About Chandra Archive Proposer Instruments & Calibration Newsletters Data Analysis HelpDesk Calibration Database NASA Archives & Centers Chandra Science Links

Chandra Users' Committee Meeting (25-26 October 2010)

Report issued on 02 Dec 2010

Back to main CUC page


Luisa Rebull
Steve Allen (by phone)
Matthias Ehle
Elizabeth Blanton
Joel Kastner
Martin Laming (chair)
Massimo Stiavelli
Joan Wrobel (by phone)
John Tomsick
Jimmy Irwin
Ann Hornschemeier

Summary of Meeting


  1. GTO Time

    This is apparently an issue that has come up and been discussed by the CUC in the past. The current GTO arrangement is unusual. The GTO teams receive a similar amount of time each year to those associated with other big observatories, but since the arrangement is open ended, they are receiving more data (and funding) than they would have done under the original plan. Presumably these data and funding (or a part thereof) would now be available to GOs if the original plan had continued. In this case the pertinent question to ask seems to be "Does the continued GTO policy benefit the Observatory in terms of maintaining the necessary engineering support, and in terms of science output?". Wilt showed data in his presentation to suggest that at least in terms of papers published, the GTO teams more than hold their own against GO science.

    An argument is also made that the continuing availability of GTO time is helpful in keeping GTO teams together, and that maintaining the integrity of these teams is vital to the long term health of the instruments on the observatory. Many of the engineering and maintenance tasks are carried out by personnel who are primarily scientists, and who stay on the project because of the access to data afforded them. The precise risk to the observatory health created by changing the GTO policy is of course difficult to quantify, but on the perhaps optimistic assumption that funding saved by eliminating the GTO program would have to be made available to the GO program for data analysis, it still seems to be an unnecessary perturbation to the Chandra organization.


    We find that the current GTO policy is very beneficial to efficient operations of the Chandra X-ray Observatory, and that maintaining the integrity of the GTO teams is important for the long term health of the Observatory. We emphatically concur with the recommendation of the Astrophysics Subcommittee that the current GTO policy be retained.

    In the event of future budget cuts, we suggest that the project itself should be allowed to decide where these cuts should fall so as to minimize the impact on Chandra science and operations. We note that in dollar amounts, the GO funding has not been cut since the beginning of the mission (obviously the buying power of those dollars has been eroded by inflation), and that so far all cuts have been absorbed by the instrument teams and other mission operations.

    While this recommendation and policy appears to make Chandra anomalous among comparable big observatories, we consider that astronomical instrumentation at this level of sophistication should not be handled with uniform policies. In particular, it appears that X-ray instrumentation is more robust and longer-lasting than optical or infra-red detectors, and that such considerations should inform the GTO data policies.


    We also suggest that instrument teams collect important papers, engineering developments, etc from recent years in case the GTO policy comes under renewed pressure. For instance, this time last year the CUC heard about the successful resolution of the MUPS pressure anomaly that occurred over the summer of 2009. This was due in no small part to having people who were familiar with the relevant spacecraft systems, including some of the instrument PIs, readily to hand, and so disaster was averted.
  2. XVPs

    The CUC were cautious about implementing two changes in one year to the proposal categories (i.e. imposing a quota of 3 Msec each for LPs and VLPs, instead of letting the boundary float, and also instituting the XVP category, since these two major changes may have unintended consequences. We were more comfortable with reinstating the (separate) quotas for LPs and VLPs, and extending/replacing the VLP category to the much broader scope proposed for the XVPs.


    We endorsed the draft announcement circulated to users in early November. In particular, adhering to our recommendation, but changing the name VLP --> XVP emphasizes the novel and anticipated legacy aspects a little more.


    In view of the relative decline in recent years of time proposed for VLPs and also in the time actually awarded, and the seemingly natural tendency for peer review panels to avoid long proposals (e.g. the article on The Hubble Multi-Cycle Treasury Science Program that was circulated to us before the meeting), we also recommend the CXC host a workshop dedicated to long projects, similar to those organized by HST.


    We also recommend the XVPs be treated similarly to the VLPs in past years, being reviewed in the relevant topical panels first. It might also be beneficial to have the review pundits arrive at the review earlier than they have in the past, also to review the XVPs in parallel with the topical panels, so that as many people as possible have seen the proposals by the time the Big Project Panel meets at the end of the review. We also suggest that pundits be chosen with care, in the hope that people who would be willing to "champion" long proposals can be identified, in order to try and combat the natural bias of peer review panels towards short proposals.

  3. Director's Discretionary Time

    The CUC consider that the DDT time is awarded in a very fair and conscientious manner, and considering that a large amount of the original DDT allocation was contributed to the Chandra Deep Field South, we concur with the addition of an extra 300 ksec to DDT from the extra time becoming available due to the evolution of Chandra's orbit.


    We endorse the transfer of 300 ksec to augment the DDT allocation for Cycle 12. Similar augmentations of the DDT time allocation for future cycles should be considered year by year at future CUC meetings.

  4. Long term planning/next Senior Review?

    The CUC expressed a desireto help Chandra position itself to fare well in the next Senior Review.


    We thought that Chandra should pursue a joint proposal arrangement with ALMA, as this would (a) broaden Chandra's user base and (b) strengthen Chandra's synergy with ground-based facilities.

  5. Sub-Pixel Event Reconstruction

    The CUC discussed the tentative identification of a PSF anomaly. The anomaly is better defined in HRC images than in ACIS (due to the better resolving power of the former), and there was some evidence that the anomaly had only appeared post-launch.


    We encourage the CXC to pursue the confirmation and characterization of the anomaly, since understanding the PSF at the sub-ACIS-pixel level will be critical to the CXC's ongoing efforts to implement subpixel event relocation (SER) -- as recommended by the most recent Senior Review -- and, even more, when trying to use SER in conjunction with deconvolution. It is also very important to investigate the anomaly's energy dependence (via ACIS imaging).

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory.
60 Garden Street, Cambridge, MA 02138 USA.    Email: cxcweb@head.cfa.harvard.edu
Smithsonian Institution, Copyright © 1998-2004. All rights reserved.