HIFI overview and status

Russ Shipman

Acknowledgements

• With special thanks to:– Carolyn McCoey (U. Waterloo)

– Sylvie Beaulieu (U. Waterloo)

– Ian (Max) Avruch (SRON)

– Tony Marston (ESAC)

– David Teyssier (ESAC)

• Many of these presentations and tutorials were prepared for the February NHSC workshop in IPAC, thanks to: – Adwin Boogert

– Colin Borys

– Steve Lord

– Pat Morris

Welcome!

By the end of this workshop, you will:

• know the current status of HIFI• have an overview of the HIFI pipeline and know how to use it• know about spectral tools in HIPE (and that plug in into HIPE)

and how to use them • learn of calibration issues affecting HIFI data and how to deal

with them• know how to export HIFI data into CLASS and FITS format• have had experience with using HIPE and working with

HIFI data

Welcome!

• The format of the workshop is a mix of presentations, demonstrations and hands-on time

• Demos will be done slowly enough that you can follow along if you want to. The scripts and data are available to take home to play with (recommended)

• Here to help:

Russ Shipman, Carolyn McCoey, Sylvie Beaulieu, Max Avruch, Miriam Rengel, and Tony Marston.

HIFI Overview

HIFI - high resolution spectroscopy

27 May 2010

Herschel Info Session - CASCA 2010

HIFI: most powerful and versatile heterodyne instrument in space for observing molecular and atomic lines in FIR/submm at ultra high spectral resolutions

• Single pixel on the sky

7 dual-polarization mixer bands• 5 x 2 SIS mixers: 480-1250 GHz (625-240 μm)• 2 x 2 HEB mixers: 1410-1910 GHz (213-157 μm)

14 LO sub-bandsLO source unit in commonLO multiplier chains

2 spectrometers-Auto-correlator (HRS) -Acousto-optical (WBS)

IF bandwidth/resolution- 2.4 and 4 GHz (in 2 polarizations)- 0.125, 0.25, 0.5, and 1 MHz- Velocity discrimination 0.1-1 km/s

Angular Resolution (w/ telescope):11”.3 (high-freq. end) to 40” (low-freq. end)

SensitivityNear-quantum noise limit sensitivity

Calibration Accuracy10% radiometric baseline, 3% goal

Herschel Workshop – CASCA 2009, 26 May - page 7

HIFI

AOT IIISpectral Scans

NHSC/HIFI (01/142008)

AOT ISingle Point Observations

AOT IIMapping Observations

Reference scheme

1 - Position Switch

2 – Dual Beam SwitchOptional continuum measurement

3 – Frequency SwitchOptional sky ref measurement

4 – Load ChopOptional sky ref measurement

Mode I – 1Point-PositionSwitch

Mode I – 2DBS

FastChop-DBS

Mode I – 3FSwitch

FSwitch-NoReference

Mode I – 4LoadChop

LoadChop-NoReference

Mode II – 2DBS-Raster

FastChop-DBS-RasterDBS-Cross

FastChop-DBS-Cross

Mode II – 3OTF-FSwitch

OTF-FSwitch-NoReference

Mode II – 1OTF

Mode III – 2SScan-DBS

SScan-FastChop-DBS

Mode III – 3SScan-FSwitch

SScan-FSwitch-NoReference

Mode II– 4OTF-LoadChop

OTF-LoadChop-NoReference

Mode III– 4SScan-LoadChop

SScan-LoadChop-NoReference

See HIFI Observers’ Manual: http://herschel.esac.esa.int/Docs/HIFI/html/hifi_om.html

HIFI Observing modes

Position Switch

• Ideal for sources in crowded fields or regions of extended emission for which accurate flux measurements are required

• Emission-free reference position must be within 2°• Mode is not continuum optimised• DBS and frequency switch more efficient

TargetPosition

ReferencePosition<2°

Dual Beam Switch

POSITION

TIM

E

TargetPosition

Ref 1Position

Ref 2Position

NOD 1

NOD 2

2

3

4

180” chop throw

180” chop throw

1

• For <3’ objects not situated in extended emission

Emission in one chop position is a common problem

• Very efficient

• Fewer problems with standing waves than other modes

• Use fast chop mode for broad lines and (more) accurate continuum

• In bands 6 & 7 fast chop mode is recommended

Frequency switch

• LO is shifted by a small amount, differencing the spectra can be used to remove baseline

• Useful in regions of extended emission, which are not expected to be line rich at the observed frequency

• Cannot be used for continuum measurements

• Use of OFF position is highly recommended, where possible, especially in bands 3 & 4. Only use no reference position if line is strong and narrow and the quality of the baseline is not a concern.

• Standing waves can still be a problem

• This mode is not recommended for bands 6 & 7

• Calibration scheme for Frequency Switch data still under discussion in the ICC

source ref

Load Chop

• The sky signal is differenced against the internal cold load.• Use this mode when it is not possible to find a clean “sky

reference” position. – However as with FSW, a reference is highly recommended.

• Without a sky reference, the baseline will likely contain standing waves.

• Not the most efficient mode because of internal drifting of the cold load requires frequent visits. May be the only choice for spatially and spectrally complex sources.

Spectral Scans

WBS (USB or LSB)

• Step WBS through a band (or part of a band)• Spectral scan data needs to be deconvolved to separate

emission from USB and LSB • Redundancy is given by number of overlap regions (R=2

above), higher R gives a better result from deconvolution• Uses DBS, Frequency Switch and Load Chop referencing

schemes (with all inherent advantages and disadvantages)• Spurs and poor baselines present a problem for deconvolution

Band

Mapping Modes

• There are three fundamentally different mapping modes: Raster, On-The-Fly, and Cross Maps:– Raster is simply observing a grid of points. Raster maps work with

all reference schemes.

– On-The-Fly: the satellite is moving and HIFI is integrating. OTFs work with position switch, load chop and FWS reference schemes.

– Cross Maps are like Raster maps but only step across the source in perpendicular directions. This is useful if the position of the source is not accurately known, but a full map is too costly (especially in bands with small beams).

• OTF is much more efficient, but baselines are not as good as in DBS Raster maps.

OTF in detail

• OTF scans by default in latitude. The user manual gives a wrong impression of scanning in longitude.– HSPOT gives the correct flow of the

observation.

• If possible use a reference position to obtain better baselines (not necessarily standing wave free, but better).

See mapping presentation

HIFI Status & Calibration

• SEUs• WBS-V Comb fade• Spurs/Purity• Sensitivities• Beam calibrations• Sideband ratio• Calibration budget

HIFI Single Event Upsets• An SEU in August 2009 attributed to cosmic ray on a sensitive memory chip in the LO control unit caused premature power-off of the LOU, killing HIFI’s Prime side (DC/DC converter failure)

• HIFI runs on its REDUNDANT side since February 2010, with new intensive fault protection S/W.

• SEU occurring statistically every 12 days

• Recovery now well established and rapid.

• One full power cycle (last resort) has been required, when HIFI stopped reacting to commands.

• ~2 ODs lost to LCU SEUs

• 5 ODs lost to ICU SEUs but PACS rescheduled so no observatory time lost.

SEUs occur and can impact observations. “The best laid plans…”

HIFI Single Event Upsets

• Recently, two SEUs in the critical area of HIFI’s memory.

• One could be recovered from in an elegant fashion

• The other required a power cycle of the instrument.

• The power cycle restored HIFI

• We expect 1 hit per year in the critical area of memory, now can be confident that another such event can be recovered from.

WBS-V comb fade• WBS-V comb has a failed component, already discovered in 2007

– The WBS-V could not be removed and repaired.• Comb power continued to drop

– Steep decay between OD 320 and OD 420, lighter since– No remaining attenuation in subband 4 (2-3 dB in others)

• Comb line intensity dropped to < 40 counts, much lower than specs.

Possible reduction of accuracy in determining comb line positions, reduced frequency calibration accuracy expected

S/N still > 400 in sub-band 4

HRS-WBS cross calibration

• Measure pair of spectra with WBS and HRS at any input (preferentially from internal 100 K hot load)

• Compute mutual correlation as function of relative shift

• HRS can be positioned to cover almost the full WBS scale

• Some On-Board S/W bugs to use this being worked out.

• Accuracy of about 100kHz (best case 30kHz)

• No issues with WBS-H so far.

Spur clean-up at instrument level

Many of the most troublesome impurities (e.g. near key lines) have been cleaned up, by (time/labor intensive) tests and changes to multiplier settings and bias voltages.

Band 1a spur eliminated (557 GHz H2O line region)

System temperature increased at upper 1.5 GHz of band

Sensitivity in band 1a is better than that in band 1b for LO frequencies up to 551.9 GHz.

V

H

V

Band 5b purification

• LO-band 5B had several LO spikes at the same time– Result is that the IF consists of several frequency bands

superposed on each other. Calibration of all frequencies within the IF was unknown

– Purification efforts took many weeks.– AORs in 5b were released in December 2010.

• Band 5B was not alone in impurities but in the diplexer bands the diplexer can moved and the signal evaluated at each setting to give purest signal more efficiently (in observing terms).– Purification in bands 3b/7b done this way (Band 5 has no diplexing).

• Purification is a major triumph for modeling of the LO chains!

Sensitivities

• Sensitivities are driven mainly by System Temperatures and Aperture (or beam) Efficiencies.

• Tsys remains essentially as measured just before launch --- some small changes at specific frequencies to mitigate impurities and unstable tunings.

Beam Calibrations• H/V beam sizes and co-alignment

• Measured mainly from Saturn, Uranus, Mars

• Beam offsets are taken into account in the HIFI pipeline since 5.0

Efficiencies• Beam efficiencies

measured on Mars

+ Overall ~10% better than pre-launch estimates

o Data taken before Nov 2010 should have somewhat better noise performance (HSpot 5.2 uses updated effciencies).

– Band 5a/b are an exception, ~10% lower.

Sideband ratios

• This is one of the main areas the ICC is actively working on to provide values to Astronomers

Error Budget

Error source B1/B2 B3/B4 B5 B6/B7

Sideband ratio <10% <30% <10% <30%

Hot Load Coupling <1% < 1% < 1% < 1%

Cold Load Coupling <1% < 1% < 1% < 1%

Hot Load Temperature < 1% < 1% < 1% < 1%

Cold Load Temperature < 1% < 1% < 1% < 1%

Beam efficiency 5-10% 5-10% 5-10% 5-10%

Pointing (APE+co-alignement) < 5% < 5% < 5% < 5%

Standing Wave 2-4% ? ? ?

Total (quadratic sum) <16 % <32 % <15% <32%

HIFI KP Science HighlightsPublications (16-03-11):

19 papers published in Herschel special A&A edition

49 papers published in HIFI A&A special edition

9 papers published elsewhere

32 submitted papers awaiting review

= 109 papers since October 2010

…and LOTS of conference proceedings