EDP Sciences
Free access
Volume 395, Number 3, December I 2002
Page(s) 977 - 981
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20021024

A&A 395, 977-981 (2002)
DOI: 10.1051/0004-6361:20021024

Microflaring of a solar bright point

O. Vilhu1, J. Huovelin1, S. Pohjolainen2, J. Virtanen1 and W. Curdt3

1  Observatory, Box 14, 00014 University of Helsinki, Finland
    e-mail: osmi.vilhu@helsinki.fi; huovelin@astro.helsinki.fi
2  Tuorla Observatory, University of Turku, Finland
    e-mail: spo@astro.utu.fi
3  Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany
    e-mail: curdt@mpae.gwdg.de

( Received 24 April 2002 / Accepted 11 July 2002 )

A $50 \times 50$ arcsec region near the solar disc center containing a bright point (BP) was observed with the SUMER- spectrograph of the SOHO observatory. The data consist of two hours observation of four far-UV emission lines formed between $2 \times 10^4$- $6\times 10^5$ K, with 2 arcsec spatial, 2.8 min temporal and 4 km s -1 spectral resolution. A striking feature was the strong microflaring of the major persistent BP (with size $8 \times 8$ arcsec) and the appearance of several short lived transients. The microflaring of each individual $2 \times 2$ arcsec pixel inside the main BP was coherent, indicating strong interaction of the possible sub arc sec building blocks (magnetic flux tubes). Using the emission measure at 10 5 K as an indicator of the loop foot point area and magnetic filling factor, we suggest 10 per cent filling factor for the BP observed. This is similar to that on the average surface of a medium-active solar type star.

Key words: Sun: UV radiation -- Sun: chromosphere -- Sun: transition region -- Sun: corona -- stars: activity

Offprint request: O. Vilh, osmi.vilhu@helsinki.fi

© ESO 2002