Slide 1

Radioactive elements in metal deficient stars

Volodymyr Yushchenko

Astronomical observatory, Odessa National University, Ukraine

Collaborators:
Vira Gopka Odessa, UkraineAlexander Yushchenko, Seoul, KoreaAngelina Shavrina, Kiev, Ukraine Sergey Andrievsky, Odessa, UkraineValery Kovtyukh, Odessa, UkraineSvetlana Vasileva, Odessa, Ukraine, Yakiv Pavlenko, Kiev, UkrainePapakaev Rittipruk, Seoul, KoreaYoung-Woon Kang, Seoul, Korea

Three metal poor stars:

PMMR 144 V=12.8 SMC red supergiant

RM_1 -667 V=13.1 LMC red supergiant

HD47536 V=5.2 Galaxy halo or intermediate population star, the host of 2 planets

For these three stars we will present:

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 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 6044.433 6619.943

PMMR 144 5989.045

PMMR 144, et al. 6044.433

Comparison of observed abundances with scaled Solar system r-process distribution
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 100Resolution R=20000 and 30000

RM_1-667

Spectral interval 5900 - 6700 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 methodFilled circles - spectrum synthesis method

RM_1-667, 2 thorium lines

6044.433 6112.837

RM_1-667 6044.433

RM_1-667 6112.837

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 100Resolution R=30000

HD 47536

Spectral interval 4105 - 8170 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

HD 47536 5989.045

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 decay2) Nuclear reactions in the star3) Radiative diffusion in hot stars4) Convection in cool stars5) Accretion of matter from outer space6)

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
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.
PupTeff = 6890 Klog g = 3.28

radiativeatmosphere

Am star, prototype of one of the subgroups of Scuti type variables

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 line in the spectrum of RM_1-667.
The emission component in the observed H 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 yourattention!

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