J/A+A/606/A55 Rotational mixing in CEMP-s stars (Matrozis+, 2017)
Rotational mixing in carbon-enhanced metal-poor stars with s-process enrichment.
Matrozis E., Stancliffe R.J.
<Astron. Astrophys. 606, A55 (2017)>
=2017A&A...606A..55M 2017A&A...606A..55M (SIMBAD/NED BibCode)
ADC_Keywords: Models, evolutionary ; Stars, double and multiple ; Abundances
Keywords: stars: carbon - stars: evolution - stars: abundances -
stars: rotation - binaries: general
Abstract:
Carbon-enhanced metal-poor (CEMP) stars with s-process enrichment
(CEMP-s) are believed to be the products of mass transfer from an
asymptotic giant branch (AGB) companion, which has long since become a
white dwarf. The surface abundances of CEMP-s stars are thus commonly
assumed to reflect the nucleosynthesis output of the first AGB stars.
We have previously shown that, for this to be the case, some physical
mechanism must counter atomic diffusion (gravitational settling and
radiative levitation) in these nearly fully radiative stars, which
otherwise leads to surface abundance anomalies clearly inconsistent
with observations. Here we take into account angular momentum
accretion by these stars. We compute in detail the evolution of
typical CEMP-s stars from the zero-age main sequence, through the mass
accretion, and up the red giant branch for a wide range of specific
angular momentum ja of the accreted material, corresponding to surface
rotation velocities, vrot, between about 0.3 and 300km/s. We find
that only for ja≳1017cm2/s (vrot>20km/s, depending on mass
accreted) angular momentum accretion directly causes chemical dilution
of the accreted material. This could nevertheless be relevant to
CEMP-s stars, which are observed to rotate more slowly, if they
undergo continuous angular momentum loss akin to solar-like stars. In
models with rotation velocities characteristic of CEMP-s stars,
rotational mixing primarily serves to inhibit atomic diffusion, such
that the maximal surface abundance variations (with respect to the
composition of the accreted material) prior to first dredge-up remain
within about 0.4dex without thermohaline mixing or about 0.5-1.5dex
with thermohaline mixing. Even in models with the lowest rotation
velocities (vrot≲1km/s), rotational mixing is able to severely
inhibit atomic diffusion, compared to non-rotating models. We thus
conclude that it offers a natural solution to the problem posed by
atomic diffusion and cannot be neglected in models of CEMP-s stars.
Description:
Summary of all rotating models that reach an age of at least 10Gyr
and do not reach critical rotation after relaxation following mass
accretion. The table contains chiefly abundances at key points of
evolution: after mass accretion, after thermohaline mixing, at the
main-sequence turn-off, after first dredge-up, and near the tip of the
RGB.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 304 1683 Summary of the models with both the default and
non-standard rotational mixing parameters
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See also:
J/A+A/490/769 : Yields from extremely metal-poor stars (Campbell+, 2008)
J/A+A/557/A106 : Evolution and CNO yields of Z=10-5 stars (Gil-Pons+, 2013)
J/ApJ/833/20 : Carbon-enhanced metal-poor (CEMP) star abundances (Yoon+ 2016)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 --- fc Rotational mixing parameter fc
(0.010, 0.033, 0.100) (1)
7- 10 F4.2 --- fmu Rotational mixing parameter fmu
(0.00, 0.05, 1.00) (1)
12 I1 --- Set [1/3] Model set (2)
14- 17 F4.2 Msun M1 [0.9/1.5] Initial mass of the AGB donor
19- 22 F4.2 Msun M2i [0.6/0.8] Initial mass of the accreting
secondary
24- 28 F5.3 Msun dM [0.001/0.3] Accreted mass
30- 34 F5.3 Msun M2f [0.8/0.95] Final mass of the secondary
36- 40 E5.0 cm2/s ja [1e+15/1e+18] Specific angular momentum of
the accreted material
42- 46 F5.3 Msun Mthmix Amount of mass mixed by thermohaline mixing (3)
48- 53 F6.3 Gyr Age Age at MSTO (main-sequence turn-off)
55- 58 I4 K Teff Effective temperature at MSTO
60- 64 F5.3 [Lsun] logL Log of luminosity at MSTO
66- 70 F5.3 [cm/s2] logg Log of gravity at MSTO
72- 80 E9.3 Msun Menv Convective envelope mass at MSTO
82- 87 F6.2 km/s vrot Surface equatorial rotation velocity at MSTO
89- 94 F6.2 km/s vcrit Critical surface equatorial rotation
velocity at MSTO
96-101 F6.4 --- Xs2 Surface mass fraction of hydrogen after mass
accretion
103-108 F6.3 --- [C/H]2 Abundance [C/H] after mass accretion
110-115 F6.3 --- [N/H]2 Abundance [N/H] after mass accretion
117-122 F6.3 --- [O/H]2 Abundance [O/H] after mass accretion
124-129 F6.3 --- [Fe/H]2 Abundance [Fe/H] after mass accretion
131-136 F6.3 --- [C/Fe]2 Abundance [C/Fe] after mass accretion
138-143 F6.4 --- Xstm ?=9.9999 Surface mass fraction of hydrogen
after thermohaline mixing (3)
145-150 F6.3 --- [C/H]tm ?=-9.999 Abundance [C/H] after thermohaline
mixing (3)
152-157 F6.3 --- [N/H]tm ?=-9.999 Abundance [N/H] after thermohaline
mixing (3)
159-164 F6.3 --- [O/H]tm ?=-9.999 Abundance [O/H] after thermohaline
mixing (3)
166-171 F6.3 --- [Fe/H]tm ?=-9.999 Abundance [Fe/H] after thermohaline
mixing (3)
173-178 F6.3 --- [C/Fe]tm ?=-9.999 Abundance [C/Fe] after thermohaline
mixing (3)
180-185 F6.4 --- Xs4 Surface mass fraction of hydrogen at MSTO
187-192 F6.3 --- [C/H]4 Abundance [C/H] at MSTO
194-199 F6.3 --- [N/H]4 Abundance [N/H] at MSTO
201-206 F6.3 --- [O/H]4 Abundance [O/H] at MSTO
208-213 F6.3 --- [Fe/H]4 Abundance [Fe/H] at MSTO
215-220 F6.3 --- [C/Fe]4 Abundance [C/Fe] at MSTO
222-227 F6.4 --- Xs6 ?=9.999 Surface mass fraction of hydrogen at
the end of FDU (4)
229-234 F6.3 --- [C/H]6 ?=-9.999 Abundance [C/H] at the end of FDU (4)
236-241 F6.3 --- [N/H]6 ?=-9.999 Abundance [N/H] at the end of FDU (4)
243-248 F6.3 --- [O/H]6 ?=-9.999 Abundance [O/H] at the end of FDU (4)
250-255 F6.3 --- [Fe/H]6 ?=-9.999 Abundance [Fe/H] at the end of FDU (4)
257-262 F6.3 --- [C/Fe]6 ?=-9.999 Abundance [C/Fe] at the end of FDU (4)
264-269 F6.4 --- Xsf ?=9.9999 Surface mass fraction of hydrogen
near the tip of the RGB (4)
271-276 F6.3 --- [C/H]f ?=-9.999 Abundance [C/H] near the tip of the
RGB (4)
278-283 F6.3 --- [N/H]f ?=-9.999 Abundance [N/H] near the tip of the
RGB (4)
285-290 F6.3 --- [O/H]f ?=-9.999 Abundance [O/H] near the tip of the
RGB (4)
292-297 F6.3 --- [Fe/H]f ?=-9.999 Abundance [Fe/H] near the tip of the
RGB (4)
299-304 F6.3 --- [C/Fe]f ?=-9.999 Abundance [C/Fe] near the tip of the
RGB (4)
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Note (1): The default rotational mixing parameters are fc=0.033 and
fmu=0.05. The non-standard models can have fc=0.01 or 0.10,
or fmu=0.0 or 1.0 (see Sect. 4.3)
Note (2): Model set number as follows:
1 = rotational mixing only
2 = rotational mixing and atomic diffusion
3 = rotational mixing, atomic diffusion, and thermohaline mixing
Note (3): Applies only to models with thermohaline mixing (set ≡ 3)
Note (4): A missing entry indicates that the model reached an age of 16Gyr
prior to reaching this stage.
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Acknowledgements:
Elvijs Matrozis, elvijs(at)astro.uni-bonn.de
(End) Patricia Vannier [CDS] 28-Jul-2017