Browsing by Subject "planetary systems : protoplanetary disks"
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Item Chronology of the Solar System's Oldest Solids(2008-03) Connelly, James N.; Amelin, Yuri; Krot, Alexander N.; Bizzarro, Martin; Connelly, James N.Determining the origins of our solar system and, by proxy, other planetary systems, depends on knowing accurately and precisely the timing and tempo of the transFormation of the disk of gas and dust to the solids that formed the planets. Relative ages based on the short-lived nuclide Al-26 indicate that high-temperature calcium-aluminum inclusions (CAIs) formed before lower temperature chondrules but these ages are heavily dependant on a model of homogeneous distribution of Al-26 within the protoplanetary disk. The competing X-wind model argues for heterogeneous distribution of Al-26 due to its Formation by intra-solar system irradiation such that this system would have no chronological significance. We report a Pb-207-Pb-206 isochron age of 4565.45 +/- 0.45 Myr for chondrules from the CV chondrite Allende, an age that is 1.66 +/- 0.48 Myr younger than the accepted Pb-Pb age for CAIs from this chondrite group. This age offset is in excellent agreement with the relative ages determined using the Al-26-Mg-26 system, an observation that supports a supernova origin for Al-26 and, importantly, the chronological significance of the Al-26-Mg-26 system in general. This is consistent with an early and brief CAI-forming event followed by recurrent chondrule Formation throughout the life span of the protoplanetary disk. The paucity of old chondrules in chondrite meteorites may reflect their early incorporation into the parent bodies of differentiated meteorites after CAIs were effectively removed from the innermost regions of the protoplanetary disk. Lastly, the agreement between the absolute and relative chronology of CAIs and chondrules requires a solar system age younger than similar to 4567.5 Myr.Item Testing The Disk Regulation Paradigm With Spitzer Observations. II. A Clear Signature Of Star-Disk Interaction In NGC 2264 And The Orion Nebula Cluster(2007-12) Cieza, Lucas; Baliber, Nairn; Cieza, LucasObservations of pre-main-sequence star rotation periods reveal slow rotators in young clusters of various ages, indicating that angular momentum is somehow removed from these rotating masses. The mechanism by which spin-up is regulated as young stars contract has been one of the longest standing problems in star formation. Attempts to observationally confirm the prevailing theory that magnetic interaction between the star and its circumstellar disk regulates these rotation periods have produced mixed results. In this paper, we use the unprecedented disk identification capability of the Spitzer Space Telescope to test the star-disk interaction paradigm in two young clusters, NGC 2264 and the Orion Nebula Cluster (ONC). We show that once mass effects and sensitivity biases are removed, a clear increase in the disk fraction with period can be observed in both clusters across the entire period range populated by cluster members. We also show that the long-period peak (P similar to 8 days) of the bimodal distribution observed for high-mass stars in the ONC is dominated by a population of stars possessing a disk, while the short-period peak (P similar to 2 days) is dominated by a population of stars without a disk. Our results represent the strongest evidence to date that star-disk interaction regulates the angular momentum of these young stars. This study will make possible quantitative comparisons between the observed period distributions of stars with and without a disk and numerical models of the angular momentum evolution of young stars.