1. Radioactive elements in metal deficient stars
Volodymyr Yushchenko
Astronomical observatory, Odessa National University, Ukraine

2. Vira Gopka Odessa, Ukraine Alexander Yushchenko, Seoul, Korea
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
Papakaev Rittipruk, Seoul, Korea
Young-Woon Kang, Seoul, Korea

3. PMMR 144 V=12.8 SMC red supergiant
Three metal poor stars:
PMMR V= SMC red supergiant
RM_ V= LMC red supergiant
HD V= Galaxy halo or
intermediate population star,
the host of 2 planets

4. 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.

5. PMMR – SMC
Spectra were obtained at meter ESO telescope (La Silla, Chile)
Observed by Hill, V.
S/N is near 100
Resolution R=20000 and 30000

6. 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

7. 7

8. PMMR 144, 3 thorium lines
Å Å Å 8

9. PMMR Å

10. PMMR 144, et al Å

11. Comparison of observed abundances with scaled Solar system r-process distribution
ошибка±0.25dex 11

12. RM_ LMC
Spectra were obtained at meter ESO telescope (La Silla, Chile)
Observed by Hill, V.
S/N is near 100
Resolution R=20000 and 30000

13. RM_1-667
Spectral interval Å
Effective temperature Teff = 3750 K
log g = -1.5
Vmicro = km/s
The atmosphere model was calculated by Ya. Pavlenko

14. Open circles – model atmospheres method
Filled circles - spectrum synthesis method

15. RM_1-667, 2 thorium lines
Å Å 15

16. RM_ Å

17. Comparison of observed abundances with scaled Solar system r-process distribution

18. HD Galaxy
Spectra were obtained at meter CTIO telescope (Chile)
Observed by Rittipruk, P.
S/N is near 100
Resolution R=30000

19. HD 47536
Spectral interval Å
Effective temperature Teff = 4400 K
log g = +1.8
Vmicro = km/s
Castelli & Kurucz (2003) atmosphere model was used

21. HD 47536, 1 thorium line Å 22

22. HD Å

23. Comparison of observed abundances with scaled Solar system r-process distribution

24. 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.

25. 1) Initial abundance ratio
We will not discuss this problem here

26. 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.

27. 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.

28. What are the possible ways to change the abundance ratios in stellar photospheres ?
1) Natural radioactive decay
2) Nuclear reactions in the star
3) Radiative diffusion in hot stars
4) Convection in cool stars
5) Accretion of matter from outer space
6) … … …
Let us discuss the fifth case

29. 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

30. Greenstein 1949, ApJ, 109, 121

31. 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 & eV) in stellar atmosphere and steal an electron from them.
The resonance energies are the ionization potentials of hydrogen and helium ( & 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.

32. 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) = Teff (B) = 5225 K, log g (B) = 4.42
The components of LX Per have convective atmospheres with strong accretion.

33. 2013, Kang Y.-W, Yushchenko A. et al. AJ, 145, 167
Emissions of calcium in the atmosphere of LX Per B

34. 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.

35. PMMR 144
Most of the elements with second ionization potentials close to 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

36. RM_1-667 The deficiency of elements with second ionization potentials
close to 13.6 eV can be a sign of accretion

37. 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.

38. 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).

39. 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.

40. Thank for your attention!