SOAR - Current Status

This document, prepared from reports received from the Director of SOAR, Steve Heathcote and the SAC Chair, Bob Blum, illustrates the current status of the telescope/instruments to March 2007. SOAR users who wish to submitt proposals for 2007B should read it carefully in order to evaluate present the capabilities of the telescope.

SOI

Further testing has confirms that, following the lens repair, SOI is now capable of doing accurate (aperture) photometry, and serves to characterize its performance:

Additional photometric grid tests confirm that there is now no dependence of sensitivity with position within the FOV beyond that registered in flat fields to less than 0.8%
Ratios of both dome flats and sky flats taken at different angles are flat to better than 1% (most cases better than 0.5%). Ratios of sky flats to dome flats are also flat to within better than 0.7% (most of which is accounted for by a few dust spots on the CCD and inside surface of the dewar window) There is still some variation in the structure of dome flats with rotator angle but this is <0.5% in I and <0.3% in B. Some of this is probably due to non-uniform illumination of the white spot, however, there is likely still some small contribution from residual scattered light (see next bullet).
Gradients of a few percent in the sky background were seen in fields close to the full moon such that it was illuminating parts of the telescope structure; these were not present when the same fields were observed with no moon. Likewise, it is still occasionally seen glints from very bright stars outside the FOV, which can be made to go away by slightly changing the telescope pointing. Opto-mechnical design of some additional on instrument baffles is under way.
Full photometric calibrations have now been obtained for the U,B,V,R,I filter set to check photmetric accuracy (0.021 mag RMS) and determine the transformations to the standard system. Similar data have been obtained for SLOAN u',g,r',i',z', but have yet to be reduced. Likewise spectrophotometric standards, and a calibrated region of the Orion nebula have been observed through the narrow band filters, to determine the sensitivity for emission line work, however again the data remain to be reduced.
The U,B,V,R,I sensitivity data has been incorporated in the exposure time calculator at http://www.noao.edu/scope/ccdtime Other filters will be added as the measurements are reduced.
Fringe frames have been obtained for I, i' and z'. As determined previously the fringing can be corrected by scaling and subtracting the fringe frames (see http://www.soartelescope.org/release/01welcome/eng_welcome/maintext.php). No other filters (that we have tried) show detectable fringing.
In general the seeing measured on the images is comparable to or better than the site seeing. This includes a period of stable 0.5 arcsec site seeing during which 4 successive 900s guided exposures each show ~0.5" FWHM images.
Astrometric calibrations have been obtained using one of the superMacho fields in the LMC. For the V-band a linear (2nd order polynomial) fit residuals are 0.02 arcsec in each axis (0.1 binned pixel), while for a 4th order fit they are 0.008 arcsec. Data has been obtained for the other filters to check for color dependant terms in the solution, but has yet to be reduced.
The superMacho data reduction pipeline is being modified to handle data from SOI. As well as allowing semi-automatic reduction of the data, the pipeline generates a lot of useful diagnostic data - for example the mean FWHM, elipticity for a large number of star in each image, which will help to monitor telescope performance on a systematic basis.

OSIRIS

Essentially commissioned and working ok. Ohio State did some recent computer upgrades which solve long standing issues that had some operational impact (mostly at startup). A new Lyot stop has been made and will be installed in May during telescope engineering. Some upgraded detector electronics boards may be installed by Ohio State in May. An analysis of the image quality of the f/3 camera (coarse pixels) coupled to the SOAR focal plane which is significantly curved shows that the astigmatic images are a feature (with perhaps some small tilt getting in somewhere). Observers should not plan on using the f/3 camera. In addition:

Full photometric calibrations have been obtained for the J,H,K and Ks filters to check photometric performance and verify the transformation to the standard system. The resulting sensitivity data has been incorporated in the imaging exposure time calculator mentioned above. Spectroscopic data is also being collected on standard stars to serve as the basis for a spectroscopic mode exposure time calculator - the current calculator is known to be very optimistic.
K band images as good as 0.3" have been obtained on nights of good seeing (record so far 0.28" at K, 0.49" DIMM at 500nm).
PR images of near IR targets are also being taken as opportunities present themselves.
As a result of high humidity and low temperatures the window of the OSIRIS dewar and the Tip-Tilt guide camera have fogged up on a couple of occasions. It has been enabled the dry Nitrogen flushing system for the OSIRIS window which appears to prevent this problem. Something similar for the guide cameras are in plan of being implementing.

Mirror Washing

All three mirrors were washed with water on 9th March. Measurements of photometric standards taken the nights before and after the wash show an increase in throughput by a factor of 1.66 in U, 1.43 in B, 1.3 in V and 1.17 in I. This is consistent with reflectometer measurements which show an increase in reflectivity of each mirror from ~81% to 88% at 470nm. It is about 5 months since the mirrors were last washed, significantly longer than the scheduled 3 months. We will be monitoring both photometric zero points, and reflectometer measurements to determine if an even shorter period between washes is required. The freshly aluminized primary mirror had a reflectivity of ~90% at 470nm. However, the post wash reflectivity after the two preceding washes is comparable to that achieved this time, so it does not appear that the post-wash reflectivity is decreasing systematically with time.