Towards precision radial velocity science with SALT’s High-Resolution Spectrograph

Lisa A. Crause; Alexei Kniazev; R. Paul Butler; Rudi Kuhn; Arpita Roy; Keith Browne; Alrin Christians; Etienne Simon; Anthony Koeslag; Jonathan Love; Roufurd Julie

doi:10.1117/12.2562004

13 December 2020 Towards precision radial velocity science with SALT’s High-Resolution Spectrograph

Lisa A. Crause, Alexei Kniazev, R. Paul Butler, Rudi Kuhn, Arpita Roy, Keith Browne, Alrin Christians, Etienne Simon, Anthony Koeslag, Jonathan Love, Roufurd Julie

Author Affiliations +

Proceedings Volume 11447, Ground-based and Airborne Instrumentation for Astronomy VIII; 1144746 (2020) https://doi.org/10.1117/12.2562004
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Conference Poster

Abstract

We describe efforts to equip the Southern African Large Telescope (SALT) for precision radial velocity (PRV) work. Our current focus is on commissioning the high-stability (HS) mode of the High-Resolution Spectrograph (HRS), the mode intended to support exoplanet science. After replacing the original commercial iodine cell with a custom-built, precisely characterised one and following established best practice in terms of observing strategy and data reduction, this system now delivers 3-4 m/s radial velocity stability on 5th and 6th magnitude stars. Unfortunately, the throughput is compromised by the HRS dichroic split being at 555 nm (i.e. roughly midway through the 100 nm span of the iodine absorption spectrum). Furthermore, SALT’s fixed elevation axis limits the exposure time available for a given target and hence the depth and/or precision achievable with the iodine cell. The HS mode’s simultaneous ThAr option uses the full 370–890 nm passband of the HRS and does not suffer gas cell absorption losses, so it may be more suitable for exoplanet work. The first step was to quantify the internal stability of the spectrograph, which requires simultaneously injecting arc light into the object and calibration fibres. The HS mode’s optical feed was modified accordingly, stability test runs were conducted and the necessary analysis tools were developed. The initial stability test yielded encouraging results and though more testing is still to be done, SAL a laser frequency comb to support the development of HRS PRV capability.

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Lisa A. Crause, Alexei Kniazev, R. Paul Butler, Rudi Kuhn, Arpita Roy, Keith Browne, Alrin Christians, Etienne Simon, Anthony Koeslag, Jonathan Love, and Roufurd Julie "Towards precision radial velocity science with SALT’s High-Resolution Spectrograph", Proc. SPIE 11447, Ground-based and Airborne Instrumentation for Astronomy VIII, 1144746 (13 December 2020); https://doi.org/10.1117/12.2562004

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