CDROM/AJ/V112/P0545 Proton Cpature Chains. I. (Pilachowski+ 1996) ================================================================================ Proton Capture Chains in Globular Cluster Stars. I. Evidence for Deep Mixing Based on Sodium and Magnesium Abundances in M13 Giants Catherine A. Pilachowski, Christopher Sneden, Robert P. Kraft, & G. E. Langer <1996, AJ, 112, 545> =1996AJ....112..545P ================================================================================ Abstract: Sodium abundances have been derived for 130 giant stars in the globular cluster M13 from spectra of the Na I doublet at lambda 5682 and 5685 A 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 lambda 5711 A. 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. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table1.dat 72 168 M13 star basic data and results table1.tex 108 264 AASTeX version of table1.dat -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 A5 --- Star *Primary designation 6- 7 2X --- --- Blank 8-14 A7 --- Alt *Alternate designation 15-20 F6.2 mag V *V magnitude 21-26 F6.2 mag B-V *[]? B-V color 27-32 F6.1 mag Mvo Estimated absolute V magnitude 33-34 2X --- --- Blank 35-37 A3 --- Branch Evolutionary status (Red Giant Branch, RGB, Asymptotic Giant Branch, AGB) 38 A1 --- u_Branch [?] Branch uncertainty flag 39 1X --- --- Blank 40 I1 --- Code *Analysis code 41-46 I6 K Teff []? Effective temperature 47-52 F6.2 cm/s2 log_g []? Log(10) of the surface gravity 53-58 F6.2 km/s vt []? Microturbulence 59-65 F7.2 dex [Na/Fe] []? Sodium abundance relative to iron 66-72 F7.2 dex [Mg/Fe] []? Magnesium abundance relative to iron -------------------------------------------------------------------------------- Notes for file: table1.dat -------------------------------------------------------------------------------- Star: Primary star name references: L = Ludendorf 1905, Publ. Astrophys. Obs. Potsdam, 15, No. 50 K = Kadla 1966, Comm. Pulkova Obs., 24, No. 181, 93 CM = Cudworth & Monet 1979, AJ, 84, 774 Alt: Alternate star name references: SA, SB = Savedoff 1956, AJ, 61, 254 V (variable stars) = Hogg 1973, Publ. David Dunlap Obs., 3, No. 6 BAUM = Baum 1954, AJ, 59, 422 "Roman numerals" = Arp 1955, AJ, 60, 317 remaining designations appear either in Arp & Johnson 1955, ApJ, 122, 171 (their Figure 4) or in Sandage 1970, ApJ, 162, 841 (his Figure 5). V, B-V: V and B-V from Cudworth & Monet 1979, AJ, 84, 774 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 magesium 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 -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 13-Aug-1996