Bibcode
Boersma, C.; Peeters, E.; Martín-Hernández, N. L.; van der Wolk, G.; Verhoeff, A. P.; Tielens, A. G. G. M.; Waters, L. B. F. M.; Pel, J. W.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 502, Issue 1, 2009, pp.175-187
Fecha de publicación:
7
2009
Revista
Número de citas
23
Número de citas referidas
22
Descripción
Context: Infrared (IR) spectroscopy and imaging provide a prime tool to
study the characteristics of polycyclic aromatic hydrocarbon (PAH)
molecules and the mineralogy in regions of star formation. Herbig Ae/Be
stars are known to have varying amounts of natal cloud material present
in their vicinity. Aims: Our aim is to study the characteristics
of the mid-IR emission originating in Herbig Ae/Be stars, especially the
extent of the emission and how this relates to the (proto-)stellar
characteristics. Methods: Today's powerful ground- and
space-based telescopes provide images and spectra at unprecedented
spectral and spatial resolution. We analyse the images and spectra from
four Herbig Ae/Be stars (IRAS 06084-0611,
CD-42 11721, TY CrA, and
HD 176386), as obtained with TIMMI2 on the ESO 3.6 m
telescope and VISIR on the VLT. These observations are supplemented with
data from ISO-SWS and Spitzer-IRAC. Results: We find evidence for
large-scale structure and extended emission in all four sources, except
for HD 176386, which only shows silicate emission, all sources show PAH
emission in their spectra. In addition, a spatially resolved silicate
and PAH spectrum could be extracted for TY CrA. Conclusions: The
variety in emission scales distinguishes two classes. In the first, the
morphology and spectral characteristics resemble those of reflection
nebulae. In the second, the characteristics are in-line with Herbig A
stars. This separation simply reflects a difference in stellar
characteristics (e.g. luminosity). In Herbig B stars, dust emission from
the surroundings dominates, where for Herbig A stars, the disk dominates
the emission. In this scheme, IRAS 06084-0611 and CD-42 11721 resemble
reflection nebulae and HD 176386 a more typical Herbig Ae/Be star. TY
CrA shows characteristics common to both genuine reflection nebulae and
Herbig B stars. We propose a geometry for TY CrA, with most notably, a
~70 AU inner gap in the 340 AU circumtertiary disk cleared by a fourth
stellar companion.
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