C. R. Benn, S. Els, T. Gregory, R. Østensen, F. Prada (ING), R. Myers
(University of Durham)
NAOMI, the WHT’s
adaptive-optics system, is now being used routinely with INGRID, the IR camera,
to obtain near-diffraction-limited images at wavelengths 1–2.2 micron (J,
H, K, and narrow-band filters). Time allocations are queue-scheduled to take
advantage of the best seeing, but visiting observers are also welcome.
The images reproduced here and on the front page are from the May 2002 commissioning
run. With bright guide stars (V<11), NAOMI improves image FWHM from 0.7
to 0.2 arcsec in J, H and K bands. For V~12, the correction is typically
from 0.7 to 0.3 arcsec, and useful correction has been obtained for guide
stars down to V~13.5. An uncorrected seeing of 0.7arcsec in H band
corresponds to 0.9 arcsec in V, well above the median for the site (0.7arcsec).
A summary of measured performance (FWHM, FWHE, Strehl) can be found on the
NAOMI web page: http://www.ing.iac.es/Astronomy/instruments/naomi/.
Figure 1. N6543 planetary nebula in Paschen beta,
600-sec integration, using central star (V=11) as a wavefront reference.
Adaptive-optics correction from 0.7 to 0.3arcsec. The finest structures
visible in the nebula are ~0.3arcsec across. Image is 30arcsec
top to bottom. [ JPEG | TIFF
Figure 2. NAOMI in GHRIL. INGRID is in the foreground.
[ JPEG | TIFF ]
Near Earth Asteroid 2002 NY40 was observed with NAOMI on the night 17 August
2002, just before its closest approach to earth. This is the first time an
NEA has been imaged with an adaptive-optics system. The asteroid was only
~750,000km away during observation, and moving across the sky at about 5arcsec
per second. Despite the technical difficulties this introduced, H-band images
were obtained with a resolution of 0.11arcsec, close to the diffraction limit
of the WHT. This sets an upper limit of 400m on the projected size of the
asteroid at the time of observation.
NAOMI’s emissivity in K-band is still high (~100%), so programmes which can
be observed in either H or K are probably best done in H until the emissivity
has been reduced.
NAOMI’s coronograph, OSCA, was successfully commissioned in May 2002, by
Peter Doel and his team from UCL. OSCA offers 6 focal-plane stops with diameter
ranging 0.2–2.0 arcsec. OSCA is offered to observers on a shared-risks basis
in 2003A. For further information, see the OSCA web page: http://www.ing.iac.es/Astronomy/instruments/osca/.
At the end of 2002, NAOMI will move to a new purpose-built enclosure, GRACE,
on the opposite Nasmyth platform (the platform formerly occupied by UES).
NAOMI will stay in GRACE permanently, and will be joined by a second science
instrument, OASIS, mid-2003. OASIS is the optical integral-field spectrograph
formerly at CFHT. NAOMI will deliver significant adaptive-optics correction
at optical wavelengths, permitting OASIS spectroscopy of galaxies (and other
targets) at high spatial resolution.
The GHRIL enclosure will revert to its original function of hosting visiting
instruments and experiments, including further tests by Durham University
of wavefront correction using a Rayleigh laser beacon.
In support of future adaptive-optics observations, and in particular in preparation
for extensive queue observing, a robotically-operated seeing monitor, RoboDIMM,
has recently been brought into use. RoboDIMM (Augusteijn, T., 2001, ING Newsl., 4,
27), delivers a measurement of the seeing every few minutes, from a small
telescope outside the WHT building.
Figure 3. RoboDIMM tower, dome and telescope. [
JPEG | TIFF ]