THEMIS/MSDP magnetic field measurements

Free access article

Issue		A&A Volume 445, Number 3, January III 2006


Page(s)		1127 - 1132
Section		The Sun
DOI		http://dx.doi.org/10.1051/0004-6361:20053295

A&A 445, 1127-1132 (2006)
DOI: 10.1051/0004-6361:20053295

THEMIS/MSDP magnetic field measurements

A. Berlicki^{1, 2}, P. Mein¹ and B. Schmieder^{1, 3}

¹ Observatoire de Paris, Section de Meudon, LESIA, 92195 Meudon Principal Cedex, France
e-mail: arkadiusz.berlicki@obspm.fr
² Astronomical Institute of the Wroclaw University, ul. Kopernika 11, 51-622 Wroclaw, Poland
³ Institute of Theoretical Astrophysics, University of Oslo, Blindern, 0315 Oslo, Norway

(Received 25 April 2005 / Accepted 11 July 2005 )

Abstract
We present an analysis of longitudinal magnetic field measurements using the spectral data obtained with the French - Italian polarisation free telescope THEMIS working in Multichannel Subtractive Double Pass (MSDP) mode. We also used SOHO/MDI data to extend our analysis. THEMIS observations in the MSDP mode allows us to perform imaging spectropolarimetry characterized by high spatial and time resolution. In our analysis we used the observations of solar active region NOAA 10484 performed on October 20, 2003. From THEMIS 2D spectral images recorded in Na D₁ 5896 Å line we obtained the longitudinal magnetic field in the active region. The value of the magnetic field was calculated at different distances from the Na D₁ line centre. We determine the LOS magnetic field at different heights in the solar atmosphere. SOHO/MDI observations provide the longitudinal magnetic field in Ni I (6768 Å) line. THEMIS/MSDP measurements at $\Delta\lambda= 0.30$ Å are similar to SOHO/MDI results. Gradients of longitudinal magnetic fields derived from MSDP measurements at $\Delta\lambda= 0.08$ and $\Delta\lambda=0.24$ Å exhibit different behaviours according to solar targets. A decrease with height is seen in spot umbrae and penumbrae, while the gradient in facular and network areas suggests a slight increase of the longitudinal magnetic field, which might be explained by the 3D-structure of canopies.

Key words: sunspots -- Sun: magnetic fields -- techniques: polarimetric

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