1. The origin of gas in debris disks
Alexis Brandeker
University of Toronto
Rodrigo Fernández Yanqin Wu

2. Why gas? Inner dust disk Inner gas disk Haisch, Lada, & Lada (2001)
Jayawardhana et al. (2006)
Inner dust disk
Inner gas disk

3. Favourable case: b Pictoris

5. Velocity at ionisation

6. Braking ions Magnetic fields Ion self-braking Ion-atom interaction
Charged dust

7. Ion fluid

8. Gas friction 0.1 MEarth [km/s]
If we assume that the disk is of cosmic composition and just scale the detected metals in gas form, we get too little gas to effectively brake the atoms – for the terminal velocities to be within a few km/s, we need a hydrogen column density two orders of magnitude higher than the observed upper limits. One can speculate that perhaps some invisible gas other than hydrogen, like oxygen, is responsible for the gas drag. Why this gas should be enhanced over hydrogen to that high degree is not clear, however, though we note that this is the case in e.g. Earth’s atmosphere, meaning this state is not impossible.
[km/s]

9. Dust braking

10. Key clues to the origin of gas
Metals approximately of solar abundance (Lagrange et al. 1998)
Strong upper limits on H2 (Lecavelier des Etangs et al. 2001)
Gas spatial distribution similar to dust (Olofsson et al. 2001, Brandeker et al. 2004)
Gas almost at rest relative to star (Lagrange et al. 1998, Brandeker et al. 2004)
NEW C is ~15× overabundant compared to metals (Roberge et al. 2006)

11. Roberge et al. 2006

12. Possible sources
Primordial gas
Comet evaporation
Grain-grain collisions

13. Other systems
β Pic
AU Mic

14. Work published in tomorrow’s issue of ApJ:
Results - predictions
Gas most likely generated in grain-grain collisions (linked to dust kinematics?)
Little Be and P in b Pic-disk, relative abundance of metals similar to grains, more volatiles relative to metals.
Very high Fe/Na ratio in AU Mic disk
Work published in tomorrow’s issue of ApJ:
Fernández, Brandeker, & Wu 2006, ApJ 643:509

15. Extra Material

18. References Brandeker, et al. 2004, A&A, 413:681
Fernández, Brandeker, Wu 2006, ApJ, 643:509
Jayawardhana et al. 2006, ApJ, submitted
Lagrange et al. 1998, A&A, 330, 1091
Lecavelier des Etangs et al. 2001, Nature, 412:706
Haisch, Lada, Lada 2001, ApJ, 553, L153
Olofsson, Liseau, Brandeker 2001, ApJ, 563, L80
Roberge et al. 2006, Nature, in press