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Post Info TOPIC: Vela supernova remnant
Blobrana


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Vela-D
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Title: Spitzer-IRAC survey of molecular jets in Vela-D
Authors: T.Giannini, D.Lorenzetti, M.De Luca, F.Strafella, D.Elia, B.Maiolo, M.Marengo, Y.Maruccia, F.Massi, B.Nisini, L.Olmi, A.Salama, H.A.Smith

We present a survey of H2 jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer -IRAC data between 3.6 and 8.0 micron. Our search has led to the identification of 15 jets and about 70 well aligned knots within 1.2 squared degree. We compare the IRAC maps with observations of the H2 1-0 S(1) line at 2.12 micron, with a Spitzer-MIPS map at 24 and 70 micron, and with a map of the dust continuum emission at 1.2 mm. We find a association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalogue of the Young Stellar Objects of VMR-D. We selected all the sources of Class II or earlier which are located close to the jet center and aligned with it. The association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 micron, suggesting they are very young protostars. Three of them are also associated with the most compact jets. The exciting source Spectral Energy Distributions have been modelled by means of the photometric data between 1.2 micron and 1.2 mm. From SEDs fits we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24] - [70] colour, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.

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Blobrana


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Posts: 131433
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RE: Vela supernova remnant
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Title: Hydrodynamic modelling of ejecta shrapnel in the Vela supernova remnant
Authors: M. Miceli, S. Orlando, F. Reale, F. Bocchino, G. Peres

Many supernova remnants (SNRs) are characterised by a knotty ejecta structure. The Vela SNR is an excellent example of remnant in which detached clumps of ejecta are visible as X-ray emitting bullets that have been observed and studied in great detail. We aim at modelling the evolution of ejecta shrapnel in the Vela SNR, investigating the role of their initial parameters (position and density) and addressing the effects of thermal conduction and radiative losses. We performed a set of 2-D hydrodynamic simulations describing the evolution of a density inhomogeneity in the ejecta profile. We explored different initial setups. We found that the final position of the shrapnel is very sensitive to its initial position within the ejecta, while the dependence on the initial density contrast is weaker. Our model also shows that moderately overdense knots can reproduce the detached features observed in the Vela SNR. Efficient thermal conduction produces detectable effects by determining an efficient mixing of the ejecta knot with the surrounding medium and shaping a characteristic elongated morphology in the clump.

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Blobrana


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Posts: 131433
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Title: Measurement of the Anisotropy of Cosmic Ray Arrival Directions with IceCube
Authors: The IceCube Collaboration: R. Abbasi, et al

We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi TeV region in the Southern sky using data from the IceCube detector. Between June 2007 and March 2008, the partially-deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 meters inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the Southern sky. The data include 4.3 billion muons produced by downgoing cosmic ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3 degrees and a median energy of ~20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first harmonic amplitude of (6.4±0.2 stat. ±0.8 syst.) x 10^{-4}.

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