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Context. For over a decade, the structure of the inner cavity in the transition disk of TW Hydrae has been a subject of debate. Modeling the disk with data obtained at different wavelengths has led to a variety of proposed disk structures. Rather than being inconsistent, the individual models might point to the different faces of physical processes going on in disks, such as dust growth and planet formation. Aims. Our aim is to investigate the structure of the transition disk again and to find to what extent we can reconcile apparent model differences. Methods. A large set of high-angular-resolution data was collected from near-infrared to centimeter wavelengths. We investigated the existing disk models and established a new self-consistent radiative-transfer model. A genetic fitting algorithm was used to automatize the parameter fitting, and uncertainties were investigated in a Bayesian framework. Results. Simple disk models with a vertical inner rim and a radially homogeneous dust composition from small to large grains cannot reproduce the combined data set. Two modifications are applied to this simple disk model: (1) the inner rim is smoothed by exponentially decreasing the surface density in the inner ∼3 AU, and (2) the largest grains (>100 µm) are concentrated towards the inner disk region. Both properties can be linked to fundamental processes that determine the evolution of protoplanetary disks: the shaping by a possible companion and the different regimes of dust-grain growth, respectively. Conclusions. The full interferometric data set from near-infrared to centimeter wavelengths requires a revision of existing models for the TW Hya disk. We present a new model that incorporates the characteristic structures of previous models but deviates in two key aspects: it does not have a sharp edge at 4 AU, and the surface density of large grains differs from that of smaller grains. This is the first successful radiative-transfer-based model for a full set of interferometric data.

We report on Keck Interferometer observations of the double-lined binary (B) component of the quadruple pre-main sequence (PMS) system HD 98800. With these interferometric observations combined with astrometric measurements made by the Hubble Space Telescope Fine Guidance Sensors (FGS), and published radial velocity observations we have estimated preliminary visual and physical orbits of the HD 98800 B subsystem. Our orbit model calls for an inclination of 66.8 ± 3.2 deg, and allows us to infer the masses and luminosities of the individual components. In particular we find component masses of 0.699 ± 0.064 and 0.582 ± 0.051 M ⊙ for the Ba (primary) and Bb (secondary) components respectively.Spectral energy distribution (SED) modeling of the B subsystem suggests that the B circumstellar material is a source of extinction along the line of sight to the B components. This seems to corroborate a conjecture by Tokovinin that the B subsystem is viewed through circumbinary material, but it raises important questions about the morphology of that circumbinary material.Our modeling of the subsystem component SEDs finds temperatures and luminosities in agreement with previous studies, and coupled with the component mass estimates allows for comparison with PMS models in the low-mass regime with few empirical constraints. Solar abundance models seem to under-predict the inferred component temperatures and luminosities, while assuming slightly sub-solar abundances bring the models and observations into better agreement. The present preliminary orbit does not yet place significant constraints on existing pre-main sequence stellar models, but prospects for additional observations improving the orbit model and component parameters are very good.

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