PACS Photometer Spatial Calibration PVPhotSpatial

Photometer Spatial Cal 1

Jan 21/22, 2009PACS PV Review

PACS Photometer Spatial CalibrationPVPhotSpatial

D.Lutz

PACS PV Review Jan 21/22 2009, MPE



PCD 2.6.2: Telescope RPE

• Goal: measure the short term variations around the intended stable pointing

• Matter of taste whether to place here or under pointing calibration/FPG, was simply implemented here in order to not forget after the procedure was available…

• Method: Nonstandard AOR doing a chopped/nodded observation but with longer than usual nod period, to avoid the uncertainties associated with repositioning the telescope

• 2 sources: non-SSO (Alf Boo) and SSO (asteroid)• Total time: ~1h



PCD 3.1.1: Central Pointing Position

• Now part of pointing calibration, see presentation by Bruno Altieri

• CAP prototype exists



PCD 3.1.2: Relation between chopper position and angular

Displacement on sky • As directly as possible and suppressing telescope

repositioning uncertainties compare a known distance on sky with chopper throw [and direction] - important for AOTs!

• Use double sources with known separation. Not trivial to find, but using a combo of star pairs, galaxy pairs and asteroid conjunctions overall satisfactory – 13 cases with useful brightness, separation and PA found in PV exercise

• Baseline procedure: Triple chop using nonstandard AOR: 13 pairs, takes ~1h total

• Fall back procedure: Chop/nod with tailored throw using nonstandard AOR: Tested on 2 pairs ~0.2h total

• Nonstandard procedures were part of SOVT2, validation started



PCD 3.1.3: Photometer FOV distortion

• What we would like to do but would need better and faster pointing:

• Note: These PACS+testoptics results have been transferred to PACS+Herschel using N.Geis’ modelling



SIMULATED pointing from testing a 3.1.3 procedure in

SOVT2 OD63



3.1.3 Method A: narrowly spaced scanmaps across bright source

• Source should be very bright for good S/N in 1/10 of a sec, a little fluff or non-point like nature ok as long a core is symmetric. Baseline PV: Mira

• 7 chopper positions, 2 orientations, cover full array at 4” cross-scan step slow scan

• Standard AOR + nonstandard AOR (latter for non-optical zero chopper positions

• ~15h total



3.1.3 Method B: Staring raster on bright source

• Sloooow due to pointing overheads and minimum OBCP duration but still an important crosscheck to scanmap results

• Only one staring raster (nonstandard AOR) 3.5”*7” pitch at optical zero, which is the chopper position used for all the scanmap AORs

• Source: Mira• Total duration: 6.5h!



3.1.3 Method C:

• Differential checks by observing a field with a priori unknown but clear structure, placing the same structure in different regions of the array and using different chop throws.

• Test with two suitable galaxy pairs, two chop throws, raster to move sources further (nonstandard AOR)

• Total duration: 7h



3.1.4 Photometer PSF

• Because of expected noticeable color effects, include a star (blue SED, e.g. Alf boo), Blazar (red SED, faint, e.g. 3C345), Asteroid (bright, blue, SSO), do for both blue and green filter

• Method A: non-standard chopped/nodded AOR moving source to the centers of all 8 blue matrices, blue+green filter, total ~7h

• Method B: default point source AOR as reference, total ~0.5h



3.1.4: Finely sampled PSFs

• For blue/green/red filter and for a star and a blazar, do more finely sample rasters (5*5 at 1.25pixel step) around chop/nod

• Method C, nonstandard AOR• Note: Pointing quality is again an issue,

but may be reconstructable from data• Total duration: ~8h



3.1.4: PSF in scanmaps

• Method D: Scan over Alf Boo and 3C345 with scanmaps at all three speeds and in blue+green filter

• Modest scan map with 15 legs spaced 3” to improve sampling, default AOR

• Total duration: ~4h• Note: parallel mode is implicitly covered

as long as current averaging scheme is kept



Support spectrometer PSF

• Non-SSO sources that are bright enough for spec PSF are not strict point sources

• Take a quick small source photometer AOR on each source scheduled for spec PSF to look for structure, accepting that core may/will be saturated

• ~0.3h/source• Source list recheck TBD



PCD 3.1.5 Ghosts

• Method A: To re-measure the ‘blue streaks’ seen in ILT, do a 5’*5’ scanmap with 4” cross-scan step on a very bright source (Mira)

• Blue at 3 chopper positions, green at 1, standard and nonstandard AOR

• Total duration ~4h• Method B: Blind search for new phenomena

using 20’ scanmap with 6” cross-scan step• Covers ~ “Herschel FOV”• Source needs to be very bright, Uranus if

available, N3256 otherwise• Total duration ~4h



PCD 3.1.6 Straylight

• 2deg*2deg ‘homogeneous coverage’ fast scanmap, default AOR

• Source: Uranus if available (could remeasure at different epoch if in doubt about nature of an effect), Mira otherwise

• Total duration: ~2h

• Not covered at this point: Straylight at very large angles due to tripod reflex. There are useful measurement methods if a good prediction can be made by straylight WG



PCD 3.1.7: Background structure

• Measure background structure and straylight between open FOV and calibration sources by doing chopper scans over full range while telescope is staring

• Different calibration source and sky flux levels help in disentangling effects

• Total duration: ~3h



Keep an eye on

• validation of non-standard AORs from SOVT2 – quicklook is encouraging

• Signs - with two dimensions an even number of sign errors may not cancel ;-)

• Software stability/efficiency

PACS Photometer Spatial Calibration PVPhotSpatial

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