External upgrades to improve the RV precision of the APOGEE Spectrographs

Wilson, John C.; Davidson, Jimmy W., Jr.; Bender, Chad; Dow, Peter; Nelson, Matt; Walters, Liam; Del Irving; Farr, Emily; Tuttle, Sarah; Nidever, David; De Lee, Nathan; Holtzman, Jon; Majewski, Steve; Fox, John; Harkins, Donald; Green, Louis; Eriksen, Jamey; Wagner, Ryan; Derwent, Mark; Jurgenson, Colby; Pogge, Rick; Wachter, Stefanie; Ramirez, Solange; Kolmeier, Juna; Evans, CJ; Bryant, JJ; Motohara, K
2022
GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY IX
DOI
10.1117/12.2630231
Several external hardware upgrades have been developed for the APOGEE Spectrographs as part of the Sloan Digital Sky Survey-V (SDSS-V) to improve their radial velocity (RV) precision from a floor of 100-200 m/sec to approx. 30 m/sec. The upgrades include: (1) Back Pressure Regulator (BPR) systems to stabilize the internal instrument LN2 tank boil-off pressure, lessening induced movement of the APOGEE optical bench; (2) Fabry-Perot Interferometer (FPI) calibration sources to improve wavelength calibration; and (3), the use of octagonal core fiber segments in the fiber train to improve radial scrambling. We discuss the fabrication, commissioning, and early performance of these upgrades.