Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21334102b&link_type=abstract
American Astronomical Society, AAS Meeting #213, #341.02; Bulletin of the American Astronomical Society, Vol. 41, p.475
Astronomy and Astrophysics
Astronomy
Scientific paper
We present observations obtained with the 10-micron beamcombiner of the VLT interferometer (MIDI). This data provides high spatial resolution (50 milli-arcseconds) information on the geometric distribution of PAH emission (7.9, 8.6, and 11.3 micron features) surrounding the post-AGB binary HR 4049.
Data is used that was obtained with the two-way beamcombiner MIDI. An N-band (8-13 micron) interferometer that combines the light from two 8-meter telescopes separated by a 40 meter projected baseline. The observations were obtained in MIDI guaranteed observing time in February and June 2004.
The MIDI spectra has contribution from over-resolved PAH emission lines at (7.9, 8.6 and 11.3 micron), the unresolved stellar disk, and the partially resolved circumstellar disk. A comparison between the high spatial resolution spectra obtained with MIDI, and the lower spatial resolution spectra obtained with ISO (theta = 3.4 arcsec), shows that there is a difference in flux balance between these different PAH features, indicative for locations at varying distance from the central star for the different PAH species. The visibilities in the PAH features indicate that they are over-resolved (i.e. that their correlated flux is close to zero), placing the bulk of their line forming region at least at 50-70 milli-arcseconds from the central star. The continuum extension is estimated to range between 23 and 28 milli-arcseconds with a Gaussian model, and is very close to the K band extensions measured with VINCI/VLTI, implying that the emitting regions of the near and mid-IR are similar. This continuum emission is attributed a circumstellar disk that has a geometry resembling that of a disk with a wall like inner surface.
A geometric model is proposed in which the PAH emission originates from the polar regions is perpendicular to the orientation of the circumstellar disk.
Bakker Eric J.
Chesneau Olivier
Lopez Belen
Menut J.
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