Contents of: VI/111/./abstract/CLEINERT_HERBIG2.abs

The following document lists the file abstract/CLEINERT_HERBIG2.abs from catalogue VI/111.
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SCIENTIFIC ABSTRACT

Many of the Herbig Ae/Be stars, i.e. young stars of intermediate mass(2-10 Msun)
 appear to be surrounded by disks of circumstellar matter, similarly as known
 for the lower mass T Tauri stars. Intermediate mass stars have not been
 studied as extensively as T Tauri stars, however it appears (Strom et al.1991)
 that their disks are by about a factor of 10 more massive, more extended and
 evolve more rapidly than inferred for the lower mass stars. This proposal
 is to provide a systematic study of the circumstellar matter of Herbig Ae/Be
stars - whatever its geometrical distribution - and of its evolution with time
 by means of multiband photometry. The sample contains Herbig Ae/Be stars
 in three groups of different association with circumstellar material,
 corresponding largely to the groups II, I and III, as introduced by
 L.Hillenbrand (1992), as well as A and B main sequence stars from three
 age groups of young nearby clusters or stellar groups, with ages of 10-20,
 30-40 and about 160 million years. The study of this sample will allow us
 to follow the temporal evolution of the amount of circumstellar matter and
 its spatial distribution around these intermediate mass stars.




OBSERVATION SUMMARY

Out of the comprehensive sample described above we will observe during
guaranteed time 15 optical Herbig Ae/Be stars (mostly group I but some
also group II or group III in Hillenbrands classification) and 10 objects
from the oldest of our subgroups (Ursae Majoris), containing approximately
equal numbers of fast and slow rotators.

PERFORMANCE TIME OVERVIEW

    Observations          priority 1   priority 2   priority 3   sum
    ------------------------------------------------------------------
    broadband photometry   15902 s      3830 s       ---       15902 s
    ------------------------------------------------------------------
                           (4.4 h)       (1.1 h)    ---        (5.5 h)

=== Detailed observing plan ===

As a rule the photometry will be performed by triangular chopping
against the surrounding background. Measurements at
160 micron and 200 micron are requested only for brighter sources, using
three or five point raster scans. For LkHa 198 and V376 Cas, which are
close to each other, a small raster map of 6-9 positions
will be performed. The diaphragm size equals to 52 arcsec. There are no 
restrictions to the actual position angle of the chopping directions.

   For sources well detected by IRAS the emphasis is on a good
determination of the long wavelength spectrum, in particular
beyond 100 micron. For the other sources the aim is to detect far-infrared
emission and to follow it to long wavelengths as far as possible. The
measurements at shorter wavelengths help to define the photospheric
component.
   With the given integration times the flux limit for the faint sources of 
the sample (about 0.3 Jy) is 10-30 mJy in the absence of cirrus (S/N about 10).
Cirrus confusion is about 100 mJy at a  wavelength 100 micron for a cirrus
brightness of 15 MJy/sr. This value is applicable to the IRAS sources,
most of which have far infrared brightnesses of at least several Jy, giving 
a S/N of at least 10. For the bright stars lower 100 micron 
background (5 MJy/sr) and lower cirrus noise (15 mJy) are to be
expected, allowing a S/N ratio of 10 or more for the brightest
sources and detection of even moderate infrared excess also for
the faint ones.


1. IRAS sources photometry

   Filter      t(on object)     t(performance)   diaphragm(") chop throw(")
   ------------------------------------------------------------------------
   P_4.85          32 s             313 s            52            90
   P_11.5          32 s                              52            90
   P_25            32 s                              52            90

   P_60  or C_60   32 s          318 s or 305 s      99           150
   P_100    C_90   32 s                              99           150

   C_160           32 s     depends on the raster --- 3 or 5 step raster ---
   C_200           32 s

  Initial acquisition              180 s
   -------------------------------------------------------------------------

2. Bright stars photometry

   Filter      t(on object)     t(performance)  diaphragm(") chop throw(")
   -----------------------------------------------------------------------
   P_3.6           32 s             457 s            52            90
   P_4.85          32 s                              52            90
   P_7.3           32 s                              52            90
   P_11.5          32 s                              52            90
   P_25            32 s                              52            90

   C_60            32 s             305 s                         150
   C_90            32 s                                           150

   C_160           32 s             214 s     --- three step raster scan ---

   Initial acquisition              180 s
   -----------------------------------

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