Abstract
Context: The structure of the inner disk of Herbig Be stars is not well understood. The continuum disks of several Herbig Be stars have inner radii that are smaller than predicted by models of irradiated disks with optically thin holes. Aims: We study the size of the inner disk of the Herbig B[e] star HD 85567 and compare the model radii with the radius suggested by the size-luminosity relation. Methods: The object was observed with the AMBER instrument of the Very Large Telescope Interferometer. We obtained K-band visibilities and closure phases. These measurements are interpreted with geometric models and temperature-gradient models. Results: Using several types of geometric star-disk and star-disk-halo models, we derived inner ring-fit radii in the K band that are in the range of 0.8 - 1.6 AU. Additional temperature-gradient modeling resulted in an extended disk with an inner radius of $0.67^{+0.51}_{-0.21}$ AU, a high inner temperature of $2200^{+750}_{-350}$ K, and a disk inclination of $53^{+15}_{-11}$$^\circ$. Conclusions: The derived geometric ring-fit radii are approximately 3 - 5 times smaller than that predicted by the size-luminosity relation. The small geometric and temperature-gradient radii suggest optically thick gaseous material that absorbs stellar radiation inside the dust disk.
Highlights
Infrared interferometric observations suggest that the circumstellar environment of Herbig Be (HBe) and Herbig Ae (HAe) stars are significantly different
This agrees with the hypothesis of shielded stellar radiation, which leads to small dust sublimation radii, which agrees with our observations
We derived geometric ring models with inner radii of 0.8–1.6 AU, which are approximately 3–5 times smaller than that predicted by the size–luminosity relation
Summary
Infrared interferometric observations suggest that the circumstellar environment of Herbig Be (HBe) and Herbig Ae (HAe) stars are significantly different. In contrast to the lower-mass HAe stars, the K-band continuum radii of several HBe stars are significantly smaller than predicted by the size–luminosity relation (Monnier et al 2005; Eisner et al 2004; Kraus et al 2008b; Weigelt et al 2011; Kreplin et al 2012). These smaller radii can be explained by the presence of an optically thick gas inside the dust disk.
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