Spectropolarimetery of UmbralFine Structures from Hinode: Evidence for Magnetoconvection

Lokesh Bharti1,2, Chandan Joshi1, S.N.A. Jaaffrey1 and Rajmal Jain3

1. Mohanlal Sukhadia University, Udaipur, India

2. Max Planck Institute for Solar System Research, Lindau, Germany

3. Physical Research Laboratory, Ahmedabad, India

Introduction

Cluster model (Parker 1976 and Choudhuri1986: UDs are the top of the intrusion of field free material between the flux tubes beneath the sunspot.Monolithic model (Weiss 2002): UDs appear as a result of magnetoconvection in monolithic flux tubeKnowledge of the nature of UDs is essential to understand the energy transport from below the sunspot.

Spectropolarimetric observations

Socas-Navarro at al. (2004) analysedperipheral UDs in detal from spectropolarimetric data and fined higher temperature ( ̴ 1 Kk), weaker field ( ̴ 500 G), small upflow ( ̴ 100 ms-1) and more inclined field (̴ 10°) in UDs.

Fig. 1.—Left: One of the best images of the observed sunspot taken in the continuum l p 5571 A° at 14:48:21 UT. Penumbral fine structure and fine structure in the light bridge are clearly visible; boxes show location of two umbral dots. Right: Umbra. UDs are clearly visible.

Fig. 2.—LOS velocity for one central UD. Upflow (blue) in center with reduction in magnitude toward outer side is visible. Narrow downflow (red) channels adjacent to upper and lower edges of this UD is seen.

Fig. 3.—Scatter plot for normalized continuum intensity vs. velocity for one central UD. This UD show positive correlation between intensity and velocity. Most of the brighter pixels show upflow while dark pixels show downflow. Some bright pixels are associated with downflowing region.

Fig. 4.—LOS velocity for one peripheral UD. Upflow (blue) in center with reduction in magnitude toward outer side is visible. Narrowdownflow (red) channels adjacent to left and right edges of this PUD are seen. Two small UD are visible around this PUD with a small upflow. At the lower left edge the upflow region belongs to penumbral filament.

Fig. 5.—Scatter plot for normalized continuum intensity vs. velocity forone peripheral UD. This UD shows positive correlation between intensity andvelocity. Most of the brighter pixels show upflow while the dark pixels show downflow.. Upflow in central part and downflow in peripheral part suggest typical overturning convecting cells.

Hinode SOT BFI G-band image on 12 Dec. 2006

Mm

G-band movie of active region on 12th December 2006

1.57 Mm

1.57 Mm

Bharti et al., ApJ Letters, 2007Rimmele T., ApJ, 2008

Spectropolarimetric data from Hinode

G-band

TCP

Cnt. Int.

At τ =1, UDs are hotter than coolest part of umbra (1 Kk)At τ =-1.6, temperature deficit in dark lane of UD ‘C’.At τ =1, magnetic field weakning by 400-900 G.Upflow: 300 - 450 ms-1

More inclined field: 10°-20° at τ=1

Results from SIR inversion

G-band

TCP

Cnt. Int.

LOS velocity at τ=-1.8

Area asymmetry mapCnt. Intensity

Discussion and ConclusionsUpflow in central part and downflowin peripheral part of UDs.Higher temperature in UDs.Temperature deficit in dark lanes. More inclined field above UDs.Weak magnetic field in UDs.Compatible with simulations by Schüssler and Vögler (2006).

------>Riethmüller et al. 2008, ApJ Letters.

Intensity

V LOS

AcknowledgementsHinode team for data. Dr. Bellot Rubio for SIR code.Dr. Juan Manuel Borrero for SIR inversion.Prof. Schüssler for discussions.