We describe the software architecture of the Local Control Units (LCU) being deployed as part of the Intelligent Observatory project of the South African Astronomical Observatory. This is an integrated system for scheduling and controlling observations across several telescopes and instruments. As part of this, each telescope and its associated instruments fall under the control of an LCU. The LCU interfaces with the observatory-wide scheduler, executing observations as requested. It also monitors observing conditions and shuts down the telescope if necessary. The software is layered, modular and distributed, and allows remote and robotic control of the various instruments and telescopes.
The Southern African Large Telescope (SALT) is developing precision radial velocity capability for its high-resolution spectrograph (HRS). The instrument's high-stability (HS) mode includes a fibre double scrambler and makes provision for simultaneous thorium-argon (ThAr) injection into the calibration fibre. Given the limitations associated with ThAr lamps, as well as the cost and complexity of turn-key commercial laser frequency combs (LFCs), we are in the process of designing and building a bespoke LFC for the Red channel of the HRS (555-890 nm). At a later stage we plan to extend the wavelength range of the LFC to include parts of the blue channel (370-555 nm) as well. A data reduction pipeline capable of delivering precision radial velocity results for the HS mode is also currently under development. We aim to have the LFC and PRV pipeline available for science operations in early 2024.
The Hydrogen Intensity and Real-time Analysis Experiment (HIRAX) is a radio interferometer array currently in development, with an initial 256-element array to be deployed at the South African Radio Astronomy Observatory Square Kilometer Array site in South Africa. Each of the 6 m, f / 0.23 dishes will be instrumented with dual-polarization feeds operating over a frequency range of 400 to 800 MHz. Through intensity mapping of the 21 cm emission line of neutral hydrogen, HIRAX will provide a cosmological survey of the distribution of large-scale structure over the redshift range of 0.775 < z < 2.55 over ∼15,000 square degrees of the southern sky. The statistical power of such a survey is sufficient to produce ∼7 % constraints on the dark energy equation of state parameter when combined with measurements from the Planck satellite. Additionally, HIRAX will provide a highly competitive platform for radio transient and HI absorber science while enabling a multitude of cross-correlation studies. We describe the science goals of the experiment, overview of the design and status of the subcomponents of the telescope system, and describe the expected performance of the initial 256-element array as well as the planned future expansion to the final, 1024-element array.
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.
We present an overview of the Intelligent Observatory (IO) and the architecture used at the South African Astronomical Observatory (SAAO) to develop instrument and telescope control and monitoring software. The IO aims to link and coordinate the usage of the SAAO telescopes and instruments for optimal efficiency. This will entail a Central Control System (CCS) selecting appropriate instruments and telescopes and controlling observations on these. This requires interoperable instrument and telescope control software. The SAAO software architecture is flexible, allows multiple user interfaces, and supports remote control and monitoring of both telescope and instrument through a web browser. Furthermore, the architecture allows an external agent (such as the IO CCS) simultaneous control of both instruments and telescopes.
To synchronise the elements of a radio interferometer array, a phase stable reference frequency from a central clock is disseminated to the different elements of array. The reference frequency is modulated onto an optical carrier and transported over optical fibre over a distance of up to 12 km. For radio interferometric efficiency, the propagation delay of the transferred reference frequency is required to be stable to less than 3 picoseconds (ps) over 20 minutes. To enable this, the optical fibre transmission line is thermally shielded to minimise length changes due to thermal expansion and contraction on the optical fibre. A test setup and procedure, that measures propagation delay changes to the required accuracy and precision, is required to verify the efficiency of the thermal shielding on the installed optical fibre. This paper describes a method using photonic and radio frequency (RF) components together with an RF vector network analyser (VNA) and post-processing to measure changes in propagation delay on the optical fibre link to sub-picosecond levels. The measurement system has been tested to a stability of < 200 femtoseconds (fs) and a resolution of < 10 fs.
Tim Gibbon, Enoch K. Rotich Kipnoo, Romeo R. G. Gamatham, Andrew W. Leitch, Renier Siebrits, Roufurd Julie, Sias Malan, Warnich Rust, Francois Kapp, Thondikulam Venkatasubramani, Bruce Wallace, Adriaan Peens-Hough, Paul Herselman
Scientific curiosity to probe the nature of the universe is pushing the boundaries of big data transport and computing for radio telescopes. MeerKAT, the South African precursor to Square Kilometre Array, has 64 antennas separated by up to 12 km. By 2018, each antenna will stream up to 160 Gbps over optical fiber to a central computing engine. The antenna digitizers require highly accurate clock signals distributed with high stability. This paper outlines requirements and key design aspects of the MeerKAT network with timing reference overlay. Fieldwork results are presented into the impact of birefringence and polarization fluctuations on clock stability.
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