Issue |
A&A
Volume 402, Number 3, May II 2003
First Science with the ODIN satellite
|
|
---|---|---|
Page(s) | 985 - 1001 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20030296 | |
Published online | 23 April 2003 |
Mg isotopic ratios in giant stars of the globular cluster NGC 6752*
1
Department of Astronomy, University of Texas, Austin, TX 78712, USA
2
Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark e-mail: fgj,pen@phys.au.dk
3
McDonald Observatory, University of Texas, HC 75, Box 1337 MCD, Fort Davis, TX 79734, USA e-mail: shetrone@astro.as.utexas.edu
Corresponding author: D. Yong, tofu,dll@astro.as.utexas.edu
Received:
13
January
2003
Accepted:
27
February
2003
Mg isotopic abundance ratios are measured in 20 bright red giants
in globular cluster NGC 6752 based on very high-resolution (),
high signal-to-noise spectra obtained with UVES on the VLT.
There is a considerable spread in the ratio 24Mg:25Mg:26Mg
with values ranging from 53:9:39 to 83:10:7.
We measured the abundances of O, Na, Mg, Al, and Fe combining our sample
with 21 RGB bump stars (Grundahl et al. 2002). The abundances of the
samples are consistent and exhibit the usual anticorrelations between O–Na and Mg–Al.
A positive correlation is found between 26Mg and Al, a mild anticorrelation is
found between 24Mg and Al, while no correlation is found between 25Mg and Al.
None of the elemental or isotopic abundances show a
dependence on evolutionary status and, as shown by Gratton et al. (2001), the abundance
variations exist even in main sequence stars. This strongly suggests that the
star-to-star abundance variations are a result of varying degrees of pollution
with intermediate mass AGB stars being likely polluters.
Consideration of the extremes of the abundance variations
provides the composition of the ambient material and the processed material.
In the least contaminated stars (lowest Na and Al and highest O and Mg abundances),
we infer a Mg isotopic ratio around 80:10:10 and a composition ([O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe])
(0.6, -0.1, 0.5, 0.0).
In the most polluted stars, we find a Mg isotopic ratio around 60:10:30 and a
composition ([O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe])
(-0.1, 0.6, 0.3, 1.2).
Even for the least polluted stars, the abundances of 25Mg and
26Mg relative to 24Mg are considerably higher
than predicted for ejecta from
supernovae. Zero metallicity AGB stars may be
responsible for these higher abundances.
Our measured Mg isotopic ratios reveal another layer to the globular cluster
star-to-star abundance variations that demands extensions of our present theoretical
knowledge of stellar nucleosynthesis by giant stars.
Key words: galaxies: clusters: general / galaxies: clusters: individual: NGC 6752 / stars: abundances / stars: evolution / stars: fundamental parameters
© ESO, 2003
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.