Several months ago, the CCDPhot detector, designated T5HA, suddenly and inexplicably became inoperable. In deciding what to replace it with, we considered several factors. First, we felt it was important not to use a CCD larger than 512 x 512 pixels in order to maintain the ease-of-setup and ease-of-use aspects of CCDPhot. Second, the new CCD must have similar noise characteristics and dynamic range as compared with T5HA. Finally, we wanted to address the concerns of users who have requested better dQE in the U band. With these points in mind, we have selected a SITe 512 x 512 pixel back-side illuminated CCD designated T5HC. This detector has the same pixel size and approximately the same read-out noise and full-well capacity as T5HA but significantly flatter response in the U band. This is illustrated in Figure 1, which shows the dQE curve for T5HC (dashed line) as compared with that of T5HA (solid line). This improved U band response over T5HA comes at a price; the cosmetic quality of T5HC is somewhat worse. It has one hot column at (386) and a series of cold columns in the range 488 < x < 502. In addition, the first 30 rows of the CCD are affected by an abnormally high dark current and should thus be avoided. However, we feel that these imperfections will not affect the normal use of CCDPhot by observers. Furthermore, it is hoped that the flatter dQE in the U band will improve the transformability of U-B (see details in the September 1995 NOAO Newsletter).
Ata Sarajedini, Ed Carder, Lindsey Davis,
Tom Kinman, George Jacoby, Tom Wolfe