EDP Sciences

Vol. 604
In section 1. Letters

Indications of a Si-rich bilateral jet of ejecta in the Vela SNR observed with XMM-Newton

by F. García, A. E. Suárez, M. Miceli, et al. A&A 604, L5


Massive stars end their life with a supernova explosion. Some of them are connected to gamma-ray bursts (GRB), brief (seconds) and intense (brightest sources in the sky) flashes of gamma-ray radiation. GRB radiation is collimated into a jet. It is very difficult to find collimated emission (linked to a GRB or not) a-posteriori in the supernova remnant which follows the explosion. Here García and collaborators reveal signs of two almost exactly antipodal structures in the Vela supernova remnant, strongly remininscent of a jet. The structures are spectrally characterised in the X-ray band as being overabundant in silicium, which originates in the depest layer of the progenitor star. This is only the second supernova remnant in which such a jet structure has been devised.

Vol. 604
In section 6. Interstellar and circumstellar

Observability of characteristic binary-induced structures in circumbinary disks

by R. Avramenko, S. Wolf, and T.F. Illenseer A&A 604, A38


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A substantial fraction of protoplanetary disks form around stellar binaries. The properties of these circumbinary disks are currently a topic of very active research. In this paper, the authors study the strong tidal forces that act on the circumbinary disk as a consequence of the non-axisymmetric gravitational potential generated by the binary system. They aim to identify structures characteristic of the binarity and to evaluate the feasibility of observing them with current and future instruments. To do this, they perform 2D hydrodynamic simulations and post-process the resulting density distributions with a 3D radiative transfer code to generate re-emission and scattered light maps. They find that both ALMA and the E-ELT are capable of tracing asymmetries in the inner region of circumbinary disks, which are affected most by the binary-disk interaction. With the E-ELT one can partially resolve the innermost parts of the disk in the infrared wavelength range, including the disk’s rim, accretion arms, and potentially the expected circumstellar disks around each of the binary components.

Vol. 604
In section 6. Interstellar and circumstellar

The chemistry of episodic accretion in embedded objects. 2D radiation thermo-chemical models of the post-burst phase

by Ch. Rab, V. Elbakyan, E. Vorobyov, et al. A&A 604, A15


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Using a new model for the chemistry of episodic accretion based on the 2D, radiation thermo-chemical disk code PRODIMO, the authors investigate observational signatures of the chemical evolution in the post-accretion burst phase for embedded protostellar sources. During an accretion burst, chemical species such as CO sublimate from the dust surfaces. When the burst ends, they freeze out again. This occurs from the inside out, because of the radial density gradient in the disk and envelope structure. The authors demonstrate that the inside-out freeze out produces clear observational signatures in spectral line emission, such as rings, and distinct features in the slope of radial intensity profiles. These can help identify post accretion burst targets in a model-independent way.

Vol. 603
In section 10. Planets and planetary systems

Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE

by M. Samland, P. Mollière, M. Bonnefoy, et al. A&A 603, A57


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51 Eridani b is a highly interesting planet discovered recently through direct imaging. It is young (20 Myr), nearby (30 pc), has a mass around ten times that of Jupiter, and an orbital distance of about 14 au. Most importantly, its angular separation makes it an excellent target for direct spectroscopic characterization. Samland et al. use SPHERE at the VLT to obtain a precise spectrum of the planet from 0.95 to 1.7 microns. The planet is outside of the color-color relations for brown dwarfs. Models indicate that it is cloudy and has a very high metallicity ([Fe/H]=1.0 +/- 0.1), significantly above that of its parent star. This latter implies that the atmosphere of 51 Eri b is as metal-rich as that of Saturn. Given the trend between increasing planetary mass and decreasing atmospheric metallicity in the solar system, this is a somewhat surprising result, but definitely a very significant one.

Vol. 603
In section 8. Stellar atmospheres

The full spectral radiative properties of Proxima Centauri

by I. Ribas, M. D. Gregg, T. S. Boyajian, and E. Bolmont A&A 603, A58


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The discovery of Proxima Centauri b, a terrestrial temperate planet, presents the opportunity of studying a nearby, potentially habitable world. Understanding the radiation environment of the planet is a prerequisite for modeling its habitability. In this paper, the authors derive top-of-atmosphere fluxes on the planet from the X-ray to the mid-IR spectral domains. They also also aim at constraining the fundamental properties of the star, namely its mass, radius, effective temperature, and luminosity. The top-of-atmosphere average XUV irradiance on Proxima b is 0.293 W m^-2, nearly 60 times higher than Earth, and the total irradiance is 877 ± 44 W m^-2 , or 64 ± 3% of the solar constant but with a significantly redder spectrum. The fundamental properties of Proxima Centuri are M = 0.120±0.003 solar mass, R = 0.146±0.007 solar radius, Teff = 2980±80K, L = 0.00151 ± 0.00008 solar luminosity. The analysis also reveals a 20% excess in the 3–30 μm range that is best interpreted as arising from warm dust in the system.

Vol. 603
In section 10. Planets and planetary systems

Observational evidence for two distinct giant planet populations

by N.C. Santos, V. Adibekyan, P. Figueira, et al. A&A 603, A30


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Giant planets are thought to form in circumstellar disks, while brown dwarfs and stars are thought to form directly by gravitational collapse and fragmentation of a gas cloud. We do not know how efficient these mechanisms are, whether they overlap in mass and whether other mechanisms also exist. Santos et al. provide observational evidence for the existence of two distinct populations of planets/brown dwarfs: objects with masses smaller than approximately four Jupiter masses show a strong preference for metal-rich stars. At larger masses, between 4 and 20 Mjup, this preference disappears, indicating that these brown dwarfs/massive giant planets formed with a different mechanism. Although the mechanisms themselves remain to be identified, statistical studies of the population of exoplanets are beginning to shed light on their formation.