Spectral Signature of Emergent Magnetic Flux

D1 神尾 精Solar Seminar

2003.05.19

Balasubramaniam,K.S., 2001, ApJ, 557, 366.Chae, J. et al., 2000, ApJ, 528, L119.

Overview

• Spectroheliogram in Ca II K line and vector magnetic field data are studied in detail.

• Ca II K spectral line anomalies are found at the location of small-scale magnetic flux emerging through the chromosphere.

Balasubramaniam,K.S., 2001, ApJ, 557, 366.

Ca II Line Profile

• Typical line profile shows 5 reversals

• Enhanced K2 emission and red asymmetry in the impulsive phase of flares (Fang et al.1992)

• Observation in active regions suggest magnetic field influences the line profile (Martinez et al. 1990)

K3

1Å

K2V K2R

K1V K1R

λ

Transition Region Line

• Enhanced emission or broadening of UV lines are correlated with magnetic field (Dere et al. 1989)

• Broadening is caused by acceleration of plasma away from the heating site eg microflare (Linsky et al. 1995)

Observation

• 1995 Aug 5AR 7896 near disk center

• SpectorgraphRBDST at Sacramento Peak/NSO7.3Å band centered on Ca II K linePixel size: 0”.258 x 0.018Å23 min x 5 scans = 115 min

• Stokes Vector PolarimeterASP at High Altitude Observatory/NSOFe I 6301.5Å and 6302.5Å

Anomalous Profile

• 3 or 5 reversals Normal• Others Anomalous

Anomalous

Separation of additional component from the line center is -16 ～ 50 km/s. Some profiles do not show recognizable K2 or K3 components.

Broadened Profile

• 3Å is much wider than the normal width of 1Å.

• Size of anomalous or broadened features are1 ～ 2".

3Å

1"

Distribution of Anomaly

• Anomalous profiles are found at the edge of strong magnetic field regions.

Temporal Variation

• Increase of magnetic flux indicates the emergent magnetic flux.

• Anomalous profiles are found in these regions

0 +23 +46 +69 min

Spectral Images

• Anomalous profiles appear at the emergent flux regions.

• Duration of anomalous profile is longer than 2 scans or 46 min.

Discussion

• Anomalous profiles are caused by summation of several Doppler shifted profiles whose velocities range from -16 to 50 km/s.

• It suggests the existence of localized flow in the emergent flux.

• Enhanced emission of K line is most likely a response to heating.

Discussion (cont.)

• One possible explanation of heating is the shock caused by supersonic flow of plasma.

• Broadening of line profile can be interpreted as microturbulence due to magnetic reconnection, same as transition region explosive events.

• Dynamic model of multi component atmosphere is necessary to explain these line profiles.

UV/EUV Brightening

• Blinkers(γ)Profiles with enhanced wing, little broadening

• Explosive events(α)Broad spectral profiles indicate the presence of high velocity plasmas.

Chae, J. et al., 2000, ApJ, 528, L119.

Observation

• 1997 Apr 26 16:00-20:30 UT• SOHO/CDS obtained 3 scans of 244” x 240”

area.He I, O V, and Mg IX

• SOHO/SUMER is fixed so that the slit scans the area of 120” x 43” by solar rotation.Si IV

Short-lived brightening

• Blinker consists of many small scale short lived berightening events.

• Duration and size of typical unit brightening events are 2-3 min and 3”-5”.

DiscussionExplosive events

Blinkers

• Explosive events and blinkers are caused by different magnetic reconnection geometries.

• Reconnection produces bidirectional flow, which appear as broadened profiles.