Péter Ábrahám, László Mosoni, Thomas Henning, Ágnes Kóspál,
Christoph Leinert, Attila Moór, Sascha P. Quanz, and Thorsten Ratzka
LOOKING INTO THE HEART OF THE OUTBURSTING STAR V1647 ORI:
FIRST AU-SCALE OBSERVATIONS WITH VLTI/MIDI

LOOKING INTO THE HEART OF THE OUTBURSTING STAR V1647 ORI:
FIRST AU-SCALE OBSERVATIONS WITH VLTI/MIDI

Péter Ábrahám(1), László Mosoni(1), Thomas Henning(2), Ágnes Kóspál(1),
Christoph Leinert(2), Attila Moór(1), Sascha P. Quanz(2), and Thorsten Ratzka(2)
(1) Konkoly Observatory of the Hungarian Academy of Sciences, P.O. Box 67, H-1525 Budapest, Hungary
(2) Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

The young eruptive star V1647 Ori was observed with MIDI, the mid-infrared interferometric instrument at the Very Large Telescope Interferometer, on March 2, 2005. We present the first spectrally resolved interferometric visibility points for this object. Our results are summarised in the following.

1. The calibrated visibilities (see figure) show that the source is resolved by MIDI on the UT3-UT4 baseline. The visibility curve suggests a non-uniform temperature distribution of the emitting material. The size of the mid-infrared emitting region is $\approx$7 AU at 10 $\mu$m.

2. The $8-13 \mu$m spectrum i) exhibit no obvious spectral features thus cannot support models consisting of optically thin components; ii) the source faded in the N-band significantly (compared to Andrews et al. 2004 ApJ 610, 45); iii) the correlated flux density, i.e. the emission of the innermost part of the circumstellar structure, contains $\approx 70$% of the total mid-infrared flux density.

3. There are proposals in the literature that the FU Ori phenomenon is triggered by a close companion (e.g. Reipurth & Aspin 2004, ApJ 608, 65). A companion would cause sinusoidal variations in the spectrally resolved visibilities with appropriate baseline position angles. The shape of our visibility curve suggests that no companion is present at the measured position angle whose separation is less than 100 AU and brightness ratio is greater than 10%. Nor do the acquisition images show any companion. However, we can exclude the companion only along the measured baseline further observations will be needed to clarify the existence of a companion.

4. A simple disk model is able to fit both the spectral energy distribution and the observed visibility values simultaneously (solid line in figure). Model parameters for the disk were the following: $T(1 \rm {AU})=680 \rm {K}$ and $T{\sim}r^{-0.53}$, inner and outer disk radii $7R_{\odot}$ and $100 \rm {AU}$, respectively, surface density ${\Sigma}{\sim}r^{-1.5}$, disk mass $M_{d}=0.05 \rm {M}_{\odot}$, inclination angle 60^.