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I was doing a project where I had to cross-match Panstarrs1 data (I took green data from there), with growth India telescope data (it is providing data red band) for NGC2682(Messier 67). After gaining the zero point bias by cross-matching both catalogues using sextractor here are the corrected (i.e r' data is in absolute magnitude scale)color magnitude diagrams ( red vs green - red) I got from using aperture and psf photometry. cmd 1

enter image description here

Now my question is that which isochrone do I fit? I used Z=0.0159, extinction as 0.064, I was using cmd 3.7 input form( http://stev.oapd.inaf.it/cgi-bin/cmd_3.7).enter image description here

This is what I get using above parameters. This seems impossible to fit.

This is log(l) vs the graph:-enter image description here

Do I have to invert the x axis of isochrone too to fit this? Is scaling allowed? I am perplexed please help me.

For psf and aperture photometry i used growth Caltech photometry jupyter notebook. For aperture photometry I took radius as 3.33.

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    $\begingroup$ Can you provide a bit more context and explain what each individual plot shows? The axes descriptions are minimal at best and to me not understandable without a bit more context. What is cmd? colour-magnitude diagramme? Please don't only use abbreviations. $\endgroup$ Sep 15, 2022 at 7:36
  • $\begingroup$ Thanks for the suggestion. Please point out if I need to add anymore info. $\endgroup$ Sep 15, 2022 at 7:57
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    $\begingroup$ You appear to be trying to interpret a colour-magnitude diagram with isochrones in a log luminosity vs te (temperature?) graph. Clearly this isn't going to work. $\endgroup$
    – ProfRob
    Sep 15, 2022 at 9:12
  • $\begingroup$ @ProfRob should i take log l vs log te or there were magnitude in different colour were given in cmd 3.7 data as well should I use them? $\endgroup$ Sep 15, 2022 at 9:17
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    $\begingroup$ You should use isochrones in magnitude versus colour. And the isochrones must be corrected for the effects of distance and extinction. $\endgroup$
    – ProfRob
    Sep 15, 2022 at 11:27

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To put an isochrone on your colour-magnitude diagram, then you need those isochrones to be predictions in terms of colour and magnitude.

There are models out there which do predict isochrones in terms of an absolute magnitude and an intrinsic colour, in a variety of standard, calibrated filter systems.

In order to use these isochrones to compare with data that has been standardised and calibrated onto one of these systems, you would also need to correct for the distance to M67 and correct the magnitudes and colours for the effects of extinction.

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