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Matching data from different dates (variable star sequence)

Ivor Trueman
in PixInsight
Over the last few months, under different sky conditions (varying brightness), I've been grabbing occasional short (1hr) OSC data sets of a variable star that will vary by approx 7 magnitudes. I'm hoping to compare the flux data with known light curves with Aperture Photometry on the green channel, but would also like to present the data as a sequence of images where the sky background level & (fixed magnitude) star sizes remain consistent. How can I do this? I've been thinking that I may need to integrate each nights data separately, apply DBE & SPCC, and then split into RGB channels. Then apply Linear Fit to each channel, recombine, and then apply the same stretching regime to each night's image. I'm not sure if this will work - any idea on alternative workflows? Is there a way to match the PSF of stars between images, so that the fixed bright stars appear ot be the same size?
Any ideas much appreciated - I think the variable star should reach it's peak magnitude in about a months time, so I'm still in the data aquisition stage at the moment...
Thanks
Ivor

Comments

  • BlockHeadBlockHead
    Hi Ivor,

    As you know, the aperture photometry (flux measurements) will be relatively insensitive to the seeing if your aperture is large enough and source bright enough. However, the appearance of stars from frame to frame (or night to night) will certainly show the effects of the seeing on the PSF. Can you do anything about this? Not so much. Technically you can try to carefully deconvolve the images to get the same PSF sizes..but good luck!

    You are on the right track with regards to Linear Fit. Whether you are doing frame to frame matching or integrating frame matching- Linear Fit is the way to go. It is a frame matching that is done on global measures (location (offset) and scaling factor). So it will not change the relative brightness of the variable star..and you will see the changes in it when you blink the frames. You do NOT need to do split the color images and all of that. I believe Linear Fit will calculate on each channel of a color image (so three calculations)- it isn't doing this on a lightness value. You should verify..but I am pretty certain. 
    Once you have matched the frames... yes, apply the same stretch to all and blink/animate.

    -the Blockhead
  • Ivor Trueman
    Thanks Adam - much appreciated!
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