Bibcode
Mikurda, K.; Beck, C.
Bibliographical reference
Solar Active Regions and 3D Magnetic Structure, 26th meeting of the IAU, Joint Discussion 3, 16-17 August, 2006, Prague, Czech Republic, JD03, #91
Advertised on:
8
2006
Citations
0
Refereed citations
0
Description
Introduction: When lacking polarimetric observations, the Bright Points
(BPs) visible in the G-band at 430 nm are commonly used as tracers for
magnetic fields. Methods: Observations presented in this paper were
taken on October 11, 2005 at the German Vacuum Tower Telescope and
involved the Tenerife Infrared Polarimeter (TIP) at 1.5 micron, the
Telecentric Etalon Solar Spectrometer (TESOS) in the Fe I spectral line
at 557.6 nm, and a speckle setup in G-band. The area scanned by TIP was
75''x33'' and covered a pore surrounded by network. The TIP spectra were
inverted with the SIR (Stokes Inversion based on Response functions)
code to retrieve the magnetic field vector. Results: We find that G-band
BPs are not cospatial with the central part of the flux concentrations.
Even at the small heliocentric angle of 12 degree, the BPs appear
projected on the limb side walls of the granules (Fig. 1), whereas the
fields are concentrated in the intergranular lanes. Discussion: Our
findings indicate that the G-band Bright Points are a result of the "hot
wall effect". The downward shift of the optical depth scale in the
presence of magnetic fields allows to see deeper and hotter layers,
where CH dissociates, in the granules next to the field concentrations.
Thus, information drawn from the observations of BPs cannot be used to
conclude on the actual variation of the magnetic field structure, as
only the outer parts of the flux concentrations are seen in the BPs.
Figure 1. Non-cospatiality of BPs and field concentrations. Top row,
left to right: line-core intensity, LOS velocity (range =+/- 1 km/s),
magnetic flux , polarity, LOS velocity from the inversion (range =+/-
1.5 km/s), field azimuth. Bottom row, left to right: polarization
degree, G-band intensity, continuum intensity at 1.5 micron, BP mask,
field strength, field inclination. The white arrow in the G-band image
denotes the limb direction, the cross marks the center of the 6.7 x 6.7
Mm field-of-view shown.