|FUSE Observer's Advisory Committee|
|Meeting Minutes No. 5|
|17 August 2001|
Present: Bregman, Dinerstein, Federman (chair), Guinan, Harper, Koratkar,
Leighly (replacing Raymond), Robert,
Starrfield (replacing Deharveng), Wannier
JHU: Andersson, Blair, Dixon, Kruk, Moos, Sankrit, Weaver
Blair opened the meeting with a report on spacecraft status, recent performance, and planning. There was a second Reaction Wheel anomaly in February, but things have remained stable since then. A second high voltage increase was applied to counter the effects of gain sag. Otherwise, the sensitivity remains excellent, channel alignment is going well, and the few single event upsets (SEU's) and bursts that do occur are now screened out in the new version of CALFUSE (v2.0). The performance continues to improve beyond nominal expectations. Acquisition has a 96% success rate and the science efficiency (time taking data/clock time) is now at 30%. With the availability of guide star checking tools, offset acquisition is straightforward. To date, 94% of Cycle 1 targets and 51% of Cycle 2 ones have been observed; most of the other observations will be completed by the end of Cycle 2.
He also described both Long Range and Short Range Planning. The Long Range Plan is iterated about once/week; constraining targets drive the Plan. As for the Short Range Plan, there is now improved flexibility because peakups, FP-SPLITs, etc. are now scheduled in a semi-automatic fashion. The Committee appreciated the fact that the PI of a program is notified of upcoming observations about a week in advance through e-mail. The Project is able to observe moving targets more easily than before. Blair also noted that CALFUSE v2.0 is almost ready (it is in beta testing) and that the archiving backlog was eliminated through the hiring of additional personnel. Finally, future plans include a revision to the Bright Limit and a procedure to do high voltage ramping during occultations.
Kruk discussed the status of the gyros and related matters since the failure of the y-axis of the Inertial Reference Unit-A (IRU-A) last spring. The gyros have already exceeded the vendor's estimated lifetime of about 1 year; the remaining life for the X and Z axes of IRU-A is not known. The FUSE Project has made the development of gyroless operations its highest priority because without a gyroless operations mode, the loss of the y-axis of IRU-B would likely mean the end of the mission. The Attitude Control System (ACS) will be switched to a cross-strapped mode should an axis fail in IRU-B. Overall, there is less jitter with IRU-B, but the slew accuracy is a bit worse. Should there be a second gyro loss, the drift rate would increase from 0.01"/sec to about 10"/sec, acquisitions would be more difficult, but the tracking would not be affected much. It was also noted that significant software changes would be required; these will be installed over the course of the next 9 months: 12/01 for ACS and 06/02 for FES/IDS.
Sonneborn reviewed the general results of the Cycle 3 review, as well as recent science news. In Cycle 3, the oversubcription rate was about 2.5:1 in observing time. The number of large proposals (22) was larger than in previous cycles, and an interesting aspect was that there was a 60% increase in proposals from US investigators. Scientific highlights included P Cygni lines in WZ Sge (a target of opportunity), the Gunn-Peterson effect in He II (which when combined with H I absorption yields the ionization fraction of the intergalactic medium), O VI emission, but no H2 absorption or emission, from the disk of beta Pic, CO and H2 emission from a comet, H2 emission from Mars (which provides an estimate of the original water abundance), and new results on the D/H ratio (D/H vs. O/H is not correlated and D/H does not vary in the local bubble).
Dixon summarized the status of calibration and analysis software. The release date for CALFUSE v2.0 is 1 Sept. The changes in this version include an improved wavelength scale, detection and removal of bursts, a walk correction (affecting low Pulse Height events), an improved scattered-light model (for background subtraction), improved flux calibration for all apertures, and an astigmatism correction (yielding a 10% improvement in resolution for point sources). Optimal/weighted extraction is now possible, in part because the ability to 'locate' the spectrum has improved. (Since the meeting, the new version of CALFUSE was implemented in October and is expected to become the default for routine pipeline processing of data during November.)
Future versions will have improved flat-fielding and the ability to correct for worms. While a GIF (extracted) spectrum is available at MAST now, plans are to have GIF images for individual channels. There are also plans to show a mask of the channel image and count rate plots at the exposure level. In a related matter, Andersson noted that a Web interface is being developed to minimize mistakes during Phase 1 submissions of proposals. One addition would be highlighting the FUSE Archive at MAST.
Much of the remainder of the meeting dealt with the Extended Mission (EM) and the upcoming NASA Senior Review. Blair described the concept for the EM. As much as possible will be automated, but there will be no new software development or hardware improvements (e.g., UPRM) in the EM. The goal is to standardize procedures, such as alignments, and to cross train personnel on all critical functions. Kruk gave an overview of specific issues. These include maintaining the calibration, the scheduled efficiency (but with lower actual efficiency), and the observing capabilities (moving targets, FP-SPLITs, etc.), but with fewer channel alignments. There will be a increase in recovery time and the affected observations may not be rescheduled, depending on their priority.
Sonneborn then led the discussion on the NRA for Cycle 4 and the upcoming Senior Review. There will be about 6 Ms of observing time available in Cycle 4 (the first cycle of the EM). Additional categories of targets will be implemented; only the highest priority targets are assured of being observed. Lower priority targets would include those with very poor fluxes. The possibility of surveys of classes of targets was discussed, in the spirit of SNAPSHOT observations with HST. Finally, ties to Chandra, XMM, etc. in the form of blocks of time was considered.
The proposal deadline for the Senior Review is in early May, 2002. The main proposal will be to extend the EM for another 2 years, through 2006 (Cycle 7). Possible plans include Legacy Projects which use the unique capabilities of FUSE for surveys, etc. New capabilities, now being tested, include observing bright targets only in the SiC channel or via defocusing.
Andersson (and Sonneborn) concluded the formal portion of the Meeting with several announcements and suggestions. Instead of another data workshop in February 2002, a program highlighting science with FUSE was discussed, as were more formal venues, including a conference in Summer of 2003 that could be part of the IAU Colloquia series. A proposal for a Joint Discussion at the next IAU General Assembly was considered as well.
The meeting ended with an executive session. The Committee appreciated the efforts made on producing GIF images of archived spectra and in notifying PI's of upcoming observations (which are especially needed for coordinated observations). There was discussion about having the FOAC meeting in conjunction with the Science Meeting (see above) and about new membership for the Fall (2002) meeting. Graham Harper will be the next Chair; Steve Federman will remain Chair until the preparations for the NASA Senior Review are completed.