Use of ISO LWS calibrators for PACS wavelength calibration 1 Introduction -------------- The LWS instrument onboard the ISO satellite covered a similar wavelength range, 43 to 197um, as the PACS spectrometer (57 to 210um). LWS had 10 detectors with central wavelengths fairly covering the range, 5 in each grating order with the short wavelength (SW) ones in 2nd order having a wavelength spacing of about 10um (46.2, 56.2, 66.1, 75.7, 84.8um) and the long wavelength (LW) ones in first order with a wavelength spacing of about 20um (102.4, 122 (TBC not in LWS Handbook!), 141.8, 160.6 and 178.0um). The spectral resolution lambda/deltalambda was 150-200, i.e. a factor of 10-20 less than the PACS spectrometer will have. The LWS wavelength standards were mainly Planetary Nebulae and HII regions. They were chosen so as to provide the largest possible sample of lines and so that several of them were visible from ISO as much as possible during the mission (to provide a wavelength calibration stability monitoring). The lines used had to be strong enough to give good signal-to-noise and to be unresolved by the grating. 2 Lines used for LWS wavelength calibration ------------------------------------------- line id. lambda(um) sources ----------------------------------------- [OIII] 51.815 1,2,3,5,6,7 [NIII] 57.330 1,2,3,5,7 [OI] 63.184 3,4,5,6,7,8 [OIII] 88.356 1,2,3,5,6,7 [NII] 121.889 7 [OI] 145.525 3,4,5,6,7,8 [CII] 157.741 3,4,5,6,7,8 ----------------------------------------- These lines are distributed as such that for 8 out of 10 detectors there were 1-3 lines for wavelength calibration. For the PACS grating orders this means 3 lines for the 3rd order range, 1(!) line for the 2nd order range and 3 lines for the 1st order range. Open issue: It should be checked which targets show the [NII] 205.178um line (probably target#7?) 3 Sources used for LWS wavelength calibration --------------------------------------------- No LWS calibrator name other name type (SIMBAD) SWS obs ----------------------------------------------------------------------------- 1 NGC 6543 IRAS F17584+6638 PN Y PN G096.4+29.9 2 NGC 6826 IRAS F19434+5024 PN Y PN G083.5+12.7 3 Gal298.2-00.3 IRAS 12073-6233 HII Y 4 NGC 7023 IRAS F21009+6758 Open Cluster Y 5 IRAS 15408-5356 GAL 326.65+00.59 HII Y 6 NGC 7027 PN G084.9-03.4 PN Y 7 NGC 6302 IRAS 17103-3702 PN Y PN G349.5+01.0 8 IRAS 23133+6050 GRS 111.62 +00.37 Emission Line star Y ----------------------------------------------------------------------------- General properties of LWS wavelength calibrators No IRAS fluxes LWS fluxes optical size FIR size 60um 100um (Jy) (Jy) ------------------------------------------------------------------------------ 1 126 61 25" diam. (bright core) <52" diam. @60um 300" diam. (faint halo) (ISOPHOT multi-aper) 19.5"(1) 2 47 20 25.0"(1) 3 4 574 1100 X2101+679 (IRAS SSS) 2.3'@60, 4.6'@100um 5 10500 16800 IRAS PS CC_60: B 6 14.0"(1) 7 850 537 44.5"(1) 8 2110 2690 ----------------------------------------------------------------------- (1) Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Acker+, 1992) [check also Angular dimensions of 312 planetary nebulae (Tylenda+, 2003)] Open issues: Intrinsic line shapes may be inferred from SWS observations of the same targets at shorter wavelengths (<45um), since SWS had a comparable spectral resolution to PACS. SWS and PACS do not really resolve the lines, typical line widths are ~50km/s meaning partial resolution at some wavelengths. On the other hand, this means that widths cannot be neglected for instrumental profile issues, one may need to specifically pick low linewidth targets for the highest spectral resolution ranges of PACS. Spatial extent will be an issue. For PACS (IFU) we need some sources extended on a 1' scale to calibrate the 'smile and frown'. In addition, given that at short wavelengths we are not fully sampling the spatial PSF, there may be some of the classical spectral resolution differences point/extended. That means, ideally we need a range of source sizes from <2" to >~1'. Draft 2, 29-Oct-2004 U. Klaas & D. Lutz