# Checking the telescope mount

A track curve is a graph of spatial offset of CCD frames, as a function of time. Such curve is used to monitor the stability and precision of telescope mount and its clock drive.

You can use the C-Munipack software to make a track curve from a set of CCD frames of a star field. As a result of the matching step during the reduction of input frames, an offset relative to a reference file in axes X and Y are stored to photometry files. The track curve tools uses this information to make a graph of offset in X and Y axis respectively, as a function of time.

## How to make a track curve

1. Process source CCD frames by normal way of reduction till star matching.

2. In the Plot menu, select the Track curve item. A new dialog window with a graph appears. The Julian date is on the horizontal axis of the graph and the offsets in pixels are on its vertical axis.

The graph consists of two data columns:

- OFFSETX - offset in horizontal direction, positive values mean the shift to the right, negative to the left.

- OFFSETY - offset in vertical direction, positive values mean the shift to the bottom, negative to the top.

The track curve

The track curve shows the periodic error of the telescope mount. The periodic error is caused by eccentricity of a tooth wheel and demonstrates itself as a sinusoidal signal in the track curve. Note that several superimposed sinusoidal signals are present on the picture, each with different period and amplitude. By finding the period of the signal, you can tell which tooth well is eccentric.

See also

Plot track curve (dialog)

## Trimming outliers from the curve

Is is possible to manually trim outlying observations from the curve. You can select an individual point by a right click, you can also select more than one point by pressing a Shift key and left mouse button and drawing a rectangle in the graph. Then, click the right mouse button on a point in the selection to open the context menu. There are two options: When you select the option delete from data set, the selected measurements are removed from the current curve, the data will be shown when you make another track curve or Rebuild the actual curve. The other option remove from project means that the frames corresponding to the selected measurements are removed permanently from the list of input files (see: Main application window) and such measurements won’t be included in any other output. It is not allowed to remove a reference frame.

See also

Track curve (dialog)