12-13 June 2003

Chandra Users' Committee

Members Attending: M. Arnaud, Y.H. Chu, J.P. Hughes (chair), W. Latter, J. Lee, K. Long, J. Krolik, and S. Snowden

By Telecon: A. Cool

Members absent: J. P. Henry, K. Mitsuda, G. Taylor, C. Reynolds

Others: A. Tennant, H. Tananbaum, B. Wilkes, F.Seward, P. Green, D. Kniffen (by telecon)


(1) The committee was concerned that the fraction of time to be awarded the large and very large projects (LP, VLP) was fixed with respect to the normal GO programs without regard to the relative science between these classes of programs. The plans as presented to the committee only allow for trading observing time between LP and VLP projects. At the same time, the amount of time reserved to the LP and VLP has doubled this round, while the amount of time going to normal GO programs remains at the same level as previously. The committee suggests that additional flexibility be incorporated into the review process. The Big project panel should be instructed that it can allocate less than 6 Ms of time to LP+VLPs. Observing time that is not allocated by the Big project panel should then revert to the individual panels roughly in proportion to their original allocations. The panels should be clearly instructed that gray area normal proposals in their panel may be promoted and therefore the proposals below the cut-off should be ranked carefully.

(2) The Big project panel should be queried concerning whether the process that separates LPs and VLPs from normal programs is likely to result (in the opinion of the Big project panel) in the highest science efficiency for Chandra. This might be a part of a somewhat larger ensemble of questions regarding the peer review. In particular, after the review, Big project panel members should be asked to respond in writing to the following (or a similar set of) questions:

The CUC would like to receive a copy of the responses, even in just a "summary" format, as one way of evaluating whether the VLP proposals were worthwhile.

(3) The committee heard about the potential gains and risks associated with a bake-out of ACIS intended to release the contamination that has reduced the low energy quantum efficiency. Based on the risks (e.g., slightly increased CTI, change in calibration) and gains (increased low energy QE), as presented, the committee strongly supports baking-out ACIS.

(4) The calibration plan as presented for the pre and post bakeout of ACIS needs to be worked more. In particular it was not clear how the spatial distribution of the contamination was going to be characterized. For example, perhaps the ACIS should be docked for some period of time both before and after to accumulate enough photons to characterize the spatial variation using the calibration sources. This is potentially a very important moment in the life of Chandra, since there will be a step function change in the performance of ACIS. All aspects of calibration should be looked at to ensure that sufficient calibration data are collected in order that all pre-bakeout observations can be analyzed accurately to maximize the science return of Chandra.

(5) Calibration Document The committee appreciates the progress that has been made in terms of documenting the calibration plan. In particular the table describing the state of calibration will be quite useful. We note that the draft calibration document appears to be based heavily on MSFC-RQMT-2229, which was written long before launch and does not reflect current on-going in-flight calibration plans or changes in instrument performance during the mission. The calibration document needs to address these aspects of calibration as well.

Here are some specific comments/suggestions on the draft document:

(6) Software issues: Four themes for beyond CIAO 3

CIAO has been rather successful overall to date and certainly stands up well compared to other astronomical software packages. The CUC agrees that it is time, at mid-mission, to assess where CIAO is headed.

The most important concern of the CUC for "beyond CIAO 3" software development is ensuring adequate support for core software for Chandra users. New software and updated threads to support new calibration requirements, to account for degradation in instrument performance, and to continue to be able to perform basic fundamental analyses must be the highest priority. This should be the most important theme for "Beyond CIAO 3".

As the CIAO software survey showed, users are also interested in modest improvements to CIAO like the ability to write scripts, improved visualization/graphics tools, enhanced speed, better syntax/interface, more documentation, and so on. To the committee, a significant critique is that CIAO is not very integrated both in terms of overall concept and in terms of look and feel. Improving each and every CIAO task/thread/script would be a large effort, but would also yield a great benefit for users. The CUC considers this to be an important theme for "Beyond CIAO 3".

The practical benefits of the proposed "Beyond CIAO 3" themes were not generally apparent to the committee (n.b., the presentations were rather heavily focussed on technical details). The themes do not appear to reflect an integrated plan oriented toward Chandra users. The CUC recommends that the software group take a serious look at what themes would be of greatest benefit to Chandra Users and propose a realistic vision for "Beyond CIAO 3" especially in the light of anticipated reduced funding during the extended phase of Chandra.

We also note specific issues related to the proposed themes.

The level of effort going into CIAO and other efforts is quite large, perhaps as large as any NASA effort. It is also clear that the CXC has plans that extend beyond Chandra. There needs to be a decision of the overall vision for CIAO and analysis efforts. Furthermore the committee urges that any long term efforts be coordinated with other large astrophysics data analysis efforts.

Other specific recommendations:

(7) Monitoring and Trends Analysis

The CUC recommends that the CXC provide a higher level of oversight to the SI performance monitoring and trending analysis program to ensure that appropriate performance quantities are being tracked.