Highlights - Volume 469-1 (July I 2007)

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HIGHLIGHTS: this week in A&A

Volume 469-1 (July I 2007)


Flare nucleosynthesis

Is 6Li in metal-poor halo stars produced in situ by solar-like flares?”, by V. Tatischeff and J.-P. Thibaud A&A 469, p. 265

Recent measurements found the abundance of the isotope 6Li in Galactic halo stars higher than predicted by Big Bang nucleosynthesis, thus challenging models of 6Li production in cosmic rays. This paper argues that this data supports the production of 6Li in the magnetic flares of rapidly rotating low-mass stars. 6Li may be the only isotope of which a major fraction is produced in flares.


Possible evidence of magnetic reconnection in the solar photosphere

Opposite magnetic polarity of two photospheric lines in single spectrum of the quiet Sun”, by R. Rezaei et al. A&A 469, p. L9

This paper presents the discovery of a pair of spectro-polarimetric line profiles with opposite magnetic polarity, measured strictly simultaneously at the same location in a region of the quiet Sun in-between two patches of opposite magnetic polarity. The authors show that the two magnetic polarities harbour mass flow receding from each other and that there is a region of enhanced temperature in-between. They interpret this as signature of ongoing magnetic reconnection in the photosphere.


In section 1. Letters

“REM observations of GRB060418 and GRB060607A: the onset of the afterglow and the initial fireball Lorentz factor determination”, by E. Molinari et al. A&A 469, p. L13

Gamma-ray burst (GRB) emission is thought to come from a highly relativistic fireball. The Lorentz factor, ratio of the actual energy to mass energy (mc2), had until now never been measured at maximum GRB emission, but was expected to be larger than 100. Using to the fast reaction of the Robotic telescope (REM, at La Silla, Chile), the authors were able to observe the early-phase of the afterglow of 2 GRB in the near infrared. For the first time, they measured the Lorentz factor: it is equal to 400, confirming the highly relativistic character of the fireball.

ESO issued a press release on these results.
In section 6. Interstellar and circumstellar matter

“Millimeter imaging of HD163296: probing the disk structure and kinematics”, by A. Isella et al. A&A 469, p. 213

This paper presents a detailed study of the circumstellar (and probably protoplanetary) disc around the Herbig Ae star HD 163296. The authors used state-of-the-art mm/submm continuum and spectral-line observations obtained with the IRAM Plateau de Bure interferometer, Submillimeter Array and NRAO Very Large Array. They show that the CO emission is more extended than the dust emission. They then conclude that the disc is strongly evolved, that the dust is depleted with respect to the gas outside 200 AU, and that this may be related to gap formation in the disc.  


© Astronomy & Astrophysics 2007