Fiber scrambling for high-resolution spectrographs. I. Lick observatory

In this article, we report all results obtained with a fiber scrambler on the Hamilton spectrograph at Lick Observatory.We demonstrate an improvement in the stability of the instrumental profile using this fiber scrambler. Additionally, we present data obtained with a double scrambler that further improves the stability of the instrument by a factor 2. These results show that errors related to the coupling between the telescope and the spectrograph are the dominant source of instrumental profile variability at Lick Observatory. In particular, we show a strong correlation between instrumental profile variations and hour angle, most likely due to pointing-dependent illumination of the spectrograph optics.