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Radioactive elements
in metal deficient stars
Volodymyr Yushchenko
Astronomical observatory, Odessa National University, Ukraine
Collaborators:
●
Vira Gopka
Odessa,
Ukraine
●
Alexander Yushchenko, Seoul,
Korea
●
Angelina Shavrina,
Kiev,
Ukraine
●
Sergey Andrievsky,
Odessa,
Ukraine
●
Valery Kovtyukh,
Odessa,
Ukraine
●
Svetlana Vasil’eva,
Odessa,
Ukraine,
●
Yakiv Pavlenko,
Kiev,
Ukraine
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Papakaev Rittipruk,
Seoul,
Korea
●
Young-Woon Kang,
Seoul,
Korea
Three metal poor stars:
PMMR 144
V=12.8
SMC red supergiant
RM_1 -667
V=13.1
LMC
HD47536
V=5.2
Galaxy halo or
intermediate population star,
the host of 2 planets
red supergiant
For these three stars we will present:
1) Chemical composition
2) Thorium lines
3) Approximation of abundance pattern by scaled
Solar system r-process distribution
The possibility of age determination for these stars
will be discussed.
PMMR – 144 SMC
Spectra were obtained at 3.6 meter ESO
telescope (La Silla, Chile)
Observed by Hill, V.
S/N is near 100
Resolution R=20000 and 30000
PMMR 144
●
Spectral interval
5790 - 6835 Å
●
Effective temperature Teff = 4100 K
• log g = -0.7
• Vmicro = 4 km/s
The atmosphere model was calculated by R. Luck
PMMR 144, 3 thorium lines
5989.045 Å
6044.433 Å
6619.943 Å
PMMR 144 5989.045 Å
PMMR 144, et al. 6044.433 Å
Comparison of observed abundances with
scaled Solar system r-process distribution
ошибка±0.25dex
RM_1-667 LMC
●
Spectra were obtained at 3.6 meter ESO
telescope (La Silla, Chile)
●
Observed by Hill, V.
●
S/N is near 100
●
Resolution R=20000 and 30000
RM_1-667
Spectral interval
5900 - 6700 Å
Effective temperature Teff = 3750 K
log g = -1.5
Vmicro = 2.4 km/s
The atmosphere model was calculated by Ya. Pavlenko
Open circles – model atmospheres method
Filled circles - spectrum synthesis method
RM_1-667, 2 thorium lines
6044.433 Å
6112.837 Å
RM_1-667 6044.433 Å
Comparison of observed abundances with
scaled Solar system r-process distribution
HD 47536 Galaxy
●
Spectra were obtained at 1.5 meter CTIO
telescope (Chile)
●
Observed by Rittipruk, P.
●
S/N is near 100
●
Resolution R=30000
HD 47536
Spectral interval
4105 - 8170 Å
Effective temperature Teff = 4400 K
log g = +1.8
Vmicro = 1.5 km/s
Castelli & Kurucz (2003) atmosphere model was used
HD 47536,
1 thorium line
5989.045 Å
HD 47536
5989.045 Å
Comparison of observed abundances with
scaled Solar system r-process distribution
How to find the age ?
The necessary conditions to determine the reliable age are:
1) the information about the initial abundance ratio, usually it is
taken from the standard cosmology; that is why it is necessary
to suppose the validity of this theory;
2) the universality of r-process, more exactly it is the hypothesis
that the abundance ratios in the products of different supernova
explosions are equal;
3) the changes of abundance ratios are mainly due to natural
radioactive decay; the influence of other factors should be
neglected or estimated.
1) Initial abundance ratio
We will not discuss this problem here
2) The universality of r-process
One of the latest investigations of possible
nonuniversality of r-process was made by
Ren, J., Chriestlib, N., & Zhao, G.
2012, A&A, 537, A118.
Result: the thorium abundances span a wide range
of about 4.0 dex, and scatter exists in the distribution
of log (Th/Eu) ratios for lower metallicity stars,
supporting previous studies suggesting the
r-process is not universal.
3) The changes of abundance ratios
are mainly due to natural
radioactive decay
It seems to be not doubted before.
The abundance patterns of
PMMR 144, RM_1-667, and HD47536
allow us to discuss this hypothesis.
What are the possible ways to change the
abundance ratios in stellar photospheres ?
●
1) Natural radioactive decay
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2) Nuclear reactions in the star
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3) Radiative diffusion in hot stars
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4) Convection in cool stars
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5) Accretion of matter from outer space
●
6) … … …
Let us discuss the fifth case
Accretion of matter from outer space
1) The accretion of interstellar gas
(Greenstein 1949, Bohm-Vitense 2006)
2) The mass transfer from binary companion
(Fowler et al., 1965, Proffitt & Michaud 1989)
3) The accretion of rocky material, asteroids & planets
(Drobyshevski 1975, Cowley 1977)
4) The dust-gas separation mechanism
(Venn & Lambert 1990, 2008)
5) The accretion of accelerated particles
(Goriely 2007)
6)
… … …
Let us discuss the
first
case only
Greenstein 1949, ApJ, 109, 121
Yushchenko A. et al. 2013, AJ, in press
ρ Pup
Teff = 6890 K
log g = 3.28
radiative
atmosphere
Am star,
prototype of one
of the subgroups of
δ Scuti type variables
Charge-exchange reactions:
High energy protons or helium ions from interstellar environment collide the resonant atoms
(the atoms with second ionization potentials close to 13.6 & 24.6 eV) in stellar atmosphere and steal
an electron from them.
The resonance energies are the ionization potentials of hydrogen and helium (13.6 & 24.6 eV).
The newly ionized atoms fly away at high velocities.
The direction of this fly coincide with the movement of the ionizing particle.
That is why part of the ionized atoms can leave the star, producing the deficiency
of corresponding chemical element.
2013, Kang Y.-W, Yushchenko A. et al. AJ, 145, 167
LX Per – eclipsing binary star,
RS Canum Venoticorum type - strong circumstellar envelope, gaseous streams,
strong accretion in the system, the source of X-rays
Teff (A) = 6225 K, log g (A) = 3.92
Teff (B) = 5225 K, log g (B) = 4.42
The components of LX Per have convective atmospheres with strong accretion.
2013, Kang Y.-W, Yushchenko A. et al. AJ, 145, 167
Emissions of calcium in the atmosphere of LX Per B
The charge-exchange reactions change the
abundances in the atmospheres of components
of LX Per
faster
than the convection motions return the
chemical composition to solar one.
PMMR 144
Most of the elements with second ionization potentials close to 13.6 eV
exhibit lower abundances than the other elements.
It can be the sign of charge-exchange reactions in the atmosphere of PMMR 144
It can be the result of higher density of interstellar medium in SMC
RM_1-667
The deficiency of elements with second ionization potentials
close to 13.6 eV can be a sign of accretion
Observed and modeled Нα line in the spectrum of RM_1-667.
The emission component in the observed Hα profile is fitted with the
temperature inversion in the upper layers of stellar atmosphere.
The emission also can be a sign of higher density of interstellar medium.
It supports the possibility of charge-exchange reactions in this star.
HD 47536, the host of 2 planets
The mass of the first planet is > 5 mass of Jupiter, the orbital period is 430 days,
the closest distance between the planet and the host star can be as small
as 1.3 astronomical units or 13 radiuses of the host star.
The possibility of accretion is higher in planetary system.
The relative underabundances of elements with second ionization potentials
close to 13.6 eV can be sign of accretion (charge-exchange reactions).
CONCLUSION
The accretion phenomena in the atmospheres of
PMMR 144, RM_1-667, and HD47536
change the surface abundances.
For these stars it is impossible to suppose that the changes of
abundance ratios are mainly due to natural radioactive decay.
The attempts to estimate the age of these stars using Th/Eu ratios will
lead to wrong results.
It is necessary to discuss the possibility of accretion events even for
the oldest stars, as these stars crossed the plane of Galaxy and
their surface abundances have been influenced by accretion of
interstellar gas.
Thank for your
attention!