The Keck Planet Finder (KPF) is an optical fiber-fed stabilized spectrograph at Keck with the goal of discovering and characterizing the masses of rocky exoplanets through precision radial velocity measurements (PRV). One challenge for PRV measurements is stellar activity that can introduce noise and sometimes even exoplanet-like signals. Monitoring the canonical Calcium II H&K lines is how many instruments combat stellar noise. Any RV signal that correlates with these lines, which trace stellar activity, is suspect. KPF ranges from 450 nm to 850 nm and pushing optical coatings down to the ~390 nm wavelengths of Ca II H&K would have sacrificed overall performance. Therefore, it was decided to have a separate UV spectrometer to monitor these lines.

This separate R~14,000 H&K spectrometer is a double pass, cross dispersed echelle spectrograph. It observes concurrently with KPF and was designed to work under similar exposure times. The instrument is pretty small (2ft x 3ft) and sits vertically in a rack in the Keck I AO electronics room. By being close to the KPF fiber injection unit, the losses through the fiber run, which are worse at blue wavelengths, can be kept to a minimum. I joined this project after its preliminary design and took over the optical design finalizing the lens design, performing stray light and ghost analyses, as well as performing the optical alignment, installation, and commissioning. It was a fun way to get well-acquainted with Zemax.

A close up of the fiber block in the Ca II H&K spectrometer for KPF.