Abstract
Aims. The cause of the UX Ori variability in some Herbig Ae/Be stars is still a matter of debate. Detailed studies of the circumstellar environment of UX Ori objects (UXORs) are required to test the hypothesis that the observed drop in photometry might be related to obscuration events. Methods. Using near- and mid-infrared interferometric AMBER and MIDI observations, we resolved the inner circumstellar disk region around UX Ori. Results. We fitted the K -, H -, and N -band visibilities and the spectral energy distribution (SED) of UX Ori with geometric and parametric disk models. The best-fit K -band geometric model consists of an inclined ring and a halo component. We obtained a ring-fit radius of 0.45 ± 0.07 AU (at a distance of 460 pc), an inclination of 55.6 ± 2.4°, a position angle of the system axis of 127.5 ± 24.5°, and a flux contribution of the over-resolved halo component to the total near-infrared excess of 16.8 ± 4.1%. The best-fit N -band model consists of an elongated Gaussian with a HWHM ~ 5 AU of the semi-major axis and an axis ration of a / b ~ 3.4 (corresponding to an inclination of ~72°). With a parametric disk model, we fitted all near- and mid-infrared visibilities and the SED simultaneously. The model disk starts at an inner radius of 0.46 ± 0.06 AU with an inner rim temperature of 1498 ± 70 K. The disk is seen under an nearly edge-on inclination of 70 ± 5°. This supports any theories that require high-inclination angles to explain obscuration events in the line of sight to the observer, for example, in UX Ori objects where orbiting dust clouds in the disk or disk atmosphere can obscure the central star.
Highlights
The UX Ori type stars are a class of photometrically active young objects, predominantly Herbig Ae stars and some amount of young F and G stars
Detailed studies of the circumstellar environment of UX Ori objects (UXORs) are required to test the hypothesis that the observed drop in photometry might be related to obscuration events
The best-fit N-band model consists of an elongated Gaussian with a HWHM ∼ 5 AU of the semi-major axis and an axis ration of a/b ∼ 3.4
Summary
The UX Ori type stars (or UXORs) are a class of photometrically active young objects, predominantly Herbig Ae stars and some amount of young F and G stars (see, e.g., Herbst et al 1994). The high linear polarization observed systematically during the deep minima motivated us to assume that the violent photometric activity of UXORs is a result of the low inclination of the CS disks to the line of sight (Grinin et al 1991). A different explanation of the UXOR physics was suggested by Herbst & Shevchenko (1999) They suggested that the photometric activity of UXORs does not depend on the disk orientation and is a result of the FUOR-like activity caused by the strong and unstable accretion activity of these stars. Interferometric observations of young stars permit us to measure the inclination of their CS disks relative to the line of sight. We present near- and mid-infrared interferometric observations of the Herbig Ae star UX Ori. In Sect.
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