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RE: Taurus
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P1010005b-2.jpg
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Date: 25th December, 2011



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Hyades
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SWScan0000100001.gif

Sketch of the Hyades cluster using a 60mm refractor



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Title: Simulations of the Hyades
Authors: A. Ernst, A. Just, P. Berczik, C. Olczak

Context: Using the recent observational data of Roser et al. we present N-body simulations of the Hyades open cluster.
Aims: We make an attempt to determine initial conditions of the Hyades cluster at the time of its formation in order to reproduce the present-day cumulative mass profile, stellar mass and luminosity function (LF).
Methods: We performed direct N-body simulations of the Hyades in an analytic Milky Way potential that account for stellar evolution and include primordial binaries in a few models. Furthermore, we applied a Kroupa (2001) IMF and used extensive ensemble-averaging.
Results: We find that evolved single-star King initial models with King parameters W_0 = 6-9 and initial particle numbers N_0 = 3000 provide good fits to the observational present-day cumulative mass profile within the Jacobi radius. The best-fit King model has an initial mass of 1721\ solar masses and an average mass loss rate of -2.2 \ solar masses/Myr. The K-band LFs of models and observations show a reasonable agreement. Mass segregation is detected in both observations and models. If 33% primordial binaries are included the initial particle number is reduced by 5% as compared to the model without primordial binaries.
Conclusions: The present-day properties of the Hyades can be well reproduced by a standard King or Plummer initial model when choosing appropriate initial conditions. The degeneracy of good-fitting models can be quite high due to the large dimension of the parameter space. More simulations with different Roche-lobe filling factors and primordial binary fractions are required to explore this degeneracy in more detail.

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RE: Taurus
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P1010026b.jpg
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Date: 02:45 GMT, 30th September, 2011
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Aldebaran and Hyades

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Date: 02:30 GMT, 26th August, 2011
Exposure: 10 seconds



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Posts: 129905
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Hyades
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Title: A deep all-sky census of the Hyades
Authors: S. Roeser, E. Schilbach, A.E. Piskunov, N.V.Kharchenko, R.-D. Scholz

On the basis of the PPMXL catalogue we perform an all-sky census of the Hyades down to masses of about 0.2 m_sun in a region up to 30 pc from the cluster centre. We use the proper motions from PPMXL in the convergent point method to determine probable kinematic members. From 2MASS photometry and CMC14 r'-band photometry, we derive empirical colour-absolute magnitude diagrams and, finally, determine photometric membership for all kinematic candidates. This is the first deep (r' < 17) all-sky survey of the Hyades allowing a full three-dimensional analysis of the cluster. The survey is complete down to at least M_{K_s} = 7.3 or 0.25 m_sun. We find 724 stellar systems co-moving with the bulk Hyades space velocity, which represent a total mass of 435 m_sun. The tidal radius is about 9 pc, and 275 m_sun (364 systems) are gravitationally bound. This is the cluster proper. Its mass density profile is perfectly fitted by a Plummer model with a central density of 2.21 m_sun*pc^-3 and a core radius of r_co = 3.10 pc, while the half-mass radius is r_h = 4.1 pc. There are another 100 m_sun in a volume between one and two tidal radii (halo), and another 60 m_sun up to a distance of 30 pc from the centre. Strong mass segregation is inherent in the cluster. The present-day luminosity and mass functions are noticeably different in various parts of the cluster (core, corona, halo, and co-movers). They are strongly evolved compared to presently favoured initial mass functions. The analysis of the velocity dispersion of the cluster shows that about 20% of its members must be binaries. As a by-product, we find that presently available theoretical isochrones are not able to adequately describe the near-infrared colour-absolute magnitude relation for those cluster stars that are less massive than about 0.6 m_sun.

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Taurus the Bull
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Posts: 129905
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Aldebaran and Hyades
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Hyadesb-1.gif
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21:55 UT, 18th March 2010

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RE: Taurus
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Aldebaran and Hyades

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Date: 22:20 GMT, 20th February, 2010
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Title: Spitzer observations of the Hyades: Circumstellar debris disks at 625 Myr of age
Authors: Lucas Cieza, William D. Cochran, Jean-Charles Augereau
(Version v2)

We use the Spitzer Space Telescope to search for infrared excess at 24, 70, and 160 micron due to debris disks around a sample of 45 FGK-type members of the Hyades cluster. We supplement our observations with archival 24 and 70 micron Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members in order to provide robust statistics on the incidence of debris disks at 625 Myr of age an era corresponding to the late heavy bombardment in the Solar System. We find that none of the 67 FGK-type stars in our sample show evidence for a debris disk, while 2 out of the 11 A-type stars do so. This difference in debris disk detection rate is likely to be due to a sensitivity bias in favour of early-type stars. The fractional disk luminosity, L_dust/L*, of the disks around the two A-type stars is ~4.0E-5, a level that is below the sensitivity of our observations toward the FGK-type stars. However, our sensitivity limits for FGK-type stars are able to exclude, at the 2-sigma level, frequencies higher than 12% and 5% of disks with L_dust/L* > 1.0E-4 and L_dust/L* > 5.0E-4, respectively. We also use our sensitivity limits and debris disk models to constrain the maximum mass of dust, as a function of distance from the stars, that could remain undetected around our targets.

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