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.
SALT, in conjunction with the SAAO, has developed and implemented an integrated safety management system. This system complies with the South African Occupational Health and Safety Act. Safety is a standard and very important consideration when the Failure Effects, Maintenance and Critical Analysis are done for current and new operations, designs, sub-system and instruments. Employee health needs special attention since the observatory is located 250 km away from proper hospitals and medical specialists. Since its full implementation, hardly any work-related safety incidents or injuries occurred. This paper details the integrated safety system and its various elements.
A threat to all telescopes is possible condensation on its instruments and primary mirror during high humidity conditions. Using too conservative delta dew-point control limits for telescope closure can reduce valuable observing time. SALT recently changed its operational procedure in high humidity conditions to gain as much additional observing time as possible, without subjecting the telescope and its instruments, to the harmful effects of condensation. This paper will describe how the SALT Operations team managed to safely reduce the delta dew-point control limit and thereby gaining valuable observation time without investing significant amounts of money.
The Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) includes a Fabry-Pérot system that provides spectroscopic imaging over the 8 arcmin diameter science field of view, covering the wavelength range 430-860 nm with spectral resolutions ranging from 300 to10000 in four resolution modes. The higher resolution modes require the simultaneous use of two etalons. We discuss the complications encountered in implementing the dual etalon modes, the mechanical and operational solutions that have been devised, and the first science verification results. We also describe an efficient method for adjusting the parallelism of etalons in situ, and the use of the dual etalon system to determine the transmission of the individual etalons. The new dual etalon system was commissioned in late 2015 and is now producing useful scientific observations.