Observations of a bright plume in solar granulation
Main Astronomical Observatory, NAS, 03680 Kyiv, Zabolotnogo str. 27, Ukraine
2 Instituto de Astrofísica de Canarias, 38205, C/ Vía Láctea, s/n, Tenerife, Spain e-mail: email@example.com
Accepted: 23 July 2007
Aims.The aim of this paper is to analyze the thermal properties, oscillatory, and flow motions of a bright, long-lasting feature observed in solar granulation, which we call the plume.
Methods.We used the spectral observations of quiet granulation at solar disc center, including the two Fe II 5234 and Fe I 6393 Å lines recorded simultaneously at the German Vacuum Tower telescope in Tenerife. The recorded data revealed a stable, bright structure of 3–4 arcsec size present during the whole 2.5 h of observations. We compare the velocity fields extracted by means of a λ-meter method and temperature and pressure stratification obtained after inversion of the profiles related to granules, intergranular lanes, and the plume.
Results.The following results were obtained: (i) the correlation between variations in convective velocity and intensity in the plume is close to zero at all observed heights; (ii) the velocity flow in the plume changes from a downflow in the deep layers to an upflow in the upper layers; (iii) the brightness of the plume increases with height; (iv) the amplitudes of the five-minute oscillations of intensity and velocity are twice lower in the plume than outside, and vertically propagating waves are observed; (v) the plume is hotter and denser than the quiet Sun in the upper photosphere.
Conclusions.We conclude that the observed phenomenon has a non-convective origin. The decrease in the amplitudes of oscillations in the plume cannot be attributed to the higher density in comparison to the surrounding atmosphere. Along with other findings, this indicates the possible presence of magnetic field.
Key words: Sun: photosphere / Sun: granulation / Sun: oscillations / Sun: magnetic fields
© ESO, 2007