The origin of the spiral structure in the HD 141569 debris disk: Flyby or differential precession?

Details The origin of the spiral structure in the HD 141569 debris disk: Flyby or differential precession? The origin of the spiral structure in the HD 141569 debris disk: Flyby or differential precession?

Oct 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005nrdd.conf....4b&link_type=abstract

Proceedings of the Miniworkshop on Nearby Resolved Debris Disks. October 19-20, 2005. Space Telescope Science Institute, Baltimo

Astronomy and Astrophysics

Astronomy

Scientific paper

The debris dust disk around the 5 Myr old star HD 141569 has been the subject of intense investigations in the recent years. Scattered light images have revealed its complex structure, with gaps, asymmetric features and a spiral structure. At least part of these features, particularly the spiral pattern, are supposed to be due to the gravitational influence of the two M2-M4 stellar companions of the primary star. There is controversy about the mechanism that generates the spiral. Augereau & Papaloizou (2004) assume that the companions are bound to the star on an eccentric orbit, and show that the spiral pattern is caused by differential precession of the orbits of the particles constituting to the disk. Conversely, Ardila et al. (2005) suppose that the companions are unbound to the primary, and show that spiral arms may have been tidally driven by a recent fly-by of the M2-M4 pair.
We propose here a way to distinguish between these two pictures. Assuming the M2-M4 are bound to the primary, we show by simulations using the symplectic integrator of Beust (2003) that the very first periastron passage of the pair actually generates a tidal spiral, but this structure vanishes after a few passages. A differential precession spiral then appears after a few Myrs and lasts several Myrs before winding up indefinitely. There is a major difference between these two successive spiral patterns: The tidal spiral is trailing with respect to the rotation sense of the disk, while the differential precession one is leading.
Recent CO observations of the gaseous counterpart of the disk have revaeled its radial velocity pattern (Augereau et al., in prep.). It is thus possible to say which side of the disk is moving towards us and which one is receding. This is not enough for determining the rotation sense of the disk. For this we need to state which side of the disk is in front of the observed images and which side is behind. If we assume as usual that forward scattering is more important than backward scattering among the dust particles, the brightest side is in front. This allows to fix the rotation sense of the disk and shows that the spiral structure is trailing; this is a strong indication for a fly-by origin for the spiral structure. Conversely, if backwards scattering dominates, the spiral structure is leading and is probably due to differential precession.

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