Contents of: VI/111/./abstract/HHABING_HJHVEGA3.abs

The following document lists the file abstract/HHABING_HJHVEGA3.abs from catalogue VI/111.
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SCIENTIFIC ABSTRACT
We want to measure the 25, 60, 90, 135 and 200 micron fluxes from a distance
limited sample of main sequence stars (B9V-K7V). The stars should be so
simple that we can reliably predict their photospheric flux at infrared
wavelengths; the stars should be so close that we can measure the predicted
flux with high accuracy (S/N at least 10) out to 60 micron, which will allow
us to detect excess fluxes of 10% or more. The simplicity argument brings us
to exclude  (i) O and (early) B stars; (ii) late K and all M dwarfs; (iii)
variable stars and (iv) multiple systems, except those in which our target
star is sufficiently isolated (i.e. nearest significant companion more that
1 arcmin distant). Because we are interested in the remnants of pre-main
sequence disks we also exclude stars that have evolved away from the main 
sequence.  
We expect the following results: theoretical atmospheres for selected stars
are believed to have reached a high level of reliability and to be very good
in the infrared; thus the predicted infrared flux should agree with the
observed value to high (i.e. a few %) accuracy. If ISO measurements show
this to be the case (no excess flux) then the star can be used as an accurate
absolute calibration source. However, some stars will have excess emission 
and, because of our rigorous selection criteria, we assume that in these 
stars the excess will be due to a VEGA type disk. Because we have a
distance  limited sample we can determine how often the VEGA phenomenon
occurs and in what intensity. This will then make it possible to relate the
presence of a VEGA-like excess to other stellar properties (notably:
rotation, chromospheric activity).

OBSERVATION SUMMARY
The far-IR energy distribution of a sample of nearby stars will be studied 
by means of photometry with PHOT. In order to cover the full spectral range
of interest, five filters were selected: 25, 60, 90, 135 and 200 micron. At
25 micron this will be done with PHT-P2 (AOT PHT03), using a 52 arcsec
aperture, and triangular chopping with a chopper throw of 90 arcsec.  For
the weakest sources this will give a S/N on the stellar continuum of about
15. At 60 and 90 micron PHT-C100 will be used (AOT PHT22). These 
observations will also be performed using triangular chopping with a 
chopper throw of 150 arcsec. S/N on the stellar continuum at these 
wavelengths should be better than 10. The photometry at the longest
wavelengths will be done with PHT-C200 (AOT PHT22). Again the observations
will be performed in chopping mode with rectangular chopping and a chopper
throw of 180 arcsec. In this case the S/N ratios on the stellar continuum
will be very low, but for a source with  an IR excess of about a factor 5,
we expect a S/N of at least 3. Because of the different chopper mode, this
AOT is separated from the 60 and 90 micron observations. The observations
(three AOTs) on each source  are concatenated, because it is only possible
to do statistics on a sample of stars if they have all been observed at the
same wavelengths. Also, if an IR excess is detected in some of these stars
it is important to know the shape of the IR excess, and thus have all
wavelengths available.


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