1998A&A...333..926D


Query : 1998A&A...333..926D

1998A&A...333..926D - Astronomy and Astrophysics, volume 333, 926-941 (1998/5-3)

The puzzling MgAl anticorrelation in globular-cluster red giants: primordial plus deep mixing scenario?

DENISSENKOV P.A., DA COSTA G.S., NORRIS J.E. and WEISS A.

Abstract (from CDS):

Star-to-star abundance variations of C, N, O, Na and Al in globular-cluster red giants have been recently supplemented by the finding that [Mg/Fe] is depleted in stars with extremely large [Al/Fe] (Shetrone, 1996AJ....112.1517S). To find out which of the magnesium isotopes is responsible for the observed depletion of [Mg/Fe] Shetrone (1996AJ....112.2639S) also undertook an isotopic analysis of Mg and found that it is 24Mg which is depleted in Al-rich giants. On the other hand, Norris & Da Costa (1995ApJ...447..680N) demonstrated that even in the massive globular cluster ω Cen which has intrinsic spreads in both [Fe/H] and the abundances of the s-process elements, [O/Fe] anticorrelates with [Na/Fe] and [Al/Fe] as in ``normal'' monometallic clusters. These new spectroscopic results allow us to test current models of stellar evolution and nucleosynthesis, as well as those of the formation and chemical enrichment of globular clusters. In an effort to explain self-consistently these observations we have considered two possibilities: (1) a deep mixing scenario which assumes that in red giants some kind of (extra)mixing transports products of nuclear reactions from the hydrogen burning shell (HBS) to the base of the convective envelope; and (2) a combination of primordial and deep mixing scenarios. It is shown that (1) cannot account for the anticorrelation of [Mg/Fe] vs. [Al/Fe] without additional ad hoc assumptions, among which we identify a strong but still undetected low energy resonance in the reaction 24Mg(p,γ)25Al, and episodical increases of the HBS temperature up to the value T≃74x106K. In (2) intermediate mass AGB stars are assumed to produce the decreased 24Mg and increased 25Mg initial abundances in some globular-cluster low mass stars and Al is synthesized at the expense of 25Mg in the HBS and transported to the surface of the red giant by extramixing. We discuss advantages and deficiencies of both scenarios and propose some observational tests.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: evolution - stars: interiors - globular clusters: general

Simbad objects: 19

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Number of rows : 19
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NGC 288 GlC 00 52 45.24 -26 34 57.4   10 8.13     ~ 984 0
2 NGC 362 GlC 01 03 14.26 -70 50 55.6     6.58     ~ 1012 0
3 SOPS IV e-94 C* 13 26 01.5892714032 -47 33 05.967491724   13.18 11.44   9.966 C1,3p 54 0
4 2MASS J13261120-4728435 RG* 13 26 11.2122788208 -47 28 43.621679532   13.98 12.50     ~ 29 0
5 2MASS J13261220-4731251 RG* 13 26 12.2030173224 -47 31 25.191967872 15.82 13.820 12.309   10.679 ~ 29 0
6 NGC 5139 150 RG* 13 26 23.6649086064 -47 42 42.409293624   13.692 11.946 11.588   ~ 34 0
7 2MASS J13263483-4734110 RG* 13 26 34.8426950352 -47 34 11.125321320 16.056 14.039 12.249 11.306 10.498 ~ 30 0
8 NGC 5139 480 RB? 13 26 47.2375070808 -47 34 12.317843964   14.196 12.923   11.655 ~ 23 0
9 NGC 5139 GlC 13 26 47.28 -47 28 46.1   6.12 5.33     ~ 3231 0
10 2MASS J13265071-4737010 RG* 13 26 50.7174210264 -47 37 01.158926736   14.28 12.71   11.159 K5 47 0
11 M 3 GlC 13 42 11.62 +28 22 38.2     6.39     ~ 2374 0
12 M 5 GlC 15 18 33.22 +02 04 51.7   7.34 5.95     ~ 1872 0
13 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1757 0
14 M 13 GlC 16 41 41.634 +36 27 40.75     5.8     ~ 2099 0
15 M 92 GlC 17 17 07.39 +43 08 09.4     6.52     ~ 1997 0
16 NGC 6397 GlC 17 40 42.09 -53 40 27.6   7.39 5.17     ~ 1876 1
17 M 22 GlC 18 36 23.94 -23 54 17.1   7.16 6.17     ~ 1295 0
18 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1894 0
19 M 71 GlC 19 53 46.49 +18 46 45.1   7.91 6.1     ~ 1072 0

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2022.05.24-07:44:36

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