Sounding Open Clusters: Asteroseismic Constraints from Kepler on the Properties of NGC 6791 and NGC 6819

Sarbani Basu (1) , Frank Grundahl (2) , Dennis Stello (3) , Thomas Kallinger (4) , Saskia Hekker (5) , Benoît Mosser (6, 7, 8) , Rafael A. Garcia (9) , Savita Mathur (10) , K. Brogaard (2) , H. Bruntt (2) , William J. Chaplin (5) , Ning Gai (11) , Yvonne P. Elsworth (5) , Lisa Esch (1) , Jérôme Ballot (12) , Timothy R. Bedding (3) , Michael Gruberbauer (13) , Daniel Huber (3) , Andrea Miglio (14) , Mutlu Yildiz (15) , Hans Kjeldsen (2) , Jörgen Christensen-Dalsgaard (2) , Ronald L. Gilliland (16) , Michael M. Fanelli (17) , Khadeejah A. Ibrahim (18) , Jeffrey C. Smith (19)

1 Department of Astronomy, Yale University
2 DASC - Danish AsteroSeismology Centre
3 SIfA - Sydney Institute for Astronomy
4 University of British Columbia [Vancouver]
5 School of Physics and Astronomy, University of Birmingham
6 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
7 Etoile
8 Pôle Planétologie du LESIA
9 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
10 High Altitude Observatory, National Center for Atmospheric Research
11 BNU - Beijing Normal University
12 LATT - Laboratoire Astrophysique de Toulouse-Tarbes
13 Institute for Computational Astrophysics, Department of Astronomy and Physics, Saint Marys University
14 Institut d'Astrophysique, Géophysique et Océanographie, Université de Liège
15 Department of Astronomy and Space Sciences, Ege University
16 STScI - Space Telescope Science Institute
17 BAER - Bay Area Environmental Research Institute
18 Orbital Sciences Corporation, NASA Ames Research Center, Moffett Field
19 SETI Institute, NASA Ames Research Center, Moffett Field

We present initial results on some of the properties of open clusters NGC 6791 and NGC 6819 derived from asteroseismic data obtained by NASA's Kepler mission. In addition to estimating the mass, radius, and log g of stars on the red giant branch (RGB) of these clusters, we estimate the distance to the clusters and their ages. Our model-independent estimate of the distance modulus of NGC 6791 is (m - M)₀ = 13.11 ± 0.06. We find (m - M)₀ = 11.85 ± 0.05 for NGC 6819. The average mass of stars on the RGB of NGC 6791 is 1.20 ± 0.01 M _sun, while that of NGC 6819 is 1.68 ± 0.03 M _sun. It should be noted that we do not have data that cover the entire RGB and the actual mass will be somewhat lower. We have determined model-dependent estimates of ages of these clusters. We find ages between 6.8 and 8.6 Gyr for NGC 6791, however, most sets of models give ages around 7 Gyr. We obtain ages between 2 and 2.4 Gyr for NGC 6819.

Domaines: Astrophysique [astro-ph]

Sarbani Basu, Frank Grundahl, Dennis Stello, Thomas Kallinger, Saskia Hekker, et al.. Sounding Open Clusters: Asteroseismic Constraints from Kepler on the Properties of NGC 6791 and NGC 6819. The Astrophysical journal letters, 2011, 729, pp.L10. ⟨10.1088/2041-8205/729/1/L10⟩. ⟨hal-03730758⟩