Abstract. This paper presents state-of-the-art spectral energy distributions (SEDs) of four Herbig Ae stars, based in part on new data in the mid and far-infrared and at millimeter wavelengths. The SEDs are discussed in the context of circumstellar disk models. We show that models of irradiated disks provide a good fit to the observations over the whole range of wavelengths. We offer a possible solution to the long-standing puzzle caused by the excess emission of Herbig Ae stars, where a large fraction of the stellar luminosity is re-radiated between ∼1.25 and 7 µm, with a peak at about 3 µm. We suggest that this general behaviour can be caused by dust evaporation in disks where the gas component is optically thin to the stellar radiation, as expected if the accretion rate is very low. The creation of a puffed-up inner wall of optically thick dust at the dust sublimation radius can account for the near-infrared characteristics of the SEDs. It can also naturally explain the H and K band interferometric observations of AB Aur (Millan-Gabet et al. 2001), which reveal a ring of emission of radius ∼0.3 AU. Finally, irradiated disk models can easily explain the observed intensity of the 10 µm silicate features and their variation from star to star.

Context. Circumstellar disks and outflows play a fundamental role in star formation. Infrared spectro-interferometry allows the inner accretion-ejection region to be resolved. Aims. We study the disk and Brγ-emitting region of MWC 297 with high spatial and spectral resolution and compare our observations with disk-wind models. Methods. We measured interferometric visibilities, wavelength-differential phases, and closure phases of MWC 297 with a spectral resolution of 12 000. To interpret our MWC 297 observations, we employed disk-wind models. Results. The measured continuum visibilities confirm previous results that the continuum-emitting region of MWC 297 is remarkably compact. We derive a continuum ring-fit radius of ∼2.2 mas (∼0.56 AU at a distance of 250 pc), which is ∼5.4 times smaller than the 3 AU dust sublimation radius expected for silicate grains (in the absence of radiation-shielding material). The strongly wavelengthdependent and asymmetric Brγ-emitting region is more extended (∼2.7 times) than the continuum-emitting region. At the center of the Brγ line, we derive a Gaussian fit radius of ∼6.3 mas HWHM (∼1.6 AU). To interpret the observations, we employ a magnetocentrifugally driven disk-wind model consisting of an accretion disk, which emits the observed continuum radiation, and a disk wind, which emits the Brγ line. The calculated wavelength-dependent model intensity distributions and Brγ line profiles are compared with the observations (i.e., K-band spectrum, visibilities, differential phases, and closure phases). The closest fitting model predicts a continuum-emitting disk with an inner radius of ∼0.3 AU and a disk wind ejection region with an inner radius of ∼0.5 AU (∼17.5 stellar radii). We obtain a disk-wind half-opening angle (the angle between the rotation axis and the innermost streamline of the disk wind) of ∼80 • , which is larger than in T Tau models, and a disk inclination angle of ∼20 • (i.e., almost pole-on). Conclusions. Our observations with a spectral resolution of 12 000 allow us to study the AU-scale environment of MWC 297 in ∼10 different spectral channels across the Brγ emission line. We show that the K-band flux, visibilities, and remarkably strong phases can be explained by the employed magneto-centrifugally driven disk wind model.

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Abstract. We present in this paper several high resolution (R = 27 000) spectra of five UXORs (UX Ori, CQ Tau, BF Ori, RR Tau, WW Vul), which cover the entire visual range, from 3900 to about 8700Å. There are between 4 and 7 spectra per star, obtained over a time interval of two years. Simultaneous or quasi-simultaneous photometric observations were also obtained at the Crimean Astrophysical Observatory. The complete, reduced and normalized spectra are available in electronic form. We show for each star a selection of the most interesting lines, and the full spectrum of UX Ori computed by averaging the spectra obtained when the star was at maximum light. For UX Ori we show also the synthetic spectrum and provide an identification of most of the lines. The spectra are too sparse to form true time sequences; however, they provide an extremely useful database for studies of UX Ori-type stars. We discuss briefly the main features of the spectra. We show that they contain many time-stable photospheric lines that can be described to a good approximation by the synthetic spectra of normal A stars with log g = 3.5−4 and we derive for each star effective temperature, gravity and rotational velocity. We examine the time variability of selected lines and study their connection with the photometric activity of the stars. Two different types of spectral variability are identified. One is common to all stars with circumstellar (CS) gas and is caused by perturbations of the physical and kinematic conditions of the emitting region. There is no correlation between this type of activity and the brightness variations of the star. On the contrary, a second type of spectral variability correlates well with the brightness variations and is very likely connected with the screening effect of an opaque dust cloud which sporadically intersects the line of sight. This type of variability has been observed in its simplest form in one of the RR Tau spectra, where the equivalent width of the forbidden line [O i] 6364Å increased by a factor of about three as the star faded by approximately the same amount.

We report the discovery of mid-infrared excess emission in the young object RZ Psc. The excess constitutes ∼8% of its L bol and is well fit by a single 500 K blackbody, implying a dust-free region within ∼0.7 AU for optically thick dust. The object displays dust obscuration events (UXOR behaviour) on a time scale that suggests dusty material on orbits of ∼0.5 AU. We also report a 12.4-year cyclical photometric variability that can be interpreted as caused by perturbations in the dust distribution. The system is characterized by a high inclination, marginal extinction (during bright photometric states), a single temperature for the warm dust, and an age estimate that puts the star beyond the formation stage. We propose that the dust occultation events present a dynamical view of an active asteroid belt whose collisional products sporadically obscure the central star.

This paper presents observations of an episode of accretion activity in the preÈmain-sequence star UX Ori. High-velocity, redshifted absorption is seen in several lines of H, Ca II, Na I, and Fe II during an interval of eight nights in the fall of 1996 with similar velocity and time evolution. A non-LTE analysis of the line optical depths shows that the infalling gas cannot be heavily hydrogen-depleted, as would be expected if it was produced by the evaporation of a solid body of chemical composition similar to solar system comets. On the contrary, the observations are consistent with gas of solar chemical composition at temperature D6000È7000 K.

Context. High angular and spectral resolution observations can provide us with fundamental clues to the complex circumstellar structure of young stellar objects (YSOs) and to the physical processes taking place close to these sources. Aims. We analyse the main physical parameters and the circumstellar environment of the young Herbig Be star HD 98922. Methods. We present AMBER/VLTI high spectral resolution (R = 12 000) interferometric observations across the Brγ line, accompanied by UVES high-resolution spectroscopy and SINFONI-AO assisted near-infrared (NIR) integral field spectroscopic data. To interpret our observations, we develop a magneto-centrifugally driven disc-wind model. Results. Our analysis of the UVES spectrum shows that HD 98922 is a young (∼5 × 10 5 yr) Herbig Be star (SpT = B9V), located at a distance of 440± 60 50 pc, with a mass accretion rate (Ṁ acc ) of ∼(9 ± 3) × 10 −7 M yr −1 . SINFONI K-band AO-assisted imaging shows a spatially resolved circumstellar disc-like region (∼140 AU in diameter) with asymmetric brightness distribution. Our AMBER/VLTI UT observations indicate that the Brγ emitting region (ring-fit radius ∼0.31 ± 0.04 AU) is smaller than the continuum emitting region (inner dust radius ∼0.7 ± 0.2 AU), showing significant non-zero V-shaped differential phases (i.e. non S-shaped, as expected for a rotating disc). The value of the continuum-corrected pure Brγ line visibility at the longest baseline (89 m) is ∼0.8 ± 0.1, i.e. the Brγ emitting region is partially resolved. Our modelling suggests that the observed Brγ line-emitting region mainly originates from a disc wind with a half opening angle of 30• , and with a mass-loss rate (Ṁ w ) of ∼2 × 10 −7 M yr −1 . The observed V-shaped differential phases are reliably reproduced by combining a simple asymmetric continuum disc model with our Brγ disc-wind model. Conclusions. In conclusion, the Brγ emission of HD 98922 can be modelled with a disc wind that is able to approximately reproduce all interferometric observations if we assume that the intensity distribution of the dust continuum disc is asymmetric.