Johan Olofsson

[2006 - 2009] PhD
Sep. 2006 - Dec. 2009: LAOG, now [IPAG]
Advisors: Jean-Charles Augereau & Jean-Louis Monin
"Planetary Formation as seen with Spitzer and the VLTI"

Transient Dust in warm debris disks - Detection of Fe-rich olivine grains

[OLOFSSON, J.; JUHASZ, A.; HENNING, Th.; MUTSCHKE, H.; TAMANAI, A.; MOOR A.; ABRAHAM, P.; MIN, M.]

We develop and present a new radiative transfer code (DEBRA) dedicated to SED modeling of optically thin disks. The DEBRA code is designed such as it can determine dust composition and disk properties simultaneously. We make use of this code on the SEDs of eight warm debris disks, in combination with recent laboratory experiments on dust optical properties. We ﬁnd that most, if not all, debris disks in our sample are experiencing a transient phase, suggesting a production of small dust grains on relatively short timescales. Dust replenishment should be eﬃcient on timescales of months for at least three sources. From a mineralogical point of view, we ﬁnd that crystalline pyroxene grains (enstatite) have small abundances compared to crystalline olivine grains. The main result of our study is that we ﬁnd evidences for Fe-rich olivine crystalline grains (Mg / [Mg + Fe] ∼ 80%) for several debris disks. This ﬁnding contrasts with studies of gas-rich protoplanetary disks, where Fe-bearing crystalline grains are usually not observed.

Warm dust resolved in the cold disk around T Chamaleontis with VLTI/AMBER

[OLOFSSON, J.; BENISTY, M.; AUGEREAU, J.-C. et al. 2011]

The transition between massive Class II circumstellar disks and Class III debris disks, with dust residuals, has not yet been clearly undertsood. Disks are expected to dissipate with time, and dust clearing in the inner regions can be the consequence of several mechanisms. Planet formation is one of them that will possibly open a gap inside the disk. We observed TCha in the H and K bands using the AMBER instrument at the VLTI and resolve a narrow inner dusty disk close to the star. According to our results, we could successfully reproduce the SED as well as the interferometric observables. We constrain the position of the inner disk to be around 0.1 AU from the central star. In a separate study, Huelamo et al. (2011) detected a companion inside the density gap of the disk (6.7 AU). This detection provides a natural explanation to the geometry of the system around TCha. In the frame of this collaboration, we possibly caught planetary formation in action, the companion shaping the circumstellar disk, in a similar way as Jupiter may have transformed the environment of the young Solar System.

C2D Spitzer-IRS spectra of disks around TTauri stars. V. Spectral decomposition

[OLOFSSON, J.; AUGEREAU, J.-C.; van Dishoeck, E. F, et al. 2010]

Dust particles evolve in size and lattice structure in protoplanetary disks, due to coagulation, fragmentation and crystallization, and are raidally and vertically mixed because of turbulent diffusion as well as stellar winds or radiation pressure. This study aims at determining the mineralogical composition and size distributions of dust grains in planet forming regions of disks around a large sample of 58 stars. We make use of the great sensitivity of the Spitzer/IRS facility to analyze mid-IR spectra obtained within the c2d program. We present, test and use a spectral decomposition model to derive the dust composition in the inner (1 AU) and outer (10-15 AU) regions of the protoplanetary disks. We first find a flattening of grain size distributions, suggesting the influence of turbulence on coagulation and fragmentation processes. We also demonstrate that crystalline grains are detected in the outer, colder regions of disks, suggesting either efficient radial transport, or crystallization via nebular shocks.

[2010 - 2012] PostDoc Sep. 2010 - Aug. 2012: MPIA - Humboldt Fellowship Jan. 2010 - Aug. 2010: MPIA - Stipendium	[2006 - 2009] PhD Sep. 2006 - Dec. 2009: LAOG, now [IPAG] Advisors: Jean-Charles Augereau & Jean-Louis Monin "Planetary Formation as seen with Spitzer and the VLTI"
[2005 - 2006] Master degree Sep. 2005 - June 2006: LAOG, now [IPAG] Master in Astrophysics	[2003 - 2006] Enginner degree Sep. 2003 - June. 2006: ENSPG, now [Phelma] Engineer degree in Physics