The 19th meeting of the Spitzer User's Panel was held March 4/5, 2007 in Pasadena. This meeting followed the last SUP meeting by only three months, thus the opportunity to address new topics was more limited than at previous meetings. Nevertheless, significant progress has occurred in several areas. As has been consistently the case, the SSC continues to execute an outstanding program of spacecraft, instrument, and user support while advancing the public awareness of the significance of Spitzer's achievements. Specific areas of discussion were: Personnel At the last SUP meeting there was concern expressed over the departure of key staff, particularly in the area of instrument support. Losses were less apparent at this meeting and excellent replacement candidates for the prior open positions had been identified. The SSC's effective advocacy for the future - particularly for the "warm" Spitzer mission and an increasing focus on the Spitzer archive - contributes to a positive atmosphere at the Center that should aid in retaining and recruiting near-term. The issue of retention at this stage in the project remains, however, and the SSC should continue to take steps to secure and entice the most critical staff who carry significant corporate knowledge. Archive The SUP applauds the creation of the "Integrated Products Team" charged with guiding the development and delivery of the Spitzer archive, ultimately handing its curation to the Infrared Science Archive (IRSA). This focus on Spitzer's ultimate products is responsive to the SUP's prior concerns about the nature of final products and integration into an NVO-like environment and will serve the community most effectively in the long term. The SUP looks forward to the first reports from this particular group. The SUP noted that, given the need for integration of the archive into the larger community environment, the Integrated Products Team might benefit from having an ex officio member selected from an external large archiving enterprise. Such hybridization can foster new ideas and approaches as well as better facilitate the integration of the archive with the outside world. Instrument Caveats Pages The SSC has responded to the SUP's request for web pages that outline specific data caveats instrument by instrument. These pages do an excellent job of addressing the desire to see instrument quirks and potential pitfalls outlined explicitly for the users. We hope that the SSC instrument teams continue to expand upon these pages and keep them up to date with the latest knowledge of instrument behavior. To that end, the SUP urges the SSC to pursue all means to make these pages more inclusive and complete. Help desk requests should be filtered to identify additional caveats. The caveats pages should be reviewed for completeness by the instrument teams (and potentially legacy project teams). On a more specific note, the pages would benefit from an indexed and linked list of the topics that follow at the top of each caveats page. The SUP also suggests that these caveat pages be highlighted at the top of each instrument page, rather than being among a general list of links of varied importance. Overall, the SUP is please to see the continuing refinement and resulting improved navigability and accessibility of the SSC's web pages. APEX and Source Extraction The SUP heard of substantial progress in validating/characterizing the behavior of the APEX source extraction utility at this meeting. The assignment of an FTE to this problem is particularly encouraging. As more details are understood about the behavior and limitations of APEX it is keenly important that the information be placed prominently for the users. Many of the issues and analyses described to the SUP should be made available to users of the APEX package. This package has been in the public domain for some time and users should be warned of any known shortcomings. As source extraction within the SSC environment becomes better characterized, the population of the final Spitzer archive with reliable source extractions becomes all the more feasible. The SUP reiterates that the long term utility of the archive will be substantially enhanced with the availability of source extractions and urges the SSC to define specific plans for archive source tables as soon as possible. Presumably this issue will be addressed by the newly formed Integrated Products Team. Need for Photometry Cookbook(s) Users have expressed a desire for step-by-step instructions leading them through the photometric extraction and calibration process and incorporating many of the insights and techniques presented at the data analysis workshops. The SSC has begun the development of cookbook web pages and the SUP encourages the SSC to place some priority in advancing these pages from the current "beta" level. In particular, in addition to the MOPEX cookbooks, a more general "best practices for photometry" that discusses the best way to get "good" photometry (including, e.g., the conversion factor for Mjy/sr to mJy/sq arcsec), and that provides links to the various aperture correction pages, would be very useful. Reference Material for Spitzer Astrometry At this meeting it became apparent that the Spitzer astrometric reference frame and access to it through FITS data headers is, in some cases ambiguous and certainly in need of formal definition. The SUP urges the SSC to develop a Spitzer Astrometric Reference document so that users have a definitive reference as well as reference frame for interpreting source positions. IRAC The primary current outstanding issue for IRAC is calibration of diffuse sources in Band 4. The SUP was encouraged by the report that the recent recognition of the role a droop component in biasing extended source photometry (in addition to the scattered light within the substrate) is leading toward convergence in understanding this issue. Beyond this long-standing issue, the remaining IRAC characterizations are focused on low-level effects such as the sub-pixel response - an issue that the SUP would like to highlight in Bands 1 and 2 to be addressed as resources permit. IRS There is some user concern that SPEC-PET sensitivities do not match with actual performance. SSC should provide some reassurance that the sensitivity calculator is a reliable gauge of real performance (for SENS-PET as well). Order mismatch and wavelength-dependent slitloss corrections in IRS continue to be user concerns. The SUP encourages the SSC to place some priority on improving the characterization and calibration of the IRS order overlaps. MIPS This meeting demonstrated wonderful progress in producing appropriate calibration for bright (> 2Jy) sources and high surface brightness ( > 500 MJy/sr) regions in the S15.3 updated pipeline. The results are now in line with the Arizona instrument teams data analysis tool. The SUP looks forward to seeing the archive reprocessed with the corrected extraction algorithms. In the meantime it is important that SSC advertise the shortcomings of pre S15.3 photometry for bright sources to the user community. The SUP was encouraged by the continued active support of the GeRT, and by the attention being paid to scan-mirror dependent flats and pleased to see the strong efforts to continue improvement of the MIPS products across the board, and in particular to address the specific concerns from the SUP 18 report. The publication of the two calibration papers co-authored by the SSC and Arizona teams will prove to be invaluable not only as a reference and guide to the instrument, but also to help inform the community about the coordinated efforts between the two groups. This answers (and dispels) one of the biggest concerns from SUP 18, namely that the user community may have misperceptions about products produced by Arizona and the SSC. Proposal process As the exhaustion of cryogen approaches, users may find that their approved programs may not ultimately be scheduled for observation. Successful proposers should be informed of their priority ranking so that they will better understand the scheduling prospects for their proposals (The SUP observes that this procedure was implemented in Cycle 4 notifications). The Spitzer proposal process remains renowned for its robustness and relative ease. One frequently repeated user complaint concerns the observations summary table required as part of the process. Since small proposals must submit full AOR's, the process of manually typing out a formatted LaTeX table with ambiguous column requirements is redundant, time consuming, and thus frustrating. SSC should examine ways to generate the summary table automatically from the AOR's enabling proposers to spend more time developing their scientific arguments. The Long Term Perspective Overall the SUP commends the SSC on its approach to long term planning. The approach to the end of the cryogenic era is robust and well considered. The Warm Mission Workshop (and the exercise to generate topical white papers in advance of the workshop) will provide extensive community input in support of the warm mission. With the end of the cryogenic mission approaching, the SSC should be more aggressive in advertising the implications for users and their proposals - in particular the shortened schedule for proposals and unique nature of Cycle 5 (specifically that approved proposal may not receive time depending on the date of cryogen exhaustion). The SUP raises this issue because random polling of our constituents resulted in a significant fraction of surprised responses concerning the non-standard nature of Cycle 5. We recommend that SSC advertise the specifics of the timeline of the end of the cryogenic mission and the "non-guaranteed" nature of Cycle-5 (and to some extent Cycle-4) "approved" programs at or near the top of the front web page . The SUP also raised the issue of the "completeness" of the final science legacy of the Spitzer mission. Although the peer-reviewed proposal process is likely a scientifically efficient means of ensuring that Spitzer's full potential has been exploited during the cryogenic mission, the SUP asked whether there had been formal discussions of science or calibrations that might have been missed by the ordinary review process. The Panel heard about a planning exercise to address this issue that involved a modest number of scientists informed by the recent Great Observatories meeting. The SUP urges SSC to make the objectives and results of this process available to the community and provide a means for community response. The SSC has stated explicitly that it plans not to provide guaranteed observing time for any of the instrument teams during the warm mission. Ultimately, this is an issue to be resolved between the SSC, the instrument team leads, and NASA headquarters. The SUP does not wish to insert itself directly in this discussion with the exception of providing any insight, provided by users, into potential value added resulting from the direct scientific exercise of the warm instrument configuration by the GTO team. Public Affairs A report from public affairs was not a part of this meeting, however the presence and effectiveness of the Spitzer public affairs group could not be missed given a number of press releases that preceded the meeting. These releases included one, regarding spectroscopy of extra-solar planet atmospheres with the Spitzer Infrared Spectrograph, that garnered more attention than any release since the initial Spitzer post-launch briefings. The SUP was particularly heartened to hear that, since the last meeting, substantial progress has been made in easing and speeding the NASA/JPL approval of public outreach products so that the Spitzer public presence can be all the more effective.