Backup Loral CCD installed in Dolores
A new thinned back-illuminated Loral CCD has been installed in Dolores during August 2006 to temporarily replace the old Loral CCD. This became necessary because of the serious problems which negatively affected the old CCD in the last ~2 years such as charge-transfer and random fluctuations of the R.O.N. mean level.
The first tests revealed that the new CCD is not affected by the above problems; nevertheless it has much more cosmetic defects of the old CCD (see Figure 1). In particular, it has a bad column close the center of the field and some dark spots and scratches across the whole field of view. Also the borders are quite poor in terms of efficiency.
Figure 1 : V-band Flat-field images of the old and new Loral CCDs.
The rough zeropoints at UBVRI bands, obtained in a photometric night are compared with those of the old CCD in Table 1.
| Band | Old CCD | New CCD | New-Old CCD |
|---|---|---|---|
| U | 24.688 | 23.920 | -0.768 |
| B | 26.655 | 26.110 | -0.545 |
| V | 26.468 | 26.176 | -0.292 |
| R | 26.516 | 26.300 | -0.216 |
| I | 25.923 | 25.810 | -0.113 |
The poorer performance of the new CCD in terms of efficiency is evident, expecially at the bluer wavelenghts.
It should be noticed, however, that these last zeropoints were done just before the aluminizing of the three TNG mirrors (mirros are at their worse reflectivity values), scheduled in september 2006. This could in part explain the large gap in performances in the U and B bands.
The new Loral CCD is a discontinued detector kindly provided by the Isaac Newton Group of telescopes (ING) and it will remain installed until the completion of the new camera with the definitive 2048x2048 13.5 /mu pixels E2V CCD.