Issue |
A&A
Volume 581, September 2015
|
|
---|---|---|
Article Number | A90 | |
Number of page(s) | 9 | |
Section | Galactic structure, stellar clusters and populations | |
DOI | https://doi.org/10.1051/0004-6361/201526157 | |
Published online | 10 September 2015 |
The white dwarf population of NGC 6397
1
Departament de Física AplicadaUniversitat Politècnica de
Catalunya,
c/Esteve Terrades 5,
08860
Castelldefels,
Spain
e-mail:
enrique.garcia-berro@upc.edu
2
Institute for Space Studies of Catalonia,
c/Gran Capita 2–4, Edif. Nexus
104, 08034
Barcelona,
Spain
3
Facultad de Ciencias Astronómicas y Geofísicas, Universidad
Nacional de La Plata, Paseo del
Bosque s/n, 1900
La Plata,
Argentina
4
Instituto de Astrofísica de La Plata, UNLP-CONICET, Paseo del Bosque s/n,
1900
La Plata,
Argentina
Received: 22 March 2015
Accepted: 31 July 2015
Context. NGC 6397 is one of the most interesting, well-observed, and most thoroughly theoretically studied globular clusters. The existing wealth of observations allows us to study the reliability of the theoretical white dwarf cooling sequences of low-metallicity progenitors, to determine the age of NGC 6397 and the percentage of unresolved binaries. We also assess other important characteristics of the cluster, such as the slope of the initial mass function or the fraction of white dwarfs with hydrogen-deficient atmospheres.
Aims. We present a population synthesis study of the white dwarf population of NGC 6397. In particular, we study the shape of the color–magnitude diagram and the corresponding magnitude and color distributions.
Methods. To do this, we used an advanced Monte Carlo code that incorporates the most recent and reliable cooling sequences and an accurate modeling of the observational biases.
Results. Our theoretical models and the observed data agree well. In particular, we find that this agreement is best for those cooling sequences that take into account residual hydrogen burning. This result has important consequences for the evolution of progenitor stars during the thermally pulsing asymptotic giant branch phase, since it implies that appreciable third dredge-up in low-mass, low-metallicity progenitors is not expected to occur. Using a standard burst duration of 1.0 Gyr, we obtain that the age of the cluster is 12.8+0.50-0.75 Gyr. Greater ages are also compatible with the observed data, but then unrealistic longer durations of the initial burst of star formation are needed to fit the luminosity function.
Conclusions. We conclude that a correct modeling of the white dwarf population of globular clusters, used in combination with the number counts of main-sequence stars, provides a unique tool for modeling the properties of globular clusters.
Key words: globular clusters: individual: NGC 6397 / stars: luminosity function, mass function / globular clusters: general / white dwarfs
© ESO, 2015
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.