J/A+A/618/A132 Pre-main sequence stars evolutionary models. II (Kunitomo+, 2018)
Revisiting the pre-main-sequence evolution of stars.
II. Consequences of planet formation on stellar surface composition.
Kunitomo M., Guillot T., Ida S., Takeuchi T.
<Astron. Astrophys. 618, A132 (2018)>
=2018A&A...618A.132K 2018A&A...618A.132K (SIMBAD/NED BibCode)
ADC_Keywords: Models, evolutionary ; Abundances ; Stars, pre-main sequence
Keywords: stars: formation - stars: pre-main sequence -
accretion, accretion disks - stars: evolution - stars: interiors -
stars: abundances
Abstract:
We want to investigate how planet formation is imprinted on stellar
surface composition using up-to-date stellar evolution models.
We simulate the evolution of pre-main-sequence stars as a function of
the efficiency of heat injection during accretion, the deuterium mass
fraction, and the stellar mass, M*. For simplicity, we assume that
planet formation leads to the late accretion of zero-metallicity gas,
diluting the surface stellar composition as a function of the mass of
the stellar outer convective zone. We estimate that in the solar
system, between 97 and 168 Mearth of condensates formed planets or
were ejected from the system. We adopt 150
Mearth(M*/Msun)(Z/Zsun) as an uncertain but plausible
estimate of the mass of heavy elements that is not accreted by stars
with giant planets, including our Sun. By combining our stellar
evolution models to these estimates, we evaluate the consequences of
planet formation on stellar surface compositions.
We show that after the first ∼0.1 million years (Myr) during which
stellar structure can differ widely from the usually assumed
fully-convective structure, the evolution of the convective zone
follows classical pre-main-sequence evolutionary tracks within a
factor of two in age. We find that planet formation should lead to a
scatter in stellar surface composition that is larger for high-mass
stars than for low-mass stars. We predict a spread in [Fe/H] of
approximately 0.05dex for stars of temperature Teff∼6500K, to 0.02dex
for Teff∼5500K, marginally compatible with differences in
metallicities observed in some binary stars with planets. Stars with
Teff≥7000K may show much larger [Fe/H] deficits, by 0.6dex or more,
in the presence of efficient planet formation, compatible with the
existence of refractory-poor lambda Boo stars. We also find that
planet formation may explain the lack of refractory elements seen in
the Sun as compared to solar twins, but only if the ice-to-rock ratio
in the solar-system planets is less than ∼0.4 and planet formation
began less than ∼1.3Myr after the beginning of the formation of the
Sun.
Description:
We use the MESA stellar evolution code with various sets of conditions
to simulate the evolution of young stellar objects. In particular, we
account for the (unknown) efficiency of accretion in burying
gravitational energy into the protostar through a parameter, xi.
Another parameter, mke, expresses the region where the accretion heat
is redistributed. We also vary the mass fraction of deuterium, XD.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 119 4200 *Stellar evolutionary models for 77 models
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Note on tablec1.dat: Settings:
Initial mass: 0.01M☉
Mass accretion rate: See Sect. 3.2
X=0.70048186, Y=0.27985523, Z=0.01966291
alphaMLT=1.81743512 (Mixing-length parameter)
fov=0.01026355 (Overshooting parameter)
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See also:
J/A+A/599/A49 : Pre-main sequence stars evolutionary models (Kunitomo+, 2017)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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2- 4 F3.1 --- xi Efficiency of accretion heat (See Eq. 2) (1)
7- 8 I2 10-6 XD Deuterium content in parts per million (1)
11- 14 F4.1 --- mke Distribution of acc. heat (See Sect. 3.1) (1)
17- 19 F3.1 Msun Mfinal Final mass (1)
23- 29 E7.2 yr Age Stellar age
34- 44 E11.6 Msun Mstar Stellar mass
49- 59 E11.6 Msun MCZ Mass of stellar surface convective zone
63- 74 E12.6 Msun MCZeff ?=-1 Effective convective zone mass (See Eq. 6)
79- 89 E11.6 Msun Rstar Stellar radius
94-104 E11.6 Msun Lstar Stellar luminosity
109-119 E11.6 K Teff Stellar effective temperature
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Note (1): Models presented:
xi = 0.5, XD = 28, mke = -1, Mfinal = 0.5-1.5
xi = 0.1, XD = 28, mke = -1, Mfinal = 0.5-1.5
xi = 0, XD = 28, mke = -1, Mfinal = 0.5-1.5
xi = 0.1, XD = 28, mke = 0.1, Mfinal = 0.5-1.5
xi = 0.5, XD = 20, mke = -1, Mfinal = 0.5-1.5
xi = 0.1, XD = 20, mke = -1, Mfinal = 0.5-1.5
xi = 0, XD = 20, mke = -1, Mfinal = 0.5-1.5
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Acknowledgements:
Masanobu Kunitomo, kunitomo(at)eps.s.u-tokyo.ac.jp
References:
Kunitomo et al., Paper I 2017A&A...599A..49K 2017A&A...599A..49K, Cat. J/A+A/599/A49
(End) Patricia Vannier [CDS] 20-Aug-2018