* Astronomy

Blobrana · L

RE: Open Clusters

Blobrana · L

Title: Asteroseismology of the open clusters NGC 6791, NGC 6811, and NGC 6819 from nineteen months of Kepler photometry
Authors: Enrico Corsaro, Dennis Stello, Daniel Huber, Timothy R. Bedding, Alfio Bonanno, Karsten Brogaard, Thomas Kallinger, Othman Benomar, Timothy R. White, Benoit Mosser, Sarbani Basu, William J. Chaplin, Jørgen Christensen-Dalsgaard, Yvonne P. Elsworth, Rafael A. García, Saskia Hekker, Hans Kjeldsen, Savita Mathur, Søren Meibom, Jennifer R. Hall, Khadeejah A. Ibrahim, Todd C. Klaus

We studied 115 red giants in the three open clusters NGC 6791, NGC 6811, and NGC 6819, based on photometric data covering more than 19 months with NASA's Kepler space telescope. We present the asteroseismic diagrams of the asymptotic parameters \Delta\nu, \delta\nu_01, \delta\nu_02 and \epsilon. When the stellar populations from the clusters are compared, we see evidence for a difference in mass of the red giant branch stars, and possibly a difference in structure of the red clump stars, from the small separations \delta\nu_01 and \delta\nu_02. Ensemble \'echelle diagrams and lower limits to the linewidth of l = 0 modes as a function of Dnu of the clusters NGC 6791 and NGC 6819 are also shown, together with a correlation between the l = 0 ridge width and T_eff. Lastly, we distinguish between red giant branch and red clump stars through the measurement of the period spacing of mixed modes in 53 stars among all the three clusters to verify the stellar classification from the colour-magnitude diagram. These seismic results also allow us to identify a number of potentially interesting stars including evolved blue stragglers and binaries, as well as stars in late He-core burning phases.

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Blobrana · L

Title: The orbits of open clusters in the Galaxy
Authors: Zhen-Yu Wu, Xu Zhou, Jun Ma, Cui-Hua Du

We present and analyse kinematics and orbits for a sample of 488 open clusters in the Galaxy. The velocity ellipsoid for our present sample is derived as (\sigma_{U}, \sigma_{V}, \sigma_{W})=(28.7, 15.8, 11.0) km s^{-1} which represents a young thin disc population. We also confirm that the velocity dispersions increase with the age of cluster subsample. The orbits of open clusters are calculated with three Galactic gravitational potential models. The errors of orbital parameters are also calculated considering the intrinsic variation of the orbital parameters and the effects of observational uncertainties. The observational uncertainties dominate the errors of derived orbital parameters. The vertical motions of clusters calculated using different Galactic disc models are rather different. The observed radial metallicity gradient of clusters is derived with a slope of b=-0.070 ±0.011 dex kpc^{-1}. The radial metallicity gradient of clusters based on their apogalactic distances is also derived with a slope of b=-0.082 ±0.014 dex kpc^{-1}. The distribution of derived orbital eccentricities for open clusters is very similar to the one derived for the field population of dwarfs and giants in the thin disc.

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