Line Profile Working Group Final Report

The line profile working group is composed of the following members :

Emmanuel Caux, Helmut Feuchtgruber, Pedro Garcia Lario, Anna di Giorgio, Cecile Gry (chair), Rosario Lorente, and Dieter Lutz.

The aim of the working group was to make sure that the necessary studies on line profiles were carried out and that the information needed by the users to analyse their spectroscopic data was made available to them. The present document is not a detailed description of the working group activities. Its purpose is rather to gather information on the line profile of the four ISO instruments.

For SWS and LWS, the studies performed during or after the ISO operations to characterize the line profiles have been reported in detail in documents written by members of the working group. In these cases, the information is not repeated here but we point to the documents so that the full information can be retrieved.

I- SWS  :  Short Wavelength Spectrometer.

I-A- SWS Grating low resolution mode SWS 01
A detailed study of the resolution  and its dependence on wavelength and scanning speed can be found in the following document  Spectral Resolution of SWS AOT 1 by R. Lorente.

I-B-  SWS Grating full resolution modes SWS02 and SWS06 A detailed study of the instrumental profiles in these modes can be found in ISO-SWS grating resolution and instrumental profile as measured by the full resolution modes SWS02 and SWS06 by D. Lutz, H. Feuchtgruber and J. Morfill.
The SWS profiles are Gaussians. Their FWHM values have been  implemented in SIA and OSIA,  via  the RESOLUTION module.

I-C-  SWS Fabry-Perot
The  spectral resolution of the FP have been measured before launch and is given in Section 6.3 of the SWS Handbook
In-flight checks of the resolution values has been performed with the internal calibrator lines and  confirm these values.    FP-SW: R = 41 900 +/-7 000   at 24.61 micron    FP-LW: R = 29 900 +/-3 600   at 24.78 micron
No indications have been found so far that the FP instrumental profile deviates from an Airy (Lorentzian) shaped profile.

II- LWS  :  Long Wavelength Spectrometer.

II-A- LWS Grating profiles
The line profiles are derived from observations of planetary nebulae and HII regions.
The characterization of the profiles and the study of their stability with time, detector, object type, is decribed in  LWS grating resolution and line profiles by C. Gry and R. Lorente. It is shown that the  pre-launch values (FWHM=0.29 for SW detectors and 0.60 for LW detectors) can be used and that although the profiles depart from Gaussian functions, the use of a Gaussian fit to derive the line flux   induces only a small  error.
The  mean grating profiles produced by the above reported study can be retrieved here  in ASCII, FITS or IDL-XDR formats.
The profiles are available in ISAP2.1  via a "smoothing" routine and  are available for profile fitting via a fitting module in SIA, which is also included in  OSIA version 2.0.

II-B- Fabry-Perot profiles
The FP profiles  has proven to be very sensitive to detector memory  (or "transient") effects, currently still under study. The report on FP  profiles will thus be completed after a  transient effects correction  procedure will be available  (in 2001).

III - PHT-S  :  ISOPHOT Spectrometer

The  PHT-S line profiles have been measured in laboratory during ground calibration assessment. The spectral range was scanned with a  monochromator (bandwidth 4 nm for SS and 8 nm for SL) with fixed step sizes of 4 nm and 8 nm, respectively.
The results of these measurements  have been publised in : Report on calibration of the ISOPHOT-S-FM (upgraded) Subexperiment IAC Report, Doc.No. IAC.FMC.002, Issue 2,  20-June-1992 by F. Garzon and J.M. Rodriguez-Espinosa.
The Full Width Half Maximum (FWHM) values are listed in Chapter 4.6 of the ISOPHOT handbook,  

IV- CAM-CVF :  ISOCAM  Circular Variable Filters

The Full Width Half Maximum (FWHM) values of the CAM-CVF have been measured on the ground before launch and the resulting resolution (Lambda/FWHM) values were listed in the  ISOCAM Observer's Manual . The resolution is given as a linear function  of  wavelength : - for SW CVF,  R = 41 - for LW CVF1, R = (1.4 * Lambda (micron)) + 30    (from 37 at 5 micron to 43 at 9.5 micron) - for LW CVF2, R = (1.875 * Lambda (micron)) + 18.125    (from  35 at 9 micron to 49 at 16.5 micron)
Although the profiles were originally given as Gaussians, the shape of the profiles is actually not known.

The profile widths have been checked on actual observations. Gaussian fits performed on strong and narrow ion lines in M16 gave :  

species	lambda microns	FWHM microns	sigma(FWHM)  microns	resolution (lambda/FWHM)	ground-based FWHM
Ar II	6.98	0.16	0.02	44	0.18
S IV	10.51	0.26	0.03	40	0.28
Ne III	15.56	0.34	0.01	46	0.33

Measured FWHMs agree with ground-based FWHM within the measurement uncertainties,  so the user  is  recommended to use the  above linear relationship to estimate R.

Cécile Gry, ISO Data Centre, 6 April 2001.