Chandra Users Committee Meeting (15-16th October 2008)

SUMMARY Report received 25 November 2008


Steve Allen
Elizabeth Blanton
Mark Dickinson
Ken Ebisawa
Matthias Ehle
Harry Ferguson
Joel Kastner
Martin Laming (chair)
Jon Miller
Lisa Storie-Lombardi
Randall Smith



Overall the CUC remains very satisfied with the support that the CXC provides to spacecraft operations, data systems and the user community. We also thank the CXC for the consideration shown to our previous recommendations and requests. In a similar spirit following the last CUC meeting presentations and subsequent discussion, we offer the following comments, suggestions and recommendations for the CXC.

  1. Readjustment of LP/VLP time. The CUC was surprised that no VLPs were approved in Cycle 10, and that LPs were more oversubscribed than other GO proposals in general. We discussed whether any change in the next CfP was warranted by this, and concluded that in the light of "small number statistics" and the inevitable year-to-year variation in proposal reviews, we should wait at least another cycle before recommending any change.

    RECOMMENDATION: No change for the time being, but possibly revisit this question in a year or two.

  2. Budgets for Joint Time Cost Proposals. Proposers to other GO programs incorporating joint time with Chandra generally receive a lower "fair share" Chandra budget than they would if they were awarded the time in the Chandra peer review. While the amount of work involved in analyzing the Chandra data is not reduced because of this arrangement, the CUC felt that some economies of scale exist with these joint time proposals and the present arrangement seems the most satisfactory procedure.

    RECOMMENDATION: We therefore recommend no change, other than that this arrangement should be made explicit in the CfP.

  3. Einstein Fellows Institution Conflicts. Now that the fellowship program administered by the CXC is expanded from five to ten fellows per year, we discussed whether any amendment to the "one fellow per institution per year" rule would be appropriate. The CUC generally supports the aim of this rule to spread fellowship holders around to a variety of institutions. We discussed whether the CfA should be treated as two institutions - Harvard and SAO - as is apparently done by the other NASA Fellowship programs.

    RECOMMENDATION: We recommend a somewhat less forceful change in that all NASA fellowship programs should treat large institutions such as the Harvard-Smithsonian CfA similarly. We recommend that the CXC discuss this with the institutions managing the Hubble and the Sagan Fellowships and work with them to formulate a common policy.

  4. Senior Review. We congratulate the CXC on achieving 2nd place in the senior review, very close in fact to the 1st placed mission (Swift).

    RECOMMENDATION: The CXC believes that a high ranking in such reviews is vital to the health of the mission. The CUC stands ready to assist in future reviews by submitting material, acting as "red team reviewers", or in any other fashion needed.

  5. Gratings. The CUC are very excited about the developments with TGCat. Most of our discussion centered around threads we would like to see. The threads presented during the meeting appear to be at the level of "graduate level", i.e. treating fairly complex problems that will be of interest mainly to users already familiar with grating observations.

    RECOMMENDATION: As examples of "freshman" level threads, to help new users get started, the CUC suggests the following:

    How to find the flux in a single isolated line?

    How to find the line centroid (to determine Doppler shift or other shift) and width (for example to determine non-thermal mass motions)?

    These simple threads could of course also be expanded to the treatment of blended lines. We are thinking here of optically thin emission lines, but another complexity would be to consider also absorption spectra.

    Would it be possible to provide a simple tool like PSEXTRACT to get grating analysis started with new data? We note that such a capability is already provided in TGCat for archive data. Also a link to this project from the CXC portal page could be considered.

  6. Calibration. The CUC is surprised that calibration issues such as the effective area of the HRMA is still not completely solved, but understands the difficulty of the problem. We are satisfied at the thoroughness and rigor being applied to the problem, but are left with the impression that the team working on this are waiting until the problem is completely resolved in all its detail before making any sort of fix available. Given the length of time this is evolving over, we feel this approach does not best serve the user community.

    The low energy filter contamination is a harder problem. The problem of the characterization of the contamination, and specifically its time dependence, was mentioned as item 6 in section B Calibration Requests of the calibration/ciao wishlist the CUC recently submitted, and appears not to have been acted upon.

    RECOMMENDATIONS: We strongly urge the calibration team to release (as part of the CALDB) the current best estimate to the corrected HRMA effective area that resolves the main issue as soon as possible. We understand that this approach may require further updates and some duplication of effort as more work is done on the problem, but feel the tradeoff for users is worthwhile.

    We also ask the calibration team to review the CIAO/Calibration wishlist and report back to the CUC about the ability of the team to address these issues. In particular, we emphasize the continued investigation of the low energy filter contamination as a matter of urgency. We are concerned that H column measurements are incorrect, and suggest that at the least, some estimate of the uncertainty in these results coming from the contamination should be made public.

    Through the electronic announcements and website, the community should be advised of the progress and given recommendations for how to proceed in the interim before the full calibration is complete. Completion of the calibration should be given very high priority.

  7. Catalog. This has been a major push of CXC for past 7+ years, and the CUC is very pleased to see these efforts finally bear fruit. The Chandra source catalog should be an important part of the legacy of this mission.

    RECOMMENDATIONS: At a high level the committee recommends that the highest priority continue to be toward providing and improving the content of the catalog, and that lower priority be given to improving the GUI interface. There are a number of specific suggestions as well:

    1. Provide a VO cone-search service. We encourage the catalog team to look at the cone search tools in HEASARC and IRSA's GATOR. If they choose not to adapt this software, they should be able to reproduce its basic functionality.
    2. Implement a VOTable option for the returned catalogs
    3. There are so many different parameters in the catalog that a novice user will have a hard time figuring out which ones to request/use. Provide some tutorials, and perhaps also some 'canned' collections of parameters that could be selected for vanilla searches.
    4. Make it clearer that the current release of the catalog is primarily for compact sources. The statement on the main CSC homepage that "The Chandra Source Catalog (CSC) is the definitive catalog of all X-ray sources detected by the Chandra X-Ray Observatory" is misleading.
    5. Seek feedback on the catalog from community (beyond the CUC), including those who advised in its development. In the last CUC meeting report it was suggested that the group of proposers who submitted Cycle-10 catalog-related archive projects might form a useful beta testing team.
    6. We urge the catalog team to develop a method/protocol to reference the Chandra source catalog from external systems not going through the Chandra proprietary catalog interface. In this manner, for example, XMM or Suzaku data centers in ESA or Japan can cross-reference the Chandra catalog sources, and popular multi-mission tools like "Aladin" may display the Chandra sources. It is recommended that an existing framework such as VizieR be adopted rather than developing a new protocol.
    7. Will there be a refereed paper describing the catalog? Currently there are conference proceedings (which is fine), but if people start using the catalog,a proper reference should be available.
  8. Revised Chandra Website Design. The CUC reviewed the new format for the Chandra web page, and generally approved it.

    RECOMMENDATIONS: The various issues we noticed were:

    There is no link to the calibration pages on the front page.

    The picture of Einstein (for the fellowship program) looks a little out of place. We would have expected to see a picture of Chandra (either the satellite or the astronomer) taking pride of place here.

    There is no link to instruments and calibration on left hand menu.

    Some of the topics on menu should be reordered/renamed. For example, "communications" could become "news", and "data analysis" should probably be above "public outreach".

    If possible, we suggest retaining the style of the link map in the fixed header on the CXC pages, since we believe those are regularly used. We also suggest using a web tool such as Google Analytics to discover in detail how users are currently accessing the CXC site.

    We also recommend live user testing. For example, how long does it take a random postdoc to find something in the new Chandra web pages?

    Finally, although we do not think the page should have the same look and feel of the page, we are impressed with parts of the design on that site and suggest consulting with the group responsible for that page as the new CXC site is developed.