Explanatory Text for April 6, 2001 Version 1.0 AORs for the The Galactic Legacy Infrared Mid-Plane Survey Extrordenaire (GLIMPSE) Survey Region: -------------- GLIMPSE is a fully-sampled 4-band IRAC mapping of the Galactic Plane from l=10-70 deg and l=290-350 deg at Galactic latitudes |b|<1 deg. Each region will be observed twice, preferably within 1-2 hours, in order to have redundant coverage and perform asteroid identification. Observing Mode: -------------- GLIMPSE will use the 2-sec full-frame AOT which has not yet been implemented. These preliminary AORs use the old 12-s HDR option. The Galactic Plane will be coverged in "segments" which are 2 deg high in latitude, and ~2 deg long in longitude. The size of the segment is limited by the data volume which we are allowed to generate in a 12-hour downlink period (as per discussions with SSC staff). We were given a rough guideline of 2 Gbits, which translates into about 2-3 hours of observing per 12 hour downlink interval. In 3 hours, can can cover ~2 deg of the Galactic Plane with two passes. Each segment requires ~1.5 hours of observing time, assuming each exposure and associated readout and data compression is 18 sec. Each segment is coverged twice. As currently scheduled, the AORs required to cover a segment the first time are CHAINED together using the CHAIN constraint. Once the first pass is complete, the same segment is observed again ~1.5 hr later, with a 10" offset. The second pass is constrainted by a FOLLOW-ON constraint. The second pass must begin within 12 hours of the first pass. Preferably the second pass would begin just 1.5 hours after the first pass during the same 12-hour period. AOR Files: -------------- Due to the large number of individual AORs needed to cover the Galactic Plane, we have written a custom program to efficiently tile the IRAC frames within the survey region. Each segment of the Plane is covered by a series of slightly-overlapping IRAC "maps". The maps are 2 x n strips, where n varies between 1 and 34, depending on the orientation of the array relative to the Plane. (We work in Galactic position angles; we hope that the new version of SPOT will report Galactic PAs.) Individual AORs have names like lLLL.LLLLLSBB.BBBBB.YYYYMMDDx l - is simply a prefix to denote longitude LLL.LLLLL - is the galactic longitude of the AOR which goes in the RA_LON field of the AOR. S - is the sign for Galactic latitude, either + or - BB.BBBBB - is the galactic latitude of the AOR which goes in the DEC_LAT fieldof the AOR YYYY - is the year that the AOR is intended to be executed MM - is the month that the AOR is intended to be executed DD - is the day that the AOR is intended to be executed x - is a flag, either "a" or "b" to indicate the first and second passes over a given segment. AORs for a given segment, including the first and second pass, are concatenated into a single unix file named seglll.l_w.w.aor, where lll.l is the mean Galactic longitude of the segment and w.w is the approximate width of the segment in degrees. In principle, an AOR for any position within the Galactic plane can be executed at any time during the visibility window. Thus, the GLIMPSE survey will be VERY easy to schedule. However, each AOR has a timing constraint, currently +/-7 days from the nominal intended execution date. This is because, in order to tile the Galactic plane efficiently with IRAC frames, the center position of each AOR depends upon the position angle of the IRAC array. Each series of CHAINED AORs comprising a segment must be constructed with a specific roll angle in mind. *Thus, the AORs are date dependent.* Strictly speaking, we cannot produce final AORs until the date of observation is known, at least to within ~7 days (more when viewing parts of the Galactic plane near l=10 where orientation does not change quickly; less near l=290 where roll angle changes significantly day-to-day). For planning purposes, we have adopted the draft campaign schedule for IRAC. We will work with the SSC to produce updated AORs as the IRAC operations schedule becomes better defined. We have tentatively agreed with SSC that we will be allowed to produce updated AORs up to 3 weeks before the actual observation, or whenever the IRAC observing schedule is finalized. Time required: -------------- Since the 2 s AOTs have not yet been implemented, the total time required to complete the survey can not yet be accurately determined. Currently, SPOT may give spurious warnings that a given AOR exceeds the maximum allowed. We estimate, assuming 18-s per IRAC frame, that the total time to complete the survey will be very near the 400 hr allocated to this program. NOTE: We have many AORs which consist of only 1-2 exposures. We hope that the nominal 180 s per-AOR overhead will not be charged against these very short AORs which are needed to efficiently tile the Galactic Plane. Caveats: ------- The current AORs are preliminary. In particular the roll angles and observing dates may be inaccurate by several days. Currently, we interpolate a table of dates and roll angles constructed manually from runing SPOT. We would very much like to have a finely-gridded table (or better yet, an algorithm) to compute more accurate roll angles and dates of visibility. Questions and Contacts: ------------------------- GLIMPSE planning lead: Chip Kobulnicky, chip@astro.wisc.edu 608-265-6768 GLIMPSE planning team: Christer Watson, watson@astro.wisc.edu, 608-262-2965 GLIMPSE PI: Ed Churchwell, ebc@astro.wisc.edu, 608-262-4909