Commissioning the SALT High Resolution Spectrograph’s iodine cell

We report on commissioning the iodine absorption cell in the High Resolution Spectrograph (HRS) on the Southern African Large Telescope (SALT). The low-, medium- and high-resolution (LR, MR and HR) modes of this fibre-fed, dual-channel, white-pupil vacuum échelle spectrograph have been in use by the SALT consortium since 2014, but the high-stability (HS) mode requires exoplanet expertise not available in our community. The original commercial HRS iodine cell was unsuitable due to an excess of iodine so it was replaced with a suitable custom-built cell. This cell was characterised at high signal-to-noise, at a resolution of 106, using the Fourier Transform Spectrometer at the National Institute of Standards and Technology before incorporation into the HRS HS bench. A combination of calibration frames and on-sky data were then used to produce an HRS-specific version of an IDL software package that derives precision radial velocities (PRVs) from spectra taken through an iodine cell. Bright stars with highly stable RVs observed during a short engineering campaign in May 2018 demonstrate that SALT HRS is currently capable of delivering Doppler precision of 4-7m/s.

[1]  Mark Clampin,et al.  Transiting Exoplanet Survey Satellite (TESS) , 2014, Astronomical Telescopes and Instrumentation.

[2]  C. G. Tinney,et al.  Catalog of nearby exoplanets , 2006 .

[3]  Darragh O'Donoghue.  Correction of spherical aberration in the Southern African Large Telescope (SALT) , 2000, Astronomical Telescopes and Instrumentation.

[4]  R. P. Butler,et al.  The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey , 2017, 1702.03571.

[5]  Steven S. Vogt.  The Lick Observatory Hamilton Echelle Spectrometer , 1988 .

[6]  Ockert J. Strydom,et al.  A happy conclusion to the SALT image quality saga , 2012, Other Conferences.

[7]  Ockert J. Strydom,et al.  Saving SALT: repairs to the spherical aberration corrector of the Southern African Large Telescope (SALT) , 2010, Astronomical Telescopes + Instrumentation.

[8]  R. P. Butler,et al.  PRECISION RADIAL VELOCITIES WITH AN IODINE ABSORPTION CELL , 1992 .

[9]  David A. H. Buckley,et al.  Design of the Southern African Large Telescope (SALT) , 2000, Astronomical Telescopes and Instrumentation.

[10]  J. Schmoll,et al.  The SALT HRS spectrograph: final design, instrument capabilities, and operational modes , 2010, Astronomical Telescopes + Instrumentation.

[11]  David A. H. Buckley,et al.  Southern African Large Telescope (SALT) project progress and status after four years , 2004, SPIE Astronomical Telescopes + Instrumentation.

[12]  Anja Schroeder,et al.  Data reductions and data quality for the high resolution spectrograph on the Southern African Large Telescope , 2016, Astronomical Telescopes + Instrumentation.

[13]  P. A. Charles,et al.  First science with the Southern African Large Telescope: peering at the accreting polar caps of the eclipsing polar SDSS J015543.40+002807.2 , 2006 .

[14]  Ray M. Sharples,et al.  Performance of the Southern African Large Telescope (SALT) High Resolution Spectrograph (HRS) , 2014, Astronomical Telescopes and Instrumentation.

[15]  William H. Press,et al.  Numerical recipes , 1990 .

[16]  Jian Swiegers,et al.  The optical design of the Southern African Large Telescope , 2003, SPIE Astronomical Telescopes + Instrumentation.

[17]  R. P. Butler,et al.  ATTAINING DOPPLER PRECISION OF 3 M S-1 , 1996 .

[18]  Debra A. Fischer,et al.  THE TWENTY-FIVE YEAR LICK PLANET SEARCH , 2013, 1310.7315.