Attached please find a copy of the report of the 17 September 1998 review of the 3.5-meter Echelle spectrograph. Please excuse the archaic troff typesetting inserts; I think it is still quite readable in this form. I am pleased to report that progress on the "aggressive and ambitious plan for delivery and installation" described in this report is good at this writing and that installation in November still appears likely. Ed Turner +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ .SH .ce REPORT ON THE 17 SEPTEMBER 1998 REVIEW OF THE APO 3.5M ECHELLE .SH INTRODUCTION .PP A group consisting of Bruce Gillespie (APO), Ed Jenkins (PU), Chris Stubbs (UW) and Ed Turner (PU, chair) visited the Echelle spectrograph group at the University of Chicago Department of Astronomy on 17 September 1998 in order to assess the state of the instrument and to make plans for its installation and commissioning at the APO 3.5-meter. The APO group spent a full day receiving presentations from and in discussions with the Echelle team, which is led by Roger Hildebrand, and with other members of the University of Chicago administration and Astronomy Department. These included D. Oxtoby (Dean), M. Turner (Dept. Chair), D. Duncan, L. Hobbs, D. York, J. Gee, G. Kelderhouse, L. Fiscelli, S. Heimsath, B. Lynch, R. Lowenstein, D. Sandford, J. Sundwall and J. Thorburn. S. Wang, who will lead the Echelle APO installation team, could not attend but has discussed related matters with some of us on various other occasions. .PP This report gives a brief summary of the findings and conclusions resulting from the visit and review. Copies of transparencies and other material provided to the group are appended to this report and provide many more technical details. .PP We, the APO group, found this exercise to be very informative and helpful; we thank our University of Chicago hosts for both their hospitality and their thorough and clear presentations. .SH INSTRUMENT STATUS .PP The Echelle was in stable laboratory operation and could routinely produce good quality spectra of both lamps (line and continua) and solar light. With two exceptions (see below), instrument performance was nominal and entirely satisfactory. The wide wavelength coverage at high dispersion and with uniform resolution and line profiles was particularly impressive. In several respects (notably wavelength coverage per exposure), performance exceeds the original design goals, and it can be expected that the instrument will be very powerful scientifically when it is fully operational at APO. .PP As of 17 September, the Echelle was being operated with an engineering grade CCD chip (high readout noise) and via a temporary lab setup of camera electronics and data system. Completion of the Echelle requires installation of the science grade chip and replacement of the test set electronics and computers with the "flight hardware" versions. Installation of the Echelle on the telescope also requires completion of a new support structure, fabrication of which is well underway. .PP In addition, one major functional capability had not yet been implemented, namely guiding. A guide camera and optics had been installed, but no supporting electronics or software was yet available. .SH PERFORMANCE ISSUES .PP Echelle performance in the lab fell significantly below design specs in one important respect. The unresolved line shapes produced by the instrument have a FWHM of 2.6 pixels, as opposed to the expected 2.0, and are moderately asymmetric. Extensive attempts to locate and correct the problem during the past few months have been unsuccessful. Although a few possible correctable causes remained to be investigated, the Echelle team felt that it might not be possible to achieve any better performance. The line widths and shapes are quite stable over the entire spectrum, thus making it practical to take account of the line PSF correctly during data reduction. [Approximately one month after the 17 September visit, the line asymmetry is reported to be substantially improved due to further work on internal spectrograph optical alignments.] .PP In addition to the known problem with optical performance, the instrument throughput remains to be determined. This quantity is very difficult to measure in the laboratory but will be relatively easy to measure "on the sky" via observations of standard stars once the instrument is installed. Although there is no particular reason to expect throughput problems, it is always a topic of concern for devices with complex optics involving many individual optical elements. The design goal is a total spectrograph throughput of 9% or better at all wavelengths above 4100 A. This would be excellent performance for an Echelle spectrograph. .SH DELIVERY AND INSTALLATION PLAN .PP An aggressive and ambitious plan for delivery and installation was adopted. It calls for immediate installation of the science grade CCD and replacement of the engineering electronics and data systems with the final "flight hardware" versions, followed by fairly quick (perhaps 10 days or so) laboratory evaluation of the reconstituted instrument. Assuming no unexpected problems are uncovered, the shipping procedure would then commence with the goal of carrying out installation of the instrument on the telescope during the early November 1998 bright time. This timeline also calls for completion of the new support structure and its shipment to APO in roughly mid-October. Finally, there would also be a parallel and fast paced software development effort aimed at allowing instrument engineering and commissioning operations at the completion of installation. .PP It is clear that this plan is optimistic and even somewhat risky (in the sense that subtle problems might not be uncovered during the brief laboratory evaluation), but it was felt to be justified by several factors, including a "window of opportunity" in the schedules of key personnel needed to carry out the work, the oncoming winter weather at APO (making work in the unheated dome difficult) and, of course, the desire to achieve science operations of the long delayed instrument at the earliest possible date. .PP Nevertheless, it was generally agreed that the Echelle should not be shipped to APO until the following five goals have been achieved: .IP - All "flight hardware", including the science grade CCD and the operational camera electronics and data systems installed and tested in the lab. .IP - Instrument performance re-characterized, at the same level of detail as now available for the engineering incarnation, and found to be essentially as good or better. .IP - Development of a software system and interface sufficient to allow engineering and science operation of the instrument on the telescope (though this is unlikely to be the "final" version of the instrument software). .IP - Preparation of user and engineering documentation, or commitment to preparation of a specific list of such documents, sufficient to allow APO maintenance and operation of the instrument. .IP - Implementation of at least a rudimentary guiding capability (none appears to exist currently) which will allow commissioning and early science operations. .SH COMMISSIONING AND EARLY SCIENCE OPERATIONS .PP A specific commissioning plan (describing tasks to be accomplished, quantities to be measured, acceptable performance, etc.) yet needs to be developed. .PP At present, there is a general plan to carry out a relatively quick first phase of commissioning via a few nights of observations (probably of standard objects of various sorts and of calibrations) immediately following installation. This should reveal any gross malfunctions or problems immediately. The "rule of thumb" criterion for .ul minimum acceptable performance is that the instrument should perform as well as the KPNO 4-meter Echelle, which has been scientifically productive for many years. This notion was suggested by Don York and met general approval but is not intended to replace a more definite and quantitative characterization of instrument performance and success. In fact, substantially better performance than the KPNO 4-meter is expected. .PP Following this initial commissioning phase, a more elaborate and extended commissioning phase is expected to blend into early science operations. This work will be carried out to a large extent by University of Chicago builders and users of the Echelle but could also profitably involve other ARC users on a "shared risk" basis. If the best projected schedule is achieved, such shared risk science operations could begin during 1Q1999. .SH EARLY ECHELLE ENHANCEMENTS .PP The discussions on 17 September revealed three possible enhancements/additions to the Echelle which will be sufficiently useful and easily accomplished that they are likely to be very early upgrade priorities. To be explicit, these are not items which are felt to be necessary before the instrument is accepted by APO as delivered, but it does seem likely that they will be among the next priorities for work on the instrument. They are enumerated below: .IP - The fundamental design of the instrument projects the spectral dispersion direction onto the sky in a direction perpendicular to the horizon. This means that differential refraction will either reduce spectral resolution or coverage (with a wide or narrow, respectively, aperture in that direction). For example, according to calculations by Chris Stubbs, spectral coverage (a primary strength of this Echelle) will be degraded by about 30% at an air mass of 1.5 and by about 50% at 1.7 with the standard 1.6" slit. This problem can be alleviated by introduction of an ADC (Atmospheric Dispersion Corrector) into the pre-slit optics. .IP - Initial guiding capability may be as primitive as manual "paddle guiding" based on watching for the target to "peep out" of the slit. This will be inefficient in terms of human resources and may be difficult for remote observers (due to net speed problems). APO OS's will not carry out this function routinely. Thus, autoguiding capability will be an early priority, and capability for on-slit guiding via a pellicle beam-splitter would be highly desirable as it would avoid unnecessary loss of spectral resolution during good image quality conditions. .IP - Laboratory tests show that the unexplained image (line shape) degradation, discussed above under "Performance Issues", disappears when the slit is replaced by a pin hole source. This implies that a pre-slit field stop device could be used to attain better spectrograph optical performance (up to design specs) for sources sufficiently bright (or integrations sufficiently long). This will surely be desirable for some applications. .PP Doug Duncan and Don York, both expecting to be frequent users of the Echelle, will work jointly as its co-instrument-scientists and will thus take leadership roles in post-commissioning development and maintenance. .SH MISCELLANEOUS COMMENTS .PP The following points were noted during the review and are recorded here in no particular order. .IP - Surface errors in the Echelle grating itself are one possible source of the poor optical performance discussed above. Ed Jenkins pointed out that this possibility could be checked via fairly simple and straightforward measurements (by Ball Brothers, perhaps) which could be made while the instrument was dis-assembled for shipping, among other possibilities. If this were confirmed as the problem, much pointless and time consuming work on optical alignment, etc. could be avoided. Also, modification of the grating support structure might correct or reduce the problem. .IP - Previous experience with other instruments suggests that it would be useful to retain capability to operate the spectrograph via "stand alone" software independent of the REMARK interface, although this mode might not be available to general users. .IP - The APO installation team, to be led by Shu-I Wang, is yet to be definitely defined. Who will be there and when, etc. .IP - Details of the post-commissioning maintenance arrangements between APO and Chicago need to be worked out. .IP - A specific/formal administrative process by which the instrument is accepted, with ownership and responsibility transferred from Chicago to APO, needs to be devised. (Tom Lutz proposed a general one for APO use many years ago, but it has never been used.) .SH FINAL COMMENTS .PP The exercised described in this report was considered to be a valuable one by all concerned and may well be considered a useful precedent for future APO 3.5-meter instrument projects. .sp 0.2i .LP Submitted by .LP B. Gillespie .LP E. Jenkins .LP C. Stubbs .LP E. Turner (chair) APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 317 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO