# Getting started

The following text describes the basic procedure for processing an observation of a short-periodic eclipsing variable stars by means of the Muniwin software, the graphical user interface which comes with the C-Munipack software.

The package with the demonstration data used in the example is available on the project home page. Download and unzip the archive to an empty folder (e.g. `~/c-munipack/sample`). The archive has the following structure:

dark / 20s / masterdark.fts

  master-dark frame (20 seconds exposure)

dark / 20s / raw / dark*.fts

  set of raw dark frames (20 seconds exposure)

flat / v / masterflat.fts

  master-flat frame (optical filter V)

flat / raw / flat-v*.fts

  set of raw flat frames (optical filter V)

data / v / frame*.fts

  sample CCD frames (optical filter V)

## General overview

The reduction of CCD observation can be described in general as a process that takes a time sequence of source frames of the same view field and a set of calibration frames and makes a table of brightness values of a selected object with respect to the time of observation, called a light curve.

The process of reduction of a CCD observation in the Muniwin software consists of the several steps:

1. Creating a new project and populating it with input files (source CCD frames)

2. Calibration of the source frames

3. Photometry and matching

4. Selection of stars

5. Selection of aperture

## Start Muniwin

Launch the Muniwin program - a way how to launch an application depends on your operating system and desktop environment. For example, on the MS Windows platform, the Muniwin program can be run from the menu Start ‣ Programs ‣ C-Munipack 2.1 folder. On POSIX-compliant platforms, execute the command `muniwin` in a terminal window. A main application window appears.

See also

Main window.

## Create a new project

In the Muniwin application, open the main menu, select item Project ‣ New. A new dialog appears.

The dialog for making a new project.

Fill in a name that will be assigned to the project (1). Because the name of the file that keeps track of the data related to the project, the project file, is derived from the name, some characters cannot appear in the project name, do not use: / ? % * : | “ < and >. In our example, let us use the designation of the variable star `GSC 2750 854`.

The field Location (2) shows a path to the directory where a new project will be created. Edit the path to change the location, you can also click the Browse button (3) to select a directory in a separate dialog.

The dialog also displays a list of available project types, called the profiles. The profile is used to specify initial settings for a new project. The installation package comes with a set of factory-provided profiles, which are listed under the section Predefined profiles. Later on, when you tune your own set of configuration parameters that you want to use repeatedly, you can create your own profiles, called User-defined profiles. See the section Profiles in the manual for instructions how to create and edit the user-defined profiles.

In this introductory demonstration tour, we will make a light curve for an eclipsing binary. Please, select the item Light curve in the section Predefined profiles in the table (4).

The dialog is closed and you should see the main application window again now. The table of input files shown there is empty.

The main application window with the table of input files, now empty.

See also

New project (dialog).

## Selecting source frames

Now, we’re going to populate the project with source files. Open the Frames menu and click on Add frames from folder. Go to the folder which contains the source CCD frames. The source CCD frames from the demonstration data are stored in the `data/v` subfolder. You should see the list of files in the center navigation pane. This dialog allows you to add all frames from folders and subfolders. If you need to specify only a subset of files from a particular folder, you the Add individual frames choice.

The dialog with the place selection box (left), the file selection box (middle) and the preview panel (right).

Push the Add 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 inserting all the files you want to process, close the dialog by pushing the Close button.

The main application window with the sample frames inserted.

See also

Add frames from folder (dialog) and Add individual frames (dialog).

## Frame reduction

Reduction of CCD frames is a process that takes the source CCD frames, performs their conversion and calibration, detects stars on each frame and measures their intensity and finally finds correlation (match) between objects that were found in the data set. The process of reduction prepares the data that are necessary for making a light curve or a variable star.

The reduction consists of the four steps - conversion, calibration, photometry and matching. Although they can be invoked step-by-step manually, the preferred way is to use the Express reduction dialog that allows to perform these steps in a batch. Using the menu, activate the Reduce ‣ Express reduction item. A new dialog appears. The dialog has several options aligned to the left, each of them relates to an optional step in the reduction process.

The dialog for setting parameters of the reduction process

Check the Fetch/convert files. In this step, the program makes copy of the source CCD frames. This is necessary, because the following calibration steps will modify them and we don’t want the program to change our precious source data.

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 necessary 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. Our sample data needs to perform the dark-frame correction, so check the Dark-frame correction option. Click the Browse button and find the file with the dark frame. For the sample data, use the file `dark / 20s / masterdark.fts`.

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 telescope is pointed to uniformly luminous area. In practice, this condition is very difficult to achieve, the clear sky before dusk is usually used instead. Our sample data needs to perform the flat-frame correction too, so check the Flat-frame correction option. Click the Browse button and find the file with the flat frame. For the sample data, use the file `flat / V / masterflat.fts`.

The photometry is a process that detects stars on a CCD frame and measures their brightness. Unlike the previous steps, the result is saved to a special 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. Check the Photometry option.

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 matching is a process which finds corresponding stars on source frames and assigns an unique identifier. Check the Matching option.

It is necessary to select one frame from the set of source frames that all other frames are matched to, this frame is called a reference frame. 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.

In previous steps, we have configured parameters of the reduction process and we are ready to start it. Click the OK button. During the execution a new window appears 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 process to finish.

The dialog displayed during time demanding operations.

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 frames could not be processed successfully, the entry is be marked with a special icon and in the Status column the error message is indicated.

The main application window after the recution.

See also

Express reduction (dialog).

## Making a light curve

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.

The Muniwin program is designed to guide you through the process of making a light curve. Open the Make menu and select the Light curve item. A new dialog appears, all fields in this dialog are optional, they allows you to include only subset of frames to the curve, apply the heliocentric correction or include the air mass coefficients to the output. Let all options unchecked and just confirm the dialog by the OK button.

The dialog for making a light curve.

Another dialog appears. The next dialog allows you to pick up a variable star, a comparison star and one or more check stars. In this dialog, the reference frame is displayed. Find a variable star and click on it using the left mouse button (1). A context menu appears. Select the Variable 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 (2) and one or more check stars (3 and 4). 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 OK button.

The dialog for selection of a variable star (red), a comparison star (green) and check stars (blue).

In the next dialog, 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.

The programs allows you to select an aperture in the following dialog, the program displays a graph of standard deviation of data for each aperture. The curve has U-like shape usually and the best aperture is in the minimum of the curve (5). For the sample data, select the aperture #2 and confirm the dialog by the OK button.

The dialog for selection of an aperture.

Now the program has got enough information to make a light curve of the selected variable star. The light curve is presented in a new window. Please keep in mind that the magnitudes displayed in the light curve are differential with respect to the selected comparison star.

The dialog with a light curve graph.

See also

Light curve.

## Exporting a light curve to a file

The light curve can be exported to a file in several formats.

See also

Export light curve in AAVSO format