The impact of solar surface dynamo magnetic fields on the chemical abundance determination

Transcription

1 The impact of solar surface dynamo magnetic fields on the chemical abundance determination N. Shchukina 1, A. Sukhorukov 1, J. Trujillo Bueno 2 1 Main Astronomical Observatory, National Academy of Sciences, Kiev, Ukraine 2 Instituto de Astrofísica de Canarias, La Laguna, Spain IAU Symposium 305, Punta Leona, Costa Rica 30/01/ November December

2 We focus on C, N, O, Fe elements. They contribute more than 80% (by mass) to the metallicity ( Z/X ) of the Sun Z/X is the ratio of the mass fraction of heavy elements to H 30/01/2015 2

3 The solar Fe, C, N, O abundances still continue to be debated in the literature 30/01/2015 3

4 Studies based on three-dimensional (3D) hydrodynamical (HD) models have decreased the solar CNO-abundances in comparison with 1Dcase by a factor of ~ AG89 GS98 AGS05 AGSS09 ratio 1D 1D 3D 3D C N O AG89:Anders & Grevesse, 1989, Geochim. Cosmochim. Acta, 53, 197 AGS05:Asplund, Grevesse & Sauval, 2005, ASP Conf. Ser. 336, 25 AGSS09:Asplund, Grevesse, Sauval, & Scott, 2009, ARA&A, 47, /01/2015 4

5 Studies based on three-dimensional (3D) convection models have decreased the solar Fe-abundances in comparison with 1D-case by a factor of ~ AG89 GS98 ANTS00 SJT01 AGSS09 ratio 1D 1D 3D HD 3D HD 3D HD AG89:Anders & Grevesse, 1989, Geochim. Cosmochim. Acta, 53, 197) ANTS00: Asplund, Nordlund, Trampedach, & Stein, 2000,AA,359,743 SJT01: Shchukina & Trujillo Bueno, 2001, ApJ, 550, 970 AGSS09: Asplund, Grevesse, Sauval. & P.Scott, 2009, ARA&A, 47, /01/2015 5

6 What are the consequences of such a downward revision? Oxygen crisis Conflict with helioseismological data Changing of the internal opacity of the Sun. A direct impact on the structure of the outer convection zone & evolutionary behaviour of the Sun due to change of the solar energy production. 30/01/2015 6

7 Oxygen crisis 30/01/2015 7

8 The use of 3D hydrodynamical (HD) solar models for abundance analysis has resulted in a downward revision of the metallicity At recent rate of decline, the Sun will run out of oxygen in around 2015 (Ayres et al.(2006) 30/01/2015 8

9 Conflict with helioseismological data 30/01/2015 9

10 Conflict with helioseismological data The new low-metallicity Z/X results in anomalously low sound speed in the Sun. It breaks down the agreement between standard solar interior models and helioseismology 30/01/

11 Till 2008 all studies ignored the impact of the solar magnetic fields on the solar abundance detertminations Investigations on the magnetism of the quiet Sun photosphere indicate the presence of a tangled magnetic field at sub-resolution scales, with a mean field strength of the order of 100 G (Trujillo Bueno, Shchukina, Asensio Ramos, 2004, Nature, 430, 326). How large is the error of the determination of chemical abundances if we ignore the fact that the solar photosphere is significantly magnetized? 30/01/

12 Impact of the solar magnetic fields 30/01/

13 Magnetic fields can affect spectral lines both directly (via Zeeman broadening) & indirectly (via the magnetically induced changes of the thermodynamical structure of the atmosphere). 30/01/

14 The first studies aimed at quantifying the role of the solar magnetic fields on the solar abundance determinations 1D-case (HSRA model). The direct impact of magnetic field on the inferred abundances of Fe, Si, C, and O is small (Borrero, 2008, ApJ, 673, 470) 3D, MHD-case. The direct+indirect impact of magnetic field on the inferred abundance of Fe is rather large: the abundance corrections can be more than 0.1 dex (Fabbian et al. 2012, AA, 548, A35). 30/01/

15 There are two types of the MHD 3D simulations which can be used for the abundance determination: 3D magneto-convection model with a given vertical field. Convective motions modify magnetic field. NO small-scale dynamo action 3D magneto-convection model with small-scale dynamo action: convective motions amplify a week seed magnetic field. Surface variations of the modulus B (with Bz sign) at continuum level 30/01/

16 Mean field strength VS height in different 3D MHD models 30/01/

17 Temperature differences in 3D magnetoconvection simulations calculated for different values of the imposed vertical field are larger than in 3D magnetoconvection simulations with local dynamo action 3D MHD model with imposed magnetic field 3D MHD model with small-scale dynamo action Fabbian et al. (2010, 2012) Rempel (2014) 30/01/

18 We solved Stokes vector transfer equation in the 3D MHD solar model atmosphere taking in to account the Zeeman effect. We used only the emergent Stokes I profiles. The profiles were spatially averaged over all surface points of the model. We obtained abundance corrections from the fitting of calculated equivalent widths of the lines to observed ones. 30/01/

19 We used 66 Fe I clean lines unlike list of Fabbian et al. (2012) where 20% of 28 FeI lines are blended We used 26 C I, 9 N I, 11 O I clean lines The lines comprise a wide range of equivalent widths, wavelengths, excitation potentials of the lower level & effective Landé factor. Such a large number of the clean lines enables us to obtain statistically meaningful conclusions about the differential abundance effects caused by impact od the solar magnetic fields. 30/01/

20 We use MHD simulation snapshot with local dynamo action (Rempel 2014) calculated for the vertical unsigned flux density < Bz > =80 G. Stationary stage. Model < Bz > = 80 G with B=0 < Bz >=80 G B 0 < Bz >=80 G B=0 Direct effect (via Zeeman broadening) 30/01/

21 We use MHD simulation snapshots with local dynamo action (Rempel 2014) calculated for two values of the vertical unsigned flux density < Bz > =80 G and < Bz > =0.5 G (kinetic growing stage) < Bz >=80 G B 0 Virtually unmagnetized model < Bz > = 0.5 G < Bz >=0.5G Direct effect (via Zeeman broadening) AND Indirect effect (via the temperature stratification) 30/01/

22 Direct effect Indirect effect (dex) Fe I C I N I O I 30/01/

23 SUMMARY Both direct and indirect effects of magnetic fields on the abundance determination of Fe & CNO elements are negligibly small if we determine the abundances using 3D MHD model atmospheres WITH local dynamo action. 30/01/

24 Thank you for your attention 30/01/

25 Wavelength variation of calculated and observed absolute continuum intensity at the solar disk center 30/01/

26 Our conclusions are based on using only two snapshots. How spatially averaged equivalent widths might deviate from the spatially and temporally averaged values obtained using a long time-sequence of snapshots? 1. Holweger & Testerman(1975) observed temporal variations of the equivalent widths of neutral lines caused by convective motions and five minute oscillations. They found that these variations are ~0.2 må for weak lines and ~1mÅ for strong lines. The rms amplitude of the temperature variations that produce such effects in the equivalent widths is about ±20 K. 2. Standard deviation of the temperature fluctuations in the HD 3D snapshots (Asplund et al. 2000) in MHD 3D snapshots (Rempel 2014) is in agreement with this value. 3. The average abundance error due to neglect of such variations is about ~0.01 dex. 30/01/

27 Differential effects on the abundance determination: Element No. lines Direct effect <ΔA>, dex Indirect effect <ΔA>, dex Direct+Indirect effects <ΔA>, dex Fe I ± ± ± OI ± ± ± CI ± ± ± NI ± ± ± /01/

28 Direct effect for Fe I lines: <ΔA> = Indirect effect for Fe I lines: <ΔA> = Direct + Indirect effect for Fe I lines: <ΔA> = /01/

29 The use of 3D hydrodynamical (HD) solar models for abundance analysis has resulted in a downward revision of the metallicity Best helioseismological fit A low metallicity breaks down the agreement between standard solar interior models and helioseismology 30/01/