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Goals of Galactic FLS
- Characterize the cirrus and background source counts at low
Galactic latitudes. This will help guide MIPS and IRAC
observers who wish to observe close to the Galactic plane.
- Characterize the internal cirrus and background source counts
toward a molecular cloud. This will be useful to observers of
stars and dust in molecular clouds. How limiting are flucuations
in the internal cirrus and extinction? How well one can distinguish
embedded and background populations?
Original Observational Definition of Galactic FLS
- IRAC and MIPS characterization of IR cirrus and source counts at low
Galactic latitudes in two "strips", each ~5 arcmin wide to give a broad
range of cirrus intensities and source counts with the -10 <= b <= +10
latitude range most important.
- First strip located at single longitude, with latitudes ranging from -30
<= b < = 0 deg. Latitudes from -10 <= b < = 0 have "continuous" coverage;
latitudes from -30 <= b <= 0 have a lower filling factor (50%).
- Second strip located at significantly different longitude and
extending over the latitude range from 0 <= b < +10 deg.
- IRAC and MIPS characterization of IR cirrus and source counts towards
a molecular cloud.
- A 5' x 2 degree strip through a molecular cloud.
- Same MIPS depth as in Galactic strip scans.
- IRAC coverage of same area but depth 10x the Galactic strip scans
- Total Survey Time: ~36 hrs
Observational Constraints
- Observing Window: December 2003.
- MIPS Scan Direction completely constrained by launch/observation date.
- MIPS scans are not perpendicular to Galactic plane, so a single strip
along a constant Galactic longitude not possible.
- Non-contiguous observations act to decrease overlap between MIPS scans
and IRAC maps due to evolution of position angle with time (~1 deg/day).
- Visibility window rules out outer-galaxy longitudinal "strip" as well
as Cham II, our original molecular cloud.
- We found a new cloud and three strips that have differing
gas/dust/stellar properties.
- Galactic strip maps now larger than those suggested in "original
definition". They provide better contiguous observations of
galactic structures and minimize concerns of MIPS and IRAC data
not overlapping due to time delays between observations.
- Want to provide good high quality 160 micron data to community, so we
had to find and include longitudes and latitudes that will not
saturate 160 micron detector.
Observing Strategies Assumed
- Galactic longitudinal Strips.
- As a result of launch slips and other constraints, strips moved
several times. l=150 became 67.5, which settled on 105.6, and l=285
became 272.17, then 290.2, and settled on 254.4.
- Individual scans/maps placed at varying galactic latitudes.
- Latitude spacing of MIPS scan centers increases with latitude.
- IRAC maps of each position with approximately
the same width/length as MIPS scans.
- Widened strips (compared to older observing strategy)
so as to make larger contiguous maps.
- Request IRAC and MIPS maps to be observed within 4 days of each
other (to minimize field rotation between observations and achieve coverage
of the same region with both IRAC and MIPS).
- Using HDR mode in IRAC to maximize dynamic range for all
positions.
- 60' by 15' wide MIPS fast scans at each latitude center
consisting of 10 scan legs with 148" forward and 35"
return scans.
- 60' by 15' IRAC maps (12 rows by 3 columns; 292.8" offsets)
using four dithers of 12 seconds in HDR mode to maximize
dynamic range at all positions.
- For l=105.6: 15' x 1 degree strips for MIPS and IRAC.
Latitudes are: -1.3, 0.35 (ISO), 2, 4, 8, 16, 32 (cirrus)
- For l=254.4: 15'x1 degree strips for MIPS and IRAC.
Latitudes are: 0, -2, -5, -9, -14.
By chance, part of our strip at -9 will go through the Vela
supernova remnant.
- Galactic Cirrus Position
- Created new position at high galactic latitude specifically
designed to better sample cirrus, etc.
- Located at +32d along the 105.6 longitude
- Uses medium-speed MIPS scan legs to fully sample the
160 micron array.
- Same footprint as other galactic strips
- IRAC covers same area.
- Star Count position
- For l=97.5: small IRAC-only maps to sample the Galactic disk.
Latitudes are: 0, -4, +4, +16.
- L1228 Molecular Cloud
- 120' by 10' MIPS fast scan across cloud center; second MIPS strip
offset by 150''. The final coverage is ~12.5'x2 degrees
- 120' by 10' IRAC map (23 rows by 2 columns; 292.8"
offsets).
- IRAC maps consist of 4 dithers of 12 seconds at each position
operating in HDR mode.
- All of the MIPS scan legs are now offset by 80''
(1/4 array).
- The L1228 MIPS observations are now a single pass of 8 scan legs. (It
used to be two separate scans separated by 12 hours.)
- Request IRAC and MIPS maps to be observed within 3 days of each other
(to minimize field rotation between observations and achieve coverage of
the same region with both IRAC and MIPS).
Go back to Galactic FLS page or
main FLS page.
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