Above: Open-loop and closed-loop I-band images of a 0.36-arcsec star pair. Observed 2004 Jul 2, click here for details.

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 wavelengths. There are currently two science instruments: the optical integral-field spectrograph OASIS, and the IR imager INGRID. OASIS offers a choice of 3 different spatial samplings, field of view up to 10 arcsec, and a choice of 15 spectroscopic modes. INGRID has a 40-arcsec field of view (0.04 arcsec/pixel), and is equipped with a variety of broad-band and narrow-band filters. A coronagraph, OSCA, can be placed in the light path to INGRID.

NAOMI can be used to observe any astronomical target having a suitable guide star (V < 14, within a few 10s arcsec). The guide star can be the science target itself, if it is 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 lenses. A Rayleigh laser guide star, GLAS, is under development, with on-sky commissioning expected summer 2006.

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). See the 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.)

Signal-to-noise predictions can be made using SIGNAL, the ING signal-to-noise calculator. The throughput 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 NAOMI optics). The throughput 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. Most of this is from surfaces in the Nasmyth derotator and in the INGRID foreoptics used with NAOMI. ING plans to recoat or replace these surfaces. Bright stars give rise to a number of ghosts, these are not yet well characterised.

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 planning observations.

NAOMI observations are usually carried out in service mode, to take advantage of the best seeing, but visiting observers are also welcome.

NAOMI was built by a team from Durham/ATC, led by Richard Myers.

ING welcomes enquiries about the technical feasibility of proposed observations.