Highlights - 22 January 2010 (vol. 509)

In section 1. Letters to the Editor

“The lunar phases of dust grains orbiting Fomalhaut”, by M. Min, M. Kama, C. Dominik, and L.B.F.M. Waters, A&A 509, L6

Optical images of the nearby star Fomalhaut show a ring of dust orbiting the central star. The ring displays a clear brightness asymmetry, which is attributed to the asymmetric scattering of the central starlight by the circumstellar dust grains. The authors show that large dust grains naturally explain the apparently backward scattering behavior. They show that one sees the phases of the dust grains in the same way as one can observe the phases of the Moon and other large solar system bodies. The material orbiting Fomalhaut appears to be in the transition phase between dust and planetesimals.  

In section 1. Letters to the Editor

“The nature of the recent extreme outburst of the Herbig Be/FU Orionis binary Z Canis Majoris”, by T. Szeifert, S. Hubrig, M. Scholler, O. Schutz, B. Stelzer, and Z. Mikulasek, A&A 509, L7

This paper presents exciting new results on the outburst of the young Z CMa system. Spectropolarimetric measurements show that the flux during outburst is dominated by the NW object. Additional data in several wavelength ranges strongly suggest that the optical outburst is more likely an opening up of the jet cavity in our direction -- allowing for a path of escape for the optical radiation - rather than a bolometric outburst.  

In section 3. Cosmology (including clusters of galaxies)

“How was the Hubble sequence 6 Gyrs ago?”, by R. Delgado-Serrano, F. Hammer, Y. B. Yang, M. Puech, H. Flores, and M. Rodrigues, A&A 509, A78

Ever since 1926 when Hubble devised his famous "tuning fork" diagram to morphologically classify the wide variety of galaxy shapes observed, astrophysicists have speculated about its physical origin and evolution. In spite of these efforts, a final answer to these questions has not yet been reached. The paper by Delgado et al. concentrates on the evolutionary aspects of the problem by linking data on nearby and distant galaxies from two broad surveys, the SDSS and the GOODS. The morphological analysis reveals a wealth of new, somewhat unexpected, facts. The resulting scenario is one in which elliptical galaxies have undergone very little evolution in the Past 6 billion years, in contrast to the vigorous emergence of spiral galaxies from a population of irregular ones during the same cosmic epoch. These results indicate that the Hubble sequence was different in the past, and might have a strong impact on current models of galaxy formation and evolution.  

In section 4. Extragalactic astronomy

“The distance to the Andromeda galaxy from eclipsing binaries”, by F. Vilardell, I. Ribas, C. Jordi, E.L. Fitzpatrick, and E.F. Guinan, A&A 509, A70

The cosmic distance scale is founded on the local calibrators and none are more abundant than normal eclipsing binary stars or nearly so free of physical uncertainties. Current detectors and ground-based telescopes for spectroscopy and photometric surveys for variables and microlensing now permit extension of the classical techniques of orbit determination and the study of the absolute physical properties of the constituent stars to the principal Local Group galaxies. This paper presents the determination of the distance to M31, 744+/-33 kpc, based on two such systems, in agreement with the Cepheid calibrations. The authors also present an especially useful summary of the uses of this method compared with the standard calibrators providing a fundamental cross check of the accuracies of the other stellar standard candles.  

In section 7. Stellar structure and evolution

“Thermonuclear explosions of rapidly rotating white dwarfs. II. Detonations”, by J.M.M. Pfannes, J.C. Niemeyer, and W. Schmidt, A&A 509, A75

Recent observations of several super-luminous Type Ia supernovae brought up the suggestion that some white dwarfs explode with masses well above the classical Chandrasekhar-mass. This paper finds that pure detonations of rotationally stabilized super-Chandrasekhar mass white dwarfs might explain the super bright Type Ia explosions, both, in terms of the observed ejected chemical species and in terms of the overall explosion energy.