4.1 MXLO Files

  To extract data from a low dispersion NEWSIPS MXLO file, you can run the procedure READMX. This procedure will return the FITS header, a wavelength array, absolutely calibrated fluxes, and (optionally) quality flags, sigmas, background, and net fluxes. The calling sequence is as follows:

READMX,'IMAGET',H,W,F,q,s,b,n,reqaper=aper,/noninter 

IMAGET	FITS file name (including extension).
H
	FITS main header, a string array. The VICAR label will be included. W
	Wavelengths (Å, computed from the starting wavelength and increment stored in the MXLO file.
F	Fluxes (erg cm-2 s-1 Å-1 ).
q	Quality flags (``$\nu$'' flags). These are bit encoded. See Section 7.2.2 for a description of the values.
s	``Sigmas''. These are errors associated with the Signal Weighted Extraction Technique (SWET), the final stage of processing in which the spectrum is fitted and extracted from the resampled image (SILO) data.
b	Chebyshev fit to the background, scaled to the net fluxes.
n	Net fluxes (``flux numbers'').
reqaper	Normally, READMX will prompt you if both large and small aperture data are available. You may set this keyword to ``large'' or ``small'' ahead of time to avoid this prompt (but if you try to select an aperture that is not available, you will still be prompted).
noninter	If this keyword is set, READMX will return large aperture data by default if both are available. For single aperture data the available aperture is returned. However, if an unavailable aperture is specified via the reqaper keyword, no data will be returned at all!

You may be prompted if there is a question of which aperture's data you want (see description of the reqaper and noninter keywords above); otherwise this is a non-interactive program.

Note that corrections for sensitivity variations, exposure time, and calibrations are already taken care of by NEWSIPS processing. You need not worry about correcting this data for the most part, and can begin analyzing the data.

For NEWSIPS data you can, if you wish, create a new FITS file similar to a MXLO file by using the procedure WRITEMX. Note: READMX does not alter the data in any way other than to discard data with $\sigma=-1$ (padded zeroes at both ends of the spectrum); if you have done nothing else to your data, it is unnecessary to save its output since you have the MXLO file on line. The calling sequence is:

WRITEMX,H,W,F,q,s,bkgd,net,filename=name 

The positional parameters are the same as those for READMX. The filename keyword allows you to set the output file name. If not specified the output file name will be the camera name and image number with an extension of .FIT (e.g., SWP12345.FIT). You may suppress writing any of the optional parameters by passing a 0 in the calling sequence.

You may read files written with WRITEMX with READMX. If you entered a zero for any variable in the calling sequence of WRITEMX, zero will be returned for that same variable when you use READMX.

There are examples of READMX and WRITEMX in Table 4.1.

 

 

Table 4.1: MXLO I/O Examples

Expression	Definition
writemx,h,w,f,q,0,b,nt	Writes out SWP12345.FIT for data from SWP 12345. Sigmas will not be included in the output file. Note that ``h'' is a FITS header and not an IUESIPS scale factor record.
writemx,h,w,f,q,s,filename='mydat.iue'	Writes out FITS file ``mydat.iue'' without the background or net fluxes.
readmx,'swp12345.fit',h,w,f,q,s,b,nt	Reads data written with writemx. The ``s'' variable will be a scalar (0) since sigmas were not written out.
readmx,'swp12345.mxlo',h,w,f,q,s,$ reqaper='large'	Read the large aperture data from the file SWP12345.MXLO. If large aperture data are not found, the user will be prompted to see whether small aperture data should be extracted.