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Post Info TOPIC: Scorpius
Blobrana


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Posts: 131433
Date:
Scorpius Centaurus horde
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Supernova left its mark in ancient bacteria

Sediment in a deep-sea core may hold radioactive iron spewed by a distant supernova 2.2 million years ago and preserved in the fossilised remains of iron-loving bacteria. If confirmed, the iron traces would be the first biological signature of a specific exploding star. Shawn Bishop, a physicist at the Technical University of Munich in Germany, reported preliminary findings on 14 April at a meeting of the American Physical Society in Denver, Colorado.
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Blobrana


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Posts: 131433
Date:
Scorpius Centaurus Complex
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Title: New Members of the Scorpius Centaurus Complex and Ages of its sub-regions
Authors: Inseok Song, Ben Zuckerman, Mike Bessell

We have spectroscopically identified about 100 G-, K- and M-type members of the Scorpius Centaurus complex. To deduce the age of these young stars we compare their Li \lamda6708 absorption line strengths against those of stars in the TW Hydrae association and beta Pictoris moving group. These line strengths indicate that Sco-Cen stars are younger than beta Pic stars whose ages of ~12 Myr have previously been derived from a kinematic traceback analysis. Our derived age, ~10Myr, for stars in the LCC and UCL subgroups of ScoCen is younger than previously published ages based on the moving cluster method and upper main sequence fitting. The discrepant ages are likely due to an incorrect (or lack of) cross-calibration between model-dependent and model-independent age-dating methods. 

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Blobrana


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Posts: 131433
Date:
Sco-Cen OB2 association
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Title: WISE Circumstellar Disks in the Young Sco-Cen Association
Authors: Aaron C. Rizzuto, Michael J. Ireland, Daniel B. Zucker

We present an analysis of the WISE photometric data for 829 stars in the Sco-Cen OB2 association, using the latest high-mass membership probabilities. We detect infrared excesses associated with 135 BAF-type stars, 99 of which are secure Sco-Cen members. There is a clear increase in excess fraction with membership probability, which can be fitted linearly. We infer that 41±5% of Sco-Cen OB2 BAF stars to have excesses, while the field star excess fraction is consistent with zero. This is the first time that the probability of non-membership has been used in the calculation of excess fractions for young stars. We do not observe any significant change in excess fraction between the three subgroups. Within our sample, we have observed that B-type association members have a significantly smaller excess fraction than A and F-type association members.

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Blobrana


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Posts: 131433
Date:
Scorpius-Centaurus OB Association
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Title: A Revised Age for Upper Scorpius and The Star-Formation History Among the F-Type Members of the Scorpius-Centaurus OB Association
Authors: Mark J. Pecaut, Eric E. Mamajek, Eric J. Bubar

We present an analysis of the ages and star-formation history of the F-type stars in the Upper Scorpius (US), Upper Centaurus-Lupus (UCL) and Lower Centaurus-Crux (LCC) subgroups of Scorpius-Centaurus (Sco-Cen). We find that 1) our empirical isochrones are consistent with the previously published age-rank of the Sco-Cen subgroups, 2) subgroups LCC and UCL appear to reach the main sequence turn-on at spectral types ~F4 and ~F2, respectively. An analysis of the A-type stars shows US reaching the main sequence at about spectral type ~A3. 3) The median ages for the pre-main sequence members of UCL and LCC are 16 Myr and 17 Myr, respectively, in agreement with previous studies, however we find that 4) Upper Sco is much older than previously thought. The luminosities of the F-type stars in US are typically a factor of ~2.5 less luminous than predicted for a 5 Myr old population for four sets of evolutionary tracks. We re-examine the evolutionary state and isochronal ages for the B-, A-, and G-type Upper Sco members, and the evolved M supergiant Antares, and estimate a revised mean age for Upper Sco of 11±1±2 Myr (statistical, systematic). Using radial velocities and Hipparcos parallaxes we calculate a lower limit on the kinematic expansion age for Upper Sco of >10.5 Myr (99% confidence). However, the data are statistically consistent with no expansion. We reevaluate the inferred masses for the known substellar companions in Upper Sco using the revised age. Specifically, we estimate the mass of 1RXS J1609-2105b to be 14^{+2}_{-3} Mjup, suggesting that it is a brown dwarf rather than a planet. Finally, we find the fraction of F-type stars exhibiting Ha emission and/or a K-band excess consistent with accretion to be 0/17 (<19%; 95% C.L.) in US at ~10 Myr, while UCL has 1/41 (2^{+5}_{-1}%; 68% C.L.) accretors and LCC has 1/50 (2^{+4}_{-1}%; 68% C.L.) accretors at ~15 Myr.

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Blobrana


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Posts: 131433
Date:
Sco OB2 association
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Title: Multi-Dimensional Bayesian Membership Analysis of the Sco OB2 moving Group
Authors: A. C. Rizzuto, M. J. Ireland, J. G. Robertson

We present a new high-mass membership of the nearby Sco OB2 association based on HIPPARCOS positions, proper motions and parallaxes and radial velocities taken from the Kharchenko et al. (2007) catalogue. The Bayesian membership selection method developed makes no distinction between subgroups of Sco OB2 and utilises linear models in calculation of membership probabilities. We select 436 members, 88 of which are new members not included in previous membership selections. We include the classical non members Alpha-Cru and Beta-Cru as new members as well as the pre-main-sequence stars HIP 79080 and 79081. We also show that the association is well mixed over distances of 8 degrees on the sky, and hence no determination can be made as to the formation process of the entire association.

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Blobrana


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Posts: 131433
Date:
Scorpius-Centaurus Association
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Title: Radioactive 26Al from the Scorpius-Centaurus Association
Authors: Roland Diehl, Michael G. Lang, Pierrick Martin, Henrike Ohlendorf, Thomas Preibisch, Rasmus Voss, Pierre Jean, Jean-Pierre Roques, Peter von Ballmoos, Wei Wang

The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic gamma-rays from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. 26Al decays within ~1 My, 1809 keV gamma-rays from its decay can be measured with current gamma-ray telescopes, such as INTEGRAL's gamma-ray spectrometer SPI. Following earlier 26Al gamma-ray mapping with NASA's Compton observatory, we test spatial emission skymaps of 26Al for a component which could be attributed to ejecta from massive stars in the Scorpius-Centaurus group of stars. Such a model fit of spatial distributions for large-scale and local components is able to discriminate 26Al emission associated with Scorpius-Centaurus, in spite of the strong underlying nucleosynthesis signal from the Galaxy at large. We find an 26Al signal above 5 sigma significance, which we associate with the Sco-Cen group. The observed flux of 6 *10^{-5}ph cm^{-2} s^{-1} corresponds to 1.1 *10^{-4} M_sol of 26Al. This traces the nucleosynthesis ejecta of several massive stars within the past several million years. We confirm through direct detection of radioactive 26Al the recent ejection of massive-star nucleosynthesis products from the Sco-Cen association. Its youngest subgroup in Upper Scorpius appears to dominate 26Al contributions from this association. Our 26Al signal can be interpreted as a measure of the age and richness of this youngest subgroup. We also estimate a kinematic imprint of these nearby massive-star ejecta from the bulk motion of 26Al and compare this to other indications of Scorpius-Centaurus massive-star activity.

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Blobrana


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RE: Scorpius
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Scorpius is one of the few constellations that actually looks like what it represents, a scorpion. The three third-magnitude stars making up its head are lined up running north to south just above the southern horizon.
The fish hook or "J"- shaped body of the constellation continues south of the head almost touching the horizon then turns up and to the left completing the fish hook shape. A very clear, very flat southern horizon will be needed to observe the entire constellation because it is so low.
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Blobrana


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Posts: 131433
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In the south-south-eastern sky this evening -- is Scorpius ( the constellation of the Scorpion).
The “Crown of the Scorpion”, the three little stars at the top of the constellation are Graffias, Dschubba, and Pi Scorpii. They are a real associations of stars in space; these stars are thought to be loosely bound by gravity, located approximately 500 light-years away.



The Scorpio-Centaurus stars share a common motion through space, and they were all born from a single vast cloud of gas and dust.

This volatile star pack is known as the Scorpius-Centaurus OB Association, and they passed relatively near the solar system several million years ago.
About 100 stars are known in the Scorpio-Centaurus horde, including Antares, the brightest star in Scorpius.
Scientists have discovered that ancient supernova may have damaged the protective ozone layer around the Earth and wreaked havoc on terrestrial life.

The next member of the gang expected to go supernova is Antares, which at roughly 500 light-years away is too distant to rattle our planet....





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