James O'Connor

Polarized QPOs from the INTEGRAL polar IGRJ14536-5522 (=Swift J1453.4-5524)

We report optical spectroscopy and high-speed photometry and polarimetry of the INTEGRAL source IGRJ14536-5522 (=Swift J1453.4-5524). The photometry, polarimetry and spectroscopy are modulated on an orbital period of 3.1564(1) h. Orbital circularly polarized modulations are seen from ∼0 to ∼−18 per cent, unambiguously identifying IGRJ14536-5522 as a polar. The negative circular polarization is seen over ∼95 per cent of the orbit, which is consistent (as viewed from the Earth) with a single-pole accretor. We estimate some of the system parameters by modelling the polarimetric observations. Some of the high-speed photometric data show modulations that are consistent with quasi-periodic oscillations (QPOs) on the order of 5–6 min. Furthermore, for the first time, we detect the (5–6) min QPOs in the circular polarimetry. We discuss the possible origins of these QPOs. In addition, we note that the source undergoes frequent changes between different accretion states. We also include details of HIgh-speed Photo-POlarimeter (HIPPO), a new high-speed photo-polarimeter, used for some of our observations. This instrument is capable of high-speed, multi-filtered, simultaneous all-Stokes observations. It is therefore ideal for investigating rapidly varying astronomical sources such as magnetic cataclysmic variables.

SALTICAM:

The Southern African Large Telescope (SALT) is a 10-m class telescope presently under construction at Sutherland in South Africa. It is designed along the lines of the Hobby-Eberly Telescope (HET) at McDonald Observatory in West Texas. SALTICAM will be the Acquisition Camera and simple Science Imager (ACSI) for this telescope. It will also function as the Verification Instrument (VI) to check the performance of the telescope during commissioning. In VI mode, SALTICAM will comprise a filter unit, shutter and cryostat with a 2x1 mosaic of 2k x 4k x 15 micron pixel CCDs. It will be mounted at the f/4.2 corrected prime focus of the telescope. In ACSI mode it will be fed by a folding flat located close to the exit pupil of the telescope. ACSI mode will have the same functional components as VI mode but it will in addition be garnished with focal conversion lenses to re-image the corrected prime focal plane at f/2. The lenses will be made from UV transmitting crystals as the wavelength range for which the instrument is designed will span 320 to 950 nm. In addition to acting as Verification Instrument and Acquisition Camera, SALTICAM will perform simple science imaging in support of other instruments, but will also have a high time resolution capability which is not widely available on large telescopes. This paper will describe the design of the instrument, emphasizing features of particular interest.

0.5M acquisition camera: every big telescope should have one

The Prime Focus Imaging Spectrograph (PFIS) is a first light instrument for the Southern African Large Telescope (SALT). PFIS is a versatile instrument designed to operate in a number of scientific modes by utilizing volume phase holographic gratings, Fabry-Perot etalons, and polarimetric optics, which are manipulated in and out of the beam using various placement mechanisms. The instrument is mounted at the prime focus 15m above the primary mirror and tilted at 37°. This remote placement and the need for 240° of rotation about the optical axis raises important design issues with mass, flexure and access. The instrument structure provides the interface to the telescope Prime Focus Instrument Platform (PFIP) as well as support points for all the optics, mechanisms and electrical equipment. The structure is a welded open truss of hollow, square-section Invar beams. The open truss provides the highest stiffness to weight ratio and minimizes the effect of wind loading, while the use of Invar negates the effects of thermal expansion. It has been designed using finite element analysis in conjunction with an optical tolerance analysis of the optics nodes to minimize effective image motion under the varying gravity load. The fundamentals of the design of the structure to minimize the flexure and its effect on image motion, the motivation for using the open Invar truss structure, and the design of the remotely operated mechanisms are discussed. In 2005 PFIS was installed and commissioned on SALT in South Africa. Included in this text are some of the results and experiences of taking PFIS into operation.

The prime focus imaging spectrograph for the Southern African Large Telescope: structural and mechanical design and commissioning

A novel speed bump energy harvester (SBH) is designed, developed, and tested to harness electricity energy from impulsion excitation when a vehicle passes through a speed bump. The challenge to harness large-scale impulse energy in short time is solved by the proposed unique energy conversion mechanism of the mechanical motion rectifier (MMR). Analogous to an electrical voltage rectifier, the MMR can directly convert irregular impulse into unidirectional rotation of the generator and maintain the high-speed rotation by disconnecting with the low-speed driving. With this motion mechanism, more energy from both downward and upward impulses can be harvested, which can produce three to four times more electricity than the conventional harvester without MMR mechanism. A prototype is tested using a passenger car. Up to 1270-W peak electrical power can be harvested from an electromagnetic generator when one-wheel axle of vehicle passes through the SBH at low speed. Moreover, in order to reveal the energy conversion mechanism of MMR and the interaction between the vehicle and SBH, a dynamic mechanical-electrical model of the MMR and a four-degree-of-freedom two-axle vehicle are established. Experimental measurement and numerical analysis demonstrate the effectiveness of the energy conversion mechanism of the MMR. Vehicle dynamics assessments under the impulse excitation show that the harvester can reduce the shock transmitted to the vehicle and improve vehicle comfort as well. The capability in generating the large-scale electrical power by the proposed SBH demonstrates the potential to power road-side electrical devices for smart transportation network.

An Electromagnetic Speed Bump Energy Harvester and Its Interactions With Vehicles

The construction of the Southern African Large Telescope (SALT) was largely completed by the end of 2005. At the beginning of 2006, it was realized that the telescopes image quality suffered from optical aberrations, chiefly a focus gradient across the focal plane, but also accompanied by astigmatism and higher order aberrations. In the previous conference in this series, a paper was presented describing the optical system engineering investigation which had been conducted to diagnose the problem. This investigation exonerated the primary mirror as the cause, as well as the science instruments, and was isolated to the interface between the telescope and a major optical sub-system, the spherical aberration corrector (SAC). This is a complex sub-system of four aspheric mirrors which corrects the spherical aberration of the 11-m primary mirror. In the last two years, a solution to this problem was developed which involved removing the SAC from the telescope, installing a modification of the SAC/telescope interface, re-aligning and testing the four SAC mirrors and re-installation on the telescope. This paper describes the plan, discusses the details and shows progress to date and the current status.

Saving SALT: repairs to the spherical aberration corrector of the Southern African Large Telescope (SALT)

Speed bumps are commonly used to control the traffic speed and to ensure the safety of pedestrians. This paper proposes a novel speed bump energy harvester (SBEH), which can generate large-scale electrical energy up to several hundred watts when the vehicle drives on it. A unique design of the motion mechanism allows the up-and-down pulse motion to drive the generator into unidirectional rotation, yielding time times more energy than the traditional design. Along with the validation of energy harvesting, this paper also addresses the advantages of this motion mechanism over the traditional design, using physical modeling and simulation. Up to 200 watts electrical peak power in one phase of three-phase generator during in-field test can be regenerated when a sedan passage car passes through the SBEH prototype at 2 km/h.

Design, Modeling and Test of a Novel Speed Bump Energy Harvester

Construction of the Southern African Large Telescope (SALT) was largely completed by the end of 2005 and since then it has been in intensive commissioning. This has now almost been completed except for the telescopes image quality which shows optical aberrations, chiefly a focus gradient across the focal plane, along with astigmatism and other less significant aberrations. This paper describes the optical systems engineering investigation that has been conducted since early 2006 to diagnose the problem. A rigorous approach has been followed which has entailed breaking down the system into the major sub-systems and subjecting them to testing on an individual basis. Significant progress has been achieved with many components of the optical system shown to be operating correctly. The fault has been isolated to a major optical sub-system. We present the results obtained so far, and discuss what remains to be done.

The image quality of the Southern African Large Telescope (SALT)

We discuss the use of a Faro Arm - a portable coordinate measuring machine - in the re-alignment and testing of the Southern African Large Telescopes Spherical Aberration Corrector. In pushing this versatile tool to its limits, we have arrived at a better understanding of its true capabilities and developed ways to compensate for some of its weaknesses. It is possible to achieve excellent results (~5 microns) when making relative measurements and keeping the Arms orientation relatively constant. The Faro is also extremely useful in providing live feedback while making fine adjustments. However, single measurements of the same position are considerably less reliable (~50 microns) when the Arm is operated in widely different orientations. If the latter is unavoidable, one may largely counteract this by taking continuous streams of measurements (1000 readings) for a given point while exercising the Arm as much as possible in order to average the encoder errors. Various other techniques and accessories that we have found useful, as well as some painful lessons, are described here and a few examples are given to demonstrate how we have used a Faro Arm in our challenging optical alignment project.

Use of a Faro Arm for optical alignment

SALT, the Southern African Large Telescope, is a 10-m class telescope presently under construction and designed along the lines of the Hobby-Eberly Telescope (HET) at McDonald Observatory in West Texas. The two first light instruments are a simple science imager, SALTICAM, which also doubles as the telescope acquisition camera, and a low resolution spectrometer, the Prime Focus Imaging Spectrograph (PFIS). The detector packages for both instruments, which are being supplied by the South African Astronomical Observatory, will have the capability of readout of a sub-array with a frequency of up to 10 Hz. This is not available on most 8-10 m class telescopes and enables deeper exploration of high-time resolution parameter space. This paper will describe general features of the detector packages, emphasizing the high speed capability, and also touching on the kind of science which is envisaged.

High-speed SALT instrument CCD detectors

Images obtained with the Southern African Large Telescope (SALT) during its commissioning phase showed degradation due to a large focus gradient and a variety of other optical aberrations. An extensive forensic investigation eventually traced the problem to the mechanical interface between the telescope and the secondary optics that form the Spherical Aberration Corrector (SAC). The SAC was brought down from the telescope in 2009 April, the problematic interface was replaced and the four corrector mirrors were optically tested and re-aligned. The surface figures of the SAC mirrors were confirmed to be within specification and a full system test following the re-alignment process yielded a RMS wavefront error of just 0.15 waves. The SAC was re-installed on the tracker in 2010 August and aligned with respect to the payload and primary mirror. Subsequent on-sky tests produced alarming results which were due to spurious signals being sent to the tracker by the auto-collimator, the instrument responsible for controlling the attitude of the SAC with respect to the primary mirror. Once this minor issue was resolved, we obtained uniform 1.1 arcsecond star images over the full 10 arcminute field of view of the telescope.