ISAAC Overview

ISAAC is an infrared (1 - 5 μm) imager and spectrograph mounted on the Nasmyth A focus of UT3. It has two independent arms, one equipped with a 1024 x 1024 Hawaii Rockwell array and the other with a1024 x 1024 InSb Aladdin array from Santa Barbara Research Center. The Hawaii arm is used at short wavelengths (1 - 2.5μm). The Aladdin arm is used predominantly at long wavelengths (3 -5 μm) but is also available for short wavelength imaging with broadband filters. Below we summarize in two tables the operational modes and predicted performance of ISAAC. Those tables are intended as a quick feasibility references only: proposers should refer to the detailed information (e.g. User's Manual, Exposure Time Calculator).All instrument modes are offered in both Visitor Mode and in Service Mode).


Imaging Modes

Instrument Mode Scale FOV limit magnitude
(''/pixel) (squared '')
SW Imaging[1] 0.148 152 x 152 J=24, H=23, Ks=22
SW Polarimetry[2] 0.148 3 x 20 x 150[2] J=23, H=22, Ks=21
LW Imaging 0.071 73 x 73 L~16, M_NB ~ 13
LW Imaging 3.21, 3.28μm 0.148 152 x 152 L ~16
[1] For both the Hawaii and Aladdin arrays
[2] In polarimetry the FOV consists of three non-overlapping strips each of 20 x 150 arcsec^2.


The limit magnitudes in the table are the J (1.25μm), H(1.65μm), Ks (2.2μm), and L (3.8μm) background limited magnitudes for a point source which would give a S/N of 5 in one hour of typical background conditions and a seeing FWHM of 0.65''. In addition to the standard J, H, Ks, and L broadband filters, ISAAC is equipped with a wide selection of narrow bands (typically =0.015μm) filters. It is not possible to observe with ISAAC with user supplied filters.

Spectroscopic Modes

Instrument Mode λ/Δλ Scale limit magnitude range
SW LRes Spectroscopy 500 0.147 18-20.5
SW MRes Spectroscopy 3000 0.147 17.5-19.5
LW LRes Spectroscopy 500 0.147 11-14
LW MRes Spectroscopy 2000 0.147 10-13


The limit magnitudes given in the above table are the short wavelength (SW) and long wavelength (LW) magnitudes of a point source spectrum which would give a S/N of 5 per resolution element in the continuum in one hour under typical background conditions, seeing FWHMof 0.65'', and using a 1.0'' slit. Limits on IR spectroscopic capabilities vary strongly with wavelength due to the absorption/emission spectrum of the atmosphere, the range of limit magnitudes given in the table reflects this variation.