Showing papers by "Garrelt Mellema published in 2004"

Planets opening dust gaps in gas disks

Abstract: We investigate the interaction of gas and dust in a protoplanetary disk in the presence of a massive planet using a new two-fluid hydrodynamics code. In view of future observations of planet-forming disks we focus on the condition for gap formation in the dust fluid. While only planets more massive than 1 Jupiter mass (Mj) open up a gap in the gas disk, we find that a planet of 0.1 M J already creates a gap in the dust disk. This makes it easier to find lower-mass planets orbiting in their protoplanetary disk if there is a significant population of mm-sized particles.

Rings in the haloes of planetary nebulae

Abstract: We present a search for rings or arcs in the haloes of planetary nebulae (PNe). We discovered such structures in eight PNe, tripling the sample of PNe with known rings. This shows that, contrary to what was believed to date, the occurrence of mass loss fluctuations with timescales of 10 2 -10 3 yrs at the end of the asymptotic giant branch phase (AGB) is common. We estimate a lower limit of the occurrence rate of rings in PN haloes to be ∼35%. Using these new detections and the cases previously known, we discuss the statistical properties of ring systems in PNe haloes. We estimate that the mass modulation producing the rings takes place during the last 10 000 or 20 000 yrs of AGB evolution. In PNe, the spacing between rings ranges from <0.01 pc to 0.06 pc, significantly larger than those seen in proto-PNe. This, together with the finding of a possible positive correlation of spacing with the post-AGB age of the nebulae, suggests that the spacing of the rings increases with time. These properties, as well as the modest surface brightness amplitudes of rings, are consistent with the predictions of the dust- driven wind instability model explored by Meijerink et al. (2003), but do not immediately exclude other proposed models.

On expansion parallax distances for planetary nebulae

Abstract: The distances to individual wind-driven bubbles such as Planetary Nebulae (PNe) can be determined using expansion parallaxes: the angular expansion velocity in the sky is compared to the radial velocity of gas measured spectroscopically. Since the one is a pattern velocity, and the other a matter velocity, these are not necessarily the same. Using the jump conditions for both shocks and ionization fronts, I show that for typical PNe the pattern velocity is 20 to 30% larger than the material velocity, and the derived distances are therefore typically 20 to 30% too low. I present some corrected distances and suggest approaches to be used when deriving distances using expansion parallaxes.

Rings in the Haloes of Planetary Nebulae

Abstract: We present a search for rings or arcs in the haloes of planetary nebulae (PNe). We discovered such structures in eight PNe, tripling the sample of PNe with known rings. This shows that, contrary to what was believed to date, the occurrence of mass loss fluctuations with timescales of ~100 to ~1000 yrs at the end of the asymptotic giant branch phase (AGB) is common. We estimate a lower limit of the occurrence rate of rings in PN haloes to be ~35%. Using these new detections and the cases previously known, we discuss the statistical properties of ring systems in PNe haloes. We estimate that the mass modulation producing the rings takes place during the last 10 or 20 kyrs of AGB evolution. In PNe, the spacing between rings ranges from <0.01 pc to 0.06 pc, significantly larger than those seen in proto-PNe. This, together with the finding of a possible positive correlation of spacing with the post-AGB age of the nebulae, suggests that the spacing of the rings increases with time. These properties, as well as the modest surface brightness amplitudes of rings, are consistent with the predictions of the dust-driven wind instability model explored by Meijerink et al. (2003), but do not immediately exclude other proposed models.