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the integral ( international gamma - ray astrophysics laboratory ) satellite was launched on 17 october 2002 . since then
, there were many observations of the gamma - ray and x - ray sources obtained .
thanks to the omc ( optical monitoring camera ) , there was collected also a large database of the observations in the visual passband .    for a detailed description of the camera , its efficiency and parameters ,
see e.g. @xcite . due to its relatively large field of view ( almost 5 @xmath1 5 degrees )
there were observed also many photometric variable stars near the gamma and x - ray sources as a by - product .
the main advantage of the omc data is the duration of the continuous time series of observations , which could reach up to a few days without any interruption .
this could not be achieved by the ground - based telescopes . due to this fact
, there could be discovered also very slow variables , or the minima of very slow algol - type eclipsing binaries ( hereafter ebs ) could be catched during one observation run .
despite the fact that the older omc observations are available on the internet ] , the data mining and the analysis are still very rare .
regarding the ebs , there were only one paper about the system v435 cas ( see @xcite ) and the collection of 236 minima timings of ebs by @xcite .
the analyses of the light curves of eclipsing binaries have not been published so far .
all observations of the selected systems were carried out by the same instrument ( 50 mm omc telescope ) and the same filter ( johnson s v filter ) .
time span of the observations ranges from november 2002 to july 2006 .
a transformation of the time scale has been done following the equation @xmath2 . only a few outliers from each data set were excluded .
the phoebe programme ( see e.g. @xcite ) , based on the wilson - devinney algorithm @xcite , was used .    due to the missing information about the stars , and having only the light curves in one filter , many of the parameters have to be fixed . at first , the temperature of the secondary component was fixed ( according to the estimated spectral type ) . the `` detached binary '' mode was used for computing and the eccentricity was set to 0 ( circular orbit ) .
the limb - darkening coefficients were interpolated from van  hamme s tables ( see @xcite ) .
the values of gravity brightening and bolometric albedo coefficients were set at their suggested values for convective atmospheres ( see @xcite ) , i.e. @xmath3 , @xmath4 .
no third light was assumed : @xmath5 .
the first system is pv  cyg (= an  93.1928 = gsc 03137 - 03117 , @xmath6  56@xmath7  29@xmath8 , @xmath9  43@xmath10  08@xmath11 , j2000.0 , @xmath12  mag ) .
this star was discovered to be a variable by @xcite and its designation as pv  cyg was introduced by @xcite . since then
, there was no detailed analysis of the system performed , only the times of minima observations were published .
the only rough estimation of its spectral types as a1+[g6iv ] were published by @xcite , but it is not very reliable .
light curve of pv  cyg.,width=521 ]    according to these spectral types , the temperature of the primary should be circa 9100  k and the temperature of the secondary about 5700  k ( according to @xcite ) . due to this fact
, the temperature of the secondary was fixed @xmath13  k and @xmath14 was calculated ( from its starting value 9100  k ) . the final fit is plotted in fig.[figpvcyg ] , while all the relevant parameters of the fit are presented in table [ tablebig ] . in this table the ephemeris @xmath15 and @xmath16 are written together with the inclination @xmath17 , the mass ratio @xmath18 , the radii ratio @xmath19 , the temperature ratio @xmath20 , the luminosity ratio @xmath21 and the kopal s potentials @xmath22 , respectively .    altogether there were obtained 795 observations of the star .
as one can see from table [ tablebig ] , the radius of the secondary is larger than the radius of the primary . despite this fact , thanks to the higher effective temperature of the primary
, the relative luminosity of the primary component is about 4 times larger .
the scatter of the individual measurements is quite high , but the final fit is satisfactory .      the eclipsing binary v822  cyg (= an  216.1935 , @xmath6  54@xmath7  08@xmath8 , @xmath23  21@xmath10  00@xmath11 , j2000.0 , @xmath24  mag ) was discovered by @xcite .
the light curve was observed and published by @xcite , but any analysis has been performed , so its parameters are still questionable . @xcite
published the first approximate estimation of the spectral types , resulting in ( a3)+[g2iv ] . but this result is again not very reliable .    from these spectral types one could derive the temperatures @xmath25  k and @xmath26  k ( according to @xcite ) .
exactly the same method as in the previous case was used .
altogether there are 1680 observations of v822  cyg .
the resulting parameters are in table [ tablebig ] and the plot is in fig.[figv822cyg ] .
light curve of v822  cyg.,width=521 ]    although the scatter of the measurements is rather high , thanks to the relatively large number of observations ( 1855 in total ) , the final fit is satisfactory and no other effects are observable in this light curve .
the last eclipsing binary selected for a detailed analysis is v1011  cyg (= gsc  02677 - 01203 , @xmath6  55@xmath7  15@xmath8 , @xmath27  12@xmath10  30@xmath11 , j2000.0 , @xmath28  mag ) .
it was discovered to be a variable by @xcite .
the spectral type a0 was presented in @xcite , while more detailed classification as a0+[g3iv ] was presented in @xcite .    according to this latter paper ,
the proposed temperature of the primary is circa 9400  k , and about 5800  k of the secondary .
altogether there are 1704 observations .
as one can see , the curve is not symmetric and the brightnesses near the phase -0.1 and near the phase 0.1 are not equal .
this could be explained e.g. by the presence of a spot . if one assume the spot to be located on the primary component , the parameters of such a spot are the following :    [ cols="^,^",options="header " , ]     the final parameters of the light - curve fit are presented in table [ tablebig ] and the fit itself is plotted in fig.[figv1011cyg ] .
the 3-d plot of the system is shown in fig.[fig3d ] .
light curve of v1011  cyg.,width=529 ]    however , the presence of spot on the primary is not able to describe the light curve in detail and at least two spots are needed .
one of them should be brighter and the other one dimmer than the surface of the star .
there is a slight difference between the shapes of the light curves obtained at different epochs .
the first observations from 2002 show larger difference in brightness near the phase -0.1 and 0.1 , while the observations from the following years show almost symmetric curve .
this could indicate the time evolution of the spots .
only further analysis would confirm the presence of the spots and their possible evolution .
the light - curve analysis of three selected systems in cygnus constellation has been done . using the light curves observed by the integral satellite , one can estimate the basic physical parameters of these systems . despite this fact , the parameters are still only the preliminary ones , affected by relatively large errors and many of the relevant parameters
were fixed at their suggested values . the detailed analysis is still needed , especially in different filters .
together with a prospective radial - velocity study , the final picture of the systems could be done .
particularly , the system v1011  cyg seems to be the most interesting one due to its asymmetric light curve .
based on data from the omc archive at laeff , pre - processed by isdc .
this investigation was supported by the grant agency of the czech republic , grants no .
205/06/0217 and no .
we also acknowledge the support from the research program msmt 0021620860 of the ministry of education . this research has made use of the simbad database , operated at cds , strasbourg , france , and of nasa s astrophysics data system bibliographic services .
three algol - type binaries in cygnus constellation were selected for an analysis from a huge database of observations made by the integral / omc camera . these data were processed and analyzed , resulting in a first light - curve study of these neglected eclipsing binaries . 
 the temperatures of the primary components range from 9500  k to 10500  k and the inclinations are circa 73@xmath0 ( for pv  cyg and v1011  cyg ) , while almost 90@xmath0 for v822  cyg . 
 all of them seem to be main - sequence stars , well within their critical roche lobes . nevertheless , further detailed analyses are still needed .    
 stars : binaries : eclipsing , stars : individual : pv  cyg , v822  cyg , v1011  cyg , stars : fundamental parameters 97.10.-q , 97.80.-d , 97.80.hn