HIFI – The instrument, its capabilities and the proposed science Frank Helmich SRON – National Institute for Space Research

- page 2 Overview Introduction to HIFI and its capabilities –Specifications –Facts and figures –Observing modes and AOT’s Some images The proposed science –General –Spectral surveys –The water Universe –Specific topics (for key programs) Preparations for interpretation of the data Note that this cannot be in presented in great depth

- page 3 Facts & Figures HIFI (Heterodyne Instrument for the Far- Infrared) is just an ordinary heterodyne spectrometer with 6 frequency bands over 7 channels! But, HIFI is complex and very sensitive!! –Band 1: GHz; –Band 2: GHz; –Band GHz; –Band GHz; –Band 5: GHz; –Band 6L+6H: GHz –480 GHz is 625 micrometer; 1910 is 158 micrometer –Bands 1-5 SIS technology, Band 6 HEB technology

- page 4 Focal Plane Unit

- page 5 Facts & Figures II At 480 GHz the beam is 42”; at 1910 GHz 13” T sys (SSB) = K ( GHz); T sys (SSB) = 1600K in Band 6 Bandwidth is up to 4 GHz; Resolution of kHz State-of- the-art mixers

- page 6 Facts & Figures III HIFI is on-axis in Herschel HIFI has a cold focal plane (15K) in which the mixers themselves are cooled to about 4 K The sky and LO-signals are combined through beam-splitters and diplexers (Martin-Puplett interferometers) The LO signal is generated in the service module and send through waveguides to the focal plane The sky signal goes from primary to the (stiff) subreflector, and via M3 the 7 (14) sky beams enter HIFI HIFI has two loads in its Calibration Source Assembly (100 and 15K) Chopper chooses between loads, sky-on and sky-chop

- page 7 Observing Modes & AOTs HIFI is thus a sensitive, versatile instrument ideally suited for measurements of high spectral resolution –Very deep for a single frequency –Relatively shallow over a large (even complete) wavelength range –Essentially a single-pixel instrument (map by moving the telescope)

- page 8 Science HIFI is very well suited for any measurement requiring very high spectral resolution in the Far- IR/submm region Special emphasis on: –The water Universe – water in all kinds of astrophysical environments –Spectral surveys – unbiased frequency sweeps The life cycle of gas and dust

- page 9 Water OH & H 3 O + are also available in the HIFI freq. range!

- page 10 Unbiased frequency scans IRAS on JCMT E. Caux et al.

- page 11 Star-formation Different stages have different characteristics!

- page 12 The warm ISM Photon-dominated regions and shocks –Determining physical, chemical and kinematic conditions. Energy balance –Stringent tests for PDR models –High spectral resolution needed!

- page 13 Late stages of stellar evolution 2mm spectral survey of Pardo & Cernicharo Water and high-J lines of CO are major targets Spectral surveys for selected sources Water in W Hya (Barlow et al. ‘96)

- page 14 ISM in other galaxies Many subtopics, –all specifically aimed at spectrally resolved lines from HIFI –And unresolved lines (in maps) from PACS and SPIRE –Large ground-based component Fischer 1997

- page 15 Solar System Water in the giant planets: what is the origin? -> Volume mixing ratios from line profiles The chemical composition of the Mars atmosphere The chemical composition of cometary material: especially water at different distances from the Sun

- page 16 Hydrides & macro molecules

- page 17 Preparation While HIFI spectra may present you with either complex or straigthforward (Gaussian) profiles, interpretation is always complex –Influence of unknown beam-source coupling; –different physical (temperature and density) environments in one single beam –abundances can change over several orders of magnitude on short distances –Influence of dust or optical depth in excitation of the molecules e.g. mid-IR pumping –Geometry: e.g. (flared) disks and outflows in spherical (or sheet-like) cores Many models will be required

- page 18 Preparation II Rate coefficients of many molecules with H2 unknown Rate coefficients of many molecules with He unknown Frequencies at THz wavelengths often unknown Chemical reaction rates often unknown or guesses Radiative transfer often approximated or 1-D This also is true for ALMA so we need vast investments in solving all of the above problems –DLR funds spectroscopy in Cologne –EU funds FP 6 RTN – The Molecular Universe –Herschel preparatory science groups (own funds) –More is needed !

- page 19 Conclusions HIFI is the instrument of choice for any high spectral resolution measurements in the Far-IR/submm –Water –Spectral surveys HIFI data is easily reduced (at least the single spectra) Interpretation of HIFI data is not straightforward: Prepare well! –Radiative transfer models –Chemical models –Laboratory date and quantum-chemical calculations –E.g. FP6 RTN “The Molecular Universe” and groups for Herschel Preparatory Research HIFI data can be very well combined with PACS, SPIRE and ALMA data