1. 1 Arcturus Exposed: Non-LTE Analysis of Carbon and Oxygen Abundances in Arcturus By: Jayme Derrah Supervisor: Dr. Ian Short AUPAC 2007

2. 2 Chemical Abundances of Stars Why do we care? Why do we care? Important for understanding stellar evolution Important for understanding stellar evolution When stars die, elements are released into space that form other stars and planets When stars die, elements are released into space that form other stars and planets

3. 3 Carbon, Oxygen and the Sun Why Carbon and Oxygen? Why Carbon and Oxygen? Oxygen is the 3 rd most common element in the universe Oxygen is the 3 rd most common element in the universe CNO cycle in stars produces C and O CNO cycle in stars produces C and O Recent studies by Asplund et al. revealed that revisions need to be made in the C and O abundances in the sun Recent studies by Asplund et al. revealed that revisions need to be made in the C and O abundances in the sun Used a realistic 3-D code that had never been done before Used a realistic 3-D code that had never been done before

4. 4 Red Giants Stage in stellar evolution after leaving the main sequence Stage in stellar evolution after leaving the main sequence Stars’ outer layers expand and cool Stars’ outer layers expand and cool Are big, bright objects that can be seen at large distances Are big, bright objects that can be seen at large distances This makes it easier to take the spectrum This makes it easier to take the spectrum

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8. 8 Arcturus: Standard Red Giant General Information: Spectral Type: K1.5III Radius: ~15.9 R sol T eff : 4300 K Surface Gravity: ~1.5 Metallicity: -0.3 to -0.7 (20- 50% of the sun)

9. 9 Arcturus: Observed Spectrum Observations done at Kitt Peak Observatory, using the Coude Feed telescope. Observations done at Kitt Peak Observatory, using the Coude Feed telescope. Hinkle, Wallace, Valenti, Harmer: Visible and Near Infrared Atlas of the Arcturus Spectrum 3727-9300 A; 2003, ASP Hinkle, Wallace, Valenti, Harmer: Visible and Near Infrared Atlas of the Arcturus Spectrum 3727-9300 A; 2003, ASP

10. 10 Arcturus: Observed Spectrum-2

11. 11 Stellar Spectroscopy Two methods used: Two methods used: Line Profile Fitting Line Profile Fitting Qualitative measure of line strength Qualitative measure of line strength Equivalent Width Measurements Equivalent Width Measurements Quantitative measure of line strength Quantitative measure of line strength Width of a rectangle centred on a spectral line that has the same area as the line Width of a rectangle centred on a spectral line that has the same area as the line

12. 12 PHOENIX Developed By: Hauschildt, P.H.; Baron, E. ; Allard, F. Developed By: Hauschildt, P.H.; Baron, E. ; Allard, F. PHOENIX is a state of the art stellar atmosphere code PHOENIX is a state of the art stellar atmosphere code Can calculate the spectra for all types of stars Can calculate the spectra for all types of stars Simultaneously treats most elements in non-LTE Simultaneously treats most elements in non-LTE Many more in LTE Many more in LTE

13. 13 LTE vs. Non-LTE: LTE Local Thermodynamic Equilibrium (LTE): Local Thermodynamic Equilibrium (LTE): Only valid in a perfect blackbody environment Only valid in a perfect blackbody environment Boltzmann and Saha relations can be used Boltzmann and Saha relations can be used In reality, radiation leaks into space, so LTE is invalid. In reality, radiation leaks into space, so LTE is invalid. Crude approximation to reality Crude approximation to reality So why use LTE? So why use LTE?

14. 14 LTE vs. Non-LTE: LTE Local Thermodynamic Equilibrium (LTE): Local Thermodynamic Equilibrium (LTE): Only valid in a perfect blackbody environment Only valid in a perfect blackbody environment Boltzmann and Saha relations can be used Boltzmann and Saha relations can be used In reality, radiation leaks into space, so LTE is invalid. In reality, radiation leaks into space, so LTE is invalid. Crude approximation to reality Crude approximation to reality So why use LTE? So why use LTE? It’s easy! It’s easy!

15. 15 LTE vs. Non-LTE: Non-LTE Non- Local Thermodynamic Equilibrium (Non-LTE): Non- Local Thermodynamic Equilibrium (Non-LTE): Must solve coupled 1 st order rate equations for the atomic transitions to get level populations Must solve coupled 1 st order rate equations for the atomic transitions to get level populations Much more realistic approximation Much more realistic approximation

16. 16 LTE vs. NLTE: Spectra

17. 17  - Enhanced Model Scaled Solar models scaled down for elements where Z>2. Why? – Easy Scaled Solar models scaled down for elements where Z>2. Why? – Easy However, all elements are made at different rates throughout galactic chemical evolution However, all elements are made at different rates throughout galactic chemical evolution  -capture makes even numbered elements  -capture makes even numbered elements Old metal poor stars have more even numbered elements than odd, relative to the Sun Old metal poor stars have more even numbered elements than odd, relative to the Sun More realistic model for Arcturus More realistic model for Arcturus

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19. 19 Results: Equivalent Widths (mA)

20. 20 Results: Equivalent Widths 2 Legend Legend x = Observed values x = Observed values y = LTE values y = LTE values z = NLTE values z = NLTE values v = NLTE- alpha enhanced values v = NLTE- alpha enhanced values

21. 21 Problems Only one Carbon line Only one Carbon line Telluric absorption in IR Telluric absorption in IR Line blending in IR Line blending in IR Two Oxygen lines could not be used Two Oxygen lines could not be used Too weak Too weak Equivalent width could not be determined (blending in observed spectrum) Equivalent width could not be determined (blending in observed spectrum)

22. 22 Conclusions Are these models accurate for Arcturus? Are these models accurate for Arcturus?

23. 23 Conclusions Are these models accurate for Arcturus? Are these models accurate for Arcturus? Nope  Nope 

24. 24 Conclusions Are these models accurate for Arcturus? Are these models accurate for Arcturus? Nope  Nope  Further revisions need to be made to current models to accurately model Arcturus Further revisions need to be made to current models to accurately model Arcturus C and O abundances need to be revised C and O abundances need to be revised Oxygen abundances depend on which line- shouldn’t be true Oxygen abundances depend on which line- shouldn’t be true Models unrealistic in other ways (i.e. 3-D effects, starspots, etc.) Models unrealistic in other ways (i.e. 3-D effects, starspots, etc.)

25. 25 Acknowledgements Dr. Ian Short Joel Tanner Questions ?