Chandra Users Committee Meeting, 17-18 October 2006

Attendees:
Harry Ferguson, Vicki Kalogera, Nobuyuki Kawai, Smita Mathur, Chris Reynolds (chair), Maria Santos-Lleo, Randall Smith, Lisa Storrie-Lombardi, Allyn-Tennant (ex-officio), Leisa Townsley

• SUMMARY OF MEETING

• Harvey Tananbaum and Paul Green welcomed the committee on behalf of the CXC. In particular, two new members of the committee (Randall Smith and Harry Ferguson) were introduced.


• Roger Brissenden presented the "CXC Manger's Status Report" in which the current status of the CXC and the observatory were summarized. As feared, the CXC was forced to reduce funding available for the GO grants programs due to the mid-year FY06 budget reduction. However, the CUC was encouraged to hear that, provided no further cuts are forthcoming, the CXC believes that the grants program can be funded at the full level in FY07. The CUC continues to be grateful for the vigor with which the CXC is protecting GO funding. The spacecraft itself appears to be operating extremely well, and the CUC was pleased to hear about successful efforts to relax thermal constraints by loosening EPHIN related constraints. We support the steps taken to further reduce constraints through the implementation of "optional" chips. As before, we appreciate and are impressed by the extensive efforts made by the CXC to maintain observing efficiency and flexibility while protecting the long-term health of the observatory. Roger also described the transition of the operations center from SGI to Linux machines. The CUC was extremely impressed by the smooth nature of this transition and completely supports the reasoning behind this step. In response to a direct request from the CUC, Roger discussed issues related to the rules that prevent Chandra GO awards being used to fund travel by non-US based collaborators to the US. The legal origin of this rule was described, as were efforts by CXC to clarify the interpretation of the rule.


• Harvey Tananbaum described the use of Directors Discretionary Time (DDT) from March 2006 to October 2006. The CUC continues to support the Director's approach to allocating DDT.


• Belinda Wilkes discussed the Cycle-8 peer review. Proposal pressure continues to be strong, with 725 proposals received giving an oversubscription by time of 6.4. Novel aspects of this review cycle were (1) the strict implementation of limits on constrained observations, (2) the possibility of alternative targets for TOOs, (3) the ability for GOs to propose for rasters/grids, (4) moving the cost proposal deadline two weeks later, (5) the availability of a new information/cheat sheet for the reviewers. All of these new features were deemed a success. The CUC appreciates the continuing efforts made by the CXC to improve the review process.


• Paul Plucinsky presented a status report on the ACIS operation. The most significant issue noted was the plan to identify "optional" chips for each given observation which can, if necessary, be turned off to reduce the thermal load on the instrument. It was noted that turning off optional chips will only be required in very few cycle-8 observations (approx 10 out of 730 targets), but that the ability to turn off optional chips may become more important for subsequent cycles. The CUC agrees with the implementation of optional chips in order to reduce thermal constraints and maintain as much flexibility in scheduling as possible. [See related recommendation below] * Larry David presented the status of the Chandra calibration. The CUC continues to support the good work of the calibration group towards systematically achieving the calibrations goals of Chandra. [see recommendation below concerning internal cross-calibration]


• Herman Marshall discussed the latest work on the cross-calibration of Chandra with other observatories, notably XMM and, to a lesser extent Suzaku. The CUC thanks the cross-calibration team for responding to the last CUC report by presenting detailed analyses of fluxes in given bands with Chandra and XMM. The CUC fully supports this continuing work and was particularly impressed by the formation and actions of the International Astronomical Consortium for High Energy Calibration (lead by the XMM-Newton team). We applaud the Chandra cross-calibration team for their participation in IACHEC. [See recommendations below]


• Mike Nowak began by discussing the status of CIAO and the up-and-coming release of new versions. The plan is to release CIAO 3.4 in December 2006; this will allow observers to correct both serial and parallel CTI as well as dead area due to cosmic blooms. The next major version of CIAO (CIAO4) will be released as a beta version in February 2007, with a full release later in 2007. Mike then proceeded to discuss several major issues related to the efforts of the Science Data Systems team:
  (1) Catalog: The requirements document has been updated and a detailed characterization and implementation plan developed. There has also been good progress on developing the analysis pipeline for the catalog, including beowulf software for paralleling the process. The CUC remains concerned about the lack of a detailed schedule for the catalog, however. [See recommendation below]
  (2) Sherpa rewrite: Responding to the previous CUC report, Mike discussed the motivation underlying the rewrite of Sherpa. The rewrite was essentially forced by infrastructure problems within the old code. It was also made explicit that the Sherpa rewrite is required for the development of the catalog.
  (3) Chips rewrite: The new version of CHIPs is being developed based on VTK.
  (4) Bad pixel files: Responding to a request by the CUC, Mike discussed the implementation of bad pixel files. He described how the current bad pixel algorithms are aimed at the requirements of the majority of "normal" users, but acknowledged that some advanced users may need to customize the bad pixel file. SDS is currently exploring options for allowing this customization.
  


• In the final session of the first day, Harvey Tananbaum discussed the proposed Extremely Large Projects (ELP) program. The proposed plan is to select one ELP (in the 3-5Ms range) once every three cycles, starting with Cycle-10. ELP proposals will be reviewed as part of the normal peer review and there will be no restriction on science topic. In order to inform the Directors Office as to the utility of such a program, there will be a call for white papers from the community (the call was issued in early Nov 2006). These white papers are for information only, i.e., they are not proposals or letters of intent. Several questions were posed to the CUC concerning this program:

  (1) Should the peer review be allowed to reduce the time for an ELP below the proposed time.
  (2) Should the peer review be allowed to reject all ELP proposals?
  (3) If the full 5Ms is not allocated, how should the unused time be utilized?
  (4) How should ELP funding be allocated?
  (5) What policy should be applied with regards to proprietary time?
  (6) What data products should be required from the successful ELP team?

  The CUC extensively discussed these issues; see recommendations below.

   

  DISCUSSION AND RECOMMENDATIONS
  

  The CUC continues to be extremely satisfied with the quality and professionalism of support that the CXC brings to the spacecraft operations, data systems, and the user community. The CUC is also extremely pleased by the responsiveness of the CXC to previous CUC recommendations and requests.

  On the basis of the presentations and subsequent committee discussion, we have a number of specific comments, suggestions and recommendations for the CXC.

  (1) Optional chips: The CUC fully supports the reasons behind the implementation of optional ACIS chips but fears that the wider user community might not be aware of the utility of this step. We recommend that a short web-page describing how thermal constraints are relaxed by turning off a small number of chips be linked to appropriately, especially to pages used in the detailed planning of observations.

  The proposed web page should also explain that a compromise has to be made between turning off CCDs and splitting observations. The web page should describe the current policy: observations that do not explicitly ask for un-interrupted scheduling can be split by Mission Planning team without further check with the PI. Observations explicitly asking for un-interrupted exposure will be considered time-constrained and hence limited by the 15 per cent maximum constrained time that can be approved.

  (2) Internal and external cross calibrations: The CUC is very pleased by all of the ongoing calibration and cross-calibration efforts, and especially encourage further participations in IACHEC and cross-calibration efforts with Suzaku. However, the CUC has two specific concerns and questions in this regards:

  (a) There has been very little discussion about cross-calibration across the Chandra instruments, e.g., between the bare ACIS-S, bare ACIS-I, ACIS-S/HETG and HRC/LETG. It remains unclear to what extent this internal cross-calibration is naturally achieved through the regular calibration efforts. The CUC requests an explicit update about internal Chandra cross-calibration. While the CUC acknowledges that it is challenging to find potential sources, it also recommends examining the cross-calibration of ACIS grating spectra with the spectrum of the zero-th order image.

  (b) The CUC notes that essentially all of the cross-calibration efforts between Chandra and XMM or Suzaku is conducted using Chandra in a grating mode. While we acknowledge that it is technically easier (given pile-up issues), it is highly desirable to also cross-calibrate bare ACIS modes. If they are not doing so already, the CUC recommends that the cross-calibration team include bare ACIS modes in their consideration.

  (3) Funding of non-US collaborators: The CUC would like to express its appreciation to the Director's Office for their efforts in requesting clarification from NASA-HQ on rules regarding the funding of non-US collaborators with GO grants.

  (4) CHIPS rewrite: The CUC is somewhat concerned about the level of effort that is being expended in rewriting CHIPS given that CHIPS appears not be to crucial to other on-going activities (such as the catalog) and it is unclear to the degree that CHIPS is used by the community. The CUC makes the following requests and recommendations:

  (a) We request that, at the next CUC meeting, we are given a clear description of why it is important to update/rewrite CHIPS and where (and how) CXC sees CHIPS eventually developing. As part of this discussion, it will be important to identify other high priorities activities for which CHIPS is an important tool.

  (b) The CUC is concerned about the direction in which the user interface for CHIPS and Sherpa is developing. We feel that it is important to make the interface as accessible and natural as possible to astronomers, not computer programmers. Forcing the user into an object-oriented environment is of particular concern - this is not a natural system for most astronomers with the result that few astronomers outside of CXC will use these tools. This, in turn, diminishes the value of the effort expended to update these tools.

  (c) We recommend that the CXC identify and examine metrics that probe the penetration of CHIPS and Sherpa into the community. For example, searching the body of Chandra related papers for "Sherpa" and "XSPEC" will give some measure of the relative use of these packages. This exercise will inform CXC and CUC as to the degree of effort that should be put into CHIPS and Sherpa development.

  (5) Catalog: The CUC continues to regard the Chandra Source Catalog as an extremely important part of Chandra's scientific contribution. The rapid community utilization of the XMM point source catalog highlights the need for Chandra to produce its catalog on the most rapid timescale possible. If it hasn't been done so already, the CUC requests that a real schedule with goals and deadlines be established for the development of the catalog. We also request that the latest version of the requirements document be made available to the committee members.

  (6) EPO proposals and activities: On the basis of community feedback, the CUC requests that the password distribution system for EPO proposals be improved. Distributing passwords via direct phone is both un-necessary use of CXC personnel and can delay a potential PI. We request that passwords be distributed via an automated email/web-based system.

  The committee also requests an update on EPO activities at the next CUC meeting.

  (7) Promotion of grating science: The CUC fully supports the idea of a science meeting targeting spectroscopic/grating science. We encourage the CXC to consider organizing a meeting in a venue which provides opportunity for engaging as many non X-ray astronomers as possible. Embedding such a meeting within the Summer 2007 AAS meeting is an attractive option.

  (8) Extremely Large Projects: The CUC is fully supportive of the Director's proposed plans with regards to ELPs. We also appreciate the cautious manner in which the Director is proceeding and fully support the call for white papers that was issued in early November. Specific recommendations of this committee are:

  (a) Reviewing the white papers: The CUC was concerned about maintaining the integrity of the intellectual property during the review of the white papers. Hence, we recommend that the review be conducted by the smallest viable group of experts chosen by (and including) the Director, and that the list of reviewers be made public after the submission deadline.

  (b) Nature of white papers: The CUC feels that the white papers should be short documents, and that CXC should accept white papers that argue *against* the ELP program on the basis of specific science that will be harshly impacted. The CUC appreciates that both of these recommendations have been adopted in the recent call for white papers.

  (c) Proprietary time: The CUC feels that ELP data should become immediately public by default, but that the proposing team be allowed to make the scientific case for a proprietary period up to a certain maximum number of months. To guide the choice of the maximum allowed period, the call for white papers should include a request for statements about the need (or lack of need) for a proprietary data period. In the event that the observations for a given ELP are spread over a period of time, data should be released as and when it is taken rather than waiting for the whole program to complete.

  The CUC also recommends that the proprietary time policy for VLP be changed to bring it into accord with the chosen policy for ELPs.

  (d) Management and deliverable plan: Given the size of these projects, the CUC believes that ELP proposals should be required to contain a specific Management and Deliverables Plan in which the management of projects is described and specific data products are proposed. This plan will provide guidance to the cost review for the proposing team.

  (e) Funding of other teams: The CUC recommends that a fraction of available ELP funding (nominally 1/3) be made available to investigators other than the successful proposing ELP team, and that there be a call for supplemental data analysis and theory proposals at the time of the regular cost proposal call.

  (f) Maximum duration of an ELP: The CUC concurs with the Director that a 2 year cap must be placed on the total duration of any ELP.

  (g) The CUC feels that the peer review should have the ability and authority to reject all ELPs if they feel that the scientific return is not sufficiently compelling. The expectation should be, however, that one ELP will be selected. The peer review should also have the authority to reduce observing time below that proposed, although the usual discouragements from doing so should apply. The CUC recommends that the Director examine the possibility of extending the nominal duration of Cycle-10 to 13+ months such that, if an ELP is not selected, the cycle can simply be ended early without running out of targets prior to Cycle-11 starting.