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</head><body><div class="main_head"><p class="head"><a href="index.html">C-Munipack 1.2</a></p><h1>Getting started</h1></div><p>The following text describes the basic procedure for processing an observation of a short-periodic variable stars by means of the Muniwin.</p><p>The package with demo data used in the example is available on the project's web pages. Download and unzip the archive to an empty folder at your hard disk (e.g. ~/c-munipack/sample). The archive has the following structure:</p><div class="program-listing"><pre>dark
20s
masterdark.fts - master-dark frame (20 seconds exposure)
raw
dark*.fts - set of raw dark frames (20 seconds exposure)
flat
v
masterflat.fts - master-flat frame (optical filter V)
raw
flat-v*.fts - set of raw flat frames (optical filter V)
data
v
frame*.fts - sample CCD frames (optical filter V)</pre></div><p>In general, the reduction of CCD data consists of the several steps:</p><ol><li><p>Building list of input files</p></li><li><p>Conversion of the input files to the working format</p></li><li><p>Calibration</p></li><li><p>Photometry and matching</p></li><li><p>Selection of stars</p></li><li><p>Making outputs</p></li></ol><p>Launch the <tt>Muniwin</tt> program - a way how to launch an application depends on your operating system and desktop environment. By default, the Muniwin program can be run from the <tt>Programs</tt> -> <tt>C-Munipack 1.2</tt> folder.</p><p>From the <tt>Files</tt> menu, choose <tt>Clear files</tt>. You will be asked for confirmation, press the <tt>Yes</tt> button. The table of input files in the main window should be now clear.</p><div class="mediaobject"><img border=0 src="main.png" alt="Main application window"/></div><p>Open the <tt>Files</tt> menu again and click on <tt>Add folder</tt>. A new dialog opens. By means of it, you can insert all files from a particular folder to the table of input files. If you need to include a subset of files from a folder only, use the <tt>Add files</tt> item. In both cases, the dialog layout is similar. Go to the folder which contains the source CCD frames. The demo data is stored in the <tt>data/v</tt> subfolder. You should see the list files in the center navigation pane.</p><div class="mediaobject"><img border=0 src="addfolder.png" alt=""Add folder" dialog"/></div><p>Push the <tt>Add</tt> button. If you want to process data taken in several nights at once, use the same procedure to add those files to the table. After insering all the files you want to process, close the dialog by pushing the <tt>Close</tt> button.</p><div class="mediaobject"><img border=0 src="inputfiles.png" alt="Main application window"/></div><p>First step of the reduction process is making a local copy of the source files. If the source files are not saved in the FITS format, the conversion will be applied to the images automatically. From the <tt>Files</tt> menu choose the the <tt>Fetch/convert files</tt> item. A new dialog opens, confirm it by the <tt>OK</tt> button.</p><div class="mediaobject"><img border=0 src="progress.png" alt="Progress dialog"/></div><p>During the conversion a new window apears displaying the state of the process; all the information is also presented there. This window will be automatically closed after finishing the process. Wait for the conversion of all the files to finish. After finishing, the icon in the file table changes; the information about the time of observation, the length of the exposition and the used filter is filled in. In case some of the files could not be converted, the entry is be marked with a special icon and in the <tt>Status</tt> column the error message is reported.</p><div class="mediaobject"><img border=0 src="inputfiles1.png" alt="Main application window"/></div><p>A raw CCD frame consists of several components. By the calibration process, we get rid of those which affect the result of the photometry. In some literature, the calibration is depicted as the peeling of an onion. There are three major components which a raw frame consists of - the current made by incident light, current made thermal drift of electrons (so-called dark current) and constant bias level. In standard calibration scheme, which we will demonstrate here, the dark-frame correction subtracts the dark current and the also the bias. Because of the nature of the dark current, it is neccessary to use a correction frame of the same exposure duration as source files and it must be carried out on the same CCD temperature, too. Thus, the properly working temperature regulation on your CCD camera is vital. To execute a dark-frame calibration, open the <tt>Calibration</tt> menu and select the <tt>Dark correction</tt> item.</p><div class="mediaobject"><img border=0 src="darkcorr.png" alt=""Dark correction" dialog"/></div><p>Then, we have to compensate the spatial non-uniformity of a detector and whole optical system. These non-uniformities are due to the fabrication process of a CCD chip and they are also natural properties of all real optical components, lenses in particular. The flat-frame correction uses a flat-frame to smooth them away. The flat-frame is a frame carried out while the telescopy is pointed to uniformly luminous area. In practice, this condition is very difficult to achieve, the clear sky before dusk is usually used instead. Open the <tt>Calibration</tt> menu and select the <tt>Flat correction</tt> item.</p><div class="mediaobject"><img border=0 src="flatcorr.png" alt=""Flat correction" dialog"/></div><p>The source frames are calibrated now. We are ready to detect stars on each frame and measure their brightness. This process is called the photometry and unlike the previous commands, the result is saved to a text-based file, so-called the photometry file. There are a lot of parameters which affect the star detection and also the brightness computation. In this example, the default values work fine, but I would suggest you to become familiar with at least two of them - FWHM and Threshold - before you start a real work. Open the <tt>Photometry</tt> menu and select the <tt>Photometry</tt> item. When the process has been finished, the number of the stars found on each frame is filled in to the table.</p><div class="mediaobject"><img border=0 src="inputfiles2.png" alt="Main application window"/></div><p>The previous command treated all source files independently. As a result of this, a star #1 in one file is not necessarily the same as a star #1 in another file. The process which finds corresponsing stars on source frames and assigns an unique identifier to each of them is called the matching. Open the <tt>Matching</tt> menu and select the <tt>Match stars</tt> item. A new dialog appears. Choose one frame, which shall be used as a reference frame. All other frames will be matched to this one. In my experience, the frame with the greatest number of stars works the best. Back to our example, let's pick up the first one. Select the first row in the dialog and click on the <tt>OK</tt> button.</p><div class="mediaobject"><img border=0 src="matching.png" alt="Matching stars"/></div><p>The sample data is the observation of an eclipsing binary star. For most of such observers, the goal is to make a light curve. A light curve is usually represented as a table, which consists of at least two columns - time stamps expressed as julian dates and differential instrumental brightness of a variable star in magnitudes. The magnitudes are called differential, because they are differences between two stars - a variable star and a comparison star. A variable star is a star that is subject of brightness variation and a comparison star is supposed to be constant. To check that the comparison star is really constant, it's advisory to use one or two additional stars, so-called check stars. They are supposed to be constant too and thus the difference between any check star and the comparison star should be constant.</p><p>Before we make a light-curve, we have to tell the program which star is a variable star and pick up a comparison and one or more check stars. Open the <tt>Plotting</tt> menu and select the <tt>Choose stars</tt> item. A new dialog appears. The reference frame is displayed in the left part of the dialog, all detected stars are highlighted. Find a variable star and click on it using the left mouse button. A context menu appears. Select the <tt>Variable</tt> item. The star is drawn in red color now and the label "var" is placed near to it. Using the same procedure, select one comparison star and one or more check stars. I would recommend you to use two check stars. If you are using the sample data, use the stars according to the following screenshot. Confirm the selection by the <tt>OK</tt> button.</p><div class="mediaobject"><img border=0 src="stars.png" alt="Choose stars"/></div><p>Now, we have to choose the aperture. You can image the aperture as a virtual circular pinhole, placed on each star on a frame to measure its brightness. All pixels that are inside the pinhole are included in computation leaving out the background pixels. The best aperture should be big enough to include most of the star's light, on the other hand, the bigger aperture is used the more background is included and the more noisy the result is. Because of this, the photometry process computes the brightness of each star in a set of predefined apertures of radius in the range of 2 and 30 pixels.</p><p>To select the best aperture, we can take advantange of a comparison and check stars - providing that they are constant, we can compute the differential magnitudes between each couple of them on each other and then compute the variance or standard deviation from the mean level. For the best aperture, the deviations are minimal.</p><p>Open the <tt>Plotting</tt> menu and select the <tt>Choose aperture</tt> item. A new dialog appears. The graph shows the standard deviation for each aperture. Find the aperture with the minimal deviation and click on it using the left mouse button. A context menu appears. Select the <tt>Select aperture</tt> item. The point is drawn in red color now and the label is placed near to it. In our example, use the aperture #2. Confirm the selection by the <tt>OK</tt> button.</p><div class="mediaobject"><img border=0 src="aperture.png" alt="Choose aperture"/></div><p>Now we are ready to make a light curve of the variable star. Open the <tt>Plotting</tt> menu again and select the <tt>Plot light-curve</tt> item. A new dialog appears. This dialog shows the light curve of the selected variable star. The magnitudes are differential with respect to the selected comparison star.</p><div class="mediaobject"><img border=0 src="lightcurve.png" alt="Light curve graph"/></div><p>Press the <tt>Save</tt> button. Locate the folder where you want to save the results and fill in the name of the output file. Confirm the dialog by the <tt>Save</tt>.</p><p>The light curve is saved to a text-based file. On its first line, the names of the columns are stored. The second line shows the aperture and color filter used. The data are stored on the followin lines. Each line corresponds to a single source frame. In the first column, there is a time of observation (center of exposure) expressed as a julian date. The second column consists of differential instrumental brightness of the variable stars with respect to the comparison star in magnitudes (V-C). The error estimation is stored in the next column. Following columns consist of differential magnitudes of comparison star and check stars and their error estimations.</p><div class="mediaobject"><img border=0 src="output.png" alt="Output file"/></div></body></html>
