VELOCITY AND MAGNETIC FIELD DISTRIBUTION IN A FORMING PENUMBRA

Journal Article · Mon Jul 01 04:00:00 EDT 2013 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/771/1/L3· OSTI ID:22118732

Romano, P.; Guglielmino, S. L. ^[1]; Frasca, D.; Zuccarello, F. ^[2]; Ermolli, I. ^[3]; Tritschler, A.

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1. INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95125 Catania (Italy)
2. Dipartimento di Fisica e Astronomia-Sezione Astrofisica, Universita di Catania, Via S. Sofia 78, I-95125 Catania (Italy)
3. INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (Italy)

We present results from the analysis of high-resolution spectropolarimetric and spectroscopic observations of the solar photosphere and chromosphere, obtained shortly before the formation of a penumbra in one of the leading polarity sunspots of NOAA active region 11490. The observations were performed at the Dunn Solar Telescope of the National Solar Observatory on 2012 May 28, using the Interferometric Bidimensional Spectrometer. The data set is comprised of a 1 hr time sequence of measurements in the Fe I 617.3 nm and Fe I 630.25 nm lines (full Stokes polarimetry) and in the Ca II 854.2 nm line (Stokes I only). We perform an inversion of the Fe I 630.25 nm Stokes profiles to derive magnetic field parameters and the line-of-sight (LOS) velocity at the photospheric level. We characterize chromospheric LOS velocities by the Doppler shift of the centroid of the Ca II 854.2 nm line. We find that, before the formation of the penumbra, an annular zone of 3''-5'' width is visible around the sunspot. In the photosphere, we find that this zone is characterized by an uncombed structure of the magnetic field although no visible penumbra has formed yet. We also find that the chromospheric LOS velocity field shows several elongated structures characterized by downflow and upflow motions in the inner and outer parts of the annular zone, respectively.

• OSTI ID: 22118732
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 771; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
ASTROPHYSICS
CHROMOSPHERE
DOPPLER EFFECT
INTERFEROMETRY
IRON IONS
MAGNETIC FIELDS
MAGNETISM
PHOTOSPHERE
POLARIMETRY
RESOLUTION
SUN
SUNSPOTS
TELESCOPES