Contents of: VI/111/./abstract/HUNN_HUNNEGAL.abs

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SCIENTIFIC ABSTRACT
>From IRAS all - sky survey data of ellipticals, it has been demonstrated that
infrared measurements are at least an order of magnitude more sensitive to
cool gas than 21 cm measurements. We propose to observe an unbiased sample of
ellipticals (Shapley - Ames ellipticals with BT <= 12.0) with ISOPHOT. The
main advantage of ISOPHOT compared to IRAS are: fainter limiting magnitude,
diffraction limited imaging, and sensitivity at 200 micron implying a better
match to the dust temperatures expected in ellipticals. For the infrared
brightest part of the sample, we propose supplemantary observations with
ISOPHOT-S and LWS.
By these new observations new insight into the chemical composition, origin
and evolution of the interstellar matter in ellipticals will, no doubt, be
gained.
We have used the PHTAOT program Version 1.2

OBSERVATION SUMMARY
We have chosen to use PHT22 in the triangular chopper mode. We will use
4 filters (60, 90, 160 and 200) and have estimated the observing times needed
for a S/N >= 5 detection. We have assumed the following detection limits:
 60 micron 0.035 Jy obs. time 16 sec
 90 micron 0.020 Jy           16 sec
160 micron 0.1   Jy           16 sec
200 micron 0.15  Jy           16 sec

in total 2 x 64 sec = 128 sec

For the concatenated PHT-S observations we have used the PHT40 aot in chopping
mode. We observe both wavelength ranges and have estimated a total spacecraft
time (S/N >= 5) of 365 sec/obj.

For the concatenated LWS observations we observe with the LWS01 aot.
Following the LWS Observer's Manual (Version 0.5). Following the example
Section 6.5.1 we find that we can get a full spectrum (with a spectral
resolution 0.29 micron/0.60 micron, S/N >= 2 per resolution element at
0.4 Jy (60 micron) and 0.5 Jy (100micron)) in a total observing time of
t = 2 * 65 * 7/0.75 sec = 1200 sec. The factor 1/0.75 takes into account
the instrumental overheads.

To estimate the overheads we have taken the following number from the
PHTAOT version 1.2 program and the ISO and ISOPHOT user's manuals (Version 1.0
and 2.0, respectively)

time for target acquisition and slewing:   180 sec
time for change wheel performance:          22 sec
time for stabilization of heated detectors: 90 sec
time for FCS exposures:                     32 sec
time for initial setup                      15 sec
total:                                     339 sec

For the concatenated PHT-S observations, we have used the following numbers for
the overheads:

time for initial setup                      15 sec
time for target acquisition and slewing:    20 sec
time for check dark exposure:               32 sec
time for change wheel performance:          42 sec
total:                                     109 sec



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