PACS Photometer Spatial Calibration PVPhotSpatial

1. PACS Photometer Spatial CalibrationPVPhotSpatial D.Lutz PACS PV Review Jan 21/22 2009, MPE Photometer Spatial Cal

2. 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 Photometer Spatial Cal

3. PCD 3.1.1: Central Pointing Position • Now part of pointing calibration, see presentation by Bruno Altieri • CAP prototype exists Photometer Spatial Cal

4. 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 Photometer Spatial Cal

5. 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 Photometer Spatial Cal

6. SIMULATED pointing from testing a 3.1.3 procedure in SOVT2 OD63 Photometer Spatial Cal

7. 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 Photometer Spatial Cal

8. 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! Photometer Spatial Cal

9. 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 Photometer Spatial Cal

10. 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 Photometer Spatial Cal

11. 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 Photometer Spatial Cal

12. 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 Photometer Spatial Cal

13. 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 Photometer Spatial Cal

14. 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 Photometer Spatial Cal

15. 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 Photometer Spatial Cal

16. 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 Photometer Spatial Cal

17. 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 Photometer Spatial Cal