Contents of: VI/111/./abstract/RSTENCEL_VEGADIS2.abs

The following document lists the file abstract/RSTENCEL_VEGADIS2.abs from catalogue VI/111.
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The IRAS discovery of far-infrared excesses among seemingly 
normal main-sequence star motivates this proposal.  These
have been interpreted in terms of disks of cold material. 
The aim of this proposal is to establish the true frequency for 
far-infrared excesses in a volume-limited sample of main 
sequence stars using PHT-P measurements, in order to address 
the success or failure of single stars in processes related to 
the forming of planetary systems.  For brighter sources, more 
extensive wavelength coverage and spatial resolution will be 
attempted, with PHT-P, PHT-C and SWS.  Finally, observations 
of Kuiper Belt material will be attempted.

This proposal is split into three parts: this is PART 2.

It is planned to obtain more accurate coordinates for the sources
in this proposal, beyond the SIMBAD information used so far.  
Exposure times were estimated using the PHT and SWS cookbooks.

Part 1: Concerns PHT03 measurements of a volume-limited 
sample of main sequence and related stars.

PART 2: Concerns spatial mapping of selected brighter far IR sources.

We request micro-scanning observations with  AOT PHT32 (C100) at a wavelength 
of 60 microns of the brightest and nearest Vega-like sources to measure the
characteristic sizes of the emitting regions and glean some information
regarding their shapes and orientations.  The sample is limited to main 
sequence stars found to have IR excesses in IRAS data, with total 60-micron 
flux greater than  0.5 Jansky and parallax distances less than 20 parsecs, 
plus a few very nearby stars of special interest, plus a few stellar point 
source standards.  The observing plan in each case will be to perform 
photometry with the P32-C100 detector and filter and 3x the diffraction 
limited step size, 15 arcseconds.  The goal originally was to use PHT12 
super-res mode and scan profiles along 3 position angles which could be 
deconvolved to 
find the intrinsic size and shape of the FWHM contour of the emitting region.
We would have done a first integration at the target position, then a series of
micro-scan steps by the focal plane chopper extending radially away
from the target position in 3 legs of a "Y" at position angles 0, 120, and 
240 degrees. The removal of PHT12 leaves us with PHT32 mapping as the only 
available comparable approach. 

An integration time as short as 32 or 64 sec seems possible given that
successive measurements along the raster scan will be viewing almost exactly 
the same source flux and background, thus "settling" time of the detector 
after each measurement should be small.  The Signal/Noise ratio in 32 sec on 
a 0.5 Jy source at 60 microns with P32-C100 with pessimistic background 
assumptions (ecliptic lat = 0 deg) should be about 32.

AOT P32 (microscan), detector C100 - 60 micron filter, 15 arcsec stepsize  
n the z-axis, 60 arcsec in y, integration time per raster scan point = 32 
or 64 seconds [NO peakup, NO repeat/reverse scans], and either 3 x 3 or 
5 x 5 raster, centered on target. 

Time spent integrating = 5 x 5 raster x 32 sec/substep = 800 sec
Time spent integrating = 3 x 3 raster x 64 sec/substep = 586 sec 
Overhead time expected from section 6.6.5 of ISOPHOT manual:
      telescope acquisition and slewing    180 sec
      instrument set-up                     15 sec
      time for FCS exposures for 3 scans ?  18 sec
      time for wheel positioning (3 wheels) 30 sec
      time for stabilizing heated detector  90 sec
      est. settle time per chop move x 30   90 sec
      TOTAL overhead                       423 sec
TOTAL time per source, integration + overhead = 1223 [5x5] or 1009 [3x3] sec
Number map lines z = 3; oversampling = 3; number samples in y = 3.

PART 3: Concerns attempted local Kuiper Belt observations.