Imaging in the Ultraviolet

The 1024 x 1024 pixel² CCD is sensitive in both the ultraviolet (UV) and extreme ultraviolet (EUV). The telescope is divided into four quadrants, three of which are designed for EUV imaging (Figure 3.3). In this thesis I work on data from the fourth quadrant, designed to image in UV wavelengths.

Figure 3.4: The four TRACE UV filter passbands are displayed. From top to bottom these are Ly, C IV, 1600 Å continuum and fused silica. The fused silica and 1600 Å continuum filters are combined to form a further filter passband centred on 1700 Å (Handy et al. 1999a)

Figure 3.5: Combined response function of TRACE UV optics and quantum efficiency of the CCDs. (Handy et al. 1999a)

The UV filter entrance has a multi-layer dielectric coating on a MgF₂ substrate, which acts to block long-wavelengths (> 2000Å), whilst optimising transmission at both C IV (1550 Å) and Ly (1216 Å). Various combinations of filters are used to image a number of wavelengths, namely 1216 Å, 1550 Å, 1600 Å, 1700 Å and white light. Details of the passbands and filters used are provided in Table 3.2 and Figure 3.4. Essentially the C IV, Ly and UV continuum (centred on 1600 Å) provide three individual passbands. The 1600 Å and fused silica filters are used in tandem to create a fourth filter, centred on 1700 Å, whilst the fused silica filter also provides white light images. The response function of each passband (including quantum efficiency of the CCDs) are displayed in Figure 3.5. Linear combinations of images in these passbands can then be used to isolate both the C IV and Ly emission from the continuum (Handy et al. 1998, Handy et al. 1999b). Depending on the aims of the observing program, images may be taken in all eight passbands, obviously at the expense of a lower cadence for the dataset.