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Latest update of this document: October 18th 2006These pages are intended to provide up to date information on the status of the SOAR telescope, its instrumentation, and mode of operation. We hope to update the information once a month or when important news is available.
Telescope status:Since the dedication ceremony in April 2004, the SOAR team has been busily preparing the telescope and its instruments for science operation. SOAR has an active optics system (AOS) that uses 120 movable axial supports to maintain the figure of the primary mirror (M1) at all times and 6 lateral supports that take up the weight of the M1 as the telescope elevation changes. The Calibration Wave Front Sensor (CWFS) is used to measure the wave front delivered by the telescope and adjust the forces applied to the axial supports, allowing us to produce seeing limited images with SOAR. The tertiary mirror (M3) is equipped with a tip-tilt control unit and can be used at up to 50Hz to improve the seeing for all mounted instruments. During this work we found that the 6 fixed lateral links rigidly couple the M1 to the steel structure of the mirror cell, thereby transferring all movements due to elevation, azimuth and temperature changes to the mirror, resulting in deformations that cause optical aberrations, mainly astigmatism. The elevation and azimuth movements produce predictable M1 deformations and we have accurately modeled these so that we can correct them by setting the M1 figure using a bright star near the science field and then applying the look-up table generated by the model, delivering seeing limited images. The random temperature variations and some hysteresis, however, cannot be modeled and this means that after a variable amount of time, typically an hour or so, the M1 has to be reset. All of this results in a somewhat reduced observing efficiency due to the typically 5-20 minute bright star plus CWFS set-up time for the M1. The permanent solution to this problem is to replace the lateral links with actively controlled units. This work has now been done and all six links are now aligned and under computer control. Initial testing has shown that the image quality is maintained equal to the site seeing as gathered fron the local seeing monitor over periods of many hours without resetting the mirror figure. Seeing has not been so good to be able to check the ultimate image quality yet but we are confident that we can reach the design specification of the telescope. Rounds images of 0.5" have been obtained. There is a small amount of residual astigmatism, probably caused by the hysteresis in the axial supports of the mirror and we are looking into how to eliminate this. In any case, the long-term plan is to have SOAR operate in closed loop mode using permanent wavefront sensing so that all aberrations are always corrected in real time and the mirror is always optimally shaped. We hope to use the novel "donut" method and tests are under way to prepare for, develop, and implement this sytem. Another improvement we recently made to SOAR is an upgrade of the telescope azimuth encoder system and we are continuing with this upgrade, extending it to the elevation and Nasmyth encoders. At some opportune time during early 2007 the mirror will be re-aluminized and we will make use of that time to make improvements to the dome shutter and windscreen mechanisms, and other improvements that are better and safer done with the mirror out of the telescope. Measurements of the sky background and sky flat fields -taken with the SOI- have shown that the telescope still has some baffling problems (no pun intended). The sky background is too high and flatfields show dependence on the SOI rotator position. Tests with a flat illumination directly in front of the SOI have shown that the problem is in the telescope, not in the instrument. Zemax modeling of the present baffling system uncovered some problems that can be solved with improved baffling on M2 and M3. Preliminary tests using an improvised baffle on top of the M3 sky baffle indicate that the flat fields are much improved by stopping down this aperture. We have now installed the new M2 baffle which has light stopping annuli and have modified the M3 baffle. We are confident that with these changes the telescope will be properly baffled and both the sky and flat fields will be normal. Tests are under way to show this is indeed the case. Related is the fact that the white spot, used for taking dome flatfields, has some specular reflectivity and is not bright enough in U and other very blue filters to be able to take flats in a reasonable time. We have identified and purchased a special white paint that shows very good Lambertian scattering and virtually no specular reflectivity. We will apply this paint to the white spot and thus improve its "flatness". We will also experiment with adding barium sulphate to this paint in an attempt to improve the blue scattering efficiency. Operation and observing:SOAR is mainly operated using remote or service observing for the partner institutions and via classical observing for NOAO approved programs. To optimize your observing with SOAR:Since the lateral links have been activated, it is no longer necessary to re-set the mirror after every telescope slew or after long exposures. This means fewer overheads and more efficient observing. At the beginning of the night the mirror is set and only if the seeing is very good (say <0.5" or so) would it be necessary to reset the mirror after a slew or several hours on a field. Once we have the closed loop operation, this will not be necessary either. Remote observing with SOAR:Recently remote observing has started at SOAR. Remote Observing at present means that the observer interacts with the telescope operators through a standard videocon; uses a VNC connection to operate the instrument -for now the SOAR Optical Imager (SOI) and OSIRIS can be used in this mode- and obtains the data automatically in his computer at the remote site within 5-20 seconds after readout, depending on his local internet bandwidth. Note that the data transfer uses BBFTP, a clever version of FTP which is based on SSH (so is safe and not really FTP at all!) and uses multiple TCP streams to transfer the data, thereby increasing the speed a lot. CCD frames from the SOI in the usual 2x2 binned format are about 8.5 MBytes each and transfer typically to both MSU and UNC in 5-10 seconds over internet 2. For much slower links, the time might be around 20s per frame. The system is set up in such a way that two or more observers can use it simultaneously. There now are directories set up for Brazil, NOAO, MSU, UNC, and "Other" where the data from the SOI goes when specified. If an observer forgets to start the transfer program (called postman) all files that have not been transferred yet will be sent but no file will be sent twice, so overwriting files is nearly impossible. To make this operatre smoothly a passwordless mode must be used and this depends on the local set-up at each remote site. Other major SOAR users could think about implementing this mode of operation too. Questions or suggestions about remote observing with the SOAR are welcome.
Tracking moving objects:Recently we have implemented the facility to observe and tracking moving objects with SOAR. The autoguider can be used during such use and the tip-tilt guider also functions. This brings asteroids, comets etc. within reach of SOAR. Required are the differential tracking rates in RA and Dec.. Instruments in use at SOAR:For detailed information on any of the SOAR instruments go to: http://www.soartelescope.org/release/06observing/eng_observing/instruments/main_instruments.html and click on the desired instrument in the picture. SOAR Optical Imager (SOI)The SOI is an imager with two EEV 2x4k CCDs and has a FoV of 5.5’ square with 77mas pixels. The instrument has a linear ADC to correct the differential refraction of the atmosphere. The SOI has been commissioned to the point that the instrument is in regular use at the telescope. Work on the instrument control GUI is ongoing and we hope to change over to the full observers version from the engineering GUI that we have used to date. The only item that is still to be fully commissioned is the linear ADC. Best image so far is an unguided Ha exposure of 200s that shows a FWHM on stellar images of 0.58”. We have recently installed more internall baffles and shielding in the SOI. This has resulted in reduced stary light and cleaner images. The power supplies for the Leach controllers have been moved and this has allowed us to remove several cables from the cable wrap, making it lighter and less rigid, improving tracking. The latest addition is an optically absorbing cover on the linear ADC track which showed some reflected light in pinhole camera images we took to look for scattered light in the telescope and instrument. The scattered light from the track has been reduced by about an order of magnitude. In the near future, the twin 2kx4k CCDs of the SOI may be exchanged for a single 4kx4k Fairchild chip. This will have the advantage of not having a gap between the CCDs and easier data handling. The QE will be slightly higher but the read-out noise too.
Ohio State Infra-Red Imager and Spectrograph (OSIRIS)OSIRIS is the near-IR camera and spectrograph that has been used at the 4m Blanco telescope on Cerro Tololo and is now available at SOAR. OSIRIS is fully commissioned and in routine operation. The f/7 mode works fine but the f/3 wide-field mode shows distortion at the outer parts of the FoV. The problem is under investigation. We have measured the detailed distortion map and this has shown that the alignment is still not perfect. By adjusting the beamsplitter in the IR-ISB we hope to improve the quality of the f/3 mode images. We installed a new Lyot stop in the instrument which improves transmission by about 15% but it's outer edge "sees" the new primary mirror baffle. This will be replaced by a correctly shaped mask during the next few weeks. In the f/7 mode the best image taken in the K band had a FWHM of 0.35”, with a site seeing of 0.29”, showing that the SOAR optics contributes only 0.2” to this value. Information on OSIRIS is at: http://www.ctio.noao.edu/instruments/ir_instruments/osiris2soar/index.html
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