J/AJ/112/545 Proton capture chains in globular clusters. I. (Pilachowski+ 1996)
Proton capture chains in globular cluster stars. I.
Evidence for deep mixing based on sodium and magnesium abundances in M13 giants
Pilachowski C.A., Sneden C., Kraft R.P., Langer G.E.
<Astron. J. 112, 545 (1996)>
=1996AJ....112..545P 1996AJ....112..545P
ADC_Keywords: Clusters, globular ; Stars, giant ; Abundances ;
Effective temperatures
Abstract:
Sodium abundances have been derived for 130 giant stars in the
globular cluster M13 from spectra of the Na I doublet at λ5682
and 5685A obtained using the KPNO 4-m Hydra fiber positioner and bench
spectrograph. Magnesium abundances have also been obtained for the
brightest 98 stars in the sample from the nearby Mg I line at
λ5711A. The stars observed in M13 range from the faintest at
MV~+1.0 and log(g)∼2.6 up to the tip of the giant branch, and
include 18 stars on the asymptotic giant branch. Among the lower
luminosity giants, the sodium abundances have a large star-to-star
range, approximately from -0.3≤[Na/Fe]≤+0.5. However, the sodium
abundances of the most luminous giants (Mv←1.7) are usually high;
typically, [Na/Fe]≥+0.3, with a much smaller star-to-star scatter.
The asymptotic giant branch stars have smaller sodium abundances on
average than do the red giant branch tip stars. The spread in [Na/Fe]
ratios is larger in M13 than it is among halo field giants of
comparable metallicity; M13 contains many more stars with high [Na/Fe]
ratios than can be found in the field, even at relatively low
luminosities on the giant branch. Magnesium is uniformly overabundant
([Mg/Fe]~+0.3) in all stars with a low sodium abundance, but the
[Mg/Fe] ratio ranges from approximately -0.3 to +0.3 in stars with a
high sodium abundance. These sodium and magnesium abundance variations
in M13 are discussed in the context of proton capture and deep mixing
hypotheses. In addition to the CN and ON hydrogen burning chains
previously discussed in the literature, the NeNa and MgAl burning
chains have also contributed to the abundance mixture observed in M13
giants. At least some of the products of proton capture chains have
been produced in situ in the giants, and brought to the surface, most
probably via deep mixing. Evidence in support of the occurrence of
proton capture nucleosynthesis and deep mixing among M13 stars
includes (1) the absence of sodium-poor stars at the red giant tip,
(2) the fact that asymptotic branch stars have lower sodium abundances
on average than do stars near the red giant tip, and (3) the existence
of a positive correlation between sodium and nitrogen abundances as
well as a partial anti-correlation of sodium and magnesium abundances.
Objects:
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RA (2000) DE Designation(s)
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16 41.7 +36 27 M 13 = NGC 6205
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 72 168 M13 star basic data and results
table1.tex 108 264 AASTeX version of table1.dat
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See also:
J/AJ/113/279 : Proton Capture Chains. II (Kraft+ 1997)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Star *Primary designation
8- 14 A7 --- Alt *Alternate designation
16- 20 F5.2 mag Vmag *V magnitude
22- 26 F5.2 mag B-V *[]? B-V color
28- 32 F5.1 mag Mvo Estimated absolute V magnitude
35- 37 A3 --- Branch Evolutionary status (Red Giant Branch, RGB,
Asymptotic Giant Branch, AGB)
38 A1 --- u_Branch [?] Branch uncertainty flag
40 I1 --- Code *Analysis code
42- 46 I5 K Teff []? Effective temperature
48- 52 F5.2 [cm/s2] log(g) []? log(10) of the surface gravity
54- 58 F5.2 km/s vt []? Microturbulence
60- 65 F6.2 --- [Na/Fe] []? Sodium abundance relative to iron
67- 72 F6.2 --- [Mg/Fe] []? Magnesium abundance relative to iron
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Note on Star:
Primary star name references:
L = Ludendorf, (1905POPot..50....1L 1905POPot..50....1L)
K = Kadla, (1966IzPul.181...93K 1966IzPul.181...93K)
CM = Cudworth & Monet, (1979AJ.....84..774C 1979AJ.....84..774C)
Note on Alt:
Alternate star name references:
SA, SB = Savedoff, (1956AJ.....61..254S 1956AJ.....61..254S)
V (variable stars) = Hogg, (1973PDDO....3....6S 1973PDDO....3....6S)
BAUM = Baum, (1954AJ.....59..422B 1954AJ.....59..422B)
"Roman numerals" = Arp, (1955AJ.....60..317A 1955AJ.....60..317A)
remaining designations appear either in Arp & Johnson, (1955ApJ...122..171A 1955ApJ...122..171A)
(their Figure 4) or in Sandage, (1970ApJ...162..841S 1970ApJ...162..841S) (his Figure 5).
Note on Vmag, B-V:
V and B-V from Cudworth & Monet, (1979AJ.....84..774C 1979AJ.....84..774C)
Note on Code:
Definitions of the code numbers:
1 = good enough spectrum to derive both sodium and magnesium abundances
2 = good enough spectrum to derive a sodium abundance, but not magnesium
3 = essentially no flux in the reduced spectrum; mis-positioned fiber?
4 = very weak absorption spectrum; possibly a warm star?
5 = hot horizontal branch star
6 = poor signal-to-noise in the reduced spectrum
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Origin: AAS CD-ROM series, Volume 7, 1996 Lee Brotzman [ADS] 13-Aug-1996
(End) [CDS] 30-Jan-1997