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Chandra Users' Committee Meeting (22-23 October 2013)

Report issued on 18 Nov 2013

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Lee Armus
Franz Bauer
Tiziana DiMatteo (by phone)
Tim Kallman
Carol Lonsdale
Hironori Matsumoto
Paul Martini
Jon Miller (Chair)
Rachel Osten
Feryal Ozel (by phone)
Pedro Rodriguez (ESA)
Martin Weisskopf (by phone)

Special Note:

The CUC was informed that Harvey Tananbaum will be stepping down as Director. On behalf of the entire community of users, we wish to express our sincere gratitude to Harvey for his leadership. His is an excellent example of how to shepherd a large mission through the approval, construction, launch, and operations phases, and the success of the observatory is a reflection of his enormous dedication.

We are ready to support and advise the new Director in the many years ahead.

Observatory health and performance:

The CUC received thorough reports from Roger Brissenden and Sabina Hurley concerning the overall health of the observatory.

The most important finding is that the spacecraft and instruments are still in excellent shape, with no issues that will impact the completion of a 20 year mission, nor even a longer mission.

The CUC notes that the mission is proactive in anticipating events and trends that could potentially impact the operation of the spacecraft and operations, and developing workarounds and mitigations in advance of any difficulties. A particularly good example is the move from the degraded EPHIN radiation monitor, to monitoring with the HRC and ACIS instruments themselves.

Another good example is switching from the aging A-side Momentum Unloading Propulsion System (MUPS) to the B-side MUPS, and exploring ways of combining A and B MUPS thrusters. The CUC notes that 6 of 8 thrusters currently work well; while only 3 are strictly required for normal science operations, loss of additional thrusters may reduce observing efficiency and would increase risk if certain other failures were to occur.

Recommendation: Flight operations and mission planning and scheduling is clearly quite complex, especially with regard to the interplay between instrument/spacecraft heating and observatory pitch angle, and the manner in which observations are conducted now can impact the longevity and efficiency of the mission. Efforts have already been made to exploit efficiencies in the staffing (e.g. cross-training different tasks). But it is also clear that any further reduction in staffing levels will have a negative impact on the mission now, and going forward. NASA and Chandra should continue to recognize the importance and value of maintaining staffing levels in flight operations, and in mission planning and scheduling.

The CUC requests continued updates in future meetings, from these segments of the mission.

Education and Public Outreach

The CUC was updated on the status of E/PO by Roger Brissenden. The situation is clearly a complex one, with unclear direction provided in proposed presidential budgets and continuing resolutions. The E/PO team has continued to deliver in a difficult situation.

Recommendation: The CUC strongly endorses all efforts made by Chandra to connect with the public and to communicate the science done by the mission. The Great Observatories are flagships for science in the US, and they have a special obligation and ability to communicate the unique science that they achieve. We are particularly impressed by the way in which Chanda shares science with the public through the web and social media, and hope to see these efforts continue.

The CUC encourages any and all efforts made by the Chandra E/PO team to partner with other NASA missions in articulating the importance of their efforts to NASA and other organizations.

Director's Discretionary Time

The CUC heard a summary of recent DDT observations from Harvey Tananbaum. This program remains a particularly important means of optimizing the science returns of the mission. It promotes flexibility and enables unique investigations.

Recommendation: The CUC looks forward to the continuation of the DDT program under a new director.

Proposal Cycles: Update and Plans for Joint Programs

The CUC heard from Belinda Wilkes an update on the Cycle 15 peer review and future plans. The CUC notes that the oversubscription remains very high (5.3), that 636 total proposals were submitted, and that approximately 20 Ms of observing time was allocated. The oversubscription clearly signals that the scientific relevance and centrality of the mission continue at a high level.

Recommendation: The mission should continue to pursue existing and new joint programs in order to maximize its scientific reach.

The CUC reiterates its support for the theory and archive proposal categories. These should be retained even in the event of future mission funding reductions.

Supporting the community to analyze Chandra data is the primary way that forefront science is achieved. The CUC would like to discuss any future budgetary reductions in an effort to ensure a balanced approach that does the utmost to preserve general observer funding.

The CUC endorses the plan to create one final XVP category in Cycle 16 by allocating 2 Ms from Cycle 17. This will take advantage of the evolving orbital parameters that will provide a small amount of additional observing time in the next two cycles.

With some very large XVPs approved, and with continued high oversubscription in the LP category, we urge that panelists and pundits evaluating XVPs explicitly compare them against the most highly-ranked but unapproved LPs, with the chance of approving a few such LPs instead of lower-ranking XVPs. XVP programs should not allocate time from the LP category.

Publication tracking

Sherry Winkelman presented new efforts to track data use, grant awards, and publications. This effort was undertaken partly based on prior advice from the CUC, and we are grateful for this quick and effective response. It is early, but there are already indications that these efforts are yielding an improved view of how Chandra data are used. We look forward to a report in 2014.

Chandra Source Catalog

The CUC was provided with an update on the Chandra Source Catalog by Ian Evans. We wish to thank the team for their efforts, especially given the difficulty of the tasks.

Prior releases of the source catalog are clearly of high value and help astronomers who work in other wavelengths to make use of Chandra data. The catalog efforts are an important means of expanding the reach of the mission, and have had positive ancillary impacts including the development of valuable new software tools in the CIAO suite. The addition of command-line access to the Chandra Source Catalog should allow a larger fraction of the user community to gain rapid and efficient access to many useful catalog products.

Release 2.0 of the catalog is behind schedule, and will likely be completed over the next 12-24 months. The delays are the result of the specific demands of making robust detections of fainter sources, the complications of stacking fields, and other functions. Reductions in staffing have contributed to these delays.

Recommendation: The CUC endorses the efforts being undertaken to complete Release 2.0. The mission has clearly been responsive to the CUC in making improvements over prior releases. The mission continues to prioritize the GO program and the CIAO suite over the source catalog, in the face of staffing reductions. We support this prioritization but we urge the completion and release of the catalog, and recommend a hard look at essential catalog aspects versus ideal catalog aspects. We also urge the consideration of staged releases, where certain parts of the sky (those that overlap with large survey efforts in other wavelengths, for instance) might be released ahead of others. Finally, the CUC was told that there are computing limitations, and we urge that the observatory explore this, as improved capacity must be available with only modest costs.


Larry David presented the committee with a summary of ongoing and new calibration efforts. The calibration team was very responsive to prior recommendations, for which the CUC is grateful. The dedication of the calibration team is one of the reasons why Chandra is a remarkable mission.

Particularly impressive efforts were undertaken to understand the nature of the PSF anomaly. Its nature remains uncertain, but it does not likely derive from simple mirror misalignment. The most important outcome of these investigations is that the anomaly is small, well characterized, and likely represents as little as 1% (or less) of the flux in the PSF core.

Recommendation: Chandra will continue to be an important spectroscopic mission over the next 10 years. Even after Astro-H launches, Chandra will offer the best spectral resolution below 4 keV. We strongly endorse the efforts of the calibration team to improve the characterization of various HETG modes and observations. An improved characterization of the zeroth order image and spectrum, in all aspects, will have broad positive impacts.

We request an update on cross-calibration efforts with other missions, in addition to updates to internal calibration efforts, at the next CUC meeting.

The CIAO Software Suite

Jonathan McDowell presented updates and improvements to the CIAO suite.

As before, the CUC is impressed by CIAO and ongoing efforts. The team continues to add helpful new tools, and to simplify the execution of important existing tools.

The development of the "srcflx" script is particularly important in that it will help astronomers with no prior X-ray experience to get model-independent flux estimates from sources in Chandra mission. This tool will improve the reach of the mission.

The HELPDESK is particularly efficient at resolving problems.

We look forward to the upcoming release of CIAO 4.6.

Recommendation: The CIAO teams continues to deliver an excellent software suite in an efficient manner, and to make sensible and useful improvements. Please keep it up.

Especially in an era of reduced staffing, it is clear that the HELPDESK staff cannot be expected to provide advice and assistance that is not directly related to Chandra data and software tools, and the team should allocate its time accordingly.

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