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Title: The Sun was not born in M 67
Authors: Barbara Pichardo, Edmundo Moreno, Christine Allen, Luigi R. Bedin, Andrea Bellini, Luca Pasquini

Using the most recent proper-motion determination of the old, Solar-metallicity, Galactic open cluster M 67, in orbital computations in a non-axisymmetric model of the Milky Way, including a bar and 3D spiral arms, we explore the possibility that the Sun once belonged to this cluster. We have performed Monte Carlo numerical simulations to generate the present-day orbital conditions of the Sun and M 67, and all the parameters in the Galactic model. We compute 3.5 x 10^5 pairs of orbits Sun-M 67 looking for close encounters in the past with a minimum distance approach within the tidal radius of M 67. In these encounters we find that the relative velocity between the Sun and M 67 is larger than 20 km/s. If the Sun had been ejected from M 67 with this high velocity by means of a three-body encounter, this interaction would destroy an initial circumstellar disk around the Sun, or disperse its already formed planets. We also find a very low probability, much less than 10^-7, that the Sun was ejected from M 67 by an encounter of this cluster with a giant molecular cloud. This study also excludes the possibility that the Sun and M 67 were born in the same molecular cloud. Our dynamical results convincingly demonstrate that M67 could not have been the birth cluster of our Solar System.

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Title: Was The Sun Born In A Massive Cluster?
Authors: Donald Dukes, Mark R. Krumholz

A number of authors have argued that the Sun must have been born in a cluster of no more than about 1000 stars, on the basis that, in a larger cluster, close encounters between the Sun and other stars would have truncated the outer Solar System or excited the outer planets into eccentric orbits. However, this dynamical limit is in tension with meteoritic evidence that the Solar System was exposed to a nearby supernova during or shortly after its formation; a 1000-star cluster is much too small for supernova contamination to be likely. In this paper we revisit the dynamical limit in the light of improved observations of the properties of young clusters. We use a series of scattering simulations to measure the velocity-dependent cross-section for disruption of the outer Solar System by stellar encounters, and use this cross-section to compute the probability of a disruptive encounter as a function of birth cluster properties. We find that, contrary to prior work, the probability of disruption is small regardless of the cluster mass, and that it actually decreases rather than increases with cluster mass. Our results differ from prior work for three main reasons: (1) unlike in most previous work, we compute a velocity-dependent cross section and properly integrate over the cluster mass-dependent velocity distribution of incoming stars; (2) we adopt realistically-short cluster lifetimes of a few crossing times, rather than assuming lifetimes of 10 to 100 Myr; and (3) following recent observations, we adopt a mass-independent surface density for embedded clusters, rather than a mass-independent radius as assumed many earlier papers. Our results remove the tension between the dynamical limit and the meteoritic evidence, and suggest that the Sun was born in a massive cluster.

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Title: On identifying the neutron star that was born in the supernova that placed 60Fe onto the Earth
Authors: R. Neuhäuser, N. Tetzlaff, T. Eisenbeiss, M. M. Hohle

Recently, 60Fe was found in the Earth crust formed in a nearby recent supernova (SN). If the distance to the SN and mass of the progenitor of that SN was known, then one could constrain SN models. Knowing the positions, proper motions, and distances of dozens of young nearby neutron stars, we can determine their past flight paths and possible kinematic origin. Once the birth place of a neutron star in a SN is found, we would have determined the distance of the SN and the mass of the SN progenitor star.

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Title: The Supernova Triggered Formation and Enrichment of Our Solar System
Authors: M. Gritschneder, D. N. C. Lin, S. D. Murray, Q.-Z. Yin, M.-N. Gong

We investigate the enrichment of the pre-solar cloud core with short lived radionuclides (SLRs), especially 26Al. The homogeneity and the surprisingly small spread in the ratio 26Al/27Al observed in the overwhelming majority of calcium-aluminium-rich inclusions (CAIs) in a vast variety of primitive chondritic meteorites places strong constraints on the formation of the the solar system. Freshly synthesized radioactive 26Al has to be included and well mixed within 20kyr. After discussing various scenarios including X-winds, AGB stars and Wolf-Rayet stars, we come to the conclusion that triggering the collapse of a cold cloud core by a nearby supernova is the most promising scenario. We then narrow down the vast parameter space by considering the pre-explosion survivability of such a clump as well as the cross-section necessary for sufficient enrichment. We employ numerical simulations to address the mixing of the radioactively enriched SN gas with the pre-existing gas and the forced collapse within 20kyr. We show that a cold clump of 10Msun at a distance of 5pc can be sufficiently enriched in 26Al and triggered into collapse fast enough - within 18kyr after encountering the supernova shock - for a range of different metallicities and progenitor masses, even if the enriched material is assumed to be distributed homogeneously in the entire supernova bubble. In summary, we envision an environment for the birth place of the Solar System 4.567Gyr ago similar to the situation of the pillars in M16 nowadays, where molecular cloud cores adjacent to an HII region will be hit by a supernova explosion in the future. We show that the triggered collapse and formation of the Solar System as well as the required enrichment with radioactive 26Al are possible in this scenario.

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Solar System formation
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Isotopes Say New Origin Stories For Some Planets

A new study shows that the ratio of oxygen and nitrogen isotopes found in the solar wind is different from the ratio here on earth, or on the moon or Mars. We've got more of the heavier versions of these atoms than our Sun does.
Now we just have to figure out why. Scientists say the excess heavy nitrogen could have come from a comet. And the heavier oxygen from a natural process that left more of the light isotope in the part of the nebula that made the sun. So we are made of star stuff. But when it comes to our elemental composition, we're not a carbon copy.

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Solar siblings
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Title: Searching for Possible Siblings of the Sun from a Common Cluster based on Stellar Space Velocities
Authors: V.V. Bobylev, A.T. Bajkova, A. Myllari, M. Valtonen

We propose a kinematic approach to searching for the stars that could be formed with the Sun in a common "parent" open cluster. The approach consists in preselecting suitable candidates by the closeness of their space velocities to the solar velocity and analysing the parameters of their encounters with the solar orbit in the past in a time interval comparable to the lifetime of stars. We consider stars from the Hipparcos catalogue with available radial velocities. The Galactic orbits of stars have been constructed in the Allen--Santillan potential by taking into account the perturbations from the spiral density wave. We show that two stars, HIP 87382 and HIP 47399, are of considerable interest in our problem. Their orbits oscillate near the solar orbit with an amplitude of about 250 pc; there are short-term close encounters to distances <10 pc. Both stars have an evolutionary status and metallicity similar to the solar ones.

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Solar supernova
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NASA Mission Suggests Sun and Planets Constructed Differently

Researchers analysing samples returned by NASA's 2004 Genesis mission have discovered that our sun and its inner planets may have formed differently than previously thought.
Data revealed differences between the sun and planets in oxygen and nitrogen, which are two of the most abundant elements in our solar system. Although the difference is slight, the implications could help determine how our solar system evolved.

"We found that Earth, the moon, as well as Martian and other meteorites which are samples of asteroids, have a lower concentration of the O-16 than does the sun. The implication is that we did not form out of the same solar nebula materials that created the sun -- just how and why remains to be discovered" - Kevin McKeegan, a Genesis co-investigator from UCLA, and the lead author of one of two Science papers published this week.

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By analysing the isotopic compositions of several elements, scientists are able to glean clues about the origin of stardust grains in the atmospheres of dying red giant stars or in exploding supernovae.
When a doctoral student heated a primitive meteorite in 1972 and it gave off pure neon-22, scientists were stunned. No known solar system process would produce this isotope without its sister isotopes neon-20 and neon-21. Gradually, they came to suspect that some part of the meteorite had come from outside of the solar system.
But which part? To find out, a group at the University of Chicago starting dissolving meteorites in strong acids - a process their leader Edward Anders, PhD, characterised as "burning down the haystack to find the needle."

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Title: Protosolar Irradiation in the Early Solar System: Clues from Lithium and Boron Isotopes
Authors: Ming-Chang Liu, Larry R. Nittler, Conel M. O'D. Alexander, Typhoon Lee

We report Li and B isotopic compositions of 10 Spinel-HIBonite spherules (SHIBs) separated from the Murchison meteorite, in order to understand their irradiation history in the early Solar System. The extremely low Be concentrations in SHIBs preclude detection of extinct 10Be, but instead allow for a search of the original Li and B isotopic ratios of the grains, as these isotopes are sensitive indicators for irradiation. We found that some of the SHIBs carried sub-chondritic 7Li/6Li and supra-chondritic 10B/11B ratios. Considering two possible irradiation scenarios that could have occurred in the early Solar System, irradiation of hibonite solids followed by addition of isotopically normal Li and B seems to be the most plausible explanation for the observed Li and B isotope ratios.

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Solar siblings
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Title: Is it possible to reveal the lost siblings of the Sun?
Authors: Yu.N. Mishurov, I.A. Acharova

We present the results of our numerical experiments on stellar scattering in the galactic disc under the influence of the perturbed galactic gravitation field connected with the spiral density waves and show that the point of view according to which stars do not migrate far from their birthplace, in general, is incorrect. Despite close initial locations and the same velocities after 4.6 Gyrs members of an open cluster are scattered over a very large part of the galactic disc. If we adopt that the parental solar cluster had ~ 10^3 stars, it is unlikely to reveal the solar siblings within 100 pc from the Sun. The problem stands a good chance to be solved if the cluster had ~ 10^4 stars.
We also demonstrate that unbound open clusters disperse off in a short period of time under the influence of spiral gravitation field. Their stars became a part of the galactic disc. We have estimated typical times of the cluster disruption in radial and azimuth directions and the corresponding diffusion coefficients.

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