<p>To put an isochrone on your <strong>colour-magnitude diagram</strong>, then you need those isochrones to be predictions <strong>in terms of colour and magnitude.</strong></p>
<p>There are models out there which do predict isochrones in terms of an absolute magnitude and an intrinsic colour, in a variety of <strong>standard, calibrated filter systems</strong>.</p>
<p>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 <a href="https://en.wikipedia.org/wiki/Extinction_(astronomy)" rel="nofollow noreferrer">extinction</a>.</p>

CC BY-SA 4.0
2022-09-15T17:19:54.467Z
2022-09-15T17:19:54.467Z
ProfRob
<p>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. <a href="https://i.sstatic.net/eNwWC.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/eNwWC.png" alt="cmd 1" /></a></p>
<p><a href="https://i.sstatic.net/eJBxr.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/eJBxr.png" alt="enter image description here" /></a></p>
<p>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( <a href="http://stev.oapd.inaf.it/cgi-bin/cmd_3.7" rel="nofollow noreferrer">http://stev.oapd.inaf.it/cgi-bin/cmd_3.7</a>).<a href="https://i.sstatic.net/NqCBN.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/NqCBN.png" alt="enter image description here" /></a></p>
<p>This is what I get using above parameters. This seems impossible to fit.</p>
<p>This is log(l) vs the graph:-<a href="https://i.sstatic.net/TFSJc.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TFSJc.png" alt="enter image description here" /></a></p>
<p>Do I have to invert the x axis of isochrone too to fit this? Is scaling allowed? I am perplexed please help me.</p>
<p>For psf and aperture photometry i used growth Caltech photometry jupyter notebook. For aperture photometry I took radius as 3.33.</p>

CC BY-SA 4.0
2022-09-15T07:36:41.940Z
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.
planetmaker
CC BY-SA 4.0
2022-09-15T07:57:49.577Z
Thanks for the suggestion. Please point out if I need to add anymore info.
Nobody recognizeable
CC BY-SA 4.0
2022-09-15T09:12:50.457Z
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.
ProfRob
CC BY-SA 4.0
2022-09-15T09:17:29.093Z
@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?
Nobody recognizeable
CC BY-SA 4.0
2022-09-15T11:27:49.887Z
You should use isochrones in magnitude versus colour. And the isochrones must be corrected for the effects of distance and extinction.
ProfRob
CC BY-SA 4.0
2022-09-16T23:20:06.997Z
+1 but I'm curious what "growth India telescope data" means.
uhoh
CC BY-SA 4.0
2022-09-17T08:25:27.423Z
@utoh https://sites.google.com/view/growthindia/ . The data I crossmatched panstarrs1 with is taken from the above telescope.
Nobody recognizeable
<observational-astronomy><star-catalogues><star-cluster>
Fitting isochrone on color magnitude diagram obtained from growth india telescope for M67
Nobody recognizeable
# Fitting isochrone on color magnitude diagram obtained from growth india telescope for M67

(Asked by: username_0 on 2022-09-15)

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](https://i.sstatic.net/eNwWC.png)](https://i.sstatic.net/eNwWC.png)

[![enter image description here](https://i.sstatic.net/eJBxr.png)](https://i.sstatic.net/eJBxr.png)

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](https://i.sstatic.net/NqCBN.png)](https://i.sstatic.net/NqCBN.png)

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

This is log(l) vs the graph:-[![enter image description here](https://i.sstatic.net/TFSJc.png)](https://i.sstatic.net/TFSJc.png)

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.

**Tags:** observational-astronomy, star-catalogues, star-cluster
> **Comments:**
> **username_1**: 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.  
> **username_0**: Thanks for the suggestion. Please point out if I need to add anymore info.  
> **username_2**: 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.  
> **username_0**: @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?  
> **username_2**: You should use isochrones in magnitude versus colour. And the isochrones must be corrected for the effects of distance and extinction.  
> **username_3**: +1 but I'm curious what "growth India telescope data" means.  
> **username_0**: @utoh https://sites.google.com/view/growthindia/ . The data I crossmatched panstarrs1 with is taken from the above telescope.  

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## 1 answers

### Answer by username_2 on 2022-09-15. Score: 2 | Accepted answer

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](https://en.wikipedia.org/wiki/Extinction_(astronomy)).


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