IRAS Server Manual

Contents

Introduction

 Astronomers who want to analyze data obtained by the InfraRed Astronomical Satellite IRAS can use the IRAS server. You can request data by sending an electronic mail (Email) message to iras_server@sron.rug.nl. You will be notified by Email when your request is processed, and how you can retrieve your data by (anonymous) FTP file transfer.

What do we do for you?

 We keep a full set of the uncalibrated IRAS data on optical disks for semi-online access in a jukebox. Your request can select the data for your area of interest, recalibrate fluxes and position of the infrared measurements, and recombine them into an image. You may set several options for this processing, to obtain the best possible reconstruction of the IR sky for your research. In view of the amount of processing and the overhead of the jukebox system, your processing time will be limited per request.

We think the best results can be achieved if you only request to extract and calibrate the data, retrieve the intermediate data set in GIPSY format, and to do the imaging interactively on your own machine, using the GIPSY software. For those who cannot use this route, the standard image run provides for non-interactive imaging with default settings, and a conversion to FITS standard.

How to generate a standard image?

Your message normally would contain the request for a standard image. For example, to get FITS file containing a 60 µm picture of the Andromeda nebula you have to send the one-line quoted string: 

"stdimage center=0h40m 41d00m instrume=60"
The complete specification looks like this (do not forget the quotes surrounding the (multi-line) request): 

"stdimage INSTRUME=<band number> 
          CENTER=<longitude> <latitude>
         [SIZE=<size>]
         [PIXELS=<resolution>]
         [COOR=<coordinate system>]       
          OBJECT=<name of object>
          OBSERVER=<name of observer>
          RESULT=<type of result file>
         [CALIB=<calibration type>]
         [OUTSET=<name of output set>]"
<band number>
is one of 12, 25, 60, 100
<longitude>
is the longitude of the plate center.
<latitude>
is the latitude of the plate.
<size>
is the size of the plate, default size = 1.0 degree
<resolution>
is the number of pixels along each side of the image default is 120 pixels.
<coordinate system>
coordinate system for plate center, one of EQUATORIAL 2000.0, (this is the default), GALACTIC, ECLIPTIC 2000.0, SUPERGALACTIC. The epoch given with ECL or EQU can give another year as well.
<name of object>
Any string, to identify the content of your image
<name of observer>
Any string, to identify the 'owner' of the image
<type of result file>
one of FITS (default), GDS, IRDS or RAW, denoting the required level of processing.
<name of output set>
the name of the file where you can find your data.
<calibration type>
one of ZODY (default) or IPAC
Concerning the calibration there are two things to note.
  1. By requesting ZODY there will be a subraction of a zodiacal emission model from the data. With IPAC that is not the case.
  2. ZODY is not very well suited for the band at 100 µm.
So a variant of the above example could be 

"stdimage center=0h40m 41d00m instrume=60 coor=EQU 1950
          SIZE=1.5 PIXELS=90 OBJECT= Andromeda Nebula
          OBSERVER=A.S. Tronomer RESULT=FITS"
There is a time limit in the server which at present is set to 20 minutes. When your request takes longer than that, it is aborted. In most cases it should be sufficient to process a standard image with default settings.

How to get an LRS spectrum?

 For obtaining an LRS spectrum there is another message to be send. The next line will produce a standard spectrum in fits format of alpha PsA: 

"stdspectrum center=22h54m53.5s -29d53m16s"
The complete specification looks like (do not forget the quotes): 

"stdspectrum center=<longitude> <latitude>
            [instrume=<band nr>]
            [coor=<coordinate system>]
            [units=<physical units>]
            [object=<name of object>]
            [observer=<name of observer>]
            [result=<type of result file>]
            [outset=<name of output file(s)>]"
All keywords can have the same values as with stdimage, except
<band nr>
is LRS (default)
<physical units>
Units of the output spectrum. Options are
Jy - F(lambda) in Jy
Wm - F(lambda) in Wm^-2mu^-1
LFL - lambda*F(lambda) in Wm^-2 (default)
L4FL - lambda^4*F(lambda) in Wm^-2mu^3
Note that the longitude and latitude that you provide with the keyword CENTER= will be the position for which the spectrum is extracted. Due to the fact that LRS is a slitless spectrometer, the position should be given with an accuracy of more than 5 arcsec. Again for the best results in LRS, it is recommended to install GIPSY at your site and run the task LRSCAL yourself.

How to access pointed observations (PO)?

 (PO's are also known as Additional Observations, AO.)

If you already know which PO you want, you can specify the keywords, additional to STDIMAGE or STDSPECTRUM,

SOPATT=<sop> <att>
OBSMODE= <observation mode>
If you want to know whether there are PO's covering a certain area you omit the SOPATT= keyword, but fill in one of the observation modes PO, AO or UNKNOWN. The logfile (GIPSY.LOG) will tell you whether there are any PO's in the area specified, and it will also give the sop-att's of these observations. The resulting set will contain the data for the first sop-att in the list. In a next request you can specify one of the other sop-att's to extract the data for them. There are some things about PO's that you must keep in mind.
  1. PO's are a more complicated data set than the survey. Eg. the gain might be set to `high' or `low' in stead of `standard', without notice. In that case it can only be processed by separately running the calibration program (see Advanced Usage, below)
  2. One IRDS can only contain one PO, although several PO's can be processed in one run of IMAGE.
  3. PO's can only be calibrated with the IPAC calibration, which is enforced for PO's in STDIMAGE.
  4. PO's will be snipped into `legs'.

How can you get the results?

 When you have made a request the server will acknowledge that the request has been received. When the request has been processed another message will be sent to you. This message will

How to get GIPSY?

 The Groningen Image Processing SYstem (GIPSY) was conceived in the early seventies to analyse the radio interferometric data from the Westerbork Synthesis Radio Telescope. Over the last two decades it has undergone many changes and extensions, the last of these being a major overhaul and a port to UNIX. The current version of GIPSY is set up to be a highly interactive environment for the reduction of various types of astronomical data. In particular a complete package for the production of IRAS images and spectra from the original raw data, has been added. GIPSY is supported on Sun-4, HP9000-700/300, Alliant FX and DEC MIPS. It makes extensive use of the X-11 protocol, but it can also run on a simple VT100 terminal. GIPSY can be obtained through anonymous ftp from kapteyn.astro.rug.nl (IP address 129.125.6.204). There's a README file available. Installation of GIPSY will take a few hours. But we highly recommend using GIPSY for obtaining the most out of the IRAS data.

Advanced usage

 Basically, your request is handled by the non-interactive version of GIPSY. You can mail any valid command script in the GIPSY command language COLA to the IRAS Server, and it would be executed in an empty scratch directory. When preparing COLA scripts for submission to vega, keep the following points in mind:
  1. There is no interaction: if keywords have no default, you have to supply them, otherwise GIPSY aborts. Of course, graphics and image display make no sense.
  2. In order to warrant reasonable service, we reserve the right the to impose limits on resource usage. Basically, these limits will always be amply sufficient to make the "STDIMAGE".
  3. To avoid problems with disk space usage, any results will be thrown away automatically after a few days. As a service to other users, you can return disk space for results that you have succesfully retrieved, by sending the (non-standard) GIPSY command "IRSERVER_UTIL CANCEL=r1:r2" where r1:r2 is the range of integers denoting the request numbers you are no longer interested in.

Problems

 If you have problems, complaints or suggestions, please mail to irasman@sron.rug.nl and the person responsible will handle it as quickly as possible.

How to get this manual and/or enlist as IRAS user?

 Send a mail to irasman@sron.rug.nl with the request to either send the manual or be registered as an IRAS user. In the latter case you will be sent this manual automatically.
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