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Steve Allen (by phone)
Martin Laming (chair)
Joan Wrobel (by phone)
Belinda Wilkes opened the meeting and welcomed the committee on behalf of the CXC. Members of the CUC then introduced themselves.
Roger Brissenden gave the "CXC Manager's Status Report" for the period April 2010 - October 2010. Chandra ranked 2nd out of 11 missions in the Senior Review, with a score of 9.5/10. The Senior Review recommended full funding for FY 12, and recommended reinstating funding to the FY 11 budget for the development of tools for sub-pixel resolution. (The Annual NASA Budget Review calls for a $3M decrease in FY11 over the previous budget.) An Education and Public Outreach proposal has been requested for 1/24/11.
The spacecraft and instruments continue to operate superbly, with nominal passage through the summer eclipse season. Software upgrades in preparation would allow some spacecraft operations to continue through periods of heightened solar activity, while safing the science instruments. This allows a faster return to science operations following a return to normal conditions.
The observing efficiency remains very good, at > 75% for the whole April - October period, with three load interrupting TOOs during this period. The observing efficiency at the moment is gradually increasing as Chandra's evolving orbit reduces the amount of time spent in the radiation belts.
Mission metrics remain good, 49.7 lbs (out of 60) MUPS fuel are left, enough for 26 more years of operations at the current usage rate (which is higher than it was over the previous six months). Data delivery, and grant award effectiveness are as efficient as ever.
A review of the health of all major Chandra subsystems reveals that only the EPHIN is degraded sufficiently (by the loss of thermal insulation) to affect performance. However the function of the EPHIN has been taken over by the anticoincidence screen of the HRC, and so this poses no real problem. All told, the Chandra vehicle health is excellent, and it is anticipated to last at least another 10 years.
Harvey Tananbaum briefed the committee on the use of Director's Discretionary Time. In the period April 2010 - October 2010, a total of up to 162 ks from Cycle 12 has been allocated, out of a total of 200 ks (remaining after the deduction of 500 ks for use on the Chandra Deep Field South). It was proposed to add another 300 ks to the DDT from the "extra" time becoming available due to the evolution of the Chandra orbit.
Belinda Wilkes summarized the Cycle 12 peer review. A total of 681 GO proposals were submitted. They represented a 5.6 oversubscription in time. These break down into 72 LPs, 5 VLPs, 62 archive and 43 theory. The evolution of the Chandra orbit allowed 3 Msec of "extra" time, reducing the time oversubscription to a factor of 4.4.
18 archive proposals were funded at $1122K representing a final 3.2 oversubscription. 10 theory proposals were funded at $689K, a final oversubscription of 4.5.
The Chandra Deep Field South (CDFS) received 14 proposals, 7 were approved for a total of $532K.
Cycle 13 proposals will be due on March 15 2011, with the peer review on 20-24 June 2011. The CfP will be issued on December 15 2010. Updates for Cycle 13 will include the possibility of multi-cycle proposals, with 10% of the time from Cycle 14 and 5% from Cycle 15 available. The RPS system has also been revised to improve the handling of proposals with long target lists, as we recommended in our 2010 Spring Meeting report.
Wilton Sanders gave a report on the Chandra Guaranteed Time Observer Policy. Unusually among big observatories, Chandra GTOs still retain a share of the observing time. Before launch, to get more data to General Observers sooner, NASA HQ initiated a change from the originally approved (and more common) procedures (100% of observing time in the first two months, 50% during months 3-20, and 20% during months 21-30) to 100% during months 1 and 2, 30% during months 3-20, and 15% for the remainder of the mission. The 15% was later reduced to 11.4%.
The issue of whether GTOs should continue to receive these data rights has come up from time to time, most notably during the recent Senior Review. Wilt presented a number of arguments, mainly in favor of the current arrangement (this was the same presentation as given to the Astrophysics Subcommittee meeting on July 8th), which we review below.
Belinda Wilkes outlined two updates for possible incorporation into the Cycle 13 Call for Proposals which aim to promote the submission and enable the selection of major science proposals requiring > 1 Msec of observing time. The first is to reinstate the 3 Msec allocation each to LPs and VLPs, rather than allowing the two types of proposals to compete without restriction for the total 6 Msec. The second was to introduce a new category, the X-ray Visionary Project (XVP), calling for major coherent proposals to address current questions in astrophysics requiring > 3Msec of observatory time, with the expectation that one project of high scientific merit might be awarded per cycle. The additional time, over and above that for the regular cycle, is made available by the evolution of Chandra's orbit. The CUC were generally receptive to these ideas. We discuss our response, which merges these two suggestions, in more detail below.
Jonathan McDowell reviewed the activities of the Science Data Systems Group. Staff changes since the last CUC meeting include the departure of Mike Noble from the MIT team, and Antonella Fruscione now working half time. The helpdesk had received 149 new tickets, of which 10 are still open. Initial response times and times to ticket resolution remain, as ever, entirely satisfactory. Google Analytics has been added to the web sites to help track usage characteristics.
There have been over 1000 downloads of the new CIAO 4.2 released in December. The breakdown among platforms has not changed significantly. An update to Sherpa, together with general documentation improvements, was released over the summer.
CIAO 4.3 is under testing for a December 2010 release. This will feature a revised CTI correction to account for temperature variation within an observation and a sub-pixel correction algorithm.
Other items under development include a spectrum rotation issue for LETG/ACIS, R&D on sub-pixel event repositioning (SER), characterizing the Chandra PSF at sub-arcsecond scales, and an update to the ATOMDB
Ian Evans presented an update on the Chandra Source Catalog (CSC). Catalog Release 1.1 was released on August 10 2010. It extends the release 1.0 point and compact source catalog by adding public HRC-Imaging observations since the start of the mission, and ACIS imaging observations that became public after release 1.0. CSCView 1.1 was released with CSC 1.1, providing a variety of updates. CSCview 1.1.1 is scheduled for release this month (11/2010), adding a source position cross-match interface, along with updates to CSC Sky in Google Earth, a Catalog limiting sensitivity service, and a CSC-SDSS cross-match.
R&D for release 2.0 is under way, with several different scientific and infrastructure enhancements envisaged. Longer term plans include simultaneous source detection across overlapping observations with different detectors and pointings (and hence different local PSFs), and the detection and classification of very extended sources.
One item that until this meeting had escaped the CUC was that point sources in some fields that also include highly extended sources have so far been excluded from the catalog. In most cases if the extended emission is restricted to a single ACIS CCD, then the data from the remaining CCDs is included in the catalog.
Larry David gave a review of recent work on the Chandra calibration. Recent products released in April, June and October include time-dependent gain and temperature dependent CTI corrections for ACIS, and HRC-I gain maps and background updates.
Current calibration projects include the ongoing calibration of the ACIS CC mode, and analysis of HETG/ACIS CC-F mode observations of X-ray bright sources. Currently, TE mode gives more consistent results than CC mode. An update for the HRC-I effective area has also recently been provided. Investigations of a feature in the PSF with the HRC-I continue. An observation of AR Lac is planned to further diagnose the effect. Further updates to the LETG/HRC-S first order effective area will be contained in the next CALDB release, following a revision of the HRC-S QE, and the LETG/HRC-S extraction region for self-consistent cross-calibration. The ACIS-I contamination model continues to be studied and updated. It remains an empirical rather than a physical model. No changes are made at this time to the ACIS-S contamination model.
Work continues on the cross-calibration of Chandra instruments with those on board other X-ray astronomy satellites, e.g. XMM Newton, Suzaku, Swift, Integral, RXTE. The status of the Chandra calibration appears to be unchanged from our summary in the Discussion and Recommendations section of the last (Spring 2010) meeting.
Martin Weisskopf described plans for the Twelve Years of Chandra meeting, which this time will be a "meeting within a meeting" at the summer AAS meeting in Boston in May 2011. Such an association will likely benefit from the presence of astronomers having less experience with X-rays.
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.
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.
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.
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.
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).
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