Aims. We investigate the structure of the circumstellar disk of the T Tauri star S CrA N and test whether the observations agree with the standard picture proposed for Herbig Ae stars. Methods. Our observations were carried out with the VLTI/AMBER instrument in the H and K bands with the low spectral resolution mode. For the interpretation of our near-infrared AMBER and archival mid-infrared MIDI visibilities, we employed both geometric and temperature-gradient models. Results. To characterize the disk size, we first fitted geometric models consisting of a stellar point source, a ring-shaped disk, and a halo structure to the visibilities. In the H and K bands, we measured ring-fit radii of 0.73 ± 0.03 mas (corresponding to 0.095 ± 0.018 AU for a distance of 130 pc) and 0.85 ± 0.07 mas (0.111 ± 0.026 AU), respectively. This K-band radius is approximately two times larger than the dust sublimation radius of ≈0.05 AU expected for a dust sublimation temperature of 1500 K and gray dust opacities, but approximately agrees with the prediction of models including backwarming (namely a radius of ≈0.12 AU). The derived temperature-gradient models suggest that the disk is approximately face-on consisting of two disk components with a gap between star and disk. The inner disk component has a temperature close to the dust sublimation temperature and a quite narrow intensity distribution with a radial extension from 0.11 AU to 0.14 AU. Conclusions. Both our geometric and temperature-gradient models suggest that the T Tauri star S CrA N is surrounded by a circumstellar disk that is truncated at an inner radius of ≈0.11 AU. The narrow extension of the inner temperature-gradient disk component implies that there is a hot inner rim.
Context. The UX Ori type variables (named after the prototype of their class) are intermediate-mass pre-main sequence objects. One of the most likely causes of their variability is the obscuration of the central star by orbiting dust clouds. Aims. We investigate the structure of the circumstellar environment of the UX Ori star V1026 Sco (HD 142666) and test whether the disk inclination is large enough to explain the UX Ori variability. Methods. We observed the object in the low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument and derived H-and K-band visibilities and closure phases. We modeled our AMBER observations, published Keck Interferometer observations, archival MIDI/VLTI visibilities, and the spectral energy distribution using geometric and temperature-gradient models. • approximately agrees with the inclination derived with the geometric model (49 ± 5 • in the K band and 50 ± 11 • in the H band). The position angle of the fitted geometric and temperaturegradient models are 163 ± 9 • (K band; 179 ± 17 • in the H band) and 169.3 +4.2 −6.7• , respectively. Conclusions. The narrow width of the inner ring-shaped model disk and the disk gap might be an indication for a puffed-up inner rim shadowing outer parts of the disk. The intermediate inclination of ∼50 • is consistent with models of UX Ori objects where dust clouds in the inclined disk obscure the central star.
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 • . 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.
<p>State-of-the-art high resolution, convection resolving NWP models and reanalysis typically operate on a horizontal resolution of 1-5 km. These models require specific data assimilation schemes with frequent analysis (every 1-6 h) and corresponding dense and frequent observations to define the detailed initial conditions. Key variables needed for convection-resolving data assimilation are, among others, the 3-dimensional fields of temperature and humidity. Both variables are not adequately (vertically, horizontally and temporally) measured by current observing systems. The vertical resolution of atmospheric profiles provided by satellite sensors is poor, especially in the atmospheric boundary layer, where convection resolving models have many layers close to the surface to better describe the surface-atmosphere exchange processes. To the necessary information, a new generation of observations through the lowest few kilometers of the atmosphere is required. A network of ground-based remote sensing sensors (e.g., microwave radiometer, MWR, or water vapor DIAL) has the potential to provide real time profile observations to forecasting centers. Maintaining an operational observing network is a difficult and expensive task. Therefore, it is essential to evaluate the impact of different components of the current observing system and to assess the potential contribution of a new observing components to the analysis of the atmospheric state.<br>In our study we perform an Observing System Simulation Experiment (OSSE) to show the potential benefit of ground-based MWR for improving the initial thermodynamic state of the atmosphere. The Nature Run (NR), representing the &#8220;true&#8221; atmosphere, is performed using the ICON-LES model for a 150x150 km domain in the western part of Germany with 500 m horizontal resolution for summer convective cases. The MWR observations, dependent on cloudiness, temperature and humidity profiles, are simulated with the radiative transfer model RTTOV-gb and assimilated into the convection resolving ICON model (2km horizontal resolution). In this contribution, we will present first impact studies of assimilating synthetic observations of single MWR instruments on the initial temperature and humidity fields and extend the approach for evaluating the effect of a network of instruments with respect to other variables relevant for solar power applications, such as precipitation and solar radiation.</p>
<p>The latest generation of active and passive ground-based remote sensing instruments, often called &#8220;profilers&#8221;, has shown its potential for continuous and high-resolution measurements of thermodynamic and kinematic vertical profiles as well as particle-related profiles. It is precisely these observations of the atmospheric boundary layer that are increasingly needed to improve the forecast quality of high-resolution numerical weather prediction (NWP) and nowcasting.</p><p>For this purpose, the DWD has initiated the project &#8220;Pilotstation&#8221; to evaluate options for a qualitative network expansion with suitable surface remote sensing profilers. Currently, we assess the following profilers in a dedicated testbed at Lindenberg Observatory: Doppler lidar, microwave radiometer, water vapor broadband-DIAL, and cloud radar. Furthermore, we plan to evaluate a compact Raman lidar in the future. At DWD, the assessment of candidate systems takes place holistically focusing on all aspects of instrument reliability, operational sustainability, data quality, and on the potential benefit for the NWP using assimilation experiments. This implies efforts to standardize data processing steps and data formats, the development of software tools to support network operations and the proper integration of the observations in the data assimilation system. After the initial testing and evaluation at the Lindenberg Observatory, a suite of instruments will be installed at the weather station in Aachen-Orsbach to enable an end-to-end testing in an operational framework.</p><p>We give an overview of the ongoing project and present results regarding the various aspects: operations and sustainability, data quality and assimilation tests for the different testbed instruments and observations. This contribution complements the efforts of network development for future operational use within the frame of the EUMETNET's E-PROFILE observations program and the COST action PROBE.</p>
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