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Paper text:
chemically peculiar stars of spectral classes a and b are objects in the atmospheres of which there are anomalies of chemical elements such as sr , cr , eu , si , etc .
these stars often have global magnetic fields which are considered to be responsible for the chemical anomalies .
the existing empirical material does not allow us to make the final choice in favor of one of the theories regarding the origin and evolution of magnetic fields .
usually , studies of stellar magnetism use spectroscopic and photometric observations .
the accumulated wealth of observational data however does not answer the main question about the formation of a global magnetic field of the star .
we propose to use another source of information  an interferometric study of binary and multiple magnetic stars .
according to current views most stars are born in groups of two or more components .
single stars are formed by the decay of such groups .
compared with single systems , binary and multiple systems have three additional quantities : the orbital angular momentum , the eccentricity of the orbit and the mass ratio of the components .
these values give us important information about the star formation process and physical conditions in protostellar matter including the presence of a magnetic field .
the study of binary and multiple magnetic stars can be a cornerstone in the issue of the origin of stellar magnetic fields . to address this question we conducted speckle interferometric observations with high angular resolution of
all known magnetic stars with global fields in the northern hemisphere ( 273 objects with @xmath1 ) .
observations were made at the 6 m telescope bta , the largest optical telescope in eurasia .
a sample of objects for observations was based on the catalog of magnetic stars ( romanyuk & kudryavtsev 2008 ) .
it contains a list of 355 chemically peculiar objects ( mostly ap / bp ) with detected global magnetic fields .
we added 17 new magnetic stars discovered after the publication of the catalog .
therefore the total number of stars in the sample is 372 . for the majority of stars in the list ( 322 objects ) only the value of the longitudinal component of the field
be is known . for 48 stars
the surface fields are determined from the splitting of zeeman components .
the vast majority of the sample objects are brighter than 10@xmath2 in the @xmath3-band .
the stars are uniformly distributed on the celestial sphere , although a relatively small number ( about 20% ) of objects belong to open clusters of different ages .
the bta can capture only 273 objects from our sample with declinations @xmath1 .
the speckle interferometric observations of 273 magnetic cp stars were carried out at the bta in 20092012 .
they were performed with the speckle interferometer engineered at the sao ras ( maksimov et al .
we used the photonmax512 camera based on an internal electron multiplying ccd97 ( emccd ) produced by princeton instruments with a @xmath4 pixel array .
the limiting magnitude of our speckle interferometer is @xmath5 in the @xmath3-band depending on seeing conditions .
basically we employed two filters : 550/20 and 800/100 nm ( central wavelength / bandwidth ) .
we took 2000 short exposure images in each filter for almost all observed objects .
high quantum efficiency and linearity of the detector permits the maximum magnitude difference between the components to reach up to 5 - 6@xmath2 depending on angular separation and weather conditions ( fig .
the minimum angular separation between the components is determined by the diffraction limit of the 6 m telescope .
it is 0.022@xmath6 and 0.033@xmath6 for 550/20 and 800/100 nm filters , respectively .
the size of the detector s
field @xmath7 allowed secondary components to be discovered at angular separations as large as 3@xmath6 from the primary star .
the accuracy of our speckle interferogram processing method may be as good as 0.02@xmath8 , 0.001@xmath6 , and 0.1@xmath9 for the component magnitude difference , angular separation , and position angle , respectively .
for 63 stars in our sample , we observed speckle interferometric companions . among the resolved systems 58
are binaries and 5 are triples .
twenty nine companions were resolved astrometrically for the first time .
the fraction of speckle interferometric binaries / multiples in the sample of 273 stars with confirmed magnetic fields is 23% .
magnitude difference and angular separation distributions for resolved pairs are shown in fig . 1 . to plot these histograms we used 56 measurements of @xmath0 and 53 @xmath10 m .
we want to draw attention to the unusual profile of the @xmath0 distribution .
speckle interferometric components of magnetic stars tend to be located close to the primary star .
half of the resolved stars have companions with @xmath11 .
this result is not a selection effect because close interferometric components are harder to detect than the wide pairs .
the distribution of @xmath10 m for 28 resolved speckle companions with @xmath11 resembles that on the left half of fig .
reconstructed images of six systems resolved for the first time on bta are presented in fig .
2 . the table below is a list of all the stars that have speckle components .
the systems resolved astrometrically for the first time are marked in bold .
.resolved stars . [ cols="<,<,<,<,<,<,<,<",options="header " , ]
according to our research the fraction of speckle interferometric binary and multiple systems in the sample of 273 cp stars with confirmed magnetic fields makes up 23% without account for undetected companions . generally the speckle interferometric components have orbital periods larger than spectroscopic and smaller than common proper motion pairs .
we expect that the total fraction of binaries / multiples in the sample with account for spectroscopic short - period systems and wide common proper motion pairs can be twice higher .
the detected speckle components have a prominent peak in the @xmath0 distribution that corresponds to the closest resolved pairs . more detailed and refined results of the presented study
will be published soon .
this work was supported by federal target program `` scientific and scientific - pedagogical personnel of innovative russia '' for 20092013 years ( n 8704 ) and grant of the president of the russian federation for the state support of young russian phd scientists ( mk-1001.2012.2 ) .
we present the results of speckle interferometric observations of 273 magnetic stars most of which are ap / bp type . 
 all observations were made at the 6-m telescope of the special astrophysical observatory of the russian academy of sciences . 
 we resolved 58 binary and 5 triple stars into individual components . 
 almost half of these stars were astrometrically resolved for the first time . 
 the fraction of speckle interferometric binaries / multiples in the sample of stars with confirmed magnetic fields is 23% . 
 we expect that the total fraction of binaries / multiples in the sample with account for spectroscopic short - period systems and wide common proper motion pairs can be twice higher . 
 the detected speckle components have a prominent peak in the @xmath0 distribution that corresponds to the closest resolved pairs .