Chandra X-Ray Observatory

Chandra Users' Committee Meeting (29-30 October 2009)

Report issued on 7 Dec 2009

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Luisa Rebull
Matthias Ehle
Elizabeth Blanton
Ken Ebisawa
Joel Kastner
Martin Laming (chair)
Jon Miller (by phone)
Steve Allen (by phone)
Ann Hornschemeier
Massimo Stiavelli
Joan Wrobel

Summary of Meeting

Discussions and Recommendations

  1. MUPS anomaly.

    The CUC strongly endorses all the actions taken to resolve this issue, and congratulates all personnel on the successful outcome. Having the necessary expertise available "on call" was clearly critical.

  2. Chandra Deep Field South.

    The CUC endorses this use of Director's Discretionary Time, and the suggestion to have archive proposals compete for the fund available to analyze this dataset at the Cycle 12 Peer Review. We recognize that a number of (good) proposals to do just this have been submitted in recent years, but have not made it through the peer review process. While peer review is the best selection mechanism we have for proposals, it is not perfect, and the use of DDT to remedy such imperfections is wholly appropriate.


    Tell the community as soon as possible that this is going ahead. It looks like this has already been done to some extent in Chandra bulletin #89, e-mailed in 11/5/2009, and in AAS Electronic Announcement #202, e-mailed on November 11.

  3. Proposal to restore separate time allocations for LPs and VLPs in Cycle 12.

    It was noted in Cycle 11 that several of the LPs approved asked for substantially more than the 300 ks LP threshold, some for 700 - 800 ks, and so we felt that there is no real bias against long observations in the big project panel. Notwithstanding our endorsement of the 2Ms DDT observation of the CDFS, the CUC is unanimously opposed to restoring separate allocations for LPs and VLPs in Cycle 12.


    We recommend for Cycle 12 at least, not to go ahead with separate LP and VLP time allocations. This is a difficult issue and should probably be revisited every year after the peer review. We are generally cautious about the unintended consequences of "over-engineering" the peer review, and prefer to leave this process alone to decide the relative merits of proposals. Of course in extreme cases, such as the Chandra Deep Field South, external intervention is necessary and desirable. We don't feel that the relative lack of approved VLP projects in Cycle 11 yet rises to this level of concern.

  4. Web site.

    Great progress has been made. We like the new instrument sites, and the way they are linked to the rest.


    The web site should be exercised externally before the Cycle 12 Call for Proposals. Some of the CUC members expressed a willingness to help in this. We also endorse better integration of the MIT sites with the Chandra web site, with e.g. lots of reciprocal links.

  5. CIAO.

    We endorse the choice of Python over S-Lang for the scripting language. It seems that Python is going to be the more widely used, and this change lowers the threshold for new users. We also endorse dropping support for Mac PPCs.


    The CIAO survey seems to have been valuable, and we suggest doing this more often. Not every year, but maybe every 2- 3 years. We also recommend looking into providing support for the Mac Snow Leopard platform, and like the idea of keeping CHIPS and SHERPA separate from CIAO in the distribution.

    In the area of long term planning, we encourage discussions between the different projects (XMM, Suzaku, etc) to coordinate approaches to issues such as platforms, operating systems, libraries, compilers etc.

  6. Senior Review.

    The CUC feels that the 2010 Senior Review is of paramount importance, especially because Chandra will be held to a high standard as the flagship high energy astrophysics mission. Both in terms of science, and science/dollar, the CUC feels that Chandra should strive to achieve the top ranking.


    The CUC urges Chandra to engage with its observing community to help develop the strongest possible proposal, and to do so on a timescale that permits revisions and reflection.

  7. Calibration.

    We recognize the extensive calibration effort that has been applied to the Chandra telescope, and the dedication of the calibration team, and endorse the approach of the calibration group in trying to understand the instrumentation as thoroughly as possible. Having said this there are still some aspects of the calibration that cause concern, particularly the cross calibration. We are aware that problems here might not be Chandra problems, but associated with the other missions. While the reanalysis of the ground calibration data undertaken since January appears to have improved things and validated the recent CALDB release, we note that the cross calibration plot only showed data from ACIS, where O VII and O VIII lines are blended together, as are Ne IX and Ne X. Data from HETG-MEG for these lines would be much more compelling, especially in comparison with the XMM Newton RGS.

    Progress on the filter contamination looks good. We appreciate that this problem is exceedingly complex, given its temporal, spatial and spectral dimensions. However ideally the CUC would really like some more insight into what the calibration team knows and how they are dealing with it.

    Concerning the Calibration website: We were told in response to our 4/09 report (see notes 1.2 and 1.3 from that report) that the Calibration team would add "new sections regarding hot topics" (like contamination and cross-calibration, we presume) and that "some prototypes for these new sections" would be presented at the 10/09 meeting. Most of these issues were discussed, but not in the context of the CXC Calibration web page, which still poses difficulties for some users.


    The cross calibration between the HETG-MEG and the RGS should be completed as soon as possible. With the change of effective area in January 2009, this comparison worsened (see e.g. slides 13 and 14 of, and it would be interesting to see whether the application of the new contamination model improves this, as it appears to do for ACIS-S3.

    As has been mentioned before, our main concern is not so much with the technical aspects of the work, which we really cannot fault, but with communication with the user community who need advice that is as clear and well justified as possible. One possibility might be a comprehensive "Status of ACIS Calibration" memo describing the issue. Such a memo should address (a) what is known about the problem (i.e., collect and explain all the relevant data in a coherent fashion), (b) the various models proposed, and their strengths and weaknesses, (c) the near-term implementation of a contamination model(s) in the CALDB, and the rationale behind the implementation (as we understand the informal discussions during our 10/09 meeting, some sort of hybrid model was just put in place, consisting of one piece for ACIS-I and one piece for ACIS-S), and (d) the calibration team's longer-term plans for contamination monitoring and modeling.

  8. Catalogs.

    Significant progress has been made since the last CUC meeting in terms of accessibility. The Google Earth interface is a very nice thing to have, and will probably prove to be of more use in getting non-experts involved in X-ray astronomy than for professional astronomers.


    The 500,000 hits on the Google Earth interface, even if only from a few thousand distinct IP addresses, is impressive. We are prompted to suggest tracking scientific use of the catalog in this way, maybe for the Senior Review in two years time, and to encourage authors to acknowledge use of the catalog in publications. We also encourage the importation of extended sources to the catalog as soon as possible.

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