Report of the 70th meeting of the CFHT SAC

Waimea, 8-10 November 2006

The meeting was attended by SAC members Pierre-Alain Duc (vice-chair), L. Ferrarese, C. Ftaclas, J. F. Gonzalez, C. Gry, H. Hoekstra, R., P. Petitjean and N. St-Louis (chair). Jeremy Lim, from the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan also attended the meeting. The CFHT director C. Veillet, D. Salmon, Kevin Ho, Loic Albert, Jean-Charles Cuillandre, Olivier Lai, Hervé Haussel (for the LS steering group) and P. Martin, participated in presentations and discussions.

Recommendation #1 Renewed technical collaboration between CFHT and CEA
Recommendation #2 Reduced cross-talk of the ESPaDOnS Spectropolarimeter
Recommendation #3 Reiteration of recommendation to decommission GECKO
Recommendation #4 LS will not be completed by the end of 2008A
Recommendation #5 Terapix request to modify the current data release agreement
Recommendation #6 Terapix request to stop processing Very Wide data
Recommendation #7 Large and multi-year programs with all major instruments
Recommendation #8 VASAO

1. Technical Activities Report

Derrick Salmon reported on the technical activities of this semester. The effects of the earthquake that occurred on 15 October 2006 were described. Although some damage did arise at headquarters and at the summit facility, these were relatively minor. The dome and its bogies move laterally by 2 cm and had to be put back in place. The precision HA incremental encoder track was damaged; its mechanical interface with the horseshoe and its drive roller were destroyed. SAC congratulates the staff for their quick and efficient work, which resulted in very little observing time being lost.

The office of Mauna Kea Management has given its approval for the grounding grid repair work and for the OHANA fibre-optic conduit to be built under the roadway. A contractor will be selected in November.

2. Instrument and Project Reports

· MegaPrime

Although the number of failures continues to decrease, some problems remain. Since our last meeting, problems in 3 main areas have arisen:

Rotating valve of the cryogenic system: The source of the problems with this system has still not been identified. The motor torque has been eliminated; contamination of the buffer volumes attached to the rotating valve assembly is being investigated. A test cryostat has been fabricated to provide a test facility for this system without being attached to the camera.

CEA has offered to supply a new version of rotating valve. This is presently being considered by CFHT but no decision has been taken yet. The test cryostat mentioned above could be used to test this new rotating valve assembly but a pulse tube would be required to do so.

CEA has proposed to visit CFHT and carry out a complete maintenance procedure of the instrument. This was not specifically requested by CFHT but the offer is being considered. Over the years, the staff has gained a considerable amount of knowledge about the instrument, which has changed substantially since it was first delivered. An in-house maintenance program has already been established and is regularly being carried-out by the staff and it evolves as a better understanding of the failures is acquired. It is not clear if some additional procedures are needed.

SAC Recommendation #1

SAC acknowledges the renewed technical collaboration between CFHT and CEA. It is now clear that MegaCam will be used at CFHT after the completion of the Legacy survey and that it has become an important component of CFHT instrumentation. We therefore suggest that lifetime and maintenance issues be clarified with regards to recommendations from CEA and experience gained at CFHT.

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Jukebox: The jukebox was found to be misaligned by 2 mm with respect to the slide rails. It was realigned and gauge blocks as well as a new brass guide for the top right slide rail, were fabricated. This seems to have reduced the amount of wear. No problems with the jukebox have been encountered since these modifications were made last July.

Guider: In May there were problems with the guider readouts, which stopped several times a night. The problem has disappeared but its source has not been identified and is still being investigated. Writing a better error-handling program seems to have alleviated the problem.

Concerning data reduction, SAC is pleased that better recipes have now been incorporated into the Elixir package and that the flats are now really consistent from one chip to the other (at the 0.5% level).


Hardware: Efforts have been made to make the instrument more robust as a whole. Major improvements have been achieved in the detector read-out speed and a saturation map has been secured. The cross-talk pattern induced on scientific images by the on-chip guider has been substantially reduced; only a faint vertical line remains when many images are stacked. Randomising the choice of the guide star to further reduce this effect has been implemented since 2006B.

One of the chips is slightly off the plane of the three others, leading to a difference in focus on that chip. The whole detector could been tilted to reduce the problem, which is thought to be caused by different thickness levels of the substrate. Removing the chips and shimming is considered risky. No decision has been taken yet on what to do. The focus sequence has been considerably shortened as it has been realised that two points are sufficient instead of a full focus curve.

The electronic gain was changed as it was realised that the full dynamic range of the detector was not being exploited. As a consequence, non-linearity corrections close to 10% instead of 5% will be required but fortunately the non-linear curve is well behaved. The maximum possible exposure time will therefore be increased which in turn will increase the observing efficiency.

Calibrations: The best way to carry out flatfielding (dome, sky or twilight) is being investigated. Standard stars are being observed to carry out the photometric calibrations. For wideband filters, the 2MASS photometry is used while for narrow-band filters, empirical zero points are being determined using appropriate 2MASS filters. The data for the absolute calibration of the Y filter are now in hand and should be implemented within the next month.

The global throughput of the instrument was estimated and found to be very high (52% in H and K and 41% in J). Also, the exposure-time calculator was found to be fairly accurate when the COSMOS team evaluated their limiting magnitude on a very deep 10-hour integration and compared it with the value predicted by the calculator.

Pipeline: The data reduction scheme has been determined after exchanges with Terapix. It was decided that CFHT provides two datasets to Terapix, one with basic sky subtraction and one without (both have full detrending). Terapix uses the first to mask faint sources on the second set in order to carry out a more accurate sky subtraction. Data reduction procedures for the two more challenging observing modes, Wide Dithering Pattern and Nodding Pattern, are still being worked on. In future months, efforts will be concentrated on automating the pipeline and improving the image processing recipes.

Up until now, no pre-processed data has been sent to CADC. The data has been distributed on a PI-request basis. This will be improved once the pipeline becomes more automated.


Since the new fibre bundles have been installed, better fibre routings have been found and protections have been installed. Tests have been devised to monitor their throughput. A temperature-based focus model has been created and will be implemented during next runs.

Testing of the new triplet lens has been carried-out and the cross-talk from circular to linear (and vice-versa) polarisation has been confirmed to be at the 2-3% level (rather than 7% before).

SAC Recommendation #2

SAC is pleased with the greatly reduced cross-talk of the ESPaDOnS Spectropolarimeter. We recommend that CFHT contact the user community to establish if there is a scientific need for further reduction.

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· FlyEyes

FlyEyes is progressing well and is in the final stages of integration with the AOB. The fibres from the lenslet array still need to be connected to the cryostat, the membrane mirror needs to be synchronised with the CCD controller before the closing of the AO loop is attempted.


SAC was informed on the first fringes that were secured in June 2005 between the two Keck telescopes (a world first!). In that experiment, the star 107 Herculis was observed and both telescopes fed their common interferometric focus with 300 metres of single-mode fibres. Since then, bad weather has delayed efforts. SAC was informed that the OHANA team did however get another full night on both Kecks during which no interference fringes were found although expected. The reason for this is not well understood but clearly needs to be resolved before more progress can be achieved. More observing nights will be requested. The next step will be to link CFHT and Gemini and subsequently Keck and Subaru. As mentioned above, the office of Mauna Kea Management has given its approval for the fibre-optic conduit for OHANA to be built under the roadway and a contractor will be selected this month (November).


Last July, the Remote Buss Monitor card caused the TCS to crash by overwhelming the CPU, The problem most likely caused by degraded electronics was temporarily solved by enabling staff to disable the interrupt when required. A new RBM card is being designed.

The computer handset function was disabled since this option was thought to be the origin of the infamous "phantom handset" problem (unexplained commands to the TCS from the handset causing random telescope jumps). The problem has not re-occurred since.

The worn bearing on the incremental encoder mount on the HA axis which caused telescope jumps has been replaced.

Finally, non-sidereal tracking was implemented to facilitate observations of Mercury and of the SMART-1 collision on the moon.

· Gecko

SAC was informed of the efforts required to get the Gecko spectrograph ready for an observing run in 2006A.

SAC Recommendation #3

In view of the fact that 2 man-months were required to get GECKO operational for a 4-night observing run in 2006B and that no GECKO proposals have been received for 2007A, we re-iterate our recommendation to de-commission it.

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· Progress report

The steering group chair presented the progress report of the Legacy Survey for the past year. Science highlights for each components of the survey (SNLS, Deep, Wide and Very Wide) were also presented. The visibility of the science from the LS is more and more acknowledged world-wide and the impact of the survey is expected to increase sharply with the first world data release which will take place in February 2007 and consists of T0003 data.

Concerning operations, SAC was informed that the introduction of the summer W4 field to alleviate the problem of securing data for the winter W2 field paid off grandly: in just one season, 66 integration hours of W4 were accumulated, almost catching up the total integration time on W2 up to now (73 hours). The validation rate remains low but this is due to very bad weather on Mauna Kea, mainly during the winter months. Although all components of the survey have suffered, the steering group points out that under unstable conditions, the Deep and Wide components suffer a lot with respect to the SNLS. Therefore, the loss of the 2+2 allocation from the Canadian and French agencies has resulted in a net loss for these two components. The steering group therefore requested that the additional 2+2 nights policy be re-instated.

SAC Recommendation #4

It has now become clear that the LS will not be completed by the end of 2008A. Even with the re-instatement of the 2+2 nights, an extension will very likely be required to complete the LS. SAC feels that allocating 2+2 additional nights to the LS would put unnecessary pressure on PI programs until 2008A and therefore does not support this request.

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SAC was informed of the progress made regarding the photometric calibration of the data. Previous versions of Elixir were not able to calibrate the images to better than 2% but refinements to recipes used and realisation of the limitations of others now lead to a calibration accurate at the 0.5% level.

A report of Terapix activities was also presented by the steering group chair. These mainly consisted in (i) the production of MegaCam and WIRCam PI data (including CFHT-LS related ones), (ii) the production of the photo-z for the CFHTLS deep data using the T0003 release, (iii) the production of the T0003 data release and (iv) development and improvement of software.

Terapix has expressed its concerns about the increasing workload generated by PI programs and the productions of the Very Wide stacks.

SAC Recommendation #5

Terapix has asked the LS steering group to modify the current data release agreement to make it yearly instead of once every semester, given that semi-annual releases have not been made so far. As we see no problem with such a change, we recommend this release schedule be implemented.

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SAC Recommendation #6

Terapix wishes to stop processing Very Wide data except when requested by PIs. SAC does not support this suggestion. Instead, to insure legacy value, SAC recommends that there be an official release of all first epoch data in stacked form within one year of the release of T0004.

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· Observing Plan for the end of the LS

The steering group chair presented a detailed plan for the end of the LS. The SNLS, Deep and Wide will continue to observe until the end of 2008A while the Very Wide component will finish observing in 2007B. In order to finish the survey as planned during the mid-term review, the Wide component will be requesting an extension in 2008B to complete observations of the W1 field and to secure pre-survey data for W4.

4. Telescope Use and Scheduling

· Joint Canada-France proposals

The members of the SAC-TAC from Canada and France met before the beginning of the SAC meeting to discuss joint Canada-France proposals. As the possibility of giving the Canadian and French TAC chairs the ability to change the ranking of proposals has not yet discussed by the Board, no changes in the rankings took place. However, the informal discussions went well and the SAC-TAC members found the exercise extremely useful. Although we note that this time there were no main disagreements, we believe that such a process could be efficient.

· Large WIRCam programs

SAC notes that the call for WIRCam programs has once again led to a small number of proposals (one joint Canada-France proposal and one from France) which were in fact re-submission of the ones from last year. However the success rate was high, as all programs were accepted.

· DDT Time

Following a request by SAC, Christian Veillet prepared and presented a report on the usage of the 10 nights of the Directors Discretionary Time (DDT) at CFHT (3 of these are given to the LS).

The CFHT scientific staff are carrying out a dynamic research programs in various branches of astronomy and using all CFHT main instrumentation. Some of the DDT is also used to prepare the scientific case for the future instruments or to solve tricky problems with the night allocations of the agencies. SAC finds this report very interesting and would like to see them continued to be prepared.

· QSO Report

Pierre Martin presented the QSO report. Two instruments are now being fully offered in queue mode (MegaCam and WIRCam). Both instruments are working extremely well in this mode although they have been severely affected by bad weather.

The observing efficiency of MegaCam was reported to have continued to increase mainly because of fast guiding acquisition and a reliable automated focus model. In spite of the un-cooperative weather (46% of QSO nights lost in 2006A), the completion rate of A+B programs in 2006A is nearly 73%.

For WIRCam, some nights have been used for engineering and commissioning. The 2006A completion rate is lower than for MegaCam but is still acceptable at 61% in view of the 48% of nights lost to weather.

In both cases, the 2006A queue validation efficiency is extremely high at 92%. General remarks that can be made for queue observing with MegaCam and WIRCam are: (i) the entire chain of operation from the planning of the queue to the commands sent to the telescope is robust and efficient, (ii) the very concept of queue observing is sound and (iii) well adapted for those programs that have time constraints. Finally, (iv) when the weather is bad, either because of non-photometric conditions or variable seeing, observing in queue is very difficult.

Operational overheads for MegaCam are still very good at 10-15% of an observing night. For WIRCam, the overheads have decreased but are still relatively high at 25-30%. They are dominated by the focus sequence, the guiding acquisition and pointing corrections and by telescope offsets.

QSO staffing is improving following the hire of the 2 new service observers at the end of 2006A. The situation is still tight but acceptable.

Integrating ESPaDOnS in QSO is starting to be discussed. One difficulty that could arise is the very different philosophy of the control software of ESPaDOnS compared to that of MegaCam and WIRCam. No specific schedule has been adopted yet for the implementation of ESPaDOnS in queue; the progress of this project will depend on the availability of resources.

For logistics reasons, the TACs have requested to be informed of the programs ranked C that CFHT carries out.

5. CFHT’s Golden age

Christian Veillet presented an update on the goals and the metrics the observatory is using as well as the means used to keep track of failures. The pressure on the telescope remains high both in France and Canada although there is a definite decrease after the peaks at the end of 2005 caused by the arrival of WIRCam and ESPaDOnS. The number of publications per year based on CFHT data remains above the goal of 50 since mid 2002. The effect of Legacy Survey is not yet included in these statistics.

The percentage of clear sky time lost to failure per run is 4.7%, above the present goal of 4% set by the management. This still represents a very small amount of failures and SAC congratulates the staff for this achievement.

The first steps towards the automation of the summit have been taken. The overall increase in the efficiency and a better maintenance program are the basis before concrete actions can be undertaken. The first stage that is being considered is to observe from headquarter in Waimea. The efforts remain modest for the moment but are slowly ramping up. It is important to define the project well.

Finally, the next users meeting in May 2007 is viewed as very important to prepare for the future of CFHT.

6. Long-term options for CFHT

· Large programs for MegaPrime and WIRCam beyond 2008

SAC discussed the possibility that large programs be extended to the other main instruments available at CFHT, Megaprime and ESPaDOnS. The possibility of allowing smaller programs to extend over several semesters was also discussed.

SAC Recommendation #7

SAC feels that there is a place at CFHT for large and multi-year programs with all major instruments and believes that the advisability of such programs and how they could be implemented needs to be explored. As this requires input from the community, SAC recommends that this should be on the agenda of the next User’s meeting. In light of the community’s views, this issue will be discussed further at the next SAC meeting.

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A feasibility study for VASAO was presented to SAC by Christian Veillet. Work on this project started one year ago and has mainly been carried out by Olivier Lai, Derrick Salmon and Christian Veillet. More staff are now getting involved such as Kevin Ho and Dan Sabin.

The ELP-OA project in France is proceeding and there has been an agreement to share expertise. Both Jean-Paul Pique (Co-I of ELP-OA) and Auguste le Van Suu (ELP-OA) visited CFHT, which was useful for them to have in mind a potential physical location for future implementation and for CFHT to gain knowledge on the one and two photon options for the laser.

CFHT wishes to test some key concepts of VASAO. A simple prototype seismometer is now being studied to monitor the vibrations of the telescope. The launch of a 330nm beam to get a clear photometric measurement of the flux provided is considered as an interesting experiment to be carried out at CFHT.

SAC has become aware that a disagreement concerning the flux efficiency of the two possible laser options (the single photon excitation with the UV 330nm line and the two photon excitation) has arisen within the ELP-OA collaboration in France. A review by independent experts, requested by the INSU ASHRA program, raised doubts on the feasibility of the single photon excitation option (supported by Jean-Paul Pique).

SAC was impressed by the very interesting presentation made by Olivier Lai on the various upcoming challenges awaiting the VASAO project. Main issues include the differential tip-tilt sensing scheme, the Laser Guide Star launch telescope, the determination and tracking of the focus, the Pueo Hou high-order AO system and slow guiding and the feedback from the seismometer. The VASAO error budget was also presented in great detail in the document presented to SAC and prepared by Derrick Salmon.

A report was recently sent to the external review committee of VASAO which consists of many renowned experts from around the world. Their reply should provide a valuable independent evaluation of the project.

In the context of VASAO, SAC believes that Fly-Eyes is an important development, a new approach to low noise detectors and applauds the recent progress achieved. We anticipate seeing on-sky testing.

SAC Recommendation #8

VASAO remains an interesting concept and we support continued development of the idea to bring it to a sufficient level of maturity where cost and schedule estimates can be generated. However the technical issues that have been raised on the use of one or two lasers should be addressed before major manpower and/or funds are committed.

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* Other options:

Christian Veillet briefly described the various responses that have been received since he issued a call for new ideas in January 2006. Among the suggestions are a large field-of-view IR camera, an IR ESPaDOnS and a very high-resolution spectrograph for asteroseismology. These will be discussed at the next users meeting in May 2007. At the next SAC meeting, we intend to prepare a summary of these discussions and devise a mechanism that will allow us to estimate the various scientific benefits of the various options and how they fit in the present context at CFHT.

7. The 8th CFHT Users meeting

Preparations for the next Users meeting are well underway. The agenda is available on the CFHT Web site. The booking of a conference room in Marseille is being looked into. The room at l’Agora des Sciences has been pre-booked but it can only contain 80 people. SAC believes that with the various important issues that will be discussed, attendance might very well be higher than this. Another conference room is being searched for.

To stimulate discussion, CFHT is planning to make a Web-based enquiry within the user community about their satisfaction with the use of the telescope and desires for future projects.

An invitation has been made by Dr Jeremy Lim to hold the CFHT 9th users meeting in Taiwan.

8. Other items


Christian Veillet informed the SAC that he has been contacted by UH for the possible purchase of CFHT12K. CFHT is presently looking into putting the camera back into working order.

· SAC membership

The SAC chair informed the committee that Dae-Sik Moon of the University of Toronto has been nominated for Canadian SAC membership. No further appointments have been made. Regarding SAC membership, some SAC members have stated that they prefer that the TAC chair from France and Canada be appointed to the SAC.

· Video conferencing of SAC meetings

SAC briefly discussed whether attendance of SAC meetings be allowed by a conference interface. The committee agreed that this is not a good idea but that if a member cannot attend, the committee can seek his opinion by telephone if he is available.

· Next meeting

The next SAC meeting will be held on the12-13 May in Cassis, France.