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<!DOCTYPE HTML>
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<title>Munipack ‒ Find Stars</title>
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<body>
<header>
<a href="munipack.html"><img src="title_logo.png" alt="Munipack's logo" class="head"></a>
<div class="headhead">
<div class="headtitle">
<a class="headtitle" href="munipack.html">Munipack</a>
<a class="headsubtitle" href="munipack.html">A general astronomical image processing software</a>
</div>
<ul class="menu">
  <li class="menu">◈ <a href="docs.html" class="menu">Documents</a></li>
  <li class="menu">☺ <a href="guide.html" class="menu">User guide</a></li>
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<h1>Find Stars</h1>

<p class="abstract">
Detects stars on frames. The stars are supposed to be a Gaussian-like peaks
with FWHM provided by user. Additional parameters are used to reject false
detection due to various defects.
</p>

<h2>Synopsis</h2>

<code>
munipack find [.. parameters ..] file(s)[,result(s)]
</code>

<h2>Description</h2>

<p>
Fully automatic detection of stars on frames is very important
and also difficult. Munipack uses an algorithm developed by P.B.Stetson
for DAOPHOT II with small changes. The algorithm is very robust,
insensitive to wide range of defects including hot pixels or cosmic-ray
events. One also detect stars on varying background (Moon shine, in 
galaxies etc).
</p>

<p class="indent">
Stars are detected on base of their shapes. One supposes
that second moments of stars are similar in vertical and horizontal
axes with value nearly to FWHM. We also suppose that PSF of stars
is not too sharp. The limits of parameters can be tuned
(while it is not needed frequently): round and sharp parameters are
in detail described in <a href="http://adsabs.harvard.edu/abs/1987PASP...99..191S">DAOPHOT - A computer program for crowded-field stellar photometry by P.B.Stetson</a>.
</p>

<h2>Algorithm</h2>

<p>
Stars detection algorithm:
</p>
<ul>
<li>As the preparation step, the background level with the noise <i>B,σ</i> 
    of image is determined on a grid covering full frame.</li>
<li>As the first step, the image is convoluted with Gaussian hat with
    FWHM provided by user. The convolution has effect of a digital filter 
    which emphasizes star-like objects and suppress point defects or 
    large-scale gradients.</li>
<li>The convoluted image is searched for local peaks. For every peak, 
    a maximum value is determined. A star candidate has the value
    above threshold level <i>B+tσ</i> (parameter <i>t</i>
    corresponds to <samp>--th</samp> switch) and below saturation <i>S</i>
    limit (given by <samp>--saturate</samp>)</li>
<li>The parameters <samp>round</samp> and <samp>sharp</samp> are determined 
    for every candidate.
    When both parameters lies inside acceptable intervals (tune it via 
    <samp>--rndlo,--rndhi,--shrplo,--shrphi</samp> options), the candidate
    is stored and classified as a star.
    </li>
<li>Rectangular coordinates and peak ratio are determined for every star.</li>
</ul>

<p class="indent">
The data under level <i>B-uσ</i> (where parameter <i>u</i> corresponds 
to <samp>--lothresh</samp>) are not used during the detection process.
</p>

<p class="indent">
This routine adds a FIND extensions to original frames
as a table, its is described in <a href="dataform_proc.html">Find Format</a>.
</p>


<h2>Relation to DAOPHOT II</h2>

<p>
The routine is on base of original code of DAOPHOT II by P.B.Stetson
(has been forked from Midas's implementation at 1996). Some additional
enhancements has been done:
</p>
<ul>
<li>Robust estimators replaces the original estimators of averages.</li>
<li>All processing is done in memory (no disc buffering is used).</li>
<!--<li>Real numbers in double precision are implemented</li>-->
<!--<li>The output of magnitudes has been abandoned.</li>-->
<li>FITS files for both input and output are used</li>
<li>Log format is changed.</li>
<li>Seldom bugs are corrected.</li>
<li>Code is updated for Fortran 95 (and perhaps above).</li>
</ul>

<h2>Input And Output</h2>

<p>
On input, list of frames with already applied photometric pre-calibrations is expected.
</p>

<p>
On output, a table with detected stars, represented by FITS extension, is added
to all input images.
</p>



<h2>Parameters</h2>

<h3>Important:</h3>
<dl>
<dt><samp>-f</samp></dt><dd>Set FWHM in pixels. The value is set by default to 3 pixels
    which will satisfactory for small telescopes. Hubble space telescope requires
    values below 1 pixel and a well sampled image has FWHM between 5 - 10 pixels.</dd>
<dt><samp>-th</samp></dt><dd>Threshold in sigmas above background.
    One affects how much and how faint stars will be detected. 
    Common values are about 5-10. 
    Brigh stars detection only requires the threshold above 10 and the 
    dim stars (and many defect) is under 1. Checking values below sky noise is not 
    recommended.
</dd>
</dl>


<h3>Searching Limits:</h3>
<dl>
<dt><samp>--saturate</samp></dt><dd>Saturation in ADU. The value is determined
                from FITS header using <a href="man_env.html">SATURATE</a> key, 
                when the keyword is not found
                the upper-limit of float numbers in single precision is supplied
                (approximate 10<sup>38</sup>). The value will usually not 
                satisfactory because the 
                saturation is primary given by electrical capacity of pixels 
                (device manufacturers supplies theirs values as the full well 
                capacity) and one is usually not related to a numerical range.</dd>
<dt><samp>--lothresh</samp></dt><dd> lower for threshold in sigmas</dd>
<dt><samp>--rndlo</samp></dt><dd> lower for round</dd>
<dt><samp>--rndhi</samp></dt><dd> higher for round</dd>
<dt><samp>--shrplo</samp></dt><dd> lower for sharp</dd>
<dt><samp>--shrphi</samp></dt><dd> higher for sharp</dd>
</dl>

<h3>Additional:</h3>
<dl>
<dt><samp>--read-noise</samp></dt><dd>Read noise in ADU. A value from 
    frame header is used by default. Use this option when the value is missing or 
    needs correction. Read noise is important for determining of photometry errors.</dd>
</dl>

<p>See <a href="man_com.html">Common options</a> for input/output filenames.</p>

  <p>
    When options for the saturation or read noise are specified, FITS header 
    is updated according to the passed value.
  </p>


<h2>Examples</h2>

<p>
Detect stars on image:
</p>
<code>
$ munipack find -f 2 -th 10 pleiades.fits
</code>

<h2>See Also</h2>
<p>
<a href="man_aphot.html">Aperture photometry</a>,
<a href="man_com.html">Common options</a>,
<a href="dataform_proc.html">Processing file</a>.
</p>

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