HIFI provides, the physical and dynamical conditions for all gaseous material along the line-of-sight can be unraveled. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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