# Finding variables

The CCD observation allows to measure brightness of all stars occurring in the field of the telescope. It may happen, that on a series of frames that apart from observed star there occurs also another variable star. By the following steps, you can perhaps discover a new variable star.

The Find variables dialog is the useful tool that provides semi-automatic scanning of variable stars in the series of source files. It is based on the relation between the standard deviations of the brightness of the stars and their mean brightness. The program reads all photometry files and compute the mean brightness and standard deviations of brightness of all stars. The algorithm automatically removes stars that are missing on majority of source frames. For the star of lower magnitude the deviation of brightness exhibits higher value than deviation for stars with a higher brightness.

First follow all steps of observed frames reduction through matching of the photometry files. Click on the Tools ‣ Find variables item in the main menu. The program show a simple dialog which allows you to specify a source of data. It is possible either to use all frames that are listed in the project or to use only frames that are currently selected in the main window. The last option allows you to process the data stored in an external file. Confirm the dialog by “OK” button.

The dialog for selecting the data source for Find variables tool.

The program computes all stars brightness data at all frames and selects one comparison star. The dialog window opens. At top left area a graph of standard deviation of brightness vs. mean brightness or an object is shown. On the right part the identification chart with variable star marked up is presented. Also the selected star light curve graph is shown.

The dialog for semi-automatic finding of variable stars.

In the top left area of the dialog, there is the graph of standard deviation of brightness vs. mean brightness of an object. According to the law of statistics, if all stars were constant, all objects would be located close to the parabola-like shape that goes from the left bottom corner of the graph to the right and turns up to its right top corner. If object’s brightness changes, the standard deviation is higher than the deviation of object of the same mean brightness - these objects are usually located above the curve.

The detail of the mag-dev curve with a variable star highlighted.

Click at any point of the graph left. The program marks the point with red circle with the var label. The same way, the corresponding star is marked up on the identification chart. In the bottom part of the dialog window, the light curve graph of the star is plotted. Sequentially indicate all stars, you suspect to be a variable star.

It may happen, that the comparison star automatically chosen is not good - it might not be constant. In this case the mag-dev curve has different character:

The detail of the mag-dev curve when the comparison star is not constant.

The comparison star is marked on the chart with green circle with the comp label. To change the comparison star manually, click on Comp button on the control panel and select the star on the identification chart. When done, click on the Var button to switch back to variable selection mode.

By the help of the buttons on the panel, the graph, chart or the light curve can be saved as data or image file.

## Exporting data

The program also provides means of exporting the brightness data of all stars for all frames to a single text file. It is possible to import the data to the Find variables tool later or process the file in an external program.

To export the data to a file, click on the Save data button on the right side of the dialog. In the following dialog select a directory and enter the name of output file where the data shall be saved to. Press the Save button.

## Processing data from an external file

The “Find variables” tool is capable of reading the data from an external file. Such file can be created by the same tool from a set of reduced CCD frames (see section Exporting data) or by an external program.

To import the data from a file, click on the :menuselection :Tools –> Find variables item in the main menu. It the following dialog, check the appropriate option and enter the path to the data file into the following edit box. Confirm the dialog by OK button.

Find variables - importing data from an external file.

## Known variable stars

If the source frames contain World Coordinate System (WCS) data, the software can show positions of known variables on the frame. You have to specify paths to the catalog files in the program settings (see Environment options (dialog)). For each catalog, the toobar on the right side of the window contains one check box that turns the catalog on and off. By clicking on the icon, a standard color selection dialog appears.

See also

Find variables (dialog), Environment options (dialog).