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Highlights - Volume 491-3 (December I 2008)

Details: Published on 18 November 2008

HIGHLIGHTS: this week in A&A

Volume 491-3 (December I 2008)

In section 1. Letters

“Embryos grown in the dead zone. Assembling the first protoplanetary cores in low mass self-gravitating circumstellar disks of gas and solids”, by W. Lyra et al., A&A 491, p. L41

A particularly difficult phase in planet formation is the growth from meter-size boulders to planetary embryos of the size of our Moon or Mars. These growing objects have been known to drift extremely rapidly in protoplanetary disks, so much so that they would generally fall into the central star in a matter of tens of thousands of years, a very short timescale compared to the million years believed to be necessary to form planets. In this issue, Lyra et al. propose a way out of this by forming planetary embryos in special zones of protoplanetary disks, just at the edge of so-called dead zones. These dead zones would be regions in which disks are passive instead of being turbulent. With hydrodynamical simulations, Lyra et al. show that material accumulating between turbulent and passive regions would be trapped into vortexes to effectively form planetary embryos of Moon- to Mars-mass.

In section 1. Letters

“An enigmatic HI cloud”, by L. Dedes et al., A&A 491, p. L45

During a wide-field survey in HI-21cm with the Arecibo telescope, the authors discovered a curious HI cloud that revealed a velocity gradient, when observed at higher resolution with the VLA. If the gradient is due to expansion, the cloud could be a circumstellar envelope around an evolved AGB star. If it is rotating, the cloud could be more distant, and be a dwarf galaxy in a dark halo. Additional observations will clarify this puzzle.

In section 10. Planets and planetary systems

“Transiting exoplanets from the CoRoT space mission.VI. CoRoT-Exo-3b: the first secure inhabitant of the brown-dwarf desert”, by M. Deleuil et al., A&A 491, p. 889

The mass distribution of the objects that radial velocity monitoring finds orbiting solar-type stars is strongly bimodal, with two peaks. One peak corresponds to binary stars, the other to planets. Both are separated by a gap known as the "brown-dwarf desert". The gap, however, is not completely empty, and in very recent years a few objects have been found with minimum masses above 15 Jupiter-masses. New observations with the COROT satellite have identified the most massive of those to date, and the first one that transits across its parent star. This fortunate circumstance allows measurements of its radius, mass, and density.

In section 6.Interstellar and circumstellar matter

“Dust processing in photodissociation regions. Mir-IR emission modelling”, by M. Compiègne et al., A&A 491, p. 797

Understanding the nature of the ubiquitous PAH emission seen in many galactic and extragalactic sources has become a matter of some importance. The detailed study in this issue of the Horsehead and NGC2023 reflection nebulae by Compiègne and collaborators is a big step in this direction.