Diagnostics of the velocity field of the quiet Sun using the lambda-meter method: the Si I λ 1082.7 nm line

1Shchukina, NG, 1Kostyk, RI
1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Kinemat. fiz. nebesnyh tel (Online) 2020, 36(1):3-23
Start Page: Solar Physics
Language: Ukrainian

The validity of the lambda-meter method for determing the quiet Sun velocity field using the Si I λ 1082.7 nm line is investigated. To this end, the intensity profiles of this line were calculated for the solar disk center by means of NLTE radiative transfer calculations in a three-dimensional snapshot model atmosphere taken from a magneto-convection simulation of the small-scale magnetic activity in the quiet solar photosphere. Theoretical NLTE profiles of the Si I λ 1082.7 nm line were degraded because of the Earth’s at¬mo¬spheric turbulence and light diffraction by apertures of the telescopes like VTT, GREGOR, and EST/DKIST.The velocity field, retreived from spatially unsmeared profiles and the profiles smeared to the resolution of ground-based observations, was compared with the velocity field of the given snapsot model atmosphere. It is shown that in the case of observations of the Si I λ 1082.7 nm line on large-diameter telescopes like GREGOR and EST/DKIST with a spatial resolution substantially better than 0.27 arsec, the lambda-meter method provides reliable values of the velocity field for the lower and upper solar photosphere. For the middle photosphere correlation between the inferred and the real velocities is worse particularly when using the smaller diameter telescopes similar to VTT. At a poor spatial resolution, exceeding 2 arcsec, information about the velocity field can be obtained only for the uppermost photospheric layers. For this case, the lambda-meter velocities turn out to be noticeably smaller than the real ones.

Keywords: formation — techniques, granulation — line, photosphere, spectroscopic — magnetohydrodynamics — radiative transfer

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