[sr #110649] Clumps with S/N smaller than threshold consider as a true clumps

[Sepideh Eskandarlou]

URL:
  <https://savannah.gnu.org/support/?110649>

                 Summary: Clumps with S/N smaller than threshold consider as a
true clumps
                 Project: GNU Astronomy Utilities
            Submitted by: sepideh
            Submitted on: Thu 12 May 2022 03:20:33 PM UTC
                Category: Segment
                Priority: 5 - Normal
                Severity: 3 - Normal
              Item Group: Output not reasonable
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
        Operating System: GNU/Linux

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Details:

I was attempting to make catalog for one of the Frontier-fields cluster. But I
realized some faint objects are not in my catalog.

I checked Segmentation map and realized this object did not consider as true
clump, while, the fainter objects considered as a clump.

I expected the S/N of main object (which did not consider as a clump) became
smaller the S/N threshold and S/N of faint objects (which considered as clump)
was larger than S/N threshold. While S/N of both of them were smaller than the
S/N threshold.

But why the fainter objects considered as clump, they should be ignored
because the S/N of these objects were smaller than S/N threshold. I think this
is a bug and it should be solved.

For producing this problem I put all the command use for making this segment
below.

At first, I downloaded a frontier-fields cluster by below command:


wget
https://archive.stsci.edu/pub/hlsp/frontier/abell2744/images/hst/v1.0/hlsp_frontier_hst_wfc3-60mas_abell2744_f160w_v1.0_drz.fits
-Oabell2744-f160w.fits


Secondly, based on the below command I crop the deeper part:


astcrop abell2744-f160w.fits -h0
--polygon="3.6034055,-30.4165889:3.5655321,-30.4135259:3.5722988,-30.3765434:3.6103451,-30.3816284"
--mode=wcs --output=crop.fits


Then I run NiseChisel on output of the astcrop:


astnoisechisel crop.fits --output=nc.fits 


Finally, I have make a flat(3*3) kernel and based on this kernel Segment was
built.


astconvert flat.txt --output=kernel.fits
astsegment nc.fits --kernel=kernel.fits --snquant=0.99 --gthresh=1000
--grownclumps --output=seg.fits






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