Re: Y Axis Values Do Not Match Data

Posted by karenacollins on Mar 13, 2025; 11:55pm
URL: http://astroimagej.170.s1.nabble.com/Y-Axis-Values-Do-Not-Match-Data-tp2670p2686.html

Hi Tom,

I finally had a chance to investigate the problem you are having with the files you sent. Although the setup is a little different than the what is in the plot you show above, the problem is probably the same in both cases. In the measurements table you sent, most of your relative flux values are negative, and most are very close to zero. This causes the normalization to blow up some of the values to much larger numbers (although still centered at 1.0). If you want to plot the actually rel_flux_T1 values without modification, you need to set the normalization option in the Y-data panel (on the row your are plotting) to "off".

I'm not sure why your rel_flux values have many negative numbers. While negative rel_flux values can legitimately occur, most values in the table being negative seems to suggest a problem with your photometry run from multi-aperture (in other word, the flux in either your target star aperture or comp star aperture is lower than the sky background, rather than brighter such as when a star is in the aperture).

Karen