Search all publications (SAO/NASA Astrophysics Data System)
ADS: "Location and sizes of forsterite grains in protoplanetary disks Interpretation from the Herschel DIGIT programme"
K. M. Maaskant; B.L. de Vries; M. Min; L.B.F.M. Waters; C. Dominik; F. Molster; A.G.G.M. Tielens
The spectra of protoplanetary disks contain mid- and far- infrared emission features produced by forsterite dust grains. The spectral features contain information about the forsterite temperature, chemical composition and grain size. We aim to characterize how the 23 and 69 micron features can be used to constrain the physical locations of forsterite in disks. We check for consistency between two independent forsterite temperature measurements: the I23/I69 feature strength ratio and the shape of the 69 micron band. We performed radiative transfer modeling to study the effect of disk properties to the forsterite spectral features. Temperature-dependent forsterite opacities were considered in self-consistent models to compute forsterite emission from proto- planetary disks.Results. Modelling grids are presented to study the effects of grain size, disk gaps, radial mixing and optical depth to the forsterite features. Independent temperature estimates derived from the I23/I69 feature strength ratio and the 69 micron band shape are most incon- sistent for HD 141569 and Oph IRS 48. A case study of the disk of HD 141569 shows two solutions to fit the forsterite spectrum. A model with T ∼ 40 K, iron-rich (∼ 0 − 1 % Fe) and 1 micron forsterite grains, and a model with warmer (T ∼ 100 K), iron-free, and larger (10 micron) grains. We find that for disks with low upper limits of the 69 micron feature (most notably in flat, self-shadowed disks), the forsterite must be hot, and thus close to the star. We find no correlation between disk gaps and the presence or absence of forsterite features. We argue that the 69 μm feature of the evolved transitional disks HD 141569 and Oph IRS 48 is most likely a tracer of larger (i.e. ~ 10 micron) forsterite grains. (2014-07)
ADS: "Polycyclic aromatic hydrocarbon ionization as a tracer of gas flows through protoplanetary disk gaps"
K. M. Maaskant; M. Min; L.B.F.M. Waters; A.G.G.M. Tielens
Planet-forming disks of gas and dust around young stars contain polycyclic aromatic hydrocarbons (PAHs). We demonstrate that fitting the PAH spectra of four transitional disks requires a contribution of ionized PAHs in ‘gas flows’ through the gap. The PAH spectra of transitional disks can be understood as superpositions of neutral and ionized PAHs. For HD 97048, neutral PAHs in the optically thick disk dominate the spectrum. In the cases of HD 169142, HD 135344 B and Oph IRS 48, small amounts of ionized PAHs located in the ‘gas flows’ through the gap are strong contributors to the total PAH luminosity. The observed trend in the sample of Herbig stars between the disk mass and PAH ionization may imply that lower-mass disks have larger gaps. Ionized PAHs in gas flows through these gaps contribute strongly to their spectra. (2014-02)
ADS: "Identifying gaps in flaring Herbig Ae/Be disks using spatially resolved mid-infrared imaging. Are all group I disks transitional?"
K. M. Maaskant; M. Honda; L.B.F.M. Waters; A.G.G.M. Tielens; C. Dominik; M. Min; A. Verhoeff; G. Meeus; M. E. van den Ancker
The evolution of protoplanetary disks towards mature planetary systems is expected to include the formation of 'gaps' in the disk possibly due to planet formation. We studied the disks of four key intermediate mass (Herbig Ae/Be) stars in order to understand the influence of gaps to their observational appearance. We investigate mid-infrared images and perform radiative transfer modeling to examine the radial distribution of dust and PAHs. Our solutions constrain the sizes of the gaps. For one particular object, HD 97048, this is the first detection of a disk gap. The large gaps deplete the entire population of silicate particles with temperatures suitable for prominent mid-infrared feature emission, while small carbonaceous grains and PAHs can still show prominent emission at mid-infrared wavelengths. The absence of silicate emission features is due to the presence of large gaps in the critical temperature regime. Our results suggest that many, if not all Herbig disks with weak or no silicate features in the spectrum are disks with large gaps and can be characterized as (pre-)transitional. We conclude that the evolution of Herbig stars follows two different paths. Competition between the timescales of inner versus outer disk evolution determine whether young protoplanetary disks evolve into transitional disks (due to planet formation in the inner disk) or into flat disks (due to the grain growth and dust settling in the outer disk). (2013-05)
ADS: "Mid-IR imaging of the transitional disk of HD169142: Measuring the size of the gap"
Honda, M.; Maaskant, Koen; Okamoto, Y. K.; Kataza, H.; Fukagawa, M.; Waters, L. B. F. M.; Dominik, C.; Tielens, A. G. G. M.; Mulders, G. D.; Min, M.; Yamashita, T.; Fujiyoshi, T.; Miyata, T.; Sako, S.; Sakon, I.; Fujiwara, H.; Onaka, T.
This research studies the geometrical structure of the protoplanetary disk of HD 169142. We proof that there is a large gap in the disk possibly caused by planets. The observed sizes as well as the steep rise of the SED near 20 micron require a disk model with an inner hole the size of 23 AU, making HD 169142 a transitional disk. HD 169142 is one of a growing number of Herbig Ae disks that are classified as group I source and that also require the presence of a large inner gap. It appears that many if not all group I sources may be strong candidates for classification as transitional disks. (2012-04)
ADS: "Sequential star formation in IRAS 06084-0611 (GGD 12-15). From intermediate-mass to high-mass stars"
K. M. Maaskant1,2, A. Bik3, L.B.F.M. Waters4,1, L. Kaper1, Th. Henning3, E. Puga5,6, M. Horrobin7, and J. Kainulainen3
This research studies the complex environment of the high mass star forming region IRAS 06084-0611. We show that the formation history of this cluster can be understood by sequential star formation along the line of sight. (2011-06)
