Re: Announcement on the revision of IRC00 2006/09/23 Dear IRC00 observers, Following extensive in-orbit tests, the IRC team has made a decision to change the parameters to drive the array of the NIR channel for the IRC00 AOT. The new IRC00 is called IRC05. It increases the reset interval by about a factor of 2 and uses Fowler 16 data reading scheme instead of Fowler 4 in IRC00. As a result, IRC05 observations could achieve nearly a background-limited performance. About a factor of 1.7 improvement has been confirmed for N2 and N3. No appreciable change is seen in the performance in N4, which is already limited by background. No changes are made for IRC05 in the MIR-S and MIR-L channels. A possible demerit of IRC05 over IRC00 is a longer reset interval, which leads to higher cosmic-ray hits in a frame and vulnerability to poor pointing stability. Despite of these potential problems, the IRC team has concluded that the merits of IRC05 are significantly large over IRC00. All IRC00 observations will be replaced by IRC05. This replacement will be made automatically in the scheduling process and observers do not need to change the parameters in their target lists by themselves. The pipeline processing will be made in the same way and the observer will not see any difference except that the FITS header of the data will be set as IRC05 instead of IRC00. Also we found that it is necessary to slightly change the target position at different pointed observations and make dithering observations manually. This will also be arranged automatically in the scheduling process. The dithering distance will be about 15 arcsec and a simple fixed pattern will be applied. If you have any preference or comments on the dithering pattern, please contact iris_help@ir.isas.jaxa.jp. Details of the IRC05 will be given in a separate document. Any questions regarding the IRC05 should be addressed to iris_help@ir.isas.jaxa.jp. Sincerely yours, AKARI Program Committee