NLTE abundance of Sr and Ba in the early Galaxy

Andrievsky S.M., Korotin S.A. et al.

Spectral material

• 35 giants

• 19 turn-off stars

• UVES VLT

• R = 45000, S/N is about 100

Most of the stars with [Fe/H] less than -3 dex

Parameters were detrmined by:

Cayrel et al. 2004, Bonifacio et al. 2007, 2009

Atomic models: Sr• Sr I – 24 levels for particle num. conservation • Sr II – 44 levels, n<13, l<5• Sr III – ground level• 4d2D and 5p2P0 – fine structure• 330 b-b transitions• accurate rad. photoionizations are for s, p, d levels • H-like approx. – for f and g levels• accurate coll. exit. rates are for 5s2S and 5p2P0, 5d2D terms• approx. coll. exit. rates are for other levels• coll. exit. rates for forbidden trans. are with a factor 1 • coll. ionizations by electrons: yes • coll. with H atoms: yes (emp. scaling coefficient is 0.01)

Sr atomic model: Grotrian diagram

Sr II line parameters lambda, Å f log γrad log γVW

------------------------------------------------------ 4077.7090 7.063E-1 8.130 -7.70 4215.5190 3.303E-1 8.100 -7.70 10036.6530 1.219E-2 7.340 -7.63 10327.3110 7.393E-2 7.320 -7.63 10914.8870 5.754E-2 7.270 -7.63

Test calculations

Program star profile fitting

NLTE corrections

Sr abundance vs. Fe abundance

Atomic models: Ba• Ba I – 31 level for particle num. conservation • Ba II–28 levels, n<12, l<5 (74 for particle num. conservation)• Ba III – ground level• 5d2D and 6p2P0 – fine structure• 91 b-b transitions• accurate rad. photoionizations are for s, p, d, f levels • H-like approx. – for g levels• accurate coll. exit. rates are for 6s2S and 6p2P0, 5d2D terms• approx. coll. exit. rates are for other levels• coll. exit. rates for forbidden trans. are with a factor 1 • coll. ionizations by electrons: yes • coll. with H atoms: yes (emp. scaling coefficient is 0.1)

Ba atomic model: Grotrian diagram

Ba II line parameters lambda, Å d(mÅ) f log γrad log γVW

------------------------------------------------------ 4554.03 0 0.364 8.20 -7.60

18 0.227 -34 0.137 5853.70 - 0.025 8.20 -7.19 6496.90 0 0.086 8.10 -7.47 -4 0.012 9 0.007

Test calculations

Program star profile fitting

NLTE corrections

NLTE corrections

Ba abundance vs. Fe abundance

Conclusions

• We obtained the most reliable data on Sr and Ba abundance in the early Galaxy (age≈1 Gyr).

• The Sr/Ba ratio is always higher than the main r-process ratio ([Sr/Br] = -0.31).

• Three-component model is the most promising one for explaining the [Sr/Ba] ratio behaviour:

• First HNe produce lighter elements including Fe.• Then high-mass SNe produce Sr (but not Ba).• After that low-mass SNe produce both Sr and Ba.• This study was partially supported by SCOPES

grant. Thanks!