J/other/Nat/498.198 Na abundances in NGC6752 (Campbell+, 2013)
Sodium content as a predictor of the advanced evolution of globular cluster
stars.
Campbell S.W., D'Orazi V., Yong D., Constantino T.N., Lattanzio J.C.,
Stancliffe R.J., Angelou G.C., Wylie-de Boer E.C., Grundahl F.
<Nature, 498, 198-200 (2013)>
=2013Natur.498..198C 2013Natur.498..198C
ADC_Keywords: Clusters, globular ; Stars, giant ; Abundances
Keywords: Stars
Abstract:
The asymptotic giant branch (AGB) phase is the final stage of nuclear
burning for low-mass stars. Although Milky Way globular clusters are
now known to harbour (at least) two generations of stars, they still
provide relatively homogeneous samples of stars that are used to
constrain stellar evolution theory. It is predicted by stellar models
that the majority of cluster stars with masses around the current
turn-off mass (that is, the mass of the stars that are currently
leaving the main sequence phase) will evolve through the AGB phase.
Here we report that all of the second-generation stars in the globular
cluster NGC 6752 - 70 per cent of the cluster population - fail to
reach the AGB phase. Through spectroscopic abundance measurements, we
found that every AGB star in our sample has a low sodium abundance,
indicating that they are exclusively first-generation stars. This
implies that many clusters cannot reliably be used for star counts to
test stellar evolution timescales if the AGB population is included.
We have no clear explanation for this observation.
Description:
We obtained high-resolution spectra (R∼24000) for a sample of
20 AGB stars and 24 red giant branch stars in the Galactic globular
cluster NGC 6752.
Objects:
----------------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------------
19 10 52.11 -59 59 04.4 NGC6752 = GCl 108
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tables1.dat 46 44 The stellar sample including atmospheric
parameters and Na abundances
--------------------------------------------------------------------------------
See also:
J/A+A/440/901 : Reddening and metallicity of NGC 6752 (Gratton, 2005)
J/A+A/464/927 : Abundances of red giants in NGC 6752 (Carretta+, 2007)
J/MNRAS/423/2901 : NGC 6752 multiwavelength survey (Thomson+, 2012)
Byte-by-byte Description of file: tables1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Type Star type (AGB or RGB)
5- 13 A9 --- ID Designation (FGJNNNNNN)
15- 18 I4 J Teff Effective surface temperature
20- 24 F5.3 [cm/s2] logg Surface gravity
26- 30 F5.3 km/s ksi Microturbulent velocity ξ
32- 35 F4.2 [-] log(Na) Na number density (H=12)
37- 41 F5.2 [Sun] [Na/Fe] Abundance [Na/Fe]
43- 46 F4.2 [Sun] e_[Na/Fe] rms uncertainty on [Na/Fe]
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 14-Aug-2013