| dc.description.abstract | Context. Unveiling the structure of the disks around intermediate-mass pre-main-sequence stars (Herbig Ae/Be stars) is essential for
our understanding of the star and planet formation process. In particular, models predict that in the innermost AU around the star, the
dust disk forms a “puffed-up” inner rim, which should result in a strongly asymmetric brightness distribution for disks seen under
intermediate inclination.
Aims. Our aim is to constrain the sub-AU geometry of the inner disk around the Herbig Ae star R CrA and search for the predicted
asymmetries.
Methods. Using the VLTI/AMBER long-baseline interferometer, we obtained 24 near-infrared (H- and K-band) spectrointerferometric
observations on R CrA. Observing with three telescopes in a linear array configuration, each data set samples three
equally spaced points in the visibility function, providing direct information about the radial intensity profile. In addition, the observations
cover a wide position angle range (∼ 97◦
), also probing the position angle dependence of the source brightness distribution.
Results. In the derived visibility function, we detect the signatures of an extended (Gaussian FWHM ∼ 25 mas) and a compact
component (Gaussian FWHM ∼ 5.8 mas), with the compact component contributing about two-thirds of the total flux (both in H- and
K-band). The brightness distribution is highly asymmetric, as indicated by the strong closure phases (up to ∼ 40◦
) and the detected
position angle dependence of the visibilities and closure phases. To interpret these asymmetries, we employ various geometric as well
as physical models, including a binary model, a skewed ring model, and a puffed-up inner rim model with a vertical or curved rim
shape. For the binary and vertical rim model, no acceptable fits could be obtained. On the other hand, the skewed ring model and
the curved puffed-up inner rim model allow us to simultaneously reproduce the measured visibilities and closure phases. From these
models we derive the location of the dust sublimation radius (∼ 0.4 AU), the disk inclination angle (∼ 35◦
), and a north-southern
disk orientation (PA∼180-190◦
). Our curved puffed-up rim model can reasonably well reproduce the interferometric observables and
the SED simultaneously and suggests a luminosity of ∼ 29 L and the presence of relatively large (& 1.2 µm) Silicate dust grains.
Our study also reveals significant deviations between the measured interferometric observables and the employed puffed-up inner
rim models, providing important constraints for future refinements of these theoretical models. Perpendicular to the disk, two bow
shock-like structures appear in the associated reflection nebula NGC 6729, suggesting that the detected sub-AU size disk is the driving
engine of a large-scale outflow.
Conclusions. Detecting, for the first time, strong non-localized asymmetries in the inner regions of a Herbig Ae disk, our study
supports the existence of a puffed-up inner rim in YSO disks. | en_GB |
