next up previous contents
Next: 10. Post-processing Up: ISOLWS DATA USERS MANUAL Previous: 8. Guide to instrument

Subsections

   
9. Getting started with LWS data

   
9.1 How to read to data

The files on the CD-ROM are ordered into subdirectories. For each observation there is a separate subdirectory on the CD-ROM (see the README file and the DATALIST file for more details). Many of the products are written in Binary FITS extension format (see chapter 8 for details on the file formats for LWS data). To read the data products observers can use several tools.

The IPAC first look tools
These are available from IPAC and allow the user to read in the FITS files, and create ASCII files from them. These tools are available for Sun/Solaris 2.4, Sun/SunOS 4.1.3, Dec/Ultrix 4.4, PC/Linux, Dec/Open VMS AXP V6.1. The tools can be downloaded from IPAC, see their worldwide web page:
http://www.ipac.caltech.edu/iso/iso.html
The ISO Spectral Analysis Package (ISAP)
This is an analysis package that was specifically written for LWS and SWS data. It can read in the product files and write a FITS file or an IDL save set. This package requires IDL4 (for ISAP 1.4) or IDL5 (for ISAP 1.5). The routines in ISAP have been tailored to reduce LWS data. The package was written jointly by IPAC, the LWS instrument team and the SWS instrument team. ISAP allows the user to flag or delete data points that are clearly wrong (due to undetected glitches for instance), average scans (using different averaging routines), to scale the detectors to make smooth spectra, to rebin spectra to a standard wavelength scale, and to subtract an off spectrum from an on source spectrum. ISAP can be downloaded from one of the following websites:
     http://www.ipac.caltech.edu/iso/isap/isap.html
     http://www.mpe.garching.mpg.de/iso/isosdc.html
The LWS Interactive Analysis (LIA)
This package is written as a set of IDL routines, to be used together with ISAP. The routines are written to allow the user to redo all or part of the automatic processing in an interactive way. It also allows some extra functionalities, like the strong source correction and the interactive FP responsivity correction. It also allows the user to tailor the processing somewhat to his needs (for instance for darkcurrent removal). LIA can be downloaded from the same sites as ISAP.
IDL with the astronomy library
Using IDL with the astronomy library, the observer can write his own code to read the data files, using the information in this IDUM (chapter 8). Below are some IDL commands that can be useful.
   To read the FITS primary header in variable hdr_prime:
   
   hdr_prime=headfits('<filename>')
   
   To read the binary header into variable hrd_bin:
   
   fxbopen,unit,'<filename>',1,hdr_bin
   
   To read the data from column N into variable X:
   
   fxbread,unit,X,N
A longer note on the use of IDL and the Astro Library to read LWS data can be found on the IPAC WWW pages (see above).

   
9.2 Where to find instrumental calibration parameters (SPD calibration)

The following table (9.1) gives the calibration files where the observer can find the instrumental calibration parameters that are used during the Derive-SPD process. The table also gives the reference to the table that describes the calibration file in this document. The descriptions of these calibration files are given in section 8.2.6. The list is given in alphabetical order.


 
Table 9.1: List of instrumental calibration parameters used in Derive-SPD.
Parameter File Table page
Analogue amplification gains LCGA none [*]
Detector amplifier (JF4) capacitances LCJF 8.21 [*]
Detector amplifier (JF4) gains LCJF 8.21 [*]
Detector read out to voltage conversion LCVC none [*]
First level deglitching parameters LCD1 8.23 [*]
Maximum voltages on the detectors LCDB 8.22 [*]
Readout limits of the electronics LCAL 8.20 [*]
Time periods to be ignored after a reset LCDT 8.19 [*]
 

   
9.3 Where to find astronomical calibration parameters (AA calibration)

The following table (9.2) gives the calibration files where the observer can find the astronomical calibration parameters that are used during the Auto Analysis process. The table also gives the reference to the table that describes the calibration file in this document. The descriptions of these calibration files are given in section 8.2.9. The list is given in alphabetical order.


 
Table 9.2: List of astronomical calibration parameters used in Auto Analysis.
Parameter File Table page
FP wavelength calibration coefficients LCFW 8.34 [*]
FPL positions for response curves LCLRZ 8.36 [*]
FPL relative response curves LCLR_n 8.35 [*]
FPS positions for response curves LCSRZ 8.38 [*]
FPS relative response curves LCSR_n 8.37 [*]
Grating relative response curves LCGR 8.32 [*]
Grating spectral bandwidth correction LCGB 8.39 [*]
Grating wavelength calibration table LCGW 8.30 [*]
Standard Illuminator photo currents LCIR 8.29 [*]
 


next up previous contents
Next: 10. Post-processing Up: ISOLWS DATA USERS MANUAL Previous: 8. Guide to instrument

ISOLWS Data Users Manual, Issue 5.0, SAI/95-219/Dc