Are there field-free gaps near tau=1 in sunspot penumbrae?

Abstract

The vertical stratification of the magnetic field strength in sunspot penumbrae is investigated by means of spectropolarimetric observations at high spatial resolution from the Hinode spacecraft. Assuming that the magnetic field changes linearly with optical depth we find that, in those regions where the magnetic field is more inclined and the Evershed flow is strongest (penumbral intraspines), the magnetic field can either increase or decrease with depth. Allowing more degrees of freedom to the magnetic field stratification reveals that the magnetic field initially decreases from \logτ_5 = -3 until \logτ_5 \simeq -1.0, but increases again below that. The presence of strong magnetic fields near the continuum is at odds with the existence of regions void of magnetic fields at, or right below, the τ_5=1 level in the penumbra. However, they are compatible with the presence of a horizontal flux-tube-like field embedded in a magnetic atmosphere.

10 pages, 11 figures (3 color figures, f2,f3,f5,f10,f11 low resolution). Accepted for publication in ApJ. To appear in issue 1, vol 686, October 2008

References in corpus (8)

• Quiet Sun internetwork magnetic fields from the inversion of Hinode measurements
• Magnetostatic penumbra models with field-free gaps
• Evidence of convective rolls in a sunspot penumbra
• Evidence of magnetic field wrapping around penumbral filaments
• Quiet Sun magnetic fields from space-borne observations: simulating Hinode's case
• The structure of sunspot penumbrae IV. MHS equilibrium for penumbral flux tubes and the origin of dark core penumbral filaments and penumbral grains
• The Fine-Structure of the Net-Circular Polarization in a Sunspot Penumbra
• Temporal evolution of the Evershed flow in sunspots. II. Physical properties and nature of Evershed clouds

Cited by in corpus (8)

• Deep probing of the photospheric sunspot penumbra: no evidence for magnetic field-free gaps
• Sunspots: from small-scale inhomogeneities towards a global theory
• Rapid Transition of Uncombed Penumbrae to Faculae during Large Flares
• Models and Observations of Sunspot Penumbrae
• Anomalous flows in a sunspot penumbra
• Expulsion of counter Evershed flows from sunspot penumbrae
• The role of the Lorentz force in sunspot equilibrium
• Chromospheric and photospheric properties of sunspots as inferred from Stokes inversions under magneto-hydrostatic and non-local-thermodynamic equilibrium