NAOMI, mounted at the WHT
Nasmyth focus, delivers
near-diffraction-limited images in J, H and K bands
(FWHM ~ 0.15 arcsec), and significant correction at shorter
There are currently two science instruments:
the optical integral-field spectrograph
and the IR imager
OASIS offers a choice of 3 different spatial samplings,
field of view up to 10 arcsec,
and a choice of 15 spectroscopic modes.
has a 40-arcsec field of view (0.04 arcsec/pixel), and is equipped with
a variety of broad-band and narrow-band filters.
, can be placed in the light path to INGRID.
NAOMI requires a natural guide star
(V < 14, within a few 10s arcsec).
The science target itself can serve as a natural guide star, if it
sufficiently bright and compact.
NAOMI has been used to study
a wide variety of objects,
including comets, binary asteroids,
cicumstellar disks, nuclei of normal galaxies,
AGN, QSO hosts and gravitational
The AO correction achieved depends on the magnitude of the guide
star, separation of the science target from the guide star,
the natural seeing, and
the wavelength of observation.
In median seeing (0.7 arcsec in the optical), a guide star with
V = 11.5
typically yields FWHM ~ 0.2 arcsec, Strehl = 0.2, out to
a radius ~ 20 arcsec in H band
(1.6 microns). The correction is usually marginal for V > 14,
or for radius of more than a few tens of
arcsec from the guide star, or in
natural seeing worse than 1.5 arcsec.
In the optical, NAOMI typically improves the FWHM by a factor of two
(e.g. from 0.6 to 0.3 arcsec).
NAOMI performance page for details.
(For guiding only, i.e. no AO correction, a star V < 19.5 within
1.5 arcmin of the target is required.)
The Rayleigh laser guide star,
GLAS is not currently offered due to a technical problem
- reduced power, which significantly compromises the
level of correction achieved.
The performance of the AO system with GLAS is still being
characterised, but it is expected that it will be similar to
that with a bright natural guide star (mag ~ 9.5).
When observing with the laser guide star, a natural guide star is
still required, to effect the tip-tilt correction, but this star
can be much fainter, V < 17, and up to 60 arcsec from the science
Signal-to-noise predictions can be made using
SIGNAL, the ING
to INGRID with NAOMI is about 0.5 times that to INGRID
mounted at the Cassegrain focus
(due to losses in the GHRIL derotator, and in the
to OASIS is similar to that of OASIS at CFHT.
In the IR, the J and H background levels are similar to those
measured with INGRID
mounted at the Cassegrain focus. However, the K thermal background is
~ 2 - 3 mag brighter than that at Cassegrain, corresponding to ~ 100%
emissivity from the telescope.
Observing overheads with adaptive-optics systems
(e.g. for PSF calibration) are higher than
for normal observing, and these overheads should be included in the
request for time, see the page on
All AO observations are carried out in service mode, by ING staff astronomers.
was built by a team from Durham/ATC, led by
about the technical feasibility of proposed