The following document lists the file abstract/HHABING_HJHVEGA3.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
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.