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<!DOCTYPE HTML>
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<title>Munipack ‒ Colour — Magnitude Diagram Tutorial</title>
</head>
<body>
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<section>
<h1>Colour — Magnitude Diagram</h1>
<p class="abstract">
How to create of a colour-magnitude (CMD) diagram which is a photometric
equivalent of the Hertzsprung-Russel diagram.
</p>
<h1>Open cluster M 67</h1>
<p>
Open cluster M 67 is an old galactic cluster with a differently
evolved stars which covers wide range of colour indexes.
All stars are approximately same old, but due to its different
initial masses and the fact that heavy stars gets older quickly,
we are observing the cluster members in different stages of evolution.
</p>
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<h2>Data Processing</h2>
<p>
To get CMD, follow these points:
</p>
<ol>
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<li>
<p class="li">
At this point, data are uncalibrated in magnitudes, but
can be used directly, if no calibration source is available.
The shape of final diagram will be shifted alongside both axis.
</p>
<p class="li">
The files M67_*_MAG.fits contains the table, which
can be matched and visualised by
<a href="http://www.star.bris.ac.uk/~mbt/topcat/">topcat</a>
(Virtual Observatory software).
</p>
<div class="table">
<table>
<tr><th>α [J2000]</th><th>δ [J2000]</th><th>instrumental magnitude</th><th>std. deviation</th></tr>
<tr><td>132.8228301</td><td>11.7562805</td><td>7.62841</td><td>.00036</td></tr>
<tr><td>…</td><td>…</td><td>…</td><td></td></tr>
</table>
</div>
</li>
<li>
<p class="li">
A photometry calibration offers determination of
astrophysical characteristics of clusters. The calibration
depends on availability of already known calibration stars.
We will take stars by UCAC4 catalogue, notwithstanding the
photometry accuracy is only about ten percents.
</p>
<pre>
$ munipack cone -r 0.2 --magmax 14 --Johnson-patch -o phcal_cone.fits -- 132.8 11.8
$ munipack phcal --photsys-ref Johnson -f B --area 0.3 --col-mag Bmag \
--col-magerr e_Bmag -c phcal_cone.fits m67_B.fits
$ munipack phcal --photsys-ref Johnson -f V --area 0.3 --col-mag Vmag \
--col-magerr e_Vmag -c phcal_cone.fits m67_V.fits
$ munipack phcal --photsys-ref Johnson -f R --area 0.3 --col-mag Rmag \
--col-magerr e_Rmag -c phcal_cone.fits m67_R.fits
</pre>
<p class="li">
The calibration utilises conversion of Gun's r,i magnitudes on
data in Johnson R filter, and determines the conversion.
Another source of calibrated magnitudes can be used, if the magnitudes
are stored in a FITS file.
</p>
</li>
</ol>
<h2>Determination of Properties of M67</h2>
<p>
Final results can be compared with models tabulated in the article
<a href="http://adsabs.harvard.edu/abs/1994A%26AS..106..275B">
Theoretical isochrones from models with new radiative opacities,
Bertelli G., Bressan A., Chiosi C., Fagotto F., Nasi E,
Astron. Astrophys. Suppl. Ser. 106, 275 (1994).
</a>
Tables can be downloaded here:
<a href="ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+AS/106/275">
ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+AS/106/275</a>.
Alternatively, isochrone models are also available via
<a href="http://www.star.bris.ac.uk/~mbt/topcat/">topcat</a>
(look for BaSTI).
</p>
<figure>
<img class="figure" src="M67cmd.png" alt="M67cmd.png" title="M 67">
<figcaption>Colour - magnitude diagram for M 67.
The star track for 10 Gyr, Z=0.0080, Y=0.25 and 1 kpc.</figcaption>
</figure>
<p>
The models can be easy plotted and one can determine
basic astrophysical characteristics of M 67 open cluster:
</p>
<ul>
<li>chemical composition</li>
<li>age</li>
<li>distance</li>
</ul>
<h2>Notes</h2>
<p>
This is the outline of the real method used to determine the parameters
of clusters in astrophysics. The fitting of the main sequence
and the turning point gives an age estimation, at least as wishful thinking.
</p>
<p>
The presented method is focused on use of Munipack. Therefore
we are ignoring some astrophysical difficulties:
</p>
<ul>
<li>Some stars on the images may be not members of the cluster. Independent
tests on base of proper motions or distance measurements should be used
to select only the right members.</li>
<li>The colours are affected by the interstellar extinction which
deforms observational data. The extinction has different fluency
onto short- and long-wavelength fluxes. One can be mapped
by using of tree filters together.</li>
<li>We are believing in theoretical models (which may be, generally,
false idea).</li>
<li>The colour indexes <i>B-V,V-R</i> can be used to construction
of extinction diagram.</li>
<li>
Instrumental magnitudes are used. To get more precise results, use
<a href="man_phcal.html">photometric calibration</a> along with
<a href="man_phfotran.html">Photometric System Transformation</a>.
</li>
</ul>
<h2>See Also</h2>
<p>
<a href="man_phcal.html">Photometry calibration</a>,
<a href="man_phfotran.html">Photometric System Transformation</a>,
<a href="dataform_photometry.html">Photometry Format</a>,
<a href="m67.sh">m67.sh</a>
</p>
</section>
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