Universität zu Köln

Taha, A. S., Labadie, L., Pantin, E., Matter, A., Alvarez, C., Esquej, P., Grellmann, R., Rebolo, R., Telesco, C. and Wolf, S. (2018). The spatial extent of polycyclic aromatic hydrocarbons emission in the Herbig star HD 179218. Astron. Astrophys., 612. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Aims. We investigate, in the mid-infrared, the spatial properties of the polycyclic aromatic hydrocarbons (PAHs) emission in the disk of HD 179218, an intermediate-mass Herbig star at similar to 300 pc. Methods. We obtained mid-infrared images in the PAH-1, PAH-2 and Si-6 filters centered at 8.6, 11.3, and 12.5 mu m, and N-band low-resolution spectra using CanariCam on the 10-m Gran Telescopio Canarias (GTC). We compared the point spread function (PSF) profiles measured in the PAH filters to the profile derived in the Si-6 filter, where the thermal continuum emission dominates. We performed radiative transfer modeling of the spectral energy distribution (SED) and produced synthetic images in the three filters to investigate different spatial scenarios. Results. Our data show that the disk emission is spatially resolved in the PAH-1 and PAH-2 filters, while unresolved in the Si-6 filter. Thanks to very good observing conditions, an average full width at half maximum (FWHM) of 0.232 '', 0.280 '' and 0.293 '' is measured in the three filters, respectively. Gaussian disk fitting and quadratic subtraction of the science and calibrator PSFs suggests a lower-limit characteristic angular diameter of the emission of similar to 100 mas, or similar to 30 au. The photometric and spectroscopic results are compatible with previous findings. Our radiative transfer (RT) modeling of the continuum suggests that the resolved emission should result from PAH molecules on the disk atmosphere being UV-excited by the central star. Simple geometrical models of the PAH component compared to the underlying continuum point to a PAH emission uniformly extended out to the physical limits of the disk model. Furthermore, our RT best model of the continuum requires a negative exponent of the surface density power-law, in contrast with earlier modeling pointing to a positive exponent. Conclusions. We have spatially resolved - for the first time to our knowledge - the PAHs emission in the disk of HD 179218 and set constraints on its spatial extent. Based on spatial and spectroscopic considerations as well as on qualitative comparison with IRS 48 and HD 97048, we favor a scenario in which PAHs extend out to large radii across the flared disk surface and are at the same time predominantly in an ionized charge state due to the strong UV radiation field of the 180 L circle dot central star.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Taha, A. S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Labadie, L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Pantin, E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Matter, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Alvarez, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Esquej, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Grellmann, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Rebolo, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Telesco, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wolf, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-189349
DOI:	10.1051/0004-6361/201732008
Journal or Publication Title:	Astron. Astrophys.
Volume:	612
Date:	2018
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language AE/BE STARS; PROTOPLANETARY DISK; AE STARS; CIRCUMSTELLAR DISKS; ISO SPECTROSCOPY; T-TAURI; DUST; RESOLUTION; INTERFEROMETRY; SPECTRA Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/18934