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Praesepe open cluster
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Title: The Age and Age Spread of the Praesepe and Hyades Clusters: a Consistent, ~800 Myr Picture from Rotating Stellar Models
Author: Timothy D. Brandt, Chelsea X. Huang

We fit the upper main sequence of the Praesepe and Hyades open clusters using stellar models with and without rotation. When neglecting rotation, we find that no single isochrone can fit the entire upper main sequence at the clusters' spectroscopic metallicity: more massive stars appear, at high significance, to be younger than less massive stars. This discrepancy is consistent with earlier studies, but vanishes when including stellar rotation. The entire upper main sequence of both clusters is very well-fit by a distribution of 800 Myr-old stars with the spectroscopically measured [Fe/H]=0.12. The increase over the consensus age of ~600-650 Myr is due both to the revised Solar metallicity (from Z_\odot \approx 0.02 to Z_\odot \approx 0.014) and to the lengthening of main sequence lifetimes and increase in luminosities with rapid rotation. Our results show that rotation can remove the need for large age spreads in intermediate age clusters, and that these clusters may be significantly older than is commonly accepted. A Hyades/Praesepe age of ~800 Myr would also require a recalibration of rotation/activity age indicators.

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RE: Messier 44
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First Planets Found Around Sun-Like Stars in a Cluster

NASA-funded astronomers have, for the first time, spotted planets orbiting sun-like stars in a crowded cluster of stars. The findings offer the best evidence yet planets can sprout up in dense stellar environments. Although the newfound planets are not habitable, their skies would be starrier than what we see from Earth.
The starry-skied planets are two so-called hot Jupiters, which are massive, gaseous orbs that are boiling hot because they orbit tightly around their parent stars. Each hot Jupiter circles a different sun-like star in the Beehive Cluster, also called the Praesepe, a collection of roughly 1,000 stars that appear to be swarming around a common center.

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The Beehive Cluster, also known as Praesepe (Latin for "manger"), M44, NGC 2632, or Cr 189, is an open cluster in the constellation Cancer.
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Beehive Cluster

Picture 902



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Praesepe cluster
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Title: Delta Scuti stars in the Praesepe cluster observed by the MOST satellite
Authors: M. Breger, M. Hareter, Markus Endl, R. Kuschnig, W. W. Weiss, J. M. Matthews, D. B. Guenther, A. F. J. Moffat, J. F. Rowe, S. M. Rucinski, D. Sasselov

The Praesepe cluster contains a number of Delta Sct and Gamma Dor pulsators. Asteroseismology of cluster stars is simplified by the common distance, age and stellar abundances. Since asteroseismology requires a large number of known frequencies, the small pulsation amplitudes of these stars require space satellite campaigns. The present study utilizes photometric MOST satellite measurements in order to determine the pulsation frequencies of two evolved (EP Cnc, BT Cnc) and two main-sequence (BS Cnc, HD 73872) Delta Sct stars in the Praesepe cluster. The frequency analysis of the 2008 and 2009 data detected up to 34 frequencies per star with most amplitudes in the submillimag range. In BS Cnc, two modes showed strong amplitude variability between 2008 and 2009. The frequencies ranged from 0.76 to 41.7 c/d. After considering the different evolutionary states and mean stellar densities of these four stars, the differences and large ranges in frequency remain.

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RE: Messier 44
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Title: The Factory and The Beehive I. Rotation Periods For Low-Mass Stars in Praesepe
Authors: Marcel Agüeros (1), Kevin Covey (2), Jenna Lemonias (1), Nicholas Law (3), Adam Kraus (4), Natasha Batalha (2), Joshua Bloom (5), S. Bradley Cenko (5), Mansi Kasliwal (6), Shrinivas Kulkarni (6), Peter Nugent (7), Eran Ofek (6), Dovi Poznanski (5,7), Robert Quimby (6) ((1) Columbia, (2) Cornell, (3) Toronto, (4) IfA, (5) Berkeley, (6) Caltech, (7) LBNL)

Stellar rotation periods measured from single-age populations are critical for investigating how stellar angular momentum content evolves over time, how that evolution depends on mass, and how rotation influences the stellar dynamo and the magnetically heated chromosphere and corona. We report rotation periods for 40 late-K to mid-M stars members of the nearby, rich, intermediate-age (~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200 observations taken by the Palomar Transient Factory of four cluster fields from 2010 February to May. Our measurements indicate that Praesepe's mass-period relation transitions from a well-defined singular relation to a more scattered distribution of both fast and slow rotators at ~0.6 Msun. The location of this transition is broadly consistent with expectations based on observations of younger clusters and the assumption that stellar-spin down is the dominant mechanism influencing angular momentum evolution at 600 Myr. However, a comparison to data recently published for the Hyades, assumed to be coeval to Praesepe, indicates that the divergence from a singular mass-period relation occurs at different characteristic masses, strengthening the finding that Praesepe is the younger of the two clusters. We also use previously published relations describing the evolution of rotation periods as a function of colour and mass to evolve the sample of Praesepe periods in time. Comparing the resulting predictions to periods measured in M35 and NGC 2516 (~150 Myr) and for kinematically selected young and old field star populations suggests that stellar spin-down may progress more slowly than described by these relations.

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A springtime beauty, Messier 44 or (also called the Praesepe or "Beehive" star cluster) is easily visible to the naked eye as a misty cloud.  Its true nature and striking beauty are revealed only with help of binoculars or rich-field telescope.  But because of its mysterious appearance to the unaided eye, the Japanese had a more ghoulish interpretation of this lovely star cluster.

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The Beehive Cluster (also known as Praesepe (Latin for "manger"), M44 or NGC 2632) is a magnitude +3.7 open cluster located ~520-610 light-years away in the constellation Cancer. It looks like a nebulous object to the naked eye under dark skies, and thus has been known since ancient times -- Aratos of Soloi in ~260 BC mentioned the star cluster in the poem, Phainomaina, as "A little Mist" in Cancer. Ptolemy called it "The nebulous mass in the breast" of Cancer. 
It is also among the first objects Galileo studied with his telescope in 1609/110.
French astronomer Charles Messier listed the Beehive Cluster in his catalogue of 'non-comets' on the 4th March 1769

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Position(2000): RA     08h 40.1m, Dec     19° 51



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