The following document lists the file abstract/RSTENCEL_VEGADIS2.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
SCIENTIFIC ABSTRACT
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.
OBSERVATION SUMMARY
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.
EXTENDED SOURCES PROGRAM
SCIENTIFIC ABSTRACT
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.
OBSERVATION SUMMARY
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.
LINKED OBSERVATIONS: Yes
FIXED TIME OBSERVATIONS: No
CONCATENATION: No