Probing magnetic fields in the solar corona using MITs MITs Magnetic-field Induced Transitions. Jon Grumer

Probing magnetic fields in the solar corona using MITs MITs Magnetic-field Induced Transitions Jon Grumer COMPAS - Division of Mathematical Physics @ Lund University jon.grumer@teorfys.lu.se ICAMDATA / Jena Germany / 21-25 September 2014

Earth-directed X-class flare An active region facing Earth erupted two weeks ago with an X 1.6 flare (largest class) - resulting in a coronal mass ejection Credit: Solar Dynamics Observatory/NASA (Sept. 10, 2014)

Earth-directed X-class flare Three days later... Credit: NASA astronaut Reid Wiseman on-board the International Space Station (twitter @astro_reid, Sept. 13, 2014)

Outline 1. Background - The Solar atmosphere, its processes and the impact on Earth - Why do we want to study coronal magnetic field strengths? - Are the fields possible to measure?

Outline 1. Background - The Solar atmosphere, its processes and the impact on Earth - Why do we want to study coronal magnetic field strengths? - Are the fields possible to measure? 2. Proposal of a new method - Using magnetic-field induced atomic transitions as direct probes

Background Background 1/24

The solar atmosphere Shows a multi-layered structure Temperature of the active corona can be as large as 2-4 MK (credit: European Space Agency) Background 2/24

Flares and CMEs The solar atmosphere generates solar activity Affects the furthest reaches of the Solar system Background 3/24

Flares and CMEs The solar atmosphere generates solar activity Affects the furthest reaches of the Solar system Much of this activity is caused by the coronal magnetic field Background 3/24

Flares and CMEs The solar atmosphere generates solar activity Affects the furthest reaches of the Solar system Much of this activity is caused by the coronal magnetic field Examples: Solar flares and the often resulting Coronal Mass Ejections (CMEs) Flare leading to a CME in May 2013 (credit: NASA) Background 3/24

Magnetic Reconnection Solar flares are believed to be triggered by magnetic reconnection Background 4/24

Magnetic Reconnection Solar flares are believed to be triggered by magnetic reconnection Magnetic energy kinetic energy Connecting and disconnecting field lines Credit: University of California Berkeley Background 4/24

The coronal magnetic field strength The coronal magnetic field drives the dynamics of the solar atmosphere Background 5/24

The coronal magnetic field strength The coronal magnetic field drives the dynamics of the solar atmosphere We therefore need to measure the strength of these fields Background 5/24

The coronal magnetic field strength The coronal magnetic field drives the dynamics of the solar atmosphere We therefore need to measure the strength of these fields Problem: No method has yet succeeded with a direct measurement Background 5/24

Why? The coronal plasma is hot and dilute Background 6/24

Why? The coronal plasma is hot and dilute Hot highly charged ions - strong internal fields B 100 1000 T Background 6/24

Why? The coronal plasma is hot and dilute Hot highly charged ions - strong internal fields B 100 1000 T Dilute weak external fields B 0.005 0.01 T Background 6/24

Why? The coronal plasma is hot and dilute Hot highly charged ions - strong internal fields B 100 1000 T Dilute weak external fields B 0.005 0.01 T Information about the corona reaches us through light emitted by these ions Background 6/24

Estimations Only estimations through indirect methods so far Background 7/24

Estimations Only estimations through indirect methods so far 1. Extrapolation of the photospheric fields using non-linear force-free field modelling [1] [1] C. J. Schrijver et al. 2008 ApJ 675 1637 Background 7/24

Estimations Only estimations through indirect methods so far 1. Extrapolation of the photospheric fields using non-linear force-free field modelling [1] 2. The photospheric field strength can be determined from the Zeeman effect - since the plasma here is...colder lower charge-state ions...denser stronger external fields [1] C. J. Schrijver et al. 2008 ApJ 675 1637 Background 7/24

Proposal of a new method Proposal of a new method 8/24

Proposal of a new method Idea: An external field can result in new exotic lines in the spectrum Magnetic-field Induced Transitions (MITs) I B 2 Proposal of a new method 9/24

Proposal of a new method Idea: An external field can result in new exotic lines in the spectrum Magnetic-field Induced Transitions (MITs) I B ( ) 2 H mag = N (1) 0 + N (1) 0 B Proposal of a new method 9/24

Proposal of a new method Idea: An external field can result in new exotic lines in the spectrum Magnetic-field Induced Transitions (MITs) I B ( ) 2 H mag = N (1) 0 + N (1) 0 B ΓMJ = n c n Γ n J n M J where c B ASF Rate: Consider the transition ΓM J Γ M J...where the final state is assumed to be pure 2s 2 1 S 0 resonance E1 decay 2s2p 1 P 1 intercombination Hmag 3 P 0,M=0 1 S 0,M=0 3 P 2 3 P 1 3 P 0 Ex) Be-like ions and the induced J = 0 J = 0 transition Proposal of a new method 9/24

Proposal of a new method Idea: An external field can result in new exotic lines in the spectrum Magnetic-field Induced Transitions (MITs) I B ( ) 2 H mag = N (1) 0 + N (1) 0 B ΓMJ = n c n Γ n J n M J where c B ASF Rate: Consider the transition ΓM J Γ M J...where the final state is assumed to be pure A MIT(B) = Cπk λ q n Γ 2 2k+1 cn J M J O π(k) q Γ nj nm J 2s 2 1 S 0 resonance E1 decay 2s2p 1 P 1 intercombination Hmag 3 P 0,M=0 1 S 0,M=0 3 P 2 3 P 1 3 P 0 Ex) Be-like ions and the induced J = 0 J = 0 transition Proposal of a new method 9/24

Proposal of a new method Idea: An external field can result in new exotic lines in the spectrum Magnetic-field Induced Transitions (MITs) I B ( ) 2 H mag = N (1) 0 + N (1) 0 B ΓMJ = n c n Γ n J n M J where c B ASF Rate: Consider the transition ΓM J Γ M J...where the final state is assumed to be pure A MIT(B) = Cπk λ q n Γ 2 2k+1 cn J M J O π(k) q Γ nj nm J = A reduced MIT B 2 2s 2 1 S 0 resonance E1 decay 2s2p 1 P 1 intercombination Hmag 3 P 0,M=0 1 S 0,M=0 Ex) Be-like ions and the induced J = 0 J = 0 transition 3 P 2 3 P 1 3 P 0 Proposal of a new method 9/24

Proposal of a new method Idea: An external field can result in new exotic lines in the spectrum Magnetic-field Induced Transitions (MITs) I B ( ) 2 H mag = N (1) 0 + N (1) 0 B ΓMJ = n c n Γ n J n M J where c B ASF Rate: Consider the transition ΓM J Γ M J...where the final state is assumed to be pure A MIT(B) = Cπk λ q n Γ 2 2k+1 cn J M J O π(k) q Γ nj nm J = A reduced MIT B 2 Magnetic-field dependent transition rate 2s 2 1 S 0 resonance E1 decay 2s2p 1 P 1 intercombination Hmag 3 P 0,M=0 1 S 0,M=0 Ex) Be-like ions and the induced J = 0 J = 0 transition 3 P 2 3 P 1 3 P 0 Proposal of a new method 9/24

But the coronal fields are tiny? MITs are slow for small external fields...remember, in the corona: B 0.005 0.01T weak lines - impossible to observe Proposal of a new method 10/24

But the coronal fields are tiny? MITs are slow for small external fields...remember, in the corona: B 0.005 0.01T weak lines - impossible to observe Dream: Find a system where the upper state is metastable and almost degenerate with a fast decaying state Proposal of a new method 10/24

Search for a suitable system Search for a suitable system 11/24

Theoretical investigations Systematic studies of isoelectronic sequences for possible strong MITs Search for a suitable system 12/24

Theoretical investigations Systematic studies of isoelectronic sequences for possible strong MITs The Cl-like sequence Search for a suitable system 12/24

The Cl-like sequence The 4 D 5/2 4 D 7/2 energy separation along Z 400 200 δe [cm -1 ] 0-200 -400 Dirac-Fock + Breit and QED + Correlation -600 18 20 22 24 26 28 Z Search for a suitable system 13/24

The degeneracy in Cl-like Fe There is an accidental degeneracy in the Cl-like sequence for Z = 26 (Fe X) - between 4 D 7/2 (M2) and 4 D 5/2 (E1) Search for a suitable system 14/24

The degeneracy in Cl-like Fe There is an accidental degeneracy in the Cl-like sequence for Z = 26 (Fe X) - between 4 D 7/2 (M2) and 4 D 5/2 (E1) Transition rate [ MIT(E1) + M2: 4 D 7/2 M J 2 P 3/2M J @ 257 Å ] Search for a suitable system 14/24

A god-given coincidence Search for a suitable system 15/24

A god-given coincidence Fe X shows strong features in the corona! Å Search for a suitable system 15/24

A god-given coincidence Fe X shows strong features in the corona! Å Ex) Its ground state M1 transition is Edléns famous coronal red line @ 6374 Å...used for temperature determination Search for a suitable system 15/24

The way forward The way forward 16/24

The way forward Main remaining task: the 4 D 5/2 4 D 7/2 energy separation - no direct measurements The way forward 17/24

The way forward Main remaining task: the 4 D 5/2 4 D 7/2 energy separation - no direct measurements We have made careful and systematic calculations (MCDHF) and confirmed the close degeneracy A direct measurement requires: 1) high enough spectral resolution 80 000 - OK! The way forward 17/24

Will this MIT be visible in an EBIT? CR-model: ratio between the MIT+M2 from 4 D 7/2 and the allowed E1 transition from 4 D 5/2 as a function of electron density and B. The way forward 18/24

Will this MIT be visible in an EBIT? CR-model: ratio between the MIT+M2 from 4 D 7/2 and the allowed E1 transition from 4 D 5/2 as a function of electron density and B. The line should be visible in the EBIT density range! The way forward 18/24

Magnetic-field dependent? The MIT+M2/E1 ratio again - but for a constant density over B The way forward 19/24

Magnetic-field dependent? The MIT+M2/E1 ratio again - but for a constant density over B Shows a strong magnetic-field dependence! The way forward 19/24

Conclusions and Outlook Conclusions and Outlook 20/24

Conclusions The origin of solar protuberances (flares) remains one of the major challenges in solar physics...related to energy contained in the photospheric magnetic fields A measurements of the magnetic field in the corona is currently inaccessible...only estimated by numerical simulations/extrapolations We propose an alternative direct method based on the intensity of Magnetic-field Induced Transitions Conclusions and Outlook 21/24

Outlook - the Fe X MIT project Accurately determine the 4 D 5/2 4 D 7/2 energy separation Conclusions and Outlook 22/24

Outlook - the Fe X MIT project Accurately determine the 4 D 5/2 4 D 7/2 energy separation With this at hand calculate the atomic response Conclusions and Outlook 22/24

Outlook - the Fe X MIT project Accurately determine the 4 D 5/2 4 D 7/2 energy separation With this at hand calculate the atomic response...and investigate feasibility of a space-based mission Conclusions and Outlook 22/24

Thank you for your attention! Thank you for your attention! 23/24

Magnetic-field induced collaborators Tomas Brage Lund University, Lund, Sweden (supervisor) Per Jönsson Malmö University, Malmö, Sweden (supervisor) Roger Hutton, Wenxian Li, Yang Yang, Yaming Zou Fudan University, Shanghai, China Tetsuya Watanabe National Astronomical Observatory of Japan (NAOJ), Tokyo, Japan Thank you for your attention! 24/24