1. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 1 HIFI Standing Waves Adwin Boogert, NHSC/IPAC, Pasadena, CA, USA

2. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 2 HIFI Standing Waves Standing wave characteristics depend on HIFI band: Bands 1-5: up to 10 optical (pre-mixing) standing waves detected. Different shapes between bands with beam-splitter (1,2,5) and diplexer (3,4). Bands 6 and 7 have electronic (post-mixing) standing waves, whose shape and amplitude depend on HEB current.

3. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 3 HIFI Standing Waves Band 2 (beamsplitter) (courtesy Ronan Higgins)

4. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 4 HIFI Standing Waves Band 4 (diplexer) (courtesy Ronan Higgins)

5. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 5 HIFI Standing Waves Diplexer vs. beamsplitter (courtesy Ronan Higgins)

6. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 6 HIFI Standing Waves (courtesy Ronan Higgins) Bands 6 and 7 Standing wave shows 'dispersed' sine wave

7. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 7 HIFI Standing Waves (courtesy Ronan Higgins) Bands 6 and 7 empirical solution: match standing wave with stability observation at equal HEB current.

8. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 8 HIFI Standing Waves To remove standing waves one needs to know if they are additive or multiplicative to stellar signal. Standing wave amplitude in principle multiplicative with incoming wave intensity Ground based telescopes thermal background MUCH larger than stellar signal. Standing wave amplitudes large w.r.t. stellar signal, but ideally they are subtracted in chop/nod process. Residual standing waves may come from system instabilities and are additive w.r.t. weak stellar signal. How about HIFI at Herschel? Will system instabilities give dominating additive residual standing wave term or only (small) multiplicative term?

9. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 9 HIFI Standing Waves Removing additive (residual) waves: If waves additive: determine properties in DSB spectrum away from stellar lines and subtract wave from entire spectrum. Multiple-sine wave fitting tool available in IDL. Being implemented in HCSS.

10. Herschel DP Workshop – ESAC, Madrid, E, 2008 Dec 4 - page 10 HIFI Pipelines and Data Products IF frequency [MHz] ILT (worst case!) Standing wave removal needed for all HIFI AOTs, either as a residual (e.g. chopped/nodded spectra) or if OFF sky not taken with FSwitch or LoadChop modes. Robust sine wave fitting routine for ISO/SWS and Spitzer/IRS defringing available in IDL. Fits multiple sine waves, using Bayesian statistics. Little user interaction. Contains line blanking routine. Tool being developed in HIPE. May be used for PACS and SPIRE spectra as well. Frequency [GHz] Normalized Intensity Band 1A: Band 1A Normalized Intensity HIFI Standing Waves

11. Herschel DP Workshop – ESAC, Madrid, E, 2008 Dec 4 - page 11 HIFI Pipelines and Data Products 'Fringes'-diagnostic plot ---  2 vs frequency, with clear minimum (red) Standing waves successfully removed in gas cell spectra. (residual) standing wave patterns likely different in space. However, algorithm very flexible! Initial guesses easily adjusted. HIFI Standing Waves

12. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 12 HIFI Standing Waves Sine wave fitting method obviously fails for multiplicative waves: (courtesy Patrick Hennebelle)

13. Deconvolution Workshop – MPIfR, Bonn, D 2008 Dec 8 - page 13 HIFI Standing Waves Before, during or after deconvolution spectral scans? Depends on pre-mixing wave stability and whether it is additive or multiplicative: If pre-mixing waves depend on LO frequency: remove before deconvolution If waves additive and pre-mixing wave independent of LO frequency, they will be deconvolved like additive stellar signals and can be removed afterwards. If waves multiplicative: need to remove wave before or during deconvolution (together with gain solution). Need to know pre-mixing wave characteristics. Needs much more testing!