2003A&A...397..275M


Query : 2003A&A...397..275M

2003A&A...397..275M - Astronomy and Astrophysics, volume 397, 275-284 (2003/1-1)

Mg, Ba and Eu abundances in thick disk and halo stars.

MASHONKINA L., GEHREN T., TRAVAGLIO C. and BORKOVA T.

Abstract (from CDS):

Our sample of cool dwarf stars from previous papers (Mashonkina & Gehren, 2000A&A...364..249M (paper I) and 2001A&A...376..232M (paper II)) is extended in this study including 15 moderately metal-deficient stars. The samples of halo and thick disk stars have overlapping metallicities with [Fe/H] in the region from -0.9 to -1.5, and we compare chemical properties of these two kinematically different stellar populations independent of their metallicity. We present barium, europium and magnesium abundances for the new sample of stars. The results are based on NLTE line formation obtained in differential model atmosphere analyses of high resolution spectra observed mainly using the UVES spectrograph at the VLT of the European Southern Observatory. We confirm the overabundance of Eu relative to Mg in halo stars as reported in our previous papers. Eight halo stars show [Eu/Mg] values between 0.23 and 0.41, whereas stars in the thick and thin disk display a solar europium to magnesium ratio. The [Eu/Ba] values found in the thick disk stars to lie between 0.35 and 0.57 suggest that during thick disk formation evolved low-mass stars started to enrich the interstellar gas by s-nuclei of Ba, and the s-process contribution to barium thus varies from 30% to 50%. Based on these results, and using the chemical evolution calculations by Travaglio et al. (1999ApJ...521..691T), we estimate that the thick disk stellar population formed on a timescale between 1.1 to 1.6 Gyr from the beginning of the protogalactic collapse. In the halo stars the [Eu/Ba] values are found mostly between 0.40 and 0.67, which suggests a duration of the halo formation of about 1.5 Gyr. For the whole sample of stars we present the even-to-odd Ba isotope ratios as determined from hyperfine structure seen in the BaII resonance line λ4554. As expected, the solar ratio 82:18 (Cameron, 1982Ap&SS..82..123C) adjusts to observations of the BaII lines in the thin disk stars. In our halo stars the even-to-odd Ba isotope ratios are close to the pure r-process ratio 54:46 (Arlandini et al., 1999ApJ...525..886A), and in the thick disk stars the isotope ratio is around 65:35 (±10%). Based on these data we deduce for thick disk stars the ratio of the s/r-process contribution to barium as 30:70 (±30%), in agreement with the results obtained from the [Eu/Ba] values.

Abstract Copyright:

Journal keyword(s): line: formation - nuclear reactions, nucleosynthesis, abundances - stars: abundances - stars: late-type - Galaxy: evolution

CDS comments: p. 277 : CD 52 2174 misprint for -52 2174

Simbad objects: 25

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Number of rows : 25
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 HD 3795 PM* 00 40 32.7939851012 -23 48 17.728718238   6.84 6.14     K0VFe-1.5CH-1.3 205 0
2 HD 18757 PM* 03 04 09.6346411530 +61 42 20.959769812   7.25   6.2   G1.5V 133 0
3 BD+66 268 PM* 03 31 17.4003449284 +66 43 49.024902152 10.48 10.57 9.91 9.30 8.87 G0 169 0
4 HD 22879 Pe* 03 40 22.0652879951 -03 13 01.124265616 7.146 7.222 6.667 6.346 6.016 G0VmF2 486 0
5 HD 25329 PM* 04 03 14.9979736362 +35 16 23.805785323 9.75 9.37 8.50 7.75 7.23 K1VbFe-2 361 0
6 HD 29907 SB* 04 38 22.3989572020 -65 24 57.594232229   10.52 9.91     F8V 97 0
7 HD 31128 PM* 04 52 09.9097086888 -27 03 50.940147636   9.55 9.14     F3/5Vw 139 0
8 HD 34328 Pe* 05 13 05.2760918664 -59 38 44.265435029   9.95 9.5     G0wA8V 130 0
9 HD 59392 Pe* 07 28 03.2212916981 -38 00 41.278587469   10.17 9.7     F0V 91 0
10 CD-52 2174 ** 07 53 21.2291826936 -52 39 13.415311116   9.90 9.49     F2V 19 0
11 HD 74000 Pe* 08 40 50.8036114756 -16 20 42.516208237 9.84 10.09 9.66     F2 265 0
12 BD-03 2525 SB* 08 59 10.1118302427 -04 01 36.525356927   10.114 9.648 9.335 9.005 F3 131 0
13 HD 84937 Pe* 09 48 56.0992891997 +13 44 39.326709913 8.49 8.68 8.32 7.97 7.70 F8Vm-5 781 0
14 HD 298986 PM* 10 17 14.8774744591 -52 29 18.694800089   10.46 10.03   9.48 F5 85 0
15 HD 97320 Pe* 11 11 00.7344001848 -65 25 37.745815656   9.769 9.269     F3V 144 0
16 HD 99383 Pe* 11 25 49.8351777360 -38 52 16.936102452   9.56 9.08     F2V 81 0
17 HD 102200 Pe* 11 45 34.2345453384 -46 03 46.386995400   9.13 8.76     F2V 111 0
18 HD 103095 Pe* 11 52 58.7673387755 +37 43 07.254113125 7.38 7.20 6.45 5.80 5.35 K1V_Fe-1.5 788 1
19 BD-04 3208 PM* 12 07 15.0721580835 -05 44 01.612773628   10.40 9.99     A7 145 0
20 BD+34 2476 PM* 13 59 09.4837849799 +33 51 39.379962282 10.25 10.44   9.7   sdF5 159 0
21 HD 122196 PM* 14 01 02.1249985961 -38 03 03.313496920   9.19 8.75     F0(V)w 117 0
22 HD 140283 Pe* 15 43 03.0971190219 -10 56 00.595693188 7.508 7.711 7.212 6.63 8.21 F9VkA5mA1 921 0
23 HD 148816 PM* 16 30 28.4586254384 +04 10 41.602836534 7.75 7.81 7.28 6.82 6.49 F7V 308 0
24 BD+18 3423 PM* 17 38 15.6094693200 +18 33 25.483804164 10.17 10.27   9.4   F6V 125 0
25 HD 193901 PM* 20 23 35.8471605389 -21 22 14.226959304 9.08 9.22 8.67 8.17 7.87 F7V 278 0

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2023.09.26-21:57:05

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