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Author(s): E. Pian (corresponding author) [1]; P. DAvanzo [2]; S. Benetti [3]; M. Branchesi [4, 5]; E. Brocato [6]; S. Campana [2]; E. Cappellaro [3]; S. Covino [2]; V. DElia [...]

The final fate of massive stars depends on many factors. Theory suggests that some with initial masses greater than 25 to 30 solar masses end up as Wolf-Rayet stars, which are deficient in hydrogen in their outer layers because of mass loss through strong stellar winds. The most massive of these stars have cores which may form a black hole and theory predicts that the resulting explosion of some of them produces ejects of low kinetic energy, a faint optical luminosity and a small mass fraction of radioactive nickel (1-3). An alternative origin for low-energy supernovae is the collapse of the oxygen-neon core of a star of 7-9 solar masses (4,5). No weak, hydrogen-deficient, core-collapse supernovae have hitherto been seen. Here we report that SN 2008ha is a faint hydrogen-poor supernova. We propose that other similar events have been observed but have been misclassified as peculiar thermonuclear supernovae (sometimes labelled SN 2002cx-like evens (6)). This discovery could link these faint supernovae to some long-duration γ-ray bursts, because extremely faint, hydrogen-stripped core-collapse supernovae have been proposed to produce such long γ-ray bursts, the afterglows of which do not show evidence of associated supernovae (7-9)., SN 2008ha was discovered on 7 Nov. 2008 4.1 h uT in the late-type galaxy UGC 12682, at an unfiltered magnitude of 18.8 (ref. 10). A spectrum obtained on 18.18 [...]

Author(s): A. Pastorello (corresponding author) [1]; S. J. Smartt [1]; S. Mattila [1]; J. J. Eldridge [1]; D. Young [1]; K. Itagaki [2]; H. Yamaoka [3]; H. Navasardyan [4]; S. [...]

In the 1980s, excess infrared emission was discovered around main-sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source. These 'debris disks' were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the β Pictoris system, in which the known planet generates an observable warp in the disk. The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units. Here we report high-contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10-60 astronomical units, persisting over intervals of 1-4 years. All these features appear to move away from the star at projected speeds of 4-10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories.