| Summary: | Today, the study of stellar magnetic fi-
elds is one of the important research field in astrophysi-
cs because it provides us, in addition to physics, with
information about space weather in the orbits of Earth-
like planets in stars other than the Sun. Local magnetic
fields on stars with convective envelopes are small-scale
magnetic fields different in nature and structure from
their global magnetic field. Unlike the Sun, through
direct measurements we are able to measure only
the magnetic field integrated over the visible disk of
stars. However, we can register the magnetic field in
the leading spot during the time interval when the
corresponding magnetic flux tube already emerges on
the surface of the star, and the magnetic flux tube
of the following spot is still hidden in the interior
under the photosphere. Our research is based on the
spectropolarimetric observations carried out with 2.6m
Shajn telescope equipped with the echelle spectrograph
ESPL, CCD, and the Stokesmeter as a circular polari-
zation analyzer. For measuring stellar magnetic fields
the Single Line (SL) technique was developed at CrAO.
This technique is based on the calculation of Zeeman
effect in individual spectral lines. A key advantage of
the SL technique is its ability to detect local magnetic
fields on the surface of stars. Using SL technique
emergence of large magnetic flux tubes at the surface of
stars of V-IV-III luminosity classes (61 Cyg A, β Aql,
β Gem) were first registered. We review the results of
the study of local magnetic fields in these stars, includi-
ng the results of modeling of magnetic field flux density
and the size of their starspots. We also present the new
results of spots modeling on β Aql. According to the
considered geometric model, the rotational variabili-
ty of the magnetic field and the extreme value of the
field obtained from observations, we assume that the
extreme radius of the spots at the surface of β Aql may
exceed 9 ◦ .
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