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TOPIC: Hyades stream

Blobrana

L

Posts: 131433

Date: May 24 00:12 2012

Hyades Supercluster	Permalink

Title: Chemically tagging the Hyades Supercluster: A homogeneous sample of F6-K4 kinematically selected northern stars Authors: H. M. Tabernero, D. Montes, J. I. Gonzalez Hernandez Stellar kinematic groups are kinematical coherent groups of stars that might have a common origin. These groups are dispersed throughout the Galaxy over time by the tidal effects of both Galactic rotation and disc heating, although their chemical content remains unchanged. The aim of chemical tagging is to establish that the abundances of every element in the analysis are homogenous among the members. We study the case of the Hyades Supercluster to compile a reliable list of members (FGK stars) based on our chemical tagging analysis. For a total of 61 stars from the Hyades Supercluster, stellar atmospheric parameters (Teff, logg, xi, and [Fe/H]) are determined using our code called StePar, which is based on the sensitivity to the stellar atmospheric parameters of the iron EWs measured in the spectra. We derive the chemical abundances of 20 elements and find that their [X/Fe] ratios are consistent with Galactic abundance trends reported in previous studies. The chemical tagging method is applied with a carefully developed differential abundance analysis of each candidate member of the Hyades Supercluster, using a well-known member of the Hyades cluster as a reference (vB 153). We find that only 28 stars (26 dwarfs and 2 giants) are members, i.e. that 46% of our candidates are members based on the differential abundance analysis. This result confirms that the Hyades Supercluster cannot originate solely from the Hyades cluster. Read more (251kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Mar 14 00:56 2011

Hyades stream	Permalink

Title: Chemically tagging the Hyades stream: Does it partly originate from the Hyades cluster? Authors: L. Pompéia, T. Masseron, B. Famaey, S. Van Eck, A. Jorissen, I. Minchev, A. Siebert, C. Sneden, J.R.D. Lépine, C. Siopis, G. Gentile, T. Dermine, E. Pasquato, H. Van Winckel, C. Waelkens, G. Raskin, S. Prins, W. Pessemier, H. Hensberge, Y. Frémat, L. Dumortier, O. Bienaymé (Version v2) The Hyades stream has long been thought to be a dispersed vestige of the Hyades cluster. However, recent analyses of the parallax distribution, of the mass function, and of the action-space distribution of stream stars have shown it to be rather composed of orbits trapped at a resonance of a density disturbance. This resonant scenario should leave a clearly different signature in the element abundances of stream stars than the dispersed cluster scenario, since the Hyades cluster is chemically homogeneous. Here, we study the metalllicty as well as the element abundances of Li, Na, Mg, Fe, Zr, Ba, La, Ce, Nd, and Eu for a random sample of stars belonging to the Hyades stream, and compare them with those of stars from the Hyades cluster. From this analysis: (i) we independently confirm that the Hyades stream cannot be solely composed of stars originating in the Hyades cluster; (ii) we show that some stars from the Hyades stream nevertheless have abundances compatible with an origin in the cluster; (iii) we emphasize that the use of Li as a chemical tag of the cluster origin of main-sequence stars is very efficient in the range 5500 - 6200 K, since the Li sequence in the Hyades cluster is very tight; (iv) we show that, while this evaporated population has a metallicity excess of ~0.2 dex w.r.t. the local thin disk population, identical to that of the Hyades cluster, the remainder of the Hyades stream population has still a metallicity excess of ~0.06 to 0.15 dex, consistent with an origin in the inner Galaxy; (v) we show that the Hyades stream can be interpreted as an inner 4:1 resonance of the spiral pattern: this then also reproduces an orbital family compatible with the Sirius stream, and places the origin of the Hyades stream up to 1 kpc inwards from the solar radius, which might explain the observed metallicity excess of the stream population. Read more (715kb, PDF) __________________

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