Cold debris disks around nearby stars

• Antragsteller: Professor Dr. Sebastian Wolf
• Fachliche Zuordnung: Astrophysik und Astronomie
• Förderung: Förderung von 2010 bis 2016
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 175010019

• Erstellungsjahr: 2015

Zusammenfassung der Projektergebnisse

Within the frame of this project we successfully a) analyzed observations of debris disks obtained through the Herschel Space Observatory key program “Dust around nearby stars” (DUNES), b) investigated the impact of assumed dust properties on the above result, and c) performed feasibility studies for future observations aimed at tracing large-scale signatures of the interaction of planets with the dust phase in debris disks: • We presented the first photometric data of debris disks around HIP 103389 (HD 199260), HIP 107350 (HN Peg, HD 206860), and HIP 114948 (HD 219482), obtained in the context of our Herschel program DUNES. All three sources potentially exhibit an unusually steep decrease of the SED in the wavelength range between 70µm and 160µm. We concluded that a new mechanism to produce the dust in the presented debris disks, deviations from the conditions required for a standard equilibrium collisional cascade, and/or significantly different dust properties would be necessary to explain the potentially steep SED shape of the three debris disks presented. Future observations aimed at a better understanding of this peculiar class of debris disks were discussed. • We developed a detailed model of the debris disk around HD 107146. A broad range of resolved data from optical scattered light to millimeter data as well as the SED has been reproduced by a single radial density profile. We concluded from our modeling results that the disk is heavily collision dominated. From remaining discrepancies between our model and the observations we find strong evidence for an additional inner disk component, possibly near the habitable zone. We did not find evidence of an orbiting planet from the available data and found that a birth ring scenario is likely responsible for the ringlike shape of the disk. • We performed two studies, investigating the impact of porous grains on the observational appearance and thus on the data analysis of circumstellar disks. The first of these studies was focused on debris disks. This study was particularly motivated by the fact that debris disk modeling using compact grains often reveals a significant discrepancy between the minimum particle size and the calculated blowout size. We found that the blowout size increases with the particle porosity and stellar luminosity. The dust temperature of porous particles is lower than the one of the compact spheres. An online tool for calculating the blowout size of porous grains was made available online (http://www1.astrophysik.uni-kiel.de/blowout/). In the second study, we investigated the effect of dust grain porosity on the appearance of protoplanetary disks. We found that the flux in the optical wavelength range and the silicate peak at ∼ 9.7µm is increased for porous grains. Furthermore, porous grains were found to be warmer than compact spheres at the optically thin/thick transition region. Finally, a polarization reversal was detected in selected disk regions, which depends on the observing wavelength, grain porosity, and disk inclination. We investigated the reversal wavelengths for numerous parameter combinations. • We investigated the observability of structures in debris disks induced by planetdisk interaction with future facilities. High-sensitivity, high angular resolution observations with large (sub-)mm interferometers and large space-based telescopes operating in the near-to midinfrared wavelength range were considered. We found that HST scattered-light observations are in most cases unable to unambiguously detect such structures, in particular in debris disks seen face-on. However, we could also show that both, ALMA and the JWST will provide the sensitivity and resolution to detect and spatially resolve the spatial dust distribution in debris disks at a level of sensitivity and resolution that allows one to distinguish between different planet-disk configurations. • We contributed to various debris disk studies related to Herschel/DUNES. Also the results of these studies were published.

Projektbezogene Publikationen (Auswahl)

• “Mid-infrared observations of the transitional disks around DH Tauri, DM Tauri, and GM Aurigae”, Astronomy and Astrophysics, 533, A89 (2011)
  C. Gräfe, S. Wolf, V. Roccatagliata, J. Sauter, and S. Ertel
  
• “Multi-wavelength modeling of the spatially resolved debris disk of HD 107146”, Astronomy and Astrophysics, 533, A132 (2011)
  S. Ertel, S. Wolf, S. Metchev, G. Schneider, J. Carpenter, et al.
  
• “A peculiar class of debris disks from Herschel/DUNES - A steep fall off in the far infrared”, Astronomy and Astrophysics, 541, A148 (2012)
  S. Ertel, S. Wolf, J.P. Marshall, C. Eiroa, J.-C. Augereau, et al.
  
• “Observing planet-disk interaction in debris disks”, Astronomy and Astrophysics, 544, A61 (2012)
  S. Ertel, S. Wolf, and J. Rodmann
  
• “Porous dust grains in debris disks”, Astronomy and Astrophysics, 552, A54 (2013)
  F. Kirchschlager, S. Wolf
  
• “Effect of dust grain porosity on the appearance of protoplanetary disks”, Astronomy and Astrophysics, 568, A103 (2014)
  F. Kirchschlager, S. Wolf