ALCHEMI Data Reduction Group: Continuum Subtraction


TIP Last Modified: JeffMangum - 06 September 2018

Table of Contents:

Current Status

See the ALCHEMI DR Meeting 2018-06-26 and later DR meeting minutes for detailed reports.
  • Most recent report from Nakanishi-san's testing
  • Most recent report from Nanase's testing
  • Conclusion: STATCONT works and we will use it for spectral baseline/continuum subtraction
  • Issues
    • [Nakanishi]: Still investigating difference between order of processing: STATCONT+PBCOR or PBCOR+STATCONT
    • [Nakanishi]: Doing PBCOR+STATCONT is much easier to do in processing
    • [Nakanishi]: I made some tests with auto-masking algorithm of tclean, in which three different ways of making mask are tested.
      • [A] frequency-independent mask; auto-masking is made on the bases on the frequency-integrated image
      • [B] normal (frequency-dependent) automask
      • [C] 5ch-binned mask; auto-masking is made on the 5ch-binned image to obtain higher S/N
      • The resultant images of (B) and (C) are almost same, so probably we do not have to use (C), as it takes longer time than normal automask.
      • The frequency-independent mask (A) is also good, but negative sidelobe patterns are less removed because the spatial shape of the negative lobes in the dirty image is also frequency-dependent.
      • The continuum image appears unaffected by the choice of masking algorithm.
      • I also quickly checked if the extended features that I reported at the previous telecon are real or not, by comparing CO 3-2 image with the CO 2-1 image.
      • The positive-latitude features are likely to be real, but the negative-latitude feature does not have obvious counterpart in the CO2-1 image. I am now trying to see if this feature becomes weak if selfcal is applied.
    • [Nanase]: Some low-level issues with ~0.5% of pixels
    • Still need to make STATCONT work within casa(?)

-- JeffMangum - 2018-09-06
Topic revision: r1 - 2018-09-06, JeffMangum
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