ST-6 Data Collection

Like the Lynxx and the ST-4, this camera has a preferred orientation with the telescope (see figure 4). The software is located in the directory D:CCDSST-6. The filter wheel can be started here with the command FW. Once the camera is attached to the telescope, and the several cables are set, the ST-6 software is started with the executable CCDOPS. The link between the computer and the camera will be established. The cooler can be set to a specific temperature. This is done by going to the camera menu, and selecting setup. The temperature control is contained in this menu. Mt. Stony Brook operates at a camera temperature of -35.00 Celsius.

Before taking images, the camera and the telescope have to be calibrated. This process is similar in operation to the calibration with the ST-4. A star is placed near the center of the field, and the camera moves the drive to detect the times for each relay. These times change depending on the region of the sky that is being observed. After moving to a new target, the calibration should be done again. The commands for calibration are under the trackmenu.

Now the telescope is ready for imaging. The focus command allows the operator to find the target and then move the telescope to center the object. The focus mode is preferable to find a target since there is an option for a low resolution readout. This produces poor quality images, but they are readout faster than a normal image. Another advantage to the focus command is the ability to move the telescope. The a, s, w, and z keys will move the telescope in the -X, +X, -Y, and +Y directions respectively. This feature will only work in the focus mode.

There are two ways to collect images with the ST-6. The first is using the grab command. This will take an image for the requested time, and then download the image. This is the normal CCD camera image mode. The second method is the track and accumulate mode. In this mode, the camera takes several short images, and then adds them together to give an image that is comparable to the same total time image as taken by the grab function. The advantage of the second method is clear when using a telescope that cannot track well. At Mt. Stony Brook, a 60 second image under grab would have star trails throughout it due to the periodic guiding error (see figure 3). A 60-second track and accumulate image contains fairly round stars. The camera calculates how far the star has moved from the first image and will move the telescope to compensate for the movement that occurred in between exposures. This is the nominal data collection method for the equipment at Mt. Stony Brook.

Another feature about the ST-6 is the dark frames can be removed from the image as the data is collected. Unlike the Lynxx, which creates a dark frame by taking an exposure of the shutter and then removing the bias level, the darks from the ST-6 include the bias level. In lieu of a shutter, the ST-6 has a vane that falls into place to collect a dark frame. When an image is taken, the electronics act as a shutter.

To save images under the ST-6 software, the file menu is used. The default filepath is usually D:CCDSST-6. This should be changed to F:. The filename can be eight characters long, and the operator has a choice of formats. The formats will be discussed in a later section. One important point: save the tracklist. After each track and accumulate image is taken, a tracklist is created. This records how far the telescope was moved each frame of the image. This must be saved to calculate the offsets needed for the flat corrections. The program prompts you for this after the track and accumulate sequence is taken.