The effective area curves for ACIS in the PIMMS AO-6 software (SW) account for the contamination layer and use the expected thickness of the layer in May 15, 2005. Chandra GOs should use these effective area curves for the predictions for their Cycle 6 proposals. The appropriate ACIS RMFs and ARFs are available at: http://cxc.harvard.edu/caldb/prop_plan/imaging/index.html.
Chandra GOs who are analyzing existing data are encouraged to use CIAO version 3.0.2 with CALDB version 2.26, since this version of CIAO and the CALDB incorporates the correction for the contamination layer which was contained in the "contamarf" SW. GOs should refer to the web pages describing changes in the CALDB for more information: "http://cxc.harvard.edu/caldb/CALDB_curr_intro.html".
For future updates, check: "http://cxc.harvard.edu/caldb/" The Chandra project is still investigating the possibility of warming up the ACIS OBF in order to "bake-off" the contaminant. Since the build-up of additional contaminant is rather slow, it was deemed important to analyze the nature of the contaminant to the extent possible, to optimize the bake-out process including parameters such as the temperature profile and positioning of the instrument during bake-out, and to make sure there were no additional risks to be encountered during the bake-out. In the latter category, the team decided to place contaminants on a spare OBF and to test it against possible breakage via thermal cycling on the ground. Even though analysis and previous experience indicated very little risk in this regard, a very conservative approach was adopted. The Chandra project will continue to work on these issues in 2004 and will make a decision on a possible bakeout later in the year.
Paul Plucinsky for the ACIS Team