Scombine changes dimension

rohit wrote on Mar 31, 2010

I have two sets of two files which I combine to create two individual files. I have been using SCOMBINE task for this. It has worked for most expect this. I do not understand why the task is changing the dimensions. Here is what the imeader command gives for these four files:

LP860apr10-9.fits[1000,11][real]: LP860-41
LP860apr9-10.fits[1000,11][real]: LP860-41

ntel_stand12-13.fits[1000,11][real]: HD141442
ntel_stand13-12.fits[1000,11][real]: HD141442

Now I combine the first two. I get the following:

20070430LP860.fits[1003,11][real]: LP860-41

This is what is expected. However when I combine the other two files, I get:

20070430-tell.fits[1002,11][real]: HD141442

I am not sure why I have "1002,11" here?

Below is my lpar for SCOMBINE. The @comb2 simply contains the names of the two files I am combining.

Any ideas?

 input = "@comb2"        List of input spectra
       output = "20070430-tell.fits" List of output spectra
     (noutput = "")             List of output number combined spectra
     (logfile = "STDOUT")       Log file\n
   (apertures = "")             Apertures to combine
       (group = "apertures")    Grouping option
     (combine = "average")      Type of combine operation
      (reject = "none")         Type of rejection\n
       (first = no)             Use first spectrum for dispersion?
          (w1 = INDEF)          Starting wavelength of output spectra
          (w2 = INDEF)          Ending wavelength of output spectra
          (dw = INDEF)          Wavelength increment of output spectra
          (nw = INDEF)          Length of output spectra
         (log = no)             Logarithmic increments?\n
       (scale = "none")         Image scaling
        (zero = "none")         Image zero point offset
      (weight = "none")         Image weights
      (sample = "")             Wavelength sample regions for statistics\n
  (lthreshold = INDEF)          Lower threshold
  (hthreshold = INDEF)          Upper threshold
        (nlow = 1)              minmax: Number of low pixels to reject
       (nhigh = 1)              minmax: Number of high pixels to reject
       (nkeep = 1)              Minimum to keep (pos) or maximum to reject (neg)
       (mclip = yes)            Use median in sigma clipping algorithms?
      (lsigma = 3.)             Lower sigma clipping factor
      (hsigma = 3.)             Upper sigma clipping factor
     (rdnoise = "0.")           ccdclip: CCD readout noise (electrons)
        (gain = "1.")           ccdclip: CCD gain (electrons/DN)
      (snoise = "0.")           ccdclip: Sensitivity noise (fraction)
    (sigscale = 0.1)            Tolerance for sigma clipping scaling corrections
       (pclip = -0.5)           pclip: Percentile clipping parameter
        (grow = 0)              Radius (pixels) for 1D neighbor rejection
       (blank = 0.)             Value if there are no pixels
        (mode = "ql")           

---

Mike Fitzpatrick wrote on Mar 31, 2010

Without seeing the images, my only guess is that there's a difference in starting wavelengths that's causing the different sizes. Since you didn't specify the wavelength parameters, the task computes them based on the existing dispersion in the images.

---

Last post on Mar 31, 2010