Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 1

PACS Sky Fields and Double Sources for Photometer Spatial Calibration

M. Nielbock1, D. Lutz2, B. Ali3, T. M¨uller2, U. Klaas1

1Max–Planck–Institut f¨urAstronomie, K¨onigstuhl17, D-69117 Heidelberg, Germany 2Max–Planck–Institut f¨urExtraterrestrische Physik, Giessenbachstraße, D-85748 Garching, Germany 3NHSC, IPAC, California Institute of Technology, Pasadena, CA 91125, USA Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 2

Contents

1 Scope and Assumptions 4

2 Applicable and Reference Documents 4

3 Stars 4 3.1 Optical Star Clusters ...... 4 3.2 Bright Binaries (V -band search) ...... 5 3.3 Bright Binaries (K-band search) ...... 5 3.4 Retrieval from PACS Pointing Calibration Target List ...... 5 3.5 Other stellar sources ...... 13 3.5.1 Herbig Ae/Be stars observed with ISOPHOT ...... 13

4 Galactic ISOCAM fields 13

5 Galaxies 13 5.1 Quasars and AGN from the Veron catalogue ...... 13 5.2 Galaxy pairs ...... 14 5.2.1 Galaxy pairs from the IRAS Bright Galaxy Sample with VLA radio observations 14

6 Solar system objects 18 6.1 Asteroid conjunctions ...... 18 6.2 Conjunctions of asteroids with pointing stars ...... 22 6.3 Planetary satellites ...... 24

Appendices 26

A 2MASS images of fields with suitable double stars from the K-band 26

B HIRES/2MASS overlays for double stars from the K-band search 32

C FIR/NIR overlays for double galaxies 38 C.1 HIRES/2MASS overlays for double galaxies ...... 38 C.2 MIPS 70 µm/2MASS overlays for double galaxies ...... 42 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 3

Document Change Record

Issue Date Paragraphs Change Draft 0.1 08-Jul-02 Initial Draft Draft 0.2 24-Jun-03 Section 3 Included 2MASS K-band search results Draft 0.3 29-Jul-03 All Small changes, fixed typos etc. 3.2 Added coordinates to table 3.4.1 Added discussion on Herbig AeBe stars 5.2 Added discussion on Condon et al. BGS double galaxies Draft 0.4 13-Aug-03 All Minor text changes 6.2 More info on Saturn satellites Draft 0.5 13-Aug-03 All, Appendix Added HIRES/2MASS quick-look, minor changes in text Issue 1.0 16-Oct-03 Appendix Changed HIRES/2MASS images for stars to correctly contoured ones Issue 2.0 14-Feb-08 All Revision and update of all information 3, 5, 6.1 Included new data and catalogues, update on asteroid encounters Issue 2.1 20-Feb-08 3.3, 5.2, 6.1 added visibility plots, more info on bright moons Issue 2.2 04-Apr-08 6.2 added encounters between asteroids and stars Issue 2.3 05-May-08 3.4, Appendix added a double star from pointing list Issue 2.4 28-May-08 3.4 included double pointing stars from PICC-MA-TN-003 Issue 2.5 02-Dec-08 all update wrt new launch date Issue 2.6 06-Jul-2009 6.l update wrt new launch date Issue 2.7 27th July 2009 3.4 removed HIP 82526 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 4

1 Scope and Assumptions

This document summarises the status of the search for fields with multiple far-infrared objects that are suited for the spatial calibration of PACS. In addition to tasks requiring single point sources, the PCD (AD-1) identifies a need for fields containing binary or multiple point sources or clusters of sufficient brightness over scales of typically a few arcminutes (Requirements 2.6.3, 3.1.2, 3.1.3). The purposes of these requirements are accurate verifications of pixel scales, optical distortions, and of chopper throw. The use of multiple sources with accurate far-infrared positions could bypass the errors induced by multiple pointings of the satellite on a single source. Ideally, all these multiple sources should have far-infrared positions accurate to the sub-arcsecond level. This document describes the results of several approaches to this problem, including unsuccessful ones. As an indication for the required fluxes, we follow PCD 3.1.2 asking for 160 mJy in the PACS bands to achieve S/N = 20 in 1 min. PCD 2.6.3 asks for yet brighter objects. The local far-infrared background has to be checked in all cases to avoid disturbances. As a working assumption, we searched for multiplicity roughly on the 0.50 to 50 scale. It is important to cover several position angles, since the PACS chop angle cannot be varied freely – only for objects near the ecliptic poles all angles are accessible, by repeated observations over a one year period. This document does not address the fallback options for some spatial calibrations of using bright and heavily structured fields that do not have a priori positional information, and of stepping over single point sources at the expense of including satellite positioning errors.

2 Applicable and Reference Documents

AD-1 PACS-MA-GS-001 PACS Calibration Document Draft 9 (PCD) RD-1 Potential ISOCAM fields for PACS spatial calibration, B. Ali, 17-May-2002 RD-2 Solar System Objects as Calibrators for Herschel, T. M¨uller,e-mail, 05-Jul-2002 RD-3 Flux estimation of satellites and rings with Herschel, R. Moreno, HCalSG#15, 26-Jun-2007 RD-4 PICC-MA-TN-003 PACS Pointing Calibration Sources, M. Nielbock et al.

3 Stars

Stars are excellent candidates because of usually accurate positions, and their point-like nature. The proper motion of some stars contributes significantly to the stellar coordinates for a given observing epoch. Precise proper motions can be obtained from catalogues like the Catalogue of Positions and Proper Motions (R¨oser& Bastian 1988, A&AS, 74, 449) as well as the Tycho 2 catalogue (Høg et al. 2000, A&A, 355, L27). The required point-like nature implies that objects with structures that are spatially resolved by PACS, e.g. large dust shells or WR star ejecta, have to be avoided. Assuming photospheric emission, the required brightness of an object with 160 mJy at 75 µm can be estimated using the formula of Engelke (1992, AJ, 104, 1248) which is valid for late type stars. The resulting requirement of K ≤ 1.8 implies severe limitations for the use of “normal” well-behaved stars as PACS spatial calibrators.

3.1 Optical Star Clusters Globular cluster stars are too faint and too densely packed. Some open clusters match the desired spatial structure but stars are too faint, again. The brightest stars of an amateur’s open cluster like Praesepe, for example, are around V = 7 and intermediate spectral types, i.e. clearly out of reach. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 5

3.2 Bright Binaries (V -band search) Bright binaries with V < 5 mag (for both components) and separations between 3000 and 30000 were searched by direct query of the Washington Visual Double Star Catalogue (Worley & Douglass 1997, A&AS, 125, 523) in Vizier and searching for V < 5 objects with such separations in the Bright Star Catalogue. After weeding out a few objects where one or both components are double themselves on the arcsecond scale, three candidate pairs remained. After cross checking with the more recent Tycho Double Star Catalogue (Fabricius et al. 2002, A&A, 384, 180) and IRAS/HIRES data, none of those remaining stars appears suitable for PACS calibration purposes.

3.3 Bright Binaries (K-band search) The 2MASS all-sky catalogue was searched based on the following two criteria: (i) both components must have 2MASS Ks < 3 mag, and (ii) the total separation between the components must be less than 50. A total of 33 fields fulfilled both criteria. These are listed in Tab. 1. The 2MASS images of the tiles on which the first star (Star 1 below) appears are shown in Appendix A (the star is not centred on the tile). The colour-colour plot for the stars is shown in Fig. 1. For comparison, the colours of the normal main-sequence dwarves and giants are shown as solid red and blue lines, respectively. The dashed lines show the reddening paths due to extinction of main sequence dwarves and giant stars. A visualisation of the expected visibilities during the first year of the Herschel mission and their solar aspect angles during the first 120 days of the K-band selected double stars as listed in Tab. 2 is shown in Fig. 2. They have been calculated based on the L2 orbit derived for a launch date of 12th April 2009 and need confirmation as soon as the actually final orbit will have been established. We additionally obtained HIRES images of the 2MASS fields discussed here. The HIRES technique uses IRAS (InfraRed Astronomical Satellite) data but employs the Maximum Correlation Method (MCM, Aumann et al. 1990, AJ, 99, 1674) to produce images with better than the nominal resolution of the IRAS data. The resulting IRAS/HIRES images are shown as contour overlays on the 2MASS fields in Appendix B. We selected the IRAS 60 µm band for these images. For each IRAS/HIRES image, 10 contour levels were drawn between the minimum and the maximum value. These overlays were used to evaluate the correlation between the FIR flux peak and the 2MASS source position. The three best matches are the fields 14, 18, and 27. They are coloured green in Fig. 1. Another 11 fields were found to be suitable for astrometric purposes. They are marked as black dots in Fig. 1. These 14 K-band selected double stars are summarised in Tab. 2. The expected range of FOV position angles was determined with HSPOT and has been added for comparison with the position angle of the double stars. Note that the position angle (PA) that originally corresponds to the observatory z-axis has been converted to be relative to the y-axis which is parallel to the chopping direction.

3.4 Retrieval from PACS Pointing Calibration Target List Scanning observations are an important observing mode to efficiently produce large maps. Therefore, the absolute and relative pointing errors of the satellite pointing during scan map observations must be evaluated (see reqs. 2.6.3 and 2.6.4 in RD-1). This can be achieved by bright enough pointing sources with relatively small separations so that they can be observed with a single scan. The brightness requirements are ≥ 400 mJy for the absolute (PCD req. 2.6.3) and ≥ 20 Jy for the relative pointing evaluation (PCD req. 2.6.4). For this purpose, we investigated the pointing source lists of the document (RD4) for pairs with separations of up to 2◦. This resulted in a list of 92 candidates with separations from a few arcminutes up to two degrees. All of them have flux densities of at least 400 mJy at 60 µm Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 6

AV = 20 3.0 well suited double stars suited double stars 2MASS Ks double stars LC V 19b LC III 24b 2.5 24a

2.0 AV = 10

19a

1.5 20a 2Mass 27a 27b (J-H) 18b 20b12b 18a 12a8a 14b31a 5b 5a 34a 1.0 11b 1a 14a 8b 6b 6a 31b9a 11a 1b 0.5 9b

0.0

34b -0.5 0.0 0.5 1.0 1.5 2.0 (H-Ks)2Mass

Figure 1: 2MASS colour-colour diagram for bright binaries from the K-band search and the pointing source list. The loci of the unreddened main-sequence (red line) and giant stars (blue line) are taken from Ducati et al. (2001, ApJ, 558, 309). The complete sample of 34 fields (68 individual stars, see Tab. 1) is marked as grey dots. The refined list of 3 well suited and 11 suitable double stars (Tab. 2) is highlighted as green and black dots. The large error bars originate from the photometric uncertainties of the 2MASS data for bright stars. and are suitable for fulfilling req. 2.6.3. However, although there are 8 pairs with one source having at least 20 Jy at 60 µm (req. 2.6.4), there is no example where both sources fulfil the specification. In Tab. 3, we list the 92 pairs of pointing sources with separations of up to two degrees and flux densities of 400 mJy at 60 µm. The first 8 entries comprise the pairs, where one object has a flux density of ≥ 20 Jy. Within the two flux bins, the calibrators are sorted according to their separations. One of the entries consists of a double star with an angular separation of < 50. Therefore, it satisfies the selection criterion (ii) for the 2MASS K-band binaries. We included this target as field no. 34 in Tab. 1. It qualifies as a primary spatial calibration target and is contained in the final calibration source list given in Tab. 2. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 7 4 4 4 4 4 4 4 ...... 15 37 68 43 73 42 42 0 . . . 0 . . 0 0 . 0 0 0 . m 4 5 0 0 3 0 0 10.7 3.31 0.73 0.72 2.86 0.78 0.54 1.47 0.74 1.37 4.95 4.27 µ < < < < < < < < < < < < < < 60 (Jy) F IRAS PSC Ks ∆ Ks 2.5572.607 0.306 2.777 0.366 2.869 0.386 1.510 0.386 2.051 0.252 2.248 0.284 2.544 0.318 2.737 0.328 2.475 0.274 2.906 0.256 1.940 0.272 2.763 0.278 2.722 0.290 2.985 0.320 2.690 0.286 1.618 0.300 2.949 0.188 1.603 0.218 2.821 9.996 1.584 0.342 2.820 0.220 2.741 0.246 1.683 0.272 2.913 0.200 1.203 0.316 2.027 0.210 2.186 0.278 0.280 1.9132.248 0.252 2.804 0.284 0.276 (mag) (mag) -0.775 0.312 ) ◦ PA )( 0 θ ( Separation 3.86 166 1.07 14 3.12 144 0.51 150 1.96 127 4.03 10 2.11 67 1.92 67 3.34 118 0.20 152 3.72 69 2.42 173 1.11 129 3.61 18 1.72 10 3.31 159 m flux was extracted from the IRAS PSC. µ –––– –––––––––––––– –––––––– –– Proper motion 5.2 2.7 1.7 -21.3 -4.8 -8.6 -4.1-1.4 1.6 2.9 -6.5-1.8 -4.8 -8.0 -1.5 -31.3 16.5 5.6 14.3 7.0 10.6 -4.5 10.3 -9.9 14.2 9.6 -23.2 -12.2 -25.6-10.1 20.3 -35.5 182.8121.2 10.9 -22.0 ∆R.A. ∆Dec. (mas/yr) (mas/yr) Epoch 2000.0 R.A. Dec. Coordinates (J2000.0) ) and position angles (counter-clockwise from North) are based on the coordinates quoted in the 20:01:27.5020:01:21.58 +50:02:32.5 +50:06:16.8 20:11:06.1520:11:07.45 +36:06:48.8 +36:07:51.1 20:31:45.2320:31:36.53 +32:31:21.3 +32:33:52.5 21:06:53.42 +38:44:53.0 21:06:54.74 +38:44:26.6 20:47:36.8020:47:29.05 +35:52:18.4 +35:53:28.9 19:12:21.2619:12:17.42 +41:18:13.3 +41:14:15.7 22:06:51.6822:06:39.92 +48:27:55.7 +48:27:06.8 02:23:24.0902:23:11.06 +57:12:43.0 +57:11:57.9 01:55:54.4801:56:09.33 +37:16:40.0 +37:15:06.6 13:23:55.63 +54:55:29.3 13:23:56.29 +54:55:18.4 06:47:19.8206:47:05.83 +08:02:14.3 +08:00:53.5 04:07:55.7404:07:57.41 +43:03:11.3 +43:00:47.5 05:30:17.7605:30:10.20 +63:03:19.5 +63:04:01.8 12:19:37.8812:19:42.61 -19:15:21.8 16:20:20.78 -19:11:56.0 16:20:26.91 -78:41:44.9 17:26:07.49 -78:40:03.1 17:26:00.05 -50:41:06.0 -50:38:00.5 θ Aps Aps Ara 2 1 κ δ δ -band selected double stars as candidates for the astrometric calibration. The coordinates and proper motions were retrieved from K 12194260-1911560 UW Crv 16202690-7840031 17260004-5038004 12193788-191521816202077-7841448 R Crv 17260749-5041059 CGCS 3822 20012749+500232520012157+5006167 Z20110615+3606488 Cyg 20110744+3607510 e Cyg V429 Cyg 20314523+3231213 V1487 Cyg 20313652+3233524 AI21065341+3844529 Cyg AD Cyg 21065473+3844265 V1803 Cyg 20473679+3552184 NSV 13546 20472904+355328919122126+4118133 V375 Cyg 19121741+4114156 RU Lyr 22065167+4827557 V552 Lyr 22063991+482706802232409+5712430 CT Lac 02231106+5711579 V403 Per 01555447+3716400 V439 Per 01560933+3715066 HD 11727 13235563+5455292 5613235629+5455183 And 06471981+080214306470582+0800535 17 Mon 04075574+4303113 ST Mon 04075741+4300475 HD 25892 05301775+6303195 IY05301020+6304017 BD+62 Per 760 17 Cam -band magnitudes have been obtained from the 2MASS database; the IRAS 60 1 2 3 4 5 6 7 8 9 List of Ks 10 11 12 13 14 15 16 No. Field 2MASS Name . list. The the Tycho 2 catalogue. Both target separations ( Table 1: Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 8 4 6 9 8 4 2 3 ...... 48 50 57 52 36 59 . 0 . . . . . 1 0 2.1 2.8 166 m 0 1 1 1 2 31 83 4 19 18 1.18 1.06 31.2 16.4 0.59 31.6 6.66 4.39 0.69 1.49 12.1 0.43 1.39 0.41 2.46 1.44 µ < < < < < < < < < < < < < 60 (Jy) F IRAS PSC Ks ∆ Ks 2.1772.610 0.284 1.987 0.408 0.911 0.216 2.442 0.174 2.360 0.214 2.990 0.186 0.095 0.324 1.688 0.186 2.856 0.220 1.948 0.260 2.345 0.244 2.996 0.268 2.907 0.306 2.263 0.326 2.266 0.262 0.276 2.0492.726 0.272 2.273 0.244 1.541 0.246 2.360 0.278 2.217 0.238 2.481 0.238 2.888 0.264 1.601 0.252 1.978 0.278 1.965 0.280 2.702 0.268 2.165 0.266 2.977 0.220 2.822 0.194 2.831 0.238 4.267 0.262 0.329 0.036 0.174 (mag) (mag) ) ◦ PA )( 0 θ ( Separation 0.96 17 3.29 4 3.60 82 4.50 149 2.36 143 4.82 178 2.17 54 3.92 64 4.13 156 2.90 139 3.51 19 3.00 158 2.37 81 2.15 132 4.23 81 1.88 159 4.26 109 –––––––––––––––––––––––––––––––––– –––––––––– Proper motion 0.54.3 -14.9 -15.1 0.6 -5.5 -2.8-7.8 0.2 -1.8 -7.8-1.0 0.1 3.8 -17.7 -2.2 -12.0 -5.9 -48.2 -12.8 -14.5 25.2 -115.4 -190.7 ∆R.A. ∆Dec. (mas/yr) (mas/yr) continued. Table 1: Epoch 2000.0 R.A. Dec. Coordinates (J2000.0) 16:47:03.0916:47:04.69 -45:52:18.9 05:28:51.71 -45:51:23.9 05:28:52.89 +32:25:22.4 +32:28:39.1 18:11:11.6318:11:27.57 -26:30:02.9 04:19:50.87 -26:29:32.5 +41:07:41.8 04:20:03.16 +41:03:50.1 06:45:17.3706:45:23.14 +12:53:43.9 +12:51:50.5 13:22:09.8313:22:08.42 -64:13:07.8 23:08:09.39 -64:08:18.8 23:07:55.98 +58:15:58.1 +58:14:42.3 17:41:10.4117:40:54.13 -30:20:53.7 -30:22:38.1 17:10:13.6917:10:04.97 -40:46:14.5 17:38:54.81 -40:42:27.6 17:38:45.49 -34:59:28.4 17:35:33.14 -34:57:17.8 17:35:37.76 -14:19:28.6 14:06:47.33 -14:16:08.9 14:06:37.42 -62:22:27.4 12:47:24.68 -62:19:40.9 12:47:43.27 -59:41:40.9 07:47:45.22 -59:41:19.4 07:47:38.53 -16:00:51.9 17:14:09.92 -15:59:26.4 17:14:27.24 -14:59:59.4 17:07:01.47 -14:59:21.0 17:06:57.91 -40:55:38.1 18:11:47.50 -40:53:52.4 18:11:54.16 +31:28:20.0 +31:24:19.3 Cru Gem β ξ 16470468-4551238 18112756-2629324 13220842-6408188 17405413-3022380 17100497-4042276 17384548-345717717353776-1416088 V492 Sco IRAS 17327-1414 14063742-6219408 12474326-5941194 07473853-155926317142723-1459209 QY Pup IRAS 17116-1455 17065791-4053524 IRAS 17034-4049 16470309-4552189 18111163-2630028 13220982-6413078 UX Cen 17411041-3020537 CD-30 14574 17101368-4046145 17385481-345928317353314-1419286 NSV 23099 14064732-6222274 FU Ser 12472467-5941409 NSV 20034 07474521-1600519 DY Cru 17140992-1459593 NSV 3741 17070146-4055380 IRC -10360 IRAS 17035-4051 05285171+322522305285288+3228391 V400 Aur V401 Aur 04195087+410741704200316+410350006451737+1253438 GM06452314+1251504 Per IR Per AT Gem 23080938+581558123075597+5814423 BD+57 2698 18114749+312819918115416+3124192 IRAS 18099+3127 IRAS 18100+3123 17 18 19 20 21 22 23 24 2526 duplicate of 24 27 28 29 30 31 32 33 34 No. Field 2MASS Name Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 9

Table 2: Final list of suitable double stars from the K-band search after inspecting the HIRES data in Appendix B of the candidates of Tab. 1. The first eight sources (3 – 32) are considered as a primary choice, while the last seven sources (1 – 31) could be used as backup targets. The visibilities were obtained with HSPOT. The observatory position angle is given relative to the y-axis that is parallel to the chopping direction. Geometry HIRES Double star visibilities (HSO y-axis) No. 2MASS Name θ PA F60µm Start PA End PA (0)(◦) (Jy) (Date) (◦) (Date) (◦) 20314523+3231213 AI Cyg 2.9 2009 Apr 12 181 2009 Jul 04 117 3 20313652+3233524 AD Cyg 3.12 144 1.0 2009 Sep 25 20 2010 Jan 02 298 19122126+4118133 RU Lyr 0.6 6 19121741+4114156 V552 Lyr 4.03 10 0.3 2009 Apr 12 171 2011 Apr 12 172 06471981+0802143 17 Mon 0.3 2009 Apr 12 8 2009 May 02 13 11 06470582+0800535 ST Mon 3.72 69 0.4 2009 Sep 03 176 2009 Nov 05 194 12193788-1915218 R Crv 1.1 2009 Jun 01 15 2009 Aug 05 34 14 3.61 18 12194260-1911560 UW Crv 0.3 2009 Dec 04 196 2010 Feb 02 213 05285171+3225223 V400 Aur 1.1 2009 Aug 16 182 2009 Oct 16 172 18 05285288+3228391 V401 Aur 3.29 4 0.9 2010 Feb 12 2 2010 Apr 13 352 06451737+1253438 ξ Gem 0.1 2009 Apr 12 7 2009 May 01 10 21 06452314+1251504 AT Gem 2.36 143 0.6 2009 Sep 03 179 2009 Nov 03 190 17385481-3459283 NSV 23099 2.4 2009 Apr 12 188 2009 Apr 15 189 27 17384548-3457177 V492 Sco 2.90 139 3.4 2009 Aug 17 355 2009 Oct 18 9 17140992-1459593 IRC -10360 1.3 2009 Aug 11 168 2009 Oct 11 0 32 17142723-1459209 IRAS 17116-1455 4.23 81 0.4 2010 Feb 08 189 2010 Apr 08 180 18114749+3128199 IRAS 18099+3127 1.9 2009 Apr 12 163 2009 May 25 124 34 18115416+3124192 V669 Her 4.26 161 1.3 2009 Jul 26 54 2009 Nov 26 303 20012749+5002325 Z Cyg 6.8 1 20012157+5006167 e Cyg 3.86 166 0.2 2009 Apr 12 182 2011 Apr 12 182 20473679+3552184 1.6 2009 Apr 12 185 2009 Jul 14 110 5 20472904+3553289 V375 Cyg 1.96 127 0.5 2009 Sep 29 21 2010 Jan 11 291 22065167+4827557 0.8 2009 Apr 22 196 2009 Aug 22 90 7 22063991+4827068 CT Lac 2.11 67 3.0 2009 Oct 25 16 2010 Feb 17 271 02232409+5712430 V403 Per 2009 Jul 07 183 2009 Sep 28 126 8 1.92 67 0.9 02231106+5711579 V439 Per 2010 Jan 05 4 2010 Mar 25 307 01555447+3716400 HD 11727 0.3 2009 Jun 30 172 2009 Sep 05 143 9 3.34 118 01560933+3715066 56 And 0.1 2009 Dec 29 352 2010 Mar 03 323 04195087+4107417 GM Per 0.6 2009 Aug 01 181 2009 Oct 04 158 20 04200316+4103500 IR Per 4.50 149 12.6 2010 Jan 28 2 2010 Apr 01 338 07474521-1600519 NSV 3741 2009 Apr 12 196 2009 Jun 01 38 31 07473853-1559263 QY Pup 2.15 132 0.6 2009 Sep 17 7 2009 Dec 03 218 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 10

Figure 2: Visibility plot (above) and solar aspect angles (below) of the best suited K-band selected double stars. They are based on L2 orbits derived for a launch date of 12th April 2009. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 11

Table 3: List of 91 pairs of pointing sources with separations of up to 2◦ and flux densities of ≥ 400 mJy. The first four lines contain eight pairs of which at least one source possesses a flux density of ≥ 20 Jy. The separations (θ) are given in arcminutes, the position angles (P. A.) are provided counter-clockwise from North. The flux densities are the values attained at the lowest wavelength as reported in (RD4). Separation Separation Objects Source θ P.A. Flux Objects Source θ P.A. Flux list [0][◦] [mJy] list [0][◦] [mJy] HIP 10995 ∗ 1092 HIP 21252 ∗ 1081 HIP 11093 ∗ 44.4 12 22005 HIP 21479 ∗ 61.3 21 140895 HIP 66738 ∗ 804 HIP 98608 ∗ 5512 Mrk 273 • 79.9 25 27450 HIP 99512 ∗ 83.1 114 26796 PPM 181320 ∗ 3049 HIP 63642 ∗ 21289 HIP 107516 ∗ 96.4 105 27825 3C 279 ∞,• 102.9 111 2200 HIP 63642 ∗ 21289 HIP 48036 ∗ 61984 PPM 159442 ∗ 114.6 10 944 HIP 48540 ∗ 117.7 127 506 2MASS J18114749+3128199 ∗ 1542 HIP 79072 ∗ 617 HIP 89172 ∗ 4.3 161 796 HIP 79086 ∗ 5.2 24 771 HIP 84329 ∗ 1026 HIP 23636 ∗ 7038 HIP 84380 ∗ 27.6 16 972 HIP 23685 ∗ 29.3 163 1165 HIP 12086 ∗ 587 HIP 96399 ∗ 437 HIP 12193 ∗ 29.8 149 1870 HD 184956 ∗ 33.1 74 1030 HIP 74558 ∗ 831 HIP 71995 ∗ 925 HIP 74633 ∗ 34.7 156 516 HIP 72105 ∗ 38.9 33 913 HIP 9306 ∗ 1643 HIP 68357 ∗ 1285 HIP 9582 ∗ 39.4 51 2480 HIP 68417 ∗ 41.6 13 2536 HIP 29450 ∗ 5112 HIP 42975 ∗ 726 HIP 29655 ∗ 42.8 124 4293 HIP 43215 ∗ 44.6 126 1605 HIP 18597 ∗ 625 HIP 113131 ∗ 660 HIP 18744 ∗ 48.0 161 1795 3C 454.3 ∞,• 48.5 11 500 HIP 53907 ∗ 494 HIP 98031 ∗ 17476 HD 95850 ∗ 51.0 148 1203 HIP 98608 ∗ 51.1 102 5512 HIP 7607 ∗ 470 HIP 57613 ∗ 1626 HIP 8034 ∗ 52.0 97 716 HD 102766 ∗ 52.1 164 1474 HIP 13262 ∗ 7762 HIP 893 ∗ 718 HIP 13290 ∗ 52.5 4 3018 HIP 1170 ∗ 56.5 112 932 HIP 29416 ∗ 3573 HIP 12193 ∗ 1870 HIP 29655 ∗ 56.8 48 4293 HIP 12557 ∗ 57.4 75 1847 HIP 114144 ∗ 573 HIP 66006 ∗ 820 HIP 114347 ∗ 57.7 140 1840 HIP 66100 ∗ 58.4 165 4810 W Aqr ∗ 2084 HIP 29416 ∗ 3573 HIP 102624 ∗ 60.0 161 1404 HIP 29450 ∗ 62.7 6 5112 HIP 71644 ∗ 6268 HIP 76844 ∗ 711 HIP 71802 ∗ 63.2 157 2916 HIP 77284 ∗ 63.8 103 960 HIP 64768 ∗ 608 HIP 106642 ∗ 12553 HIP 64852 ∗ 64.6 164 666 HIP 107140 ∗ 68.2 70 1014 HIP 114114 ∗ 6437 HIP 11021 ∗ 483 HIP 114144 ∗ 68.2 176 573 HIP 11350 ∗ 70.4 119 2037 HIP 12086 ∗ 587 HIP 88722 ∗ 621 HIP 12557 ∗ 71.5 98 1847 HIP 88832 ∗ 74.8 170 1617 HIP 36284 ∗ 444 HIP 76307 ∗ 411 HIP 36675 ∗ 76.8 118 3545 HIP 76844 ∗ 77.3 111 711 ∗: from pointing star list ∞: from blazar list •: from QSO, RG, ULIRG list Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 12

Table 3: continued. Separation Separation Objects Source θ P.A. Flux Objects Source θ P.A. Flux list [0][◦] [mJy] list [0][◦] [mJy] HIP 113131 ∗ 660 PPM 288087 ∗ 1187 HIP 113390 ∗ 79.7 36 1014 HIP 53078 ∗ 80.8 58 2081 CT UMa ∗ 1324 HIP 117591 ∗ 1384 HIP 52546 ∗ 80.9 137 4462 HD 224126 ∗ 81.4 34 5106 HIP 101056 ∗ 1734 HIP 77284 ∗ 960 AF Del ∗ 81.6 113 918 HIP 77501 ∗ 81.7 24 3227 HIP 76343 ∗ 477 HIP 29919 ∗ 1468 HIP 76573 ∗ 82.3 154 2322 HIP 30945 ∗ 84.2 89 2703 HIP 71490 ∗ 723 HIP 53564 ∗ 774 HIP 71995 ∗ 84.5 99 925 CS Dra ∗ 87.5 56 4263 HIP 104755 ∗ 603 HIP 106062 ∗ 1620 HIP 106044 ∗ 88.0 65 2727 HIP 106140 ∗ 88.6 9 666 3C 272.1 • 700 HIP 112155 ∗ 1150 3C 274.0 • 89.4 109 610 HIP 112680 ∗ 94.0 121 2183 HIP 110146 ∗ 430 HIP 94162 ∗ 2385 HIP 110509 ∗ 94.1 137 441 HIP 94376 ∗ 94.7 9 468 HIP 65006 ∗ 4466 HIP 79233 ∗ 6759 HIP 65309 ∗ 96.2 23 452 HIP 79349 ∗ 96.5 169 1039 HIP 1158 ∗ 688 HIP 114489 ∗ 1800 HIP 1562 ∗ 96.7 130 431 3C 459 • 97.1 124 1035 HIP 116264 ∗ 1459 HIP 12302 ∗ 2671 HIP 116307 ∗ 99.7 176 432 HIP 13262 ∗ 99.8 92 7762 PPM 704303 ∗ 1921 HIP 98500 ∗ 504 HIP 41664 ∗ 100.5 148 3617 HIP 98815 ∗ 101.5 161 494 HIP 8565 ∗ 1636 HIP 50230 ∗ 4826 HIP 9306 ∗ 102.7 51 1643 HIP 51087 ∗ 102.9 70 1754 HIP 84833 ∗ 454 HIP 85302 ∗ 105.2 131 703 HIP 71490 ∗ 723 HIP 95413 ∗ 13793 HIP 72105 ∗ 106.2 79 913 HIP 96198 ∗ 106.3 124 603 HIP 114724 ∗ 877 HIP 101810 ∗ 4233 HIP 114939 ∗ 107.5 160 1522 HIP 102440 ∗ 108.3 96 6594 HIP 109070 ∗ 13281 T Com ∗ 1920 HIP 109089 ∗ 110.5 179 730 HIP 63950 ∗ 111.3 106 1566 HIP 89172 ∗ 796 HIP 29655 ∗ 4293 HD 168829 ∗ 111.9 79 3315 HIP 30343 ∗ 112.0 90 6445 HIP 8 ∗ 1961 HIP 76844 ∗ 711 HIP 536 ∗ 112.0 50 621 HIP 77501 ∗ 112.1 57 3227 2MASS J18114749+3128199 ∗ 1542 HIP 12302 ∗ 2671 HD 168829 ∗ 112.6 81 3315 HIP 13290 ∗ 113.0 65 3018 HIP 32768 ∗ 690 HIP 114930 ∗ 1205 HIP 33779 ∗ 113.4 115 500 HIP 115242 ∗ 115.0 151 1285 HIP 114757 ∗ 642 PPM 30600 ∗ 3934 HIP 115530 ∗ 117.0 65 412 HIP 33100 ∗ 117.5 54 686 HIP 13092 ∗ 3490 HIP 49950 ∗ 887 HIP 13654 ∗ 117.6 65 3452 HIP 50697 ∗ 118.1 74 3539 HIP 114114 ∗ 6437 HIP 98337 ∗ 1226 HIP 114347 ∗ 119.8 159 1840 HIP 98438 ∗ 120.0 171 1102 ∗: from pointing star list ∞: from blazar list •: from QSO, RG, ULIRG list Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 13

3.5 Other stellar sources 3.5.1 Herbig Ae/Be stars observed with ISOPHOT Abrah´amet´ al. (2000, A&A, 354, 965) present ISOPHOT data for a number of Herbig Ae/Be stars, including two pairs with interesting spacings (36 and 104 arcsec) . The young stellar nature and com- plex environment calls for some caution about the far-infrared morphology. Indeed there is evidence for a third mid-infrared source in the LkHα198/V376 Cas pair (Lagage et al. 1993), extended emission in the PACS wavelength regime (Natta et al. 1992), and yet another source in the mm (Henning et al. 1998). Extended FIR emission is also seen in the BD+65 1637/LkHα234 region, with the FIR peak likely offset from the optical star LkH234. While both pairs are FIR bright and scientifically interesting, the prerequisite for use as spatial calibrators (accurately predictable FIR morphology at PACS resolution) appears insufficiently met.

4 Galactic ISOCAM fields

We have searched the ISO archive for ISOCAM rasters with low diffuse background but a large number of point sources, with the hope of then using 2MASS astrometry and the ISOCAM photometry to extrapolate to FIR sources. The main advantage offered by this approach is that non-photospheric emission from the program stars (e.g. dust shells, outflows, etc.) is more easily detected at mid-IR wavelengths than near-IR or shorter wavelengths. Knowledge about such emission sources is needed to ensure that the point-source assumption is not invalidated at PACS wavelengths. RD-1 describes this search. Fields with large source densities are indeed identified, but typical 15 µm fluxes are < 1 Jy with a few objects above 3 Jy, i.e. too faint for PACS if a photospheric extrapolation is assumed. If objects are dusty (HII regions, YSOs, late stars with dust shells) fluxes would be higher but the applicability of 2MASS positions would need more critical investigation for individual objects. This approach is not considered to be as useful as simply obtaining the results from 2MASS and searching for additional information on the 2MASS selected targets with IRAS/ISO data.

5 Galaxies

There is a large number of galaxies sufficiently bright for PACS, some of them conveniently placed in pairs or groups. Inferring the FIR position/structure from other wavelengths is a problem, however, which may be solved easily for compact or distant objects with radio counterparts but not so easily for more normal nearby galaxies.

5.1 Quasars and AGN from the Veron catalogue Bright Quasars are point-like for PACS and often have accurately known positions. Assuming the mean quasar energy distribution of Elvis et al. (1994, ApJS, 95, 1), quasars with V < 15.5 are needed to get > 160 mJy at 75 µm. We have searched the merged lists of quasars, active galaxies, and BL Lac candidates from the 10th edition of the Veron catalogue (from Vizier) for V < 15.5, z > 0.01 objects with separations between 3000 and 30000. Three pairs are found, all formed of inconspicuous nearby Seyfert 2 or Liner NGC objects (NGC 70/71, NGC 833/835, NGC 7679/7682). For the purpose of PACS spatial calibration these objects are likely no better than other galaxy pairs. Real quasar pairs are found only at fainter magnitudes or larger separations. For test purposes, we also searched for V < 17.5, z > 0.1 pairs and found 11 candidates. Only one QSO in one of these pairs has an IRAS FSC counterpart, however. Sufficient far-infrared brightness is hence not ensured. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 14

5.2 Galaxy pairs The Arp-Madore catalogue or other catalogues of interacting galaxies could provide a long list of galaxy pairs for which total IRAS fluxes can be retrieved, but the issue of flux distribution over the two objects and of precise FIR centroids is difficult to solve accurately without additional information. Objects with interferometric radio continuum data are worth considering, in case the radio mapping is good enough to (i) estimate accurate centroids for the two components, (ii) estimate a rough FIR brightness ratio by assuming FIR flux ratio = radio flux ratio and (iii) filter out objects which are dominated by off-nuclear regions which have hard to predict morphologies (like the Antennae NGC 4038/39). The following subsection provides a first such list from VLA-observed IRAS BGS sources. Additional literature search could probably enlarge the sample significantly, by starting from inter- acting Galaxy samples and then introducing IRAS and radio information. The NVSS, e.g., may often give a first indication of the radio emission in a galaxy pair but is not well matched in spatial resolution to PACS.

5.2.1 Galaxy pairs from the IRAS Bright Galaxy Sample with VLA radio observations Condon et al. (1990, ApJS, 73, 359; 1996, ApJS, 103, 81) published a VLA 1.4 GHz atlas of the IRAS Bright Galaxy Sample. With S(60 µm) > 5.24 Jy these are very bright sources at PACS sensitivities, even if several components contribute. A candidate list of suitable galaxy pairs was compiled based on the following criteria: 1. Mapped in VLA B or C configuration or both (sometimes also A), i.e. at spatial resolution FWHM = 2400 or better. Objects with only D configuration data were not considered. 2. Double radio source, with each component dominated by a single unresolved or slightly resolved component. Component separation 3000 < θ < 30000. 3. Double radio morphology similar to optical or near-IR (2MASS) double morphology, to include double galaxies but exclude unrelated background radio sources (or double lobe radio galaxies), for which the radio morphology is a bad guess of the far-infrared morphology. The catalogues have been revised by Sanders et al. (2003, AJ, 126, 1607) and complemented by a HIRES study of Surace et al. (2004, AJ, 127, 3235) providing FIR positions for each member of the galaxy pairs. Appendix C.1 shows overlaps of 2MASS Ks-band and HIRES IRAS 60 µm images for the objects listed in the table. The far-infrared morphology is mostly consistent with the radio information listed above – small separations and high contrast systems are of course unresolved in the IRAS data. The plot showing the NGC 3994/3995 system has an associated third far-infrared source related to NGC 3991, itself an interacting system for which a far-infrared centroid is not easily specified. Additionally, Spitzer/MIPS 70 µm data with a point-source FWHM of 1800 exist for almost every target allowing a further improvement of the knowledge about the source coordinates, their compactness, separations and position angles. Overlays with 2MASS Ks-band images are shown in Appendix C.2. The list of those galaxy pairs suitable for astrometric calibration is given in Tab. 4. A visualisation of the expected visibilities during the first year of the Herschel mission and their solar aspect angles during the first 120 days of the galaxy pairs is shown in Fig. 3. They have been calculated based on the L2 orbit derived for a launch date of 12th April 2009 and need confirmation as soon as the actually final orbit will have been established. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 15 ) ◦ End PA (Date) ( 2009 Aug 102010 Feb 10 183 2009 Sep 072010 Mar 05 3 150 2009 May 06 330 2009 Nov 082009 Jun 8 18 188 2009 Dec 192009 34 Jun 29 215 2009 Dec 292009 38 Jul 08 218 2010 Jan 072009 Jul 18 12 198 2010 Jan 102009 Sep 20 189 9 2010 Mar 182009 34 Sep 04 214 2010 Mar 03 354 2009 Sep 15 173 2010 Mar 13 355 2011 174 Apr 122009 Jul 144 202010 Jan 17 128 2009 Jul 17 309 2010 Jan 15 144 2009 Jul 13 324 2010 Jan 11 149 2009 Jul 19 329 2010 Jan 16 150 330 ) ◦ Galaxy visibilities (HSO y-axis) Start PA (Date) ( 2009 May 122009 Nov 13 118 2009 Jul 05 297 2010 Jan 03 170 2009 Apr 12 351 2009 Sep 092009 Apr 7 12 186 2009 Oct 142009 Apr 5 20 184 2009 Oct 242009 May 06 5 186 2009 Nov 08 29 2009 May 01 210 2009 Nov 03 45 2009 Jul 14 226 2010 Jan 122009 Jun 13 183 3 2009 Dec 152009 50 Jul 02 229 2010 Jan 01 38 2009 218 Apr 122009 May 144 022009 Nov 03 178 2009 May 12 359 2009 Nov 13 168 2009 May 10 348 2009 Nov 12 165 2009 May 17 344 2009 Nov 163 18 343 ) ◦ PA ) and position angles (counter-clockwise from North) are based )( θ Target 0 θ ( 1.18 172 0.79 52 2.44 36 0.62 75 2.85 153 1.19 115 1.83 56 0.70 90 0.64 7 0.80 57 1.53 139 0.68 131 2.42 115 1.35 25 0.52 68 m µ 5.0 5.2 7.9 2.1 3.5 4.9 2.1 3.1 20.2 m 70 µ –– 5.4 2.6 2.06.21.6 5.2 6.8 2.6 8.0 2.8 7.6 5.8 8.2 7.4 7.7 7.35.12.1 – 5.0 5.1 3.8 2.7 5.8 9.6 4.2 1.57.1 3.9 8.9 2.68.06.4 2.9 10.1 7.0 7.4 4.0 – – 10.9 – 12.0 23.1 (Jy) (Jy) 60 HIRES MIPS ? ? ? ? m maps. The HIRES data were taken from Surace et al. (2004), except for NGC 7463/7465, µ Epoch 2000.0 R.A. Dec. Coordinates (J 2000.0) 01:36:23.3201:36:24.15 -37:19:17.3 02:23:18.87 -37:20:27.3 02:23:21.82 +32:11:19.3 +32:11:48.7 07:09:18.14 +20:38:11.8 07:09:12.01 +20:36:13.2 09:13:36.3309:13:38.75 -10:19:28.7 09:45:47.9 -10:19:19.0 09:45:42.6 -14:22:04 11:25:45.01 -14:19:31 11:25:49.49 +14:40:36.8 +14:40:06.5 11:57:36.8411:57:44.04 +32:16:38.2 +32:17:39.0 14:57:41.1214:57:44.97 -43:07:56.8 14:57:00.35 -43:07:56.6 +24:36:26.0 14:57:00.69 +24:37:04.1 15:34:32.3615:34:35.15 +15:11:39.2 +15:12:05.2 16:58:23.8516:58:31.62 +58:57:22.2 +58:56:13.0 22:19:27.7022:19:30.06 +29:23:45.4 +29:23:18.5 23:02:01.023:01:51.9 +15:57:48 23:03:15.52 +15:58:51 23:03:17.82 +08:52:25.3 +08:53:38.9 23:27:56.54 +08:46:44.4 23:27:58.50 +08:46:56.1 Names List of IR-bright galaxy pairs suitable for the astrometric calibration. If not mentioned otherwise, the coordinates have been obtained from IRAS/HIRES NGC 633 ESO297-G012 MCG+05-06-035MCG+05-06-036 Mrk 1034 NGC 2342 NGC 2341 IRAS 09111-1007 NGC 2993NGC 2992 IC 2810 Arp 245 NGC 3994NGC 3995 IC 4518A UGC 06436 IC 4518B Arp 313 UGC 09618NGC 5953NGC 5954 Arp 302 NGC 6285NGC 6286 Arp 091 NGC 7253ANGC 7253B Arp 293 NGC 7465 NGC Arp 7463 278 NGC 7469IC 5283 NGC 7674NGC 7674A Arp? 298 Arp 182 Table 4: Gaussian fitting of thefor emission which peaks they in were theon retrieved MIPS from the 70 the coordinates IPAC datacounter-clockwise quoted with archive. in respect Both to the target the separations list. HSO ( y-axis The (chopper axis). visibility periods were obtained with the HSPOT tool. The observatory position angles are counted Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 16

Figure 3: Visibility plot (above) and solar aspect angles (below) of the galaxy pairs. They are based on L2 orbits derived for a launch date of 12th April 2009. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 17 (right). The double h (left) and 12 h stars are representedcalibrators by are circles, depicted by among crosses. which Note the how most ones of selected the double as stars astrometric are calibrators located towards are the filled. galactic plane. The extragalactic astrometric Figure 4: Celestial coverage of all double sources in equatorial coordinates centred around R.A.=0 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 18

6 Solar system objects

6.1 Asteroid conjunctions Asteroids provide a large number of effectively point-like FIR sources slowly moving across the sky. This makes them potential spatial calibrators with variable separations during the mostly short time during their encounters. Fig. 5 provides an overview of apparent movements of 55 prime asteroids while they are visible with the HSO.

Figure 5: The apparent movements on the sky in 00/h for the 55 prime asteroid calibrators are shown while they are visible during the Herschel mission. Note that at certain times some targets show almost no apparent motion.

A general analysis of the orbits of these 55 asteroids yields 30 encounters with separations of less than 1◦ while they are visible from the HSO between 2009 and 2013. Nine encounters with the planets Mars, Jupiter, Saturn, Uranus and Neptune of less than 1◦ were derived, putting some restrictions to possible observing periods due to stray-light effects from the bright planets. The distribution of the asteroid paths during the Herschel mission is shown in Fig. 6. Regions of high confusion noise have been rejected. Their positions are known with an accuracy of < 100. When extending the analysis to 721 asteroids having an IRAS 60 µm flux of > 1 Jy, 2826 encounters within less than 1◦ were detected, while 80 encounters have separations of up to 30, and are therefore potential candidates for astrometric calibration purposes. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 19

Figure 6: The distribution of the 55 prime asteroids on the sky. Their paths within their multiple visibility periods during the Herschel mission are shown. The regions with high confusion noise have been taken out. The positional accuracy for these well-known targets is significantly better than 100 on the sky (HSO-centric frame).

A more detailed statistical analysis of close encounters of the 721 asteroids was based on the following selection criteria: • maximum separation in HSO-centric reference frame: 60

• encounter only during visibility periods, i.e. at solar elongations of 60◦ − 120◦

• the flux of both asteroids at 70 µm is ≥ 0.5 Jy

• time period: 12-Apr-2009 until 31-Dec-2013

• time resolution: 1 day

The summary of the result of this study is given in Tab. 5. One example of a close asteroid encounter is presented in Fig. 7. Table 6 lists the detailed results of the events with separations ≤ 60 for the year 2009 based on an improved time resolution of 1 hour, including the smallest separations and the expected FIR flux densities. During close encounters, the asteroids typically stay for hours or Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 20

Table 5: Statistical analysis of close encounters of 721 asteroids during the Herschel mission within their visibility periods based on the current HSO orbit. The number of encounters for apparent separations of ≤ 60 and ≤ 30 are calculated for each year. Encounters Period ≤ 60 ≤ 30 Jan-Dec 2009 35 14 Jan-Dec 2010 47 18 Jan-Dec 2011 38 14 Jan-Dec 2012 33 12 Jan-Dec 2013 40 18 even days within the 30 range. Note that the analysis is based on a relatively coarse timimg raster of one hour leading to an uncertainty of the derived distances of 0.05. Therefore, all encounters have to be re-calculated with a finer time resolution using the final Herschel orbit predictions as soon as the launch date is fixed.

Figure 7: Paths of the asteroids 53 Kalypso and 423 Diotima across the sky during a close encounter in August 2009 in the HSO-centric reference frame assuming the current best HSO orbit with a launch date 12-Apr-2009. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 21

Table 6: Compilation of 14 close asteroid encounters in 2009 with separations of ≤ 60 in the satellite reference frame. Note that due to the coarse time resolution, the uncertaintiy of the smallest sepa- rations is of the order of 0.05. They are based on a launch date of 14th May 2009 and the orbit file H20090622 0001.LOE. Date Asteroids smallest separation F (70µm) F (100µm) F (160µm) (00) (Jy) (Jy) (Jy) 659 Nestor 0.7 0.4 0.2 08/09-Jul-2009 25 743 Eugenisis 0.8 0.4 0.2 692 Hippodamia 0.3 0.2 0.1 03/04-Aug-2009 957 Camelia 158 1.2 0.7 0.3 276 Adelheid 2.8 1.6 0.7 03/04-Aug-2009 971 Alsatia 57 1.0 0.5 0.2 53 Kalypso 5.7 3.2 1.4 07/08-Aug-2009 423 Diotima 12 8.0 4.6 2.1 283 Emma 10.5 6.0 2.6 23/24-Aug-2009 712 Boliviana 164 14.7 8.2 3.6 276 Adelheid 2.3 1.3 0.6 30/31-Aug-2009 295 2621 Goto 0.3 0.2 0.1 26 Proserpina 3.5 2.0 0.9 01/02-Sep-2009 249 695 Bella 0.9 0.5 0.2 205 Martha 2.7 1.5 0.7 23/24-Sep-2009 866 Fatme 276 2.2 1.3 0.6 179 Klytaemnestra 1.9 1.1 0.5 09/11-Oct-2009 417 Suevia 73 0.4 0.2 0.1 10 Hygiea 26.1 15.1 6.8 18/19-Oct-2009 113 Amalthea 266 0.7 0.4 0.2 37 Fides 3.1 1.8 0.8 01/03-Nov-2009 213 Lilaea 287 2.7 1.5 0.7 66 Maja 2.6 1.5 0.6 02/03-Nov-2009 204 605 Juvisia 2.0 1.1 0.5 877 Walkure 1.0 0.5 0.2 28-Nov-2009 325 1735 ITA 1.0 0.6 0.3 126 Velleda 1.3 0.7 0.3 26/27-Dec-2009 1143 Odysseus 99 1.0 0.6 0.3 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 22

6.2 Conjunctions of asteroids with pointing stars As for the asteroids alone, encounters can also be observed between asteroids and stars. Therefore, they can be used for spatial calibration as well. For this purpose, we extracted 169 stars with eclip- tical latitudes between ±15◦ from the final pointing calibration stars list in RD-4. They have been investigated for close asteroid encounters with separations smaller than 60. In Tab. 7 we present the closest conjunctions for each event found until December 2010. As before, all these encounters will have to be re-calculated with a finer time resolution using the final Herschel orbit predictions as soon as the launch date is fixed.

Table 7: Compilation of 49 close asteroid encounters with pointing calibration stars from April 2009 until 2010 with separations of ≤ 60 in the L2-centric reference frame. They will be used as candidates for encounters with separations of ≤ 30 in the HSO-centric frame after fixating of the launch date and the actual satellite orbit is known. Asteroid min. apparent Confusion noise Flux density Date and distance speed F (100µm) F (70µm) F (100µm) Star (0) (00/h) (mJy) (Jy) (Jy) 2697 Albina 39.60 0.33 0.19 2009-Apr-25 HIP 110396 2.8 0.57 3.90 0012 Victoria 40.25 2.95 1.68 2009-May-14 HIP 40534 5.7 0.54 10.07 0371 Bohemia 26.92 1.14 0.65 2009-Jun-01 HD 95850 4.4 0.54 1.20 1109 Tata 36.50 0.74 0.42 2009-Jun-10 HIP 49029 5.9 0.54 0.66 0511 Davida 45.97 19.72 11.30 2009-Jun-19 3.7 0.54 HIP 51353 0.33 0476 Hedwig 37.93 5.83 3.29 2009-Jun-25 4.8 0.59 HIP 117628 0.41 0510 Mabella 25.35 2.91 1.63 2009-Jul-13 HIP 117628 4.6 0.59 0.41 0972 Cohnia 30.94 0.61 0.36 2009-Jul-18 HIP 57917 3.2 0.55 2.18 0186 Celuta 24.06 1.94 1.09 2009-Jul-21 HIP 70969 1.3 0.64 5.86 0695 Bella 26.92 1.16 0.65 2009-Aug-07 HIP 76075 2.6 1.00 0.92 0058 Concordia 43.44 2.17 1.24 2009-Aug-29 5.9 1.43 HIP 25945 4.09 1351 Uzbekistania 30.49 1.05 0.60 2009-Sep-18 3.4 2.96 HIP 26718 2.48 0016 Psyche 14.65 32.52 18.45 2009-Oct-08 HIP 101984 5.5 0.55 0.55 0133 Cyrene 6.03 0.96 0.56 2009-Nov-14 HIP 40388 3.9 0.56 1.23 0060 Echo 58.20 2.84 1.58 2009-Nov-19 HIP 49029 5.2 0.54 0.66 0846 Lipperta 50.12 0.59 0.34 2009-Nov-29 HIP 101984 1.7 0.55 0.55 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 23

Table 7: continued. Asteroid min. Apparent Confusion noise Flux density Date and distance speed F (100µm) F (70µm) F (100µm) Star (0) (00/h) (mJy) (Jy) (Jy) 0126 Velleda 47.08 1.09 0.61 2010-Jan-09 HIP 4906 1.4 0.56 0.19 1356 Nyanza 16.68 0.99 0.57 2010-Jan-14 HIP 63090 5.0 0.54 3.49 0229 Adelinda 14.38 2.00 1.15 2010-Jan-20 HIP 13092 5.2 0.61 3.49 0678 Fredegundis 44.56 0.33 0.19 2010-Mar-01 HIP 90496 3.1 3.39 0.51 0011 Parthenope 38.01 7.24 4.12 2010-Apr-01 HIP 29655 5.8 2.95 4.29 1315 Bronislawa 32.02 0.57 0.33 2010-Apr-01 5.4 1.38 HIP 25945 4.09 0702 Alauda 28.22 6.89 3.98 2010-Apr-13 HIP 33929 4.3 0.58 0.60 0785 Zwetana 49.96 0.63 0.36 2010-Apr-25 HIP 110146 2.6 0.54 0.43 0465 Alekto 24.51 1.94 1.10 2010-Apr-29 HIP 44862 4.8 0.55 4.29 0613 Ginevra 28.14 1.62 0.93 2010-May-09 HIP 105881 5.4 0.55 0.18 0010 Hygiea 30.16 37.16 21.32 2010-May-12 HIP 44862 4.5 0.55 4.29 0313 Chaldaea 77.22 4.92 2.73 2010-May-22 3.8 0.54 HIP 41028 1.84 0426 Hippo 33.33 3.08 1.77 2010-Jun-02 3.1 0.56 HIP 114971 0.27 0069 Hesperia 53.61 4.95 2.81 2010-Jun-13 HIP 48540 2.3 0.54 0.51 0674 Rachele 39.87 2.67 1.53 2010-Jun-13 HD 99635 5.3 0.54 2.48 0409 Aspasia 37.52 9.79 5.54 2010-Jun-14 HIP 115242 1.7 0.57 1.29 0786 Bredichina 33.30 3.47 1.97 2010-Jun-27 HIP 64768 5.9 0.54 0.61 0103 Hera 18.43 5.07 2.87 2010-Jul-02 1.7 0.55 HIP 114724 0.88 0567 Eleutheria 28.44 2.68 1.53 2010-Jul-11 4.7 0.55 HIP 66100 4.81 0381 Myrrha 20.31 4.93 2.82 2010-Jul-13 HIP 72122 4.8 0.55 0.22 0704 Interamnia 22.95 18.80 10.89 2010-Jul-27 HIP 68895 3.5 0.58 0.45 0182 Elsa 36.92 0.46 0.26 2010-Aug-01 HIP 66803 1.9 0.56 0.60 0977 Philippa 40.45 0.82 0.47 2010-Aug-08 HD 120806 5.9 0.55 2.08 0005 Astraea 10.36 5.55 3.17 2010-Aug-13 3.8 0.54 HIP 7884 0.31 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 24

Table 7: continued. Asteroid min. Apparent Confusion noise Flux density Date and distance speed F (100µm) F (70µm) F (100µm) Star (0) (00/h) (mJy) (Jy) (Jy) 0579 Sidonia 36.45 1.30 0.75 2010-Sep-07 HIP 29416 4.6 7.18 3.57 0419 Aurelia 32.66 2.88 1.66 2010-Sep-08 5.5 7.18 HIP 29416 3.57 0671 Carnegia 33.48 0.57 0.33 2010-Sep-23 4.6 2.56 HIP 82912 6.56 0066 Maja 55.91 2.34 1.31 2010-Sep-27 HIP 35617 4.4 0.57 1.69 1520 Imatra 40.48 0.50 0.29 2010-Oct-04 HIP 40534 5.0 0.54 10.07 0596 Scheila 35.97 2.36 1.36 2010-Oct-25 HIP 46146 1.3 0.54 0.23 0357 Ninina 40.79 1.56 0.90 2010-Dec-04 HIP 63090 4.7 0.54 3.49 0713 Luscinia 25.18 1.14 0.67 2010-Dec-09 6.0 0.55 HIP 57917 2.18 0119 Althaea 55.92 1.18 0.67 2010-Dec-15 3.4 0.57 HIP 110396 3.90

6.3 Planetary satellites An inventory of approximate angular separations from the planet, and of FIR fluxes (RD-2, RD-3) suggests that at least the Galilean satellites of Jupiter and perhaps the Saturn moons Titan and Iapetus are possible objects (see Tab. 8). The Galilean satellites are so bright that they should easily stand out of the Jupiter stray-light. Possible limitations for bolometer operations from the presence of nearby extremely bright objects have to be verified.

Table 8: Solar system planets and their brightest satellites that can be used as astrometric calibrators during close encounters. Largest Name separation Tb F (75µm) (00) (K) (Jy/beam) Jupiter – 107.90 18371 Io 114.1 123.92 470 Europa 181.4 121.23 331 Ganymede 289.0 135.20 1146 Callisto 508.3 140.95 1042 Saturn – 77.44 8237 Titan 167.7 99.21 148 Iapetus 488.8 102.01 12

One disadvantage must be noted: Position angles of any Jupiter satellite pairs or multiples are always close to the plane of the ecliptic. The PACS chopping direction will be approximately orthogonal to the ecliptic while viewing the ecliptic. This makes Jovian satellites difficult to use for chop throw calibration. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 25

The inclination of the Saturn satellite system during the actual Herschel mission changes. The Saturn rings are very bright and might produce strong background radiation or stray-light affecting the detectability of the moons with an increasing opening angle. Using the Saturn Ephemeris Generator 2.3 (http://ringmaster.arc.nasa.gov/tools/ephem2 sat.html), the Saturn ring opening angle towards Earth is shown in Tab. 9.

Table 9: Propagation of the opening angle of the Saturn rings between 2009 and 2013. Date Ring opening angle 01-Jan-2009 −0.8 01-Jan-2010 4.9 01-Jan-2011 10.1 01-Jan-2012 14.8 01-Jan-2013 18.8

For an anticipated Herschel launch in 2009, first such observations might occur of that year. Then, suitable configurations of the bright moons like Titan and Iapetus may still be found (see example in Fig. 8 from the Saturn viewer from the same web site). The situation will get worse with time because of the decreasing inclination of the ring system.

Figure 8: Example view of the Saturn satellite system for 01-Aug-2009 (Left: FOV = 20; right: FOV = 200). Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 26

Appendices

A 2MASS images of fields with suitable double stars from the K- band

Field 1 Field 2

Field 3 Field 4

Field 5 Field 6 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 27

Field 7 Field 8

Field 9 Field 10

Field 11 Field 12 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 28

Field 13 Field 14

Field 15 Field 16

Field 17 Field 18 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 29

Field 19 Field 20

Field 21 Field 22

Field 23 Field 24 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 30

Field 26 Field 27

Field 28 Field 29

Field 30 Field 31 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 31

Field 32 Field 33

Field 34 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 32

B HIRES/2MASS overlays for double stars from the K-band search

Field 1 Field 2

Field 3 Field 4

Field 5 Field 6 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 33

Field 7 Field 8

Field 9 Field 10

Field 11 Field 12 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 34

Field 13 Field 14

Field 15 Field 16

Field 17 Field 18 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 35

Field 19 Field 20

Field 21 Field 22

Field 23 Field 24 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 36

Field 26 Field 27

Field 28 Field 29

Field 30 Field 31 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 37

Field 32 Field 33

Field 34 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 38

C FIR/NIR overlays for double galaxies

C.1 HIRES/2MASS overlays for double galaxies The displays are overlays of 2MASS Ks-band (grey-scale) and IRAS 60 µm HIRES processed images (contours 0.2, 0.5, 1, 2, 5 etc. MJy/sr). The scale shown is in arcseconds. Because of limited size of the 2MASS image tiles obtained from NED, the size of the panels changes and the object of interest is often not centred on the panel. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 39 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 40 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 41 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 42

C.2 MIPS 70 µm/2MASS overlays for double galaxies The displays are overlays of 2MASS Ks-band (grey-scale) and Spitzer/MIPS 70 µm contours. Some of the contours include obvious artifacts originating from insufficient background processing in the MIPS pipeline data reduction. In all cases, the targets are free from large scale FIR background emission. Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 43 Document: PACS-ME-TN-035 PACS Date: 27th July 2009 Herschel Version: 2.7 Fields and Double Sources for Spatial Calibration Page 44