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emission line stars ( els ) range from young to evolved stars ( ttauri , herbig ae / be , wr , planetary nebulae , etc ) , from hot to cool stars ( classical be star , oe , supergiant star , mira ceti , flare stars , etc ) . among the els , here , we focus on the classical be stars . they are non - supergiant b type stars , which have displayed at least once emission lines in their spectra , mainly in the balmer series of the hydrogen . the emission lines come from a circumstellar decretion disk formed by episodic matter ejection of the central star . it appears that the be phenomenon is related to fast rotation and probably additional properties such as non - radial pulsation or magnetic fields . for a comprehensive review of be stars in the milky way we refer the reader to * ? ? ? it seems also that the low metallicity plays a role @xcite : at low metallicity , typical of the small magellanic cloud ( smc ) , the stellar radiatively driven winds are less efficient than at high metallicity ( typical of the milky way [ mw ] ) , thus the mass loss is lower and the stars keep more angular momentum . as a consequence , b - type stars rotate faster in the smc / lmc than in the mw @xcite . it is then expected that the metallicity has also an effect on the be - phenomenon itself as reported by * ? ? ? * or * ? ? ? * , while the evolutionary phase could also play a role @xcite . in most cases , the study of open clusters was done by using photometric observations , in the mw . the work by * ? ? ? * is a typical example . to test these issues and improve the comparisons between smc and mw , spectroscopic observations of stars in open clusters have to be done . in the smc , a survey of emission line objects was performed by * ? ? ? * using photographic plates . however , they were not able to study the stars in open clusters but mainly in the field . this paper deals with our slitless spectroscopic survey of els and oe / be / ae stars in smc open clusters , while in the whole smc 3 million spectra were obtained . to increase the number of open clusters studied in the smc ( 1 to 6 in the previous photometric studies of * ? ? ? * or * ? ? ? * ) , to improve the statistics , and to quantify the evolution of the rates of be stars to b stars with decreasing metallicity , we performed a slitless spectroscopic survey of the smc . the observations were obtained on september 25 , 2002 with the eso wide field imager ( wfi , see * ? ? ? * ) at the 2.2 m mpg telescope located at la silla in chile . we used its slitless spectroscopic mode with the r50 grism and a narrow filter centered on h@xmath0 to reduce the crowding of observed areas . we recall that this kind of instrumentation is not sensitive to the diffuse ambient nebulosities and does not allow weak emission lines to be found . with 10-minutes exposures with wfi , it is possible to detect emission lines with ew@xmath110   or with a relative intensity to the continuum equal to 2 down to v magnitudes around 17.5 . for fainter stars , due to the noise in the spectra , it is only stronger emission lines are within reach . as an example of this kind of observations , see the study by * ? ? ? * in the mw ngc6611 open cluster and the eagle nebula . the ccd image treatment was performed using iraf tasks . the spectra extraction was done using the sextractor code @xcite . the treatment of spectra and search for stars with emission were done by using the album code ( see * ? ? ? details about the samples used in this study are given in table  [ tab1 ] . .details and comparison of samples used in this study [ cols="^,^,^",options="header " , ] after the data - reduction , the objects were sorted by categories ( definite or candidate els , absorption stars ) , and the astrometry of the stars was performed with an accuracy of 0.5  with the astrom package of . + we then cross - matched our catalogues with ogle photometric catalogues in smc open clusters from * ? ? ? * , * ? ? ? * , and * ? ? ? * , in order to obtain the b , v , i magnitudes of the stars , the reddening , and the age of open clusters . with this information , the absolute magnitudes and the derreddened colour indices of the stars were derived . several open clusters are found with high ratios of be to b stars , occasionally even higher than in ngc330 , an open cluster already known for its rich be content . in order to abstract from the large variations from one open cluster to another in their frequency of be stars , the stars were grouped in a global sample . we classified the 4300 stars in our sample by using the calibration provided by * ? ? ? * . fig.[figs1 ] shows the corresponding global hr colour / magnitude diagrammes . from these results it seems that the smc sample is complete for the els till spectral types b3-b4 , while for absorption stars it is complete till b5 . + to highlight and quantify a potential trend of the rates of be stars to b stars with decreasing metallicity , we compared these ratios by spectral - type categories with the study of * ? ? ? * in the mw . the same calibration for the classification of the stars was used in the mw . the comparison of the rates is shown in fig . [ figs3 ] . down to the completness limit of our study of els , one can see that the ratios are several times higher in the smc than in the mw . thus , there is an impact of the metallicity on the number of be stars probably corresponding to the increase of the rotational velocities in the smc in comparison with the mw . + the distribution of be stars by spectral type categories in the smc and mw was also studied . in the mw , the results from * ? ? ? * in open clusters , and from * ? ? ? * in the field , were used . the result is shown in fig . [ figs4 ] . it appears that the maximum of be stars is reached at the spectral type b2 in the smc and mw . there is also another peak at b5-b6 , which can be seen in the mw studies ( complete for the whole b - main sequence ) . the first peak corresponds to the maximum of the emission intensity , the second one to the combined effects of the decrease of the emission intensity and the increase of the initial mass function of stars towards late type stars . + from preliminary results it appears that predominantly young open clusters + ( age@xmath2100myears ) are found to contain classical be ( cbe ) stars , but depending on the types of the stars , certain cbe stars could have reached the terminal - age main sequence ( tams ) . for example in the case of b0e stars , the tams is reached in @xmath310 myears . some other old open clusters ( age@xmath4100myears ) host cbe stars . from these results , it seems that certain cbe could be born as cbe stars and some others appear during their evolution . this point needs more investigations star by star . preliminary studies have shown a trend of the increase of the fraction of be stars with decreasing metallicity . however , up to now , the studies were only performed on a very limited sample of open clusters ( less than 10 in the smc ) and with photometric data . using the eso / wfi in its slitless spectroscopic mode , we observed 84 open clusters in the smc . thanks to different codes and ogle data , we were able to find and classify the emission line stars and absorption stars ( @xmath34300 stars ) . the ratios of be stars to b stars in the smc and mw were studied . the comparison allows to quantify the increase of the number of be stars with decreasing metallicity . be stars in the smc are 2 to 4 times more abundant than in the mw depending on the spectral types . it seems also that early be stars follow the same distribution in the smc and mw with a maximum at the spectral type b2 . about the stellar phases at which be stars appear , from our preliminary results , it seems that certain be stars could be born as be stars , while others could appear during the main sequence depending also probably on the metallicity and spectral types of stars . c.m . acknowledges funding from the esa / belgian federal science policy in the framework of the prodex program ( c90290 ) . thanks support from eso s dgdf 2006 , the iaus soc / loc for the iaus grant , and the fnrs for the travel grant .
at low metallicity , b - type stars show lower loss of mass and , therefore , angular momentum so that it is expected that there are more be stars in the magellanic clouds than in the milky way . 
 however , till now , searches for be stars were only performed in a very small number of open clusters in the magellanic clouds . using the eso / wfi in its slitless spectroscopic mode 
 , we performed a halpha survey of the large and small magellanic cloud . 
 eight million low - resolution spectra centered on halpha were obtained . for their automatic analysis 
 , we developed the album code . here , we present the observations , the method to exploit the data and first results for 84 open clusters in the smc . 
 in particular , cross - correlating our catalogs with ogle positional and photometric data , we classified more than 4000 stars and were able to find the b and be stars in them . 
 we show the evolution of the rates of be stars as functions of area density , metallicity , spectral type , and age .