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WIYN Achieves 0.45" Seeing (1Sep94)
(from NOAO HIGHLIGHTS!, NOAO Newsletter No. 39, 1 September 1994)

WIYN has become a telescope. The optics were installed in April and the first
"optical tests" occurred late one evening in April, as witnessed by a small
group of dedicated eyeballs. In the intervening months,the optics have been
collimated, the support systems tuned up, the primary mirror thermal controls
installed, and some remaining parts of the control system installed and
debugged. Progress in the quality of the images produced by the WIYN
telescope has been extraordinary, and the WIYN telescope is now routinely
producing the best images on Kitt Peak.


                            [Figure not included]

     Images of Jupiter obtained with the WIYN 3.5-m telescope.
     The "before impact" image (left) was obtained in 0.66 arcsec seeing.
     The post SL9 impact image was obtained in 1.35 arcsec seeing.

The main Project objectives over the last few months were to complete optics
installation, evaluate the system performance of the installed optics, tune
the active optics servo loops, continue supporting the installation of the
control system, and prepare the Observatory for facility instrumentation and
commissioning.

Optical system performance and tuning have been the main tasks since the
secondary and tertiary mirrors were installed in late April. Once the optics
were mechanically aligned, a cooled science grade STIS CCD was mounted at one
WIYN Nasmyth port and optical collimation was completed. With the assistance
of Claude Roddier (Hawaii), wave front curvature (WFC) mapping was then
initiated to tune the primary mirror support actuators. A more extensive WFC
mapping effort lead by Nick Roddier (NOAO) ultimately lead to the
construction of "open loop" lookup tables to control the primary mirror
shape, secondary tilt, and system focus as a function of elevation. These
initial look-up tables appear to be encouragingly stable and repeatable,
reflecting the stability of the WIYN active optics system. This stability
will be tested regularly over the next year, and the tables will be updated
as necessary.

Based on the analysis of WFC data, it was apparent that the primary and
secondary were well-matched, e.g. the total system spherical aberration could
be set to zero by spacing the two mirrors properly. To assess the secondary
mirror high frequency quality, high resolution, high signal-to-noise out of
focus stellar images were acquired with the secondary at its nominal position
and then with the secondary rotated 90 deg in its cell. The before and after
images were essentially identical, indicating that any residual high
frequency optical features are associated with the primary. These features
are quite small and should have no impact on the ultimate optical performance
of the WIYN. When compared to other telescopes tested in a similar manner by
the Roddiers, the WIYN optical system appears to be at least as good if not
better than any other 4-m class telescope in the world.

Concurrent with this optical work, the installation of the primary mirror
active thermal control system was completed. The thermal system has been
active during all subsequent night-time operations. It is quite common to
maintain the primary mirror temperature within +/- 0.2 deg C of the ambient
temperature all night long, starting shortly after sunset.

Since the end of these parallel efforts, it has been quite common to achieve
0.6-0.7 arcsec images at telescope elevations greater than 20x for short
(10-20 s) exposure times in R-band images using the current "open loop"
optical system look-up tables. Image quality is degraded at longer exposures
times due to poor telescope tracking. Poor tracking is not unexpected at this
time since the Project has not yet tuned the telescope pointing and tracking
parameters. Tuning telescope pointing and tracking will be the Project's main
activity during the next month. Once that is completed, longer duration
exposures will be acquired to assess image stability.


                            [Figure not included]

     Left: An early WIYN stellar image obtained with the secondary
     and tertiary mirrors resting on their hard points. Right:
     After a round of tuning the support systems, 0.45" FWHM stellar
     images were obtained. The scale is 0.2"/pixel.

The MOS Nasmyth port wide-field corrector lenses have recently been received
from Rayleigh Optical of Tucson and are being tested in the NOAO optical
shop. Once accepted, the lenses will be anti-reflection coated, assembled
into their cell, and installed at WIYN in early September. The Hydra/MOS
instrument team plans to test the MOS port wide-field in late September.

The WIYN Nasmyth port atmospheric dispersion corrector optical contract has
been awarded to Rayleigh Optical, and delivery is expected in early 1995. Work
on the WIYN port Instrument Adaptor System (IAS) ("guider") continues with the
goals of starting IAS assembly in late September and starting IAS
installation and testing in early December. The NOAO Mountain Programming
Group has begun work on adapting the 4-m Telescope Control System (TCS)
Graphical User Interface (GUI) to the University of Wisconsin (UW) Controls
Group WIYN TCS, and testing of WIYN GUI prototypes is underway. The first
release of the complete WIYN GUI is scheduled for early September.

The WIYN control system has been mostly delivered by the UW Controls Group.
Although some detailed control system work remains, the only remaining
undelivered major subsystem is the image processing hardware and software
necessary for closed-loop guiding. Delivery of that sub-system is scheduled
for mid-September. The UW Controls Group is currently engaged in such
activities as refining dome control, tuning the main telescope axis servo
controls, and supporting the Project staff's tracking/pointing tuning effort.

Preparations for facility instrumentation installation and commissioning are
nearing completion. Delivery of major instrument components has begun, and
instrument commissioning activities should ramp up to full effort by
mid-October.

The current project schedule milestone goals are: (1) complete telescope
commissioning activities by 1 October 1994; (2) complete facility instrument
commissioning activities by 1 January 1995; (3) complete university
instrumentation and IAS commissioning by 1 March 1995; and (4) start WIYN
"shared risk" science operations on or about 1 March 1995.

The WIYN Observatory Dedication is scheduled for 15 October 1995.

Dave Silva, Dave Sawyer

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