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Hyades
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Hyades

Picture 007



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RE: Taurus
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Title: The Hyades Cluster: Identification of a Planetary System and Escaping White Dwarfs
Authors: B. Zuckerman, B. Klein, S. Xu, M. Jura

Recently, some hot DA-type white dwarfs have been proposed to plausibly be escaping members of the Hyades. We used hydrogen Balmer lines to measure the radial velocities of seven such stars and confirm that three, and perhaps two others, are/were indeed cluster members and one is not. The other candidate Hyad is strongly magnetic and its membership status remains uncertain. The photospheres of at least one quarter of field white dwarf stars are "polluted" by elements heavier than helium that have been accreted. These stars are orbited by extended planetary systems that contain both debris belts and major planets. We surveyed the seven classical single Hyades white dwarfs and the newly identified (escaping) Hyades white dwarfs and found calcium in the photosphere of LP 475-242 of type DBA (now DBAZ), thus implying the presence of an orbiting planetary system. The spectrum of white dwarf GD 31, which may be, but probably is not, an escaping member of the Hyades, displays calcium absorption lines; these originate either from the interstellar medium or, less likely, from a gaseous circumstellar disk. If GD 31 was once a Hyades member, then it would be the first identified white dwarf Hyad with a cooling age >340 Myr.

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Hyades Stars
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Title: Evidence of Rocky Planetesimals Orbiting Two Hyades Stars
Authors: J. Farihi, B. T. Gänsicke, D. Koester

The Hyades is the nearest open cluster, relatively young and containing numerous A-type stars; its known age, distance, and metallicity make it an ideal site to study planetary systems around 2-3 Msun stars at an epoch similar to the late heavy bombardment. Hubble Space Telescope far-ultraviolet spectroscopy strongly suggests ongoing, external metal pollution in two remnant Hyads. For ongoing accretion in both stars, the polluting material has log[n(Si)/n(C)] > 0.2, is more carbon deficient than chondritic meteorites, and is thus rocky. These data are consistent with a picture where rocky planetesimals and small planets have formed in the Hyades around two main-sequence A-type stars, whose white dwarf descendants bear the scars. These detections via metal pollution are shown to be equivalent to infrared excesses of Lir/L* ~ 1e-6 in the terrestrial zone of the stars.

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Hyades moving group
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Title: Extending the Hyades
Authors: Paul J. McMillan

We explore the implications of models of the Hyades moving group in which it has a resonant origin, for regions of the Galaxy beyond the Solar neighbourhood. We show that while models associated with different resonances can produce nearly identical substructure in the local velocity distribution, the velocity distribution away from the Solar neighbourhood has different properties for different models. In particular there is a variation between different models of where in Galactocentric radius the observed Hyades signal in velocity space is strongest, at a given Galactic azimuth. We note, however, that the uncertainties in currently available data, primarily due to uncertain distances to stars, hide these signatures rather effectively, meaning we are not yet able to determine which resonance is the cause of the Hyades.

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RE: Taurus
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P5030009b.jpg
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Date: 15th November, 2012



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P3020025b.jpg P3020023b.jpg
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Date: 14 September, 2012



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Photo sketch of the Hyades open cluster using a 60mm refractor

Hyadesb.jpg



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hayb.jpg 


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hyadesP1B-1.jpg

The Hyades and Pleiades



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Posts: 128681
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Hyades
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Title: High-contrast imaging in the Hyades with snapshot LOCI
Authors: Katie M. Morzinski, Bruce A. Macintosh, Laird M. Close, Christian Marois, Quinn Konopacky, Jenny Patience

To image faint substellar companions obscured by the stellar halo and speckles, scattered light from the bright primary star must be removed in hardware or software. We apply the "locally-optimised combination of images" (LOCI) algorithm to 1-minute Keck Observatory snapshots of GKM dwarfs in the Hyades using source diversity to determine the most likely PSF. We obtain a mean contrast of 10^{-2} at 0.01", 10^{-4} at <1", and 10^{-5} at 5". New brown dwarf and low-mass stellar companions to Hyades primaries are found in a third of the 84 targeted systems. This campaign shows the efficacy of LOCI on snapshot imaging as well as on bright wide binaries with off-axis LOCI, reaching contrasts sufficient for imaging 625-Myr late-L/early-T dwarfs purely in post-processing.

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