On-fiber guiding

As it is now, to keep a star on the fiber we use the telescope (auto)guiding to follow the star, but visual check the light reflected from the fiber head to see if the star moves out, manually correcting if needed. We have been looking at the option of doing direct on-fiber guiding, i.e., use the image from the fiber head to steer the telescope and keep the star in the fiber using software. An advantage of using such a system is that this would make sure that the star is maintained in the center of the fiber at all times, likely improving the radial-velocity stability.

A system to do on-fiber guiding is used at the Mercator telescope on La Palma for their HERMES high-resolution spectrograph, and a check of the system in action looks very promising. They use freely available Python ``pyguide'' routines, which could be implemented in our observing system for FIES. The image-analysis software in pyguide may also be used to automate the first step in acquiring a source in which a full-frame, direct image is used to select a target and move the telescope such that the light of the star is directed to the selected fiber.

The software also appears as a viable option for the NTE slit-guiding system.