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 -----------------------------------
Instrument
PHT03 , PHT22
Temporal Coverage
1997-11-26T06:11:16Z/1998-01-25T18:07:33Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the world's first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, 1999, Herbig Ae\/Be Stars And The Evolution Of Their Circumstellar Material , 1.0, European Space Agency, https://doi.org/10.5270/esa-fy8vrxa
