Optical outflows associated with Herbig Ae/Be stars
Corcoran, David (1993) Optical outflows associated with Herbig Ae/Be stars. PhD thesis, Dublin City University.
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Optical outflows (HH objects and jets) have only recently been found to be associated with high luminosity sources (> 50 L®) such as the Herbig Ae/Be stars. In this thesis,
using deep narrow band CCD imaging, the regions about three Herbig Ae/Be stars, V380 Ori, LkHa 198 and V376 Cas, together with one high luminosity embedded infrared
source Cepheus A, have been examined in detail. In most cases, these young stellar objects, have been known or have been suspected in the past to be associated with
HH objects. However, each of these regions is found to be considerably more complex than previously thought with the detection of at least twenty new HH objects, many
of which are examined by spectroscopy. For LkHa 198, a bright HH knot previously thought to be associated with it, is in fact, not related. This object appears to be
part of an optical outflow, the source of which is a newly discovered star located 5" to the northeast. A jet is seen to emanate from LkHa 198 and the presence of these
two outflows in close proximity not only explains many of the existing observations such as polarimetric measurements, but draws into question previous interpretations of the molecular outflow source and the presence of a far infrared halo about LkHa 198. For
V376 Cas, a number of nearby HH emission knots are reported some of which may be associated. Perhaps one of the most remarkable discoveries, is that of a HH “loop” to the
east of Cepheus A. Taken together with GGD 37, it is argued that one observes here a bipolar poorly collimated wind, orientated East-West in the plane of the sky. A similar
emission line “loop” structure is also observed to the west of V380 Ori, and while it is clear tha t this “loop” and the molecular outflow to the east, delineate a bipolar poorly collimated wind, it is unclear whether the more distant components of the “loop” are HH or HII emission. Importantly, the presence of LiIA6708 in the spectrum of V380 Ori, suggests th a t it is not a Herbig Ae/Be star but is in fact a T-Tauri star. The high luminosity of the star and the HH emission seen nearest to it, is taken as evidence of a variable poorly collimated wind, which emanates from V380 Ori and is interacting with a cavity left over from some previous outburst. A poorly collimated HH component is also seen for LkHa 198, and using all the observations made here and those collected from existing data, it seems increasingly more obvious that optical outflows are more poorly collimated from higher rather than lower luminosity sources (e.g. the T-Tauri stars).
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