Highlights - Volume 506-2 (November I 2009)

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HIGHLIGHTS: this week in A&A

Volume 506-2 (November I 2009)


In section 7. Stellar structure and evolution

“S2DFS: analysis of temporal changes of drifting subpulses”, by M. Serylak, B. W. Stappers, and P. Weltevrede, A&A 506, p. 865

Serylak et al. develop a visualization method for elucidating structure in a pulse sequence that can also be exploited for the study of other transient phenomena beyond pulsars. This paper contains extensive modeling showing how to separate stochastic and coherent effects. 


In section 10. Planets and planetary systems

“Planet migration in three-dimensional radiative discs”, by W. Kley, B. Bitsch, and H. Klahr, A&A 506, p. 971

Type I migration has been a major problem in explaining the formation and survival of planets around stars because it leads to a fast inward migration of planets from Earth to Uranus mass. It was proposed by Paardekooper and Mellema (A&A 2006) that accounting for radiative transfer in the protoplanetary disks may help to solve the problem. Kley et al. use an extensive set of 3D simulations to confirm that migration can be directed outwards for planets up to masses of ~33M_Earth around solar-type stars, thus effectively preventing the loss of Earth-mass planets into the central star.  


In section 1. Letters

“A ~4.6h quasi-periodic oscillation in the BL Lacertae PKS 2155-304?”, by P. Lachowicz et al., A&A 506, p. L17

Quasi-periodic oscillation (QPO) are frequently observed in X-ray binaries including either a black hole or a neutron star. They are due to oscillations in the accretion disk, near the last stable orbit. But none has yet been detected around an AGN (supermassive black hole at the nucleus of a galaxy). The authors detect for the first time an X-ray QPO of 4.6h in the blazar PKS 2155-304.

“Disk formation during collapse of magnetized prestellar cores”, by P. Hennebelle and A. Ciardi, A&A 506, p. L29

The formation of a disk around a young protostar depends on the angular momentum of the gas falling in towards the central mass concentration. This in turn depends on the degree to which magnetic braking has transported angular momentum to large radii and indeed, some recent studies have suggested that, given current measurements of field strength in prestellar cores, disks should not form! However, disks clearly do form and this article explores this paradox. The authors conclude that the angle between the rotation axis of the protostellar envelope and the local magnetic field plays an important role and configurations where these axes are not well aligned are far more likely to produce disks.
In section 12. Atomic, molecular, and nuclear data

“New study of the quasi-molecular Lyman-gamma satellites due to H-H+ collisions”, by N.F. Allard et al., A&A 506, p. 993

Quasi-molecular satellite lines in the red wings of the Lyman series of atomic hydrogen of stars arise from radiative collisions. Their presence complicates the analysis of spectra and needs to be carefully taken into account in model atmospheres to produce reliable results. In their work, Allard et al. address this problem using a unified theory, which takes into account the dependence of the dipole moments on internuclear distance during the collision, and derive synthetic spectra that reproduce more closely the observations.


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© Astronomy & Astrophysics 2009