摘要：Aims.The expansion with height of the solar photospheric magnetic field and the plasma flows is investigated for three isolated bright points (BPs).Methods.The BPs were observed simultaneously with three different instruments attached to the 1.5 m GREGOR telescope: (1) filtergrams of Ca IIH and blue continuum (4505 Å) with the HiFI, (2) imaging spectroscopy of the Na ID2line at 5890 Å with the GFPI, and (3) slit spectropolarimetry in the 1μm spectral range with the GRIS. Spectral-line inversions were carried out for the Si I10827 Å Stokes profiles.Results.Bright points are identified in the Ca IIH and blue continuum filtergrams. Moreover, they are also detected in the blue wing of the Na ID2and Si I10827 Å lines, as well as in the Ca I10839 Å line-core images. We carried out two studies to validate the expansion of the magnetic field with height. On the one hand, we compare the photospheric StokesVsignals of two different spectral lines that are sensitive to different optical depths (Ca Ivs. Si I). The area at which the StokesVsignal is significantly large is almost three times larger for the Si Iline – sensitive to higher layers – than for the Ca Ione. On the other hand, the inferred line-of-sight (LOS) magnetic fields at two optical depths (logτ = −1.0 vs. −2.5) from the Si Iline reveal spatially broader fields in the higher layer, up to 51% more extensive in one of the BPs. The dynamics of BPs are tracked along the Na ID2and Si Ilines. The inferred flows from Na ID2Doppler shifts are rather slow in BPs (≲1 km s−1). However, the Si Iline shows intriguing Stokes profiles with important asymmetries. The analysis of these profiles unveils the presence of two components, a fast and a slow one, within the same resolution element. The faster one, with a smaller filling factor of ∼0.3, exhibits LOS velocities of about 6 km s−1. The slower component is slightly blueshifted.Conclusions.The present work provides observational evidence for the expansion of the magnetic field with height. Moreover, fast flows are likely present in BPs but are sometimes hidden because of observational limitations.
关键词：enSun: photosphereSun: chromosphereSun: magnetic fieldsmethods: data analysistechniques: polarimetrictechniques: high angular resolution
