Optical and Infrared Telescopes.

The atmosphere is totally transparent at visible wavelengths (7600-4000Å ), and infrared (IR) wavelengths of 8-11$\mu\$m, with other windows at 1.25, 1.6, 2.2, 3.6, 5.0 and 21$\mu\$m (corresponding to $J, H, K, L, M$ and $N$ bands), a plot of the transmission of the atmosphere from 1-5$\mu\$m is shown in figure 2.3, the data are taken from the UKIRT web pages, http://www.jach.hawaii.edu/JACpublic/UKIRT/astronomy/calib/index1-tx.html. Thus astronomy at these wavelengths can be achieved with ground-based telescopes.

Figure 2.3: Transparency of the atmosphere at infrared wavelengths.

The limiting resolution of a telescope is given by,

$$\theta=\frac{1.22 \lambda}{D}$$ (9)

where $D$ is the diameter of the telescope aperture and $\theta$ is in radians. Thus for a 3.8m telescope such as UKIRT (see section 2.2.2) the limiting resolution is $\approx 0.1$ arcseconds at 2.2$\mu\$m and for an 8m telescope such as Subaru (section 2.2.3) the resolution is $\approx 0.02$ arcseconds at 6000Å . However, in practice the limiting resolution achievable is determined by the scattering of light by the particles in the atmosphere, known as seeing. On Mauna Kea, Hawaii (where both the telescopes discussed here are situated) the typical seeing in $K$ is $\sim 0.5$ arcseconds and in $V$ it is $\sim 0.7$ arcseconds. Modern telescopes have the ability to correct for seeing through the use of adaptive optics.

Short descriptions of the United Kingdom Infrared Telescope (UKIRT) and the UKIRT Fast Track Imager (UFTI) along with the Subaru telescope and the SuprimeCam, both of which were used in the acquisition of data for this thesis, are given in sections 2.2.2 and 2.2.3. First an introduction to charge-coupled devices is made.