Context. Z CMa is a binary composed of an embedded Herbig Be and an FU Ori class star separated by ~100 au. Observational evidence indicates a complex environment in which each star has a circumstellar disk and drives a jet, and the whole system is embedded in a large dusty envelope.
Aims. We aim to probe the circumbinary environment of Z CMa in the inner 400 au in scattered light.
Methods. We use high-contrast imaging polarimetry with VLT/NaCo at the H and Ks bands.
Results. The central binary is resolved in both bands. The polarized images show three bright and complex structures: a common dust envelope, a sharp extended feature previously reported in direct light, and an intriguing bright clump located south of the binary, which appears spatially connected to the sharp extended feature.
Conclusions. We detect orbital motion when compared to previous observations, and report a new outburst driven by the Herbig star. Our observations reveal the complex inner environment of Z CMa in unprecedented detail and contrast.
Authors: H. Canovas, S. Perez, C. Dougados, J. de Boer, F. Ménard, S. Casassus, M. R. Schreiber, L. A. Cieza, C. Caceres and J. H. Girard
The origin of type Ia supernovae, the standard candles used to reveal the presence of dark energy in the universe, is one of astronomy’s most beguiling mysteries. Astronomers know they occur when a white dwarf explodes in a binary system with another star, but the properties of that second star — and how it triggers the explosion — have remained elusive for decades.
Now, a team of astronomers from the intermediate Palomar Transient Factory (iPTF), including those associated with UC Santa Barbara, have witnessed a supernova smashing into a nearby star, shocking it, and creating an ultraviolet glow that reveals the size of the companion. The discovery involved the rapid response and coordination of iPTF, NASA’s Swift satellite and the new capabilities of the Las Cumbres Observatory Global Telescope Network (LCOGT).
The hydrogen-deficient, carbon-rich R Coronae Borealis (RCB) stars are known for being prolific producers of dust which causes their large iconic declines in brightness. Several RCB stars, including R CrB, itself, have large extended dust shells seen in the far-infrared. The origin of these shells is uncertain but they may give us clues to the evolution of the RCB stars. The shells could form in three possible ways. 1) they are fossil Planetary Nebula (PN) shells, which would exist if RCB stars are the result of a final, helium-shell flash, 2) they are material left over from a white-dwarf merger event which formed the RCB stars, or 3) they are material lost from the star during the RCB phase. Arecibo 21-cm observations establish an upper limit on the column density of H I in the R CrB shell implying a maximum shell mass of less than 0.3 solar masses. A low-mass fossil PN shell is still a possible source of the shell although it may not contain enough dust. The mass of gas lost during a white-dwarf merger event will not condense enough dust to produce the observed shell, assuming a reasonable gas-to-dust ratio. The third scenario where the shell around R CrB has been produced during the star's RCB phase seems most likely to produce the observed mass of dust and the observed size of the shell. But this means that R CrB has been in its RCB phase for approximately 10^4 yrs.
Authors: Edward J. Montiel, Geoffrey C. Clayton, Dominic C. Marcello, Felix J. Lockman
A team of astronomers has used the High Dispersion Spectrograph on the Subaru Telescope to conduct spectroscopic observations of Sun-like "superflare" stars first observed and cataloged by the Kepler Space Telescope. The investigations focused on the detailed properties of these stars and confirmed that Sun-like stars with large starspots can experience superflares.
The team targeted a set of solar-type stars emitting very large flares that release total energies 10-10000 times greater than the biggest solar flares.
This work follows up on observations made in 2012 (Maehara et al. Nature on 2012 May 24), where the team reported finding several hundred superflares on solar-type stars by analyzing stellar observation data from Kepler Space Telescope. This discovery was very important since it enabled the astronomers to conduct statistical analysis of superflares for the first time. However, more detailed observations were needed to investigate detailed properties of superflare stars and whether such massive flares can occur on ordinary single stars similar to our Sun.