Optimization of the preparation and analysis of interferometric observations in the infrared of circumstellar disks
Final Report Abstract
Motivated by the availability of a new generation of beam combiners, e.g., for the Very Large Telescope Interferometer (VLTI), we investigated selected aspects concerning the potential of long-baseline interferometric observations to study the evolution of protoplanetary disks around young stars and the process of planet formation in their innermost regions. Moreover, we evaluated the impact of complementary observations, to be obtained at other wavelength ranges and/or angular resolutions in order to better constrain conclusions derived from interferometric observations in the infrared alone. The individual studies performed within this project cover A. Numerical studies in which we investigated the potential of infrared interferometry in the context of protoplanetary disk studies, B. Observational studies of selected protoplanetary disks, making use of infrared long-baseline interferometers, and C. Feasibility studies to apply infrared interferometry to better constrain the phenomenon of "Hot Exozodiacal Dust" around main-sequence stars. In the following, the main individual studies performed in this project are summarized in brief: (1) We quantify the potential capabilities of detecting local brightness asymmetries, i.e., the signature of embedded companions in circumstellar disks with the MATISSE, a 2nd generation beam combiner at the VLTI, operating in the mid-infrared wavelength range. In particular, visibilities and closure phases are calculated to simulate observations with MATISSE. We find that the flux ratio of the embedded source to the central star can be as low as 0.5 to 0.6 % for a detection at a feasible significance level. Furthermore, the likelihood for detection is highest for sources at intermediate distances r ≈ 2–5 au and disk masses not higher than ≈ 10^−4 M. (2) We evaluate the advantage of combining observations with MATISSE/VLTI and ALMA to constrain the radial and vertical structure of the dust in the innermost region of circumstellar disks in nearby star-forming regions. We find that constraining the dust density structure in the innermost 5 au around the central star is challenging with MATISSE alone, whereas ALMA observations with reasonable integration times allow us to derive significant constraints on the disk surface density. However, we find that the estimation of the different disk parameters can be considerably improved by combining MATISSE and ALMA observations. (3) We investigate the variability of the brightness distribution and the changing density structure of the protoplanetary disk around DR Tau, a classical T Tauri star. We are able to reproduce the spectral energy distribution as well as the mid-infrared visibility for one of the three epochs with a basic disk model. Also, it is possible to reproduce the very different visibility measurements obtained nine years earlier with a very similar baseline, using the same disk model, but a smaller scale height.(4) We present an analysis of the young binary T-Tauri system VV Corona Australis, in which both components host disks, but only one is visible at optical wavelengths. New mid-infrared interferometry and near-infrared spectroscopy is considered along with archival millimetre-wave observations, which resolve the binary at 1.3 mm for the first time. Comparing the results of our model to evolutionary models suggests stellar masses 1.7 M and an age for the system of 3.5 Myr. (5) Recent interferometric surveys of nearby main-sequence stars show a faint but significant nearinfrared excess in roughly two dozen systems, i. e. around 10 % to 30 % of stars surveyed. We use previously published interferometric observations to constrain the properties and distribution of this hot dust. We find that grains have to be sufficiently absorbing to be consistent with the observed excess, while dielectric grains with pure silicate compositions fail to reproduce the observations. The dust should be located within ∼ 0.01 − 1 au from the star depending on its luminosity. Subsequently, we explore the potential of mid-infrared interferometry, in particular using MATISSE, to find stronger constraints for the properties and the origin of the hot exozodiacal dust. We find that the M band possesses the best conditions to detect hot dust emission, closely followed by L and N bands. In particular, observations in the mid-infrared could help to determine whether the dust piles up at the sublimation radius or is located at radii up to 1 au.
Publications
- "DR Tauri: Temporal variability of the brightness distribution in the potential planet-forming region", Astronomy and Astrophysics 585, A100 (2016)
R. Bunngräber, S. Wolf, Th. Ratzka, F. Ober
(See online at https://doi.org/10.1051/0004-6361/201526691) - "Understanding discs in binary YSOs: detailed modelling of VV CrA", Monthly Notices of the Royal Astronomical Society, Volume 458: 2476-2491 (2016)
P. Scicluna, S. Wolf, T. Ratzka, G. Costigan, R. Launhardt, C. Leinert, F. Ober, C.F. Manara, L. Testi
(See online at https://doi.org/10.1093/mnras/stw460) - "Constraints on the structure of hot exozodiacal dust belts", Monthly Notices of the Royal Astronomical Society, 467,1614 (2017)
F. Kirchschlager, S. Wolf, A.V. Krivov, H. Mutschke, R. Brunngräber
(See online at https://doi.org/10.1093/mnras/stx202) - "Constraints on observing brightness asymmetries in protoplanetary disks at solar system scale", Astronomy and Astrophysics 611, A90 (2018)
R. Bunngräber, S. Wolf
(See online at https://doi.org/10.1051/0004-6361/201731907) - "Modelling of mid-infrared interferometric signature of hot exozodiacal dust emission", Monthly Notices of the Royal Astronomical Society, 473, 2633 (2018)
F. Kirchschlager, S. Wolf, R. Brunngräber, A. Matter, A.V. Krivov, A. Labdon
(See online at https://doi.org/10.1093/mnras/stx2515) - "The potential of combining MATISSE and ALMA observations: constraining the structure of the innermost region in protoplanetary disks", Astronomy and Astrophysics 622, A147 (2019)
J. Kobus, S. Wolf, R. Bunngräber
(See online at https://doi.org/10.1051/0004-6361/201833784)
