Belinda Wilkes welcomed the committee on behalf of the CXC. Members of the CUC introduced themselves.
Roger Brissenden presented the "CXC Manager's Status Report", summarizing the current status of the observatory and the CXC. The FY08 budget survived unscathed at the planned level. Staffing levels, and the staff themselves, remain essentially unchanged. Other budget items are the expansion of the Chandra Fellowship Program, now renamed Einstein Fellows, to incorporate the GLAST (now Fermi) fellows and other Physics of the Cosmos fellowships. NASA also continues to work on a CXC contract extension to continue Chandra operations and science for up to an additional ~10 years.
The OCC's backup computer system has been shown to be capable of handling commands and telemetry. A test with the spacecraft is planned.
The spacecraft continues to operate extremely well overall. Spacecraft anomalies were reported in August. The telemetry processor of the Command and Telemetry Unit reset on 8/12, leading to a transition to Normal Sun Mode. One orbit of observing time was lost, with the spacecraft returning to Normal Pointing Mode on 8/15. The likely cause was a single event upset.
Mission metrics are good and do not pose limits to the mission lifetime. Observers continue to receive data approximately one day after they are taken. The backlog in issuing grants has now been eliminated. As of September 2008, no grants are outstanding. The CUC continues to be very pleased with the management of the observatory and the CXC.
Harvey Tananbaum reported on the use of Director's Discretionary Time (DDT) for the period April 2008 - October 2008. 118 ks was awarded, bringing the total for Cycle 9 to 233 ks with 115 ks previously allocated. The largest DDT award in this period was 30 ks, and a significant portion of the 700 ks available remains unused. The CUC continues to support the director in his operation of this program.
Belinda Wilkes summarized the outcome of the Cycle 10 call for proposals. A total of 639 proposals were received, representing a 5.6 oversubscription of observing time. This oversubscription is higher with respect to Large Proposals, being about 6.5. The only significant changes from Cycle 9 were that the time requested in LP and grating proposals were increased, and in VLPs decreased, bringing Cycle 10 statistics closer to those for Cycles prior to 9. For the first time LP and VLP together share 6 Ms, with no minimums or maximums individually. A little surprisingly, no VLPs were accepted.
Archive and theory proposals were well represented, and due to the panel grading of these proposals, a total of $1340K and $730K were awarded respectively, up from the nominal sums available of $1100K and $600K. It is clear that across the board, from GO, archive and theory proposal submission, interest in Chandra in the user community remains very high. See RECOMMENDATIONS 1 & 2 for the CUC discussion and responses to a couple of issues arising.
Nancy Evans discussed the latest developments in the fellowship programs. NASA has reorganized the former Michelson, Hubble, Spitzer, Chandra and Fermi fellowships around science themes rather than missions. Chandra and Fermi fellowships are now subsumed into the Einstein Fellowship program adhering to the "Physics of the Cosmos" science theme. While the CUC is disappointed to see the "Chandra" fellowships disappear, we recognize that the actual outcome of NASA's reorganization is satisfactory. We also wish to convey our appreciation of Nancy's efforts on behalf of the fellowship program, both in the reorganization and in revising the call for proposals. The CUC's response to possible institutional conflicts among fellows, now that there are 10 per year rather than 5, is deferred to the RECOMMENDATIONS section, item 3.
Larry David gave an update on Chandra calibration issues. A number of releases during the period April - September 2008 relate to gain correction for ACIS, order separation for HETG, and background filtering for HRC-S. Studies of the ACIS filter appear to show a leveling off of the C contamination since 2006. However while the O and F contamination appears to be quantitatively understood, the same is not true at the C edge.
The most serious issue still relates to the High Resolution Mirror Assembly (HRMA) effective area. A ~5% energy-dependent correction appears to have been applied twice, once via an empirical (pre-flight correction) and once as a physical contamination model. Pre-flight calibration data for the HRMA shells have been reanalyzed, and the depth of hydrocarbon contaminant on each shell inferred. Larry showed how this oversight came to light, in comparison of cluster temperatures determined by Chandra/ACIS and XMM/PN and XMM/MOS. Cluster temperatures derived from hard band vs. broad band measurements (2-7 keV vs. 0.5-7 keV) are still not completely consistent, both within Chandra and XMM. In the Chandra case at least, this presumably relates to the filter contamination, which still remains to be completely understood at the lowest energies. CUC RECOMMENDATIONS are discussed below in item 6.
Paul Plucinsky reported on the temperature control of the focal plane. Since 7 April 2008 the ACIS Detector Housing heater has been turned off. This was in response to the increased heating of the ACIS focal plane by the Earth (when in ACIS radiator field of view) and the Sun (when on the backside of the SIM), ultimately caused by aging of the thermal insulation. This change has greatly reduced the number of OBSIDs performed at temperatures > -119.2 C, which produces the intended effect of obtaining a much higher fraction of the science data at colder temperatures. The possibility of turning off a heater on the SIM focus assembly to provide more margin on the ACIS focal plane is currently being studied. The CUC thank Paul Plucinsky and the rest of the group for their careful work on this issue, and applaud the proactive way in which further options are already being studied.
Jonathan McDowell reported on progress within the Science Data Systems (SDS) group. CIAO 4.1 is on schedule for release in December 2008. CIAO workshops have been restarted, with 33 attendees at the next event (the week after the CUC meeting).
The helpdesk/testing staff has been increased. 55 new helpdesk tickets were reported between Jun 1 and Oct 1, with 3 still open. Response times and the time taken to close tickets (median time 1 day, average 3 days) strike the CUC as entirely satisfactory.
Ian Evans gave an update on progress with the Chandra Source catalog. The CUC was pleased to learn that the catalog database was made available for public access on October 8, including ~50,000 source detections, corresponding to ~35,000 distinct sources on the sky, and that the formal release 1 of the catalog is still scheduled for January 2009. Catalog production started on September 15, currently processing about 500 observations per week. Currently only point (or "compact") sources are included.
Ian gave a demonstration of the Catalog Web Interface (CSCview). A URL interface is also provided for users who want to query the catalog using a command-line interface or script. Other planned interfaces include a simplified view through the ds9 "catalog" interface and a Python scripting interface. Further CUC RECOMMENDATIONS are discussed below in item 7.
Dave Huenemoerder summarized the state of TGCat, the Chandra catalog of grating observations. This is now in a beta release, and provides data files, calibration and ancillary products to allow users to get started in data analysis, for over 800 sources. The CUC welcome this effort, and feel that it eliminates or mitigates many significant obstacles to new users entering the field of grating spectroscopy.
Dave also gave a demonstration of threads developed for analysis of grating data. Proposal planning threads included a simulation and fitting of the He-like "triplet", and an LETG/HRC-S multi-order and background modeling and fitting. A new analysis thread, a LETG/HRC-S crowded field using tgextract2 on two close sources was also presented. CUC RECOMMENDATIONS are discussed below in item 5.
Finally Pat Slane gave an update on Chandra observing constraints, arising from the EPHIN temperature restrictions. The maximum dwell time at certain pitch angles (centered on 90 degrees) are limited by the temperature increase of the EPHIN, and are likely to become more restrictive in years to come as the Chandra orbit evolves, reducing the amount of time it spends at perigee, and therefore reducing the time in which the EPHIN may cool down. These are difficult issues, which will not become any easier, and the CUC is impressed with the way the fraction of observing time available has been maintained despite them.
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.
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.
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.
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.
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.
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.
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.
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:
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: