A spatial study of the mid-IR emission features in four Herbig Ae/Be stars

Details A spatial study of the mid-IR emission features in four Herbig Ae/Be stars A spatial study of the mid-IR emission features in four Herbig Ae/Be stars

Jul 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...502..175b&link_type=abstract

Astronomy and Astrophysics, Volume 502, Issue 1, 2009, pp.175-187

Astronomy and Astrophysics

Astrophysics

6

Techniques: Spectroscopic, Infrared: Ism, Ism: Molecules, Astrochemistry

Scientific paper

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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