From owner-uumpia@jach.hawaii.edu Wed Aug 21 07:39 MET 1996 Date: Tue, 20 Aug 1996 19:34:43 -1000 (HST) From: Tim Hawarden <hawarden@jach.hawaii.edu> To: uujac@jach.hawaii.edu, uuroe@jach.hawaii.edu, uumpia@jach.hawaii.edu, Dolores Walther <dolores@jach.hawaii.edu>, Thor Wold <thor@jach.hawaii.edu>, Tim Carroll <carroll@jach.hawaii.edu> Subject: More Upgrades Progress Mime-Version: 1.0

Dear Colleagues,

At the time I completed my last Unofficial Progress Report I was just about to come off Mauna Kea, leaving Andreas and Nick with Dolores to continue checkout and testing.

As the report indicated, things were looking pretty encouraging generally.

HOWEVER we had had two nights when our "optical" seeing (i.e. on the TV) looked pretty good, other telescopes reported good seeing (e.g. Keck "0.4-0.5 arcsec"), but we got rather poor IR images, typically 0.8 to 1.1 arcsec, which reduced to maybe 0.5-0.7 arcsec with T-T. I was really beginning to worry that something was wrong: maybe the print-through was much more important than we realised, etc etc.

The following night the seeing situation reversed, with UKIRT getting BETTER seeing than Keck and CFHT, 0.5-0.7 arcsec while they got 1.0 even 2.0 arcsec. (This suggests that we are also getting something right about dome seeing too...)

When stabilised the UKIRT images near focus appeared double because of astigmatism. After a little trial and error with the primary control system this was removed. Now the near-focus images were triangular, so using a WFS (Black Box) measurement for reference some trefoil was applied and all structure went away. The remaining capacity of the Primary Control System was then applied to Spherical aberration, removing about 0.35 um of Z11.

(The resulting wavefronts appear excellent. The most significant remaining aberration is probably second order trefoil (Z18: 0.53 um). We can't correct this with the primary and, as well as spherical, it may be a case for ion figuring. However it is possible that it may be caused by thermal stress as the secondary support was assembled at temperatures well above operating and this will be looked into. Nevertheless, the telescope appears now to have intrinsic optical perfomance close to the diffraction limit at 2 microns.)

Images were then secured as follows:

V = 11.4 magn (star V=9.4; old dichroic)

04:07 TT 100Hz FWHM = 0."31 (30s exp) [FWHM measured conservatively by pixel-counting!]

04:09 Uncorr. " = 0."56 ( " " )

04:15 TT 100Hz " = 0."29 (10s exp)

04:17 TT 100Hz " = 0."25 ( " " )

04:15-17 TT 100Hz " = 0."30 (100sec = 10x10s)

04:18 Uncorr " = 0."58 (10s exp)

V = 12.9 magn (.. +1.5m ND filter)

04:21 TT 100 Hz FWHM = 0."39 (10s exp) 04:25 TT 70 Hz " = 0."29 ( " " ) 04:27 TT 40 Hz " = 0."26 ( " " )

V = 11.5 m (9.5 star, old dichroic; Windshake)

04:44 Uncorr FWHM = 0."59 (30s exp)

04:45 TT 100 Hz " = 0."28 ( " " )

V = 11.4 (9.4 star, old dichroic)

04:52 Uncorr FWHM = 0."51 (10s exp)

Later experiments to explore limiting magnitude appear to have been affected by deteriorating seeing and brightening skies.

It is clear that the Tip-Tilt system is performing close to expectations. There are still unresolved issues, including quite a lot of higher-frequency signal in a rang of high-Q "spikes" above 10Hz, (where we are actually amplifying it as can be seen from theb power spectra), most of this appearing in DEC.

***********

The primary mirror figure adjustments were left in, and the imaging performance was greeted with glee by the observers the following night. Gillian Wright, the CGS4 instrument scientist, says she got spectra with more signal in one (1.2") row than she had seen since the 3" pixels were in use: and then only when the telescope was in good adjustment and tracking well!

Dolores tells us that it is now nearly impossible to focus in the optical; using CGS4 movie and signal displays, however, it can be done to 0.01mm (i.e. shifts of this size can readily be detected). This is a little over 1/2 of the diameter of the 2.2 micron diffraction spot, and while it is about 3x more sensitive than we have ever been before we still have a way to go.

But in the meantime, everything continues to look very good.

Tim H

PS: Andreas is sending out a much prettier document....