The magnetic properties of G-band
bright points in a sunspot moat
C. Beck1, L.R. Bellot Rubio1,
R. Schlichenmaier1, P. Sütterlin2
1
Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany
2
Sterrekundig Instituut Utrecht, The Netherlands
Observations
VTT: polarimetry with
? TIP, 1.5µm
? POLIS, 630nm
DOT: filtergrams in
? G-band, 430.5nm
? Continuum, 431.8nm
? CaII H, 397 nm
9.8.03, NOAA 04025, θ = 27◦
Aligned data
Blue contour:
Polarization degree >1%
DOT G-Band
Polarization deg.
IR Intensity
BP mask
Red contour: G-band BP
BPs identified by
threshold in difference
image (DI) of G-band
and blue continuum.
⇒ BPs are co-spatial to
magnetic fields
Field strength: two methods
? Splitting of V lobes for
triplet of FeI 1564.8 nm
? 2-component inversion of all
profiles with magnetic/nonmag. component
⇒ BPs have fields around 1 kG
⇒ NBPs have exponential decay for probability distribution
LOS velocities
? Zero-crossing velocity
? Line core velocity
? Velocity of inversion
components
630.25 nm
1564.8 nm
Zero-crossing velocity BPs
661 m/s
404 m/s
Line core velocity BPs
22 m/s
-266 m/s
⇒ BPs show downflows
Requirements for BP
Influence on difference image (DI)
? Minimum flux:
Φ ∼ 2 · 1016 Mx
? Minimum field strength:
|B| ∼ 500 G
? Temperature inside magnetic field
∼ 1000 K higher at log τ =0...-2
⇒ DI depends only slightly on Φ, B, T
LOS Inclination vs. DI
DI(γ) = α∆R =
α·d
I0 − α · d +
sinγ
[α] = counts/length
⇒ DI depends mainly on angle between LOS and magnetic field
Summary
530 BP identified in DOT data, simultaneous inversion of IR
and visible spectral lines.
⇒ BPs exhibit downflow in the magnetic atmosphere
⇒ BPs appear if sufficient flux is concentrated to produce
evacuated and hotter flux tube/sheet
⇒ G-band BP intensity depends on angle between LOS and
magnetic field, not on |B|, temperature, or flux
Thanks a lot for your attention....