HIFI – The instrument, its capabilities and the proposed science

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

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

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: 480-640 GHz; • Band 2: 640-800 GHz; • Band 3 800-960 GHz; • Band 4 960-1120 GHz; • Band 5: 1120-1250 GHz; • Band 6L+6H: 1410-1910 GHz • 480 GHz is 625 micrometer; 1910 is 158 micrometer • Bands 1-5 SIS technology, Band 6 HEB technology

4. Focal Plane Unit

5. Facts & Figures II • At 480 GHz the beam is 42”; at 1910 GHz 13” • Tsys(SSB) = 200-500K (480-1250 GHz); • Tsys(SSB) = 1600K in Band 6 • Bandwidth is up to 4 GHz; • Resolution of 135-270-539-1100 kHz State-of-the-art mixers

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

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)

8. Science The life cycle of gas and dust • 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

9. Water OH & H3O+ are also available in the HIFI freq. range!

10. Unbiased frequency scans IRAS 16293-2422on JCMT E. Caux et al.

11. Star-formation Different stages have different characteristics!

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!

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)

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

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

16. Hydrides & macro molecules

17. Preparation • While HIFI spectra may present you with either complex or straigthforward (Gaussian) profiles, interpretation isalways 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

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 !

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