2014A&A...568A..29C


Query : 2014A&A...568A..29C

2014A&A...568A..29C - Astronomy and Astrophysics, volume 568A, 29-29 (2014/8-1)

Clues on the Galactic evolution of sulphur from star clusters.

CAFFAU E., MONACO L., SPITE M., BONIFACIO P., CARRARO G., LUDWIG H.-G., VILLANOVA S., BELETSKY Y. and SBORDONE L.

Abstract (from CDS):

The abundances of α-elements are a powerful diagnostic of the star formation history and chemical evolution of a galaxy. Sulphur, being moderately volatile, can be reliably measured in the interstellar medium (ISM) of damped Ly-α galaxies and extragalactic HII regions. Measurements in stars of different metallicity in our Galaxy can then be readily compared to the abundances in external galaxies. Such a comparison is not possible for Si or Ca that suffer depletion onto dust in the ISM. Furthermore, studying sulphur is interesting because it probes nucleosynthetic conditions that are very different from those of O or Mg. In this context measurements in star clusters are a reliable tracers of the Galactic evolution of sulphur. The aim of this paper is to determine sulphur abundances in several Galactic clusters that span a metallicity range -1.5<[Fe/H]<0.0. We use a standard abundance analysis, based on 1D model atmospheres in local thermodynamical equilibrium (LTE) and literature corrections for non-LTE (NLTE), as well as 3D corrections based on hydrodynamical model atmospheres, to derive sulphur abundances in a sample of stars in the globular cluster M4, and the open clusters Trumpler5, NGC2477, and NGC5822. We find <A(S)>NLTE=6.11±0.04 for M4, <A(S)>NLTE=7.17±0.02 for NGC2477, and <A(S)>NLTE=7.13±0.06 for NGC5822. For the only star studied in Trumpler 5 we find A(S)NLTE=6.43±0.03 and A(S)LTE=6.94±0.05. Our measurements show that, by and large, the S abundances in Galactic clusters trace reliably those in field stars. The only possible exception is Trumpler 5, for which the NLTE sulphur abundance implies an [S/Fe] ratio lower by roughly 0.4dex than observed in field stars of comparable metallicity, even though its LTE sulphur abundance is in line with abundances of field stars. Moreover the LTE sulphur abundance is consistent only with the abundance of another α-element, Mg, in the same star, while the low NLTE value is consistent with Si and Ca. We believe that further investigation of departures from LTE is necessary, as well as observation of other SI lines in this star and in other stars of the same cluster, before one can conclude that the sulphur abundance in Trumpler5 is indeed 0.4dex lower than in field stars of comparable metallicity. The S abundances in our sample of stars in clusters imply that the clusters are chemically homogeneous for S within 0.05dex.

Abstract Copyright:

Journal keyword(s): stars: abundances - Galaxy: abundances - globular clusters: individual: M 4 - Galaxy: halo

CDS comments: Table 2 stars in M4 are [MVB2012], star in Trumpler 5 is Cl* Trumpler 5 K 3-3416, stars in NGC 5822 are respectively CPD-53 6232 (2397), CPD-53 6243 (13292), CPD-53 6231 (16450), Cl* NGC 5822 MMU 102 (18897) , star in NGC 2477 are Cl* NGC 2477 MMU NNNN.

Simbad objects: 33

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Number of rows : 33
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20     4.09     ~ 3889 0
2 Cl Trumpler 5 OpC 06 36 30.2 +09 27 54           ~ 120 0
3 Cl* Trumpler 5 K 3-3416 HB* 06 36 40.2001267056 +09 29 47.779130328   16.566 15.042     ~ 17 0
4 Cl Berkeley 29 OpC 06 53 04.2 +16 55 39   14.3       ~ 174 0
5 NAME Saurer A Cluster OpC 07 20.9 +01 48           ~ 64 0
6 Cl* NGC 2477 MMU 7273 RB? 07 51 47.4746570160 -38 32 36.246092496   13.568 12.338     ~ 16 0
7 Cl* NGC 2477 MMU 7266 RB? 07 51 49.2109483032 -38 32 08.549475000   13.48 12.290     ~ 17 0
8 Cl* NGC 2477 MMU 5043 RB? 07 52 09.7076603712 -38 35 53.857089708   13.35 12.171     ~ 6 0
9 NGC 2477 OpC 07 52 11.0 -38 32 13   6.64 5.8     ~ 289 0
10 Cl* NGC 2477 MMU 5076 RB? 07 52 14.7652374960 -38 37 45.165151704   13.61 12.392     ~ 13 0
11 Cl* NGC 2477 MMU 8216 RB? 07 52 15.5249031888 -38 27 26.377836444   13.541 12.250     ~ 14 0
12 NGC 2477 902 * 07 52 21.0641141736 -38 34 37.925246388   13.351 12.153     ~ 17 0
13 Cl* NGC 2477 KVI 1492 RB? 07 52 36.5274077976 -38 37 54.357311496   13.428 12.231   10.995 ~ 22 0
14 NGC 5822 87 * 15 03 49.4167331160 -54 20 10.602411612 12.61 11.88 10.84 10.285   ~ 28 0
15 NGC 5822 OpC 15 04 12.2 -54 21 58           ~ 207 0
16 CD-53 5838 SB* 15 04 14.1717628224 -54 25 47.306503992 12.10 11.35 10.29 9.725   ~ 21 0
17 CPD-53 6232 * 15 04 17.0648038392 -54 28 23.401661916 12.26 11.47 10.46     ~ 14 0
18 CPD-53 6243 * 15 04 39.4239264528 -54 21 04.106654280 12.20 11.43 10.37 9.820   ~ 28 0
19 2MASS J16231181-2632045 * 16 23 11.8124140488 -26 32 04.582509360   18.789 17.807     ~ 3 0
20 2MASS J16231564-2626467 * 16 23 15.6429156576 -26 26 46.912320204   17.422 16.526     ~ 3 0
21 [MVB2012] 30303 **? 16 23 16.89 -26 34 55.0   17.399 16.499     ~ 4 0
22 2MASS J16232371-2637422 * 16 23 23.7124411152 -26 37 42.319847820   18.041 17.238     ~ 6 0
23 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1841 0
24 [MVB2012] 58195 * 16 23 38.280 -26 26 18.90   17.649 16.801     ~ 2 0
25 [BH2018] J245.940875-26.392667 * 16 23 45.810 -26 23 33.60           ~ 2 0
26 2MASS J16234987-2630533 * 16 23 49.8777113184 -26 30 53.317514376   17.320 16.465     ~ 3 0
27 [MPB2015] 57462 * 16 23 54.0220598664 -26 32 50.931800628   17.633 16.816     ~ 2 0
28 2MASS J16240464-2627346 * 16 24 04.6406729112 -26 27 34.635348288   17.379 16.606     ~ 3 0
29 2MASS J16241693-2633187 * 16 24 16.9411409400 -26 33 18.881335548   17.390 16.581     ~ 3 0
30 NGC 6397 GlC 17 40 42.09 -53 40 27.6     5.17     ~ 1965 0
31 NAME SDG G 18 55 03.1 -30 28 42   4.5 3.6     ~ 2164 2
32 NGC 6752 GlC 19 10 52.11 -59 59 04.4           ~ 1988 0
33 Cl Terzan 7 GlC 19 17 43.92 -34 39 27.8           ~ 426 0

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