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pulsating components of binary systems are of special interest because the masses of the components can be derived directly if the inclination angle @xmath1 can be constrained sufficiently .
these masses can then be compared to theoretical predictions from evolution theory and pulsation theory .
* thompson et al . ( 2012 ) ) propose a class of eccentric binary systems with dynamic tidal distortions found among _
_ light curves .
they coined the term  heartbeat stars  for this class .
the light variation allows to constrain orbital elements such as orbital period , inclination , argument of periastron and eccentricity .
stars are located within the classical instability strip extended to the main sequence .
they pulsate in p modes with typical frequencies ranging from 5 to 50 . for a detailed review
we refer to ( * ? ? ?
* breger ( 2000 ) ) and ( * ? ? ?
* pamyatnykh ( 2000 ) ) .
the binary hd51844 was observed in the corot lra02 for 117 days continuously .
the high - quality light curve shows multi - mode  pulsation and a periodic brightening event .
fig.[fig - lc ] shows the corot light curve together with two running averages ( 300 and 3000 points ) to illustrate the p - mode pulsation and the light variation due to the orbital motion of the stars .
the outliers and jumps were removed in an iterative approach by involving prewhitening of the @xmath0 sct type pulsation and correcting the residuals .
the removal of outlying data points involved a 3-@xmath2 clipping on the residuals rather than the original data . since the pulsation frequencies are well separated from the binary light variation we constructed a simple binary light curve by calculating a fit from the first fifteen harmonics of the orbital frequency .
the subsequent frequency analysis was performed on the corrected data where the binary model was subtracted . in this paper
we focus on the effects of the binary nature .
a more detailed frequency analysis will be published elsewhere , though a brief summary shall be given below .
the frequency analysis using sigspec ( @xcite ) resulted in more than 700 peaks using a significance limit of 6 .
the pulsation frequencies range from 5 to 15  where four frequencies have amplitudes larger than 1.4 mmag ( in the integrated light from both components ) .
these dominant frequencies ( f@xmath3 to f@xmath4 ) are 12.213 , 7.054 , 6.943 and 8.141 , respectively . around the two dominant modes ( f@xmath3 and f@xmath5 ) there are closely spaced frequencies .
f@xmath4 is a single frequency outside of the groups and reveals an exact 3/2 ratio to the dominant mode .
this ratio was also detected among a few frequencies with lower amplitude .
the high - quality of the corot seismo data allows to detect frequency modulation due to the orbital motion . in an eccentric binary system a more complex structure of the side lobes
is expected ( ( * ? ? ?
* shibahashi & kurtz 2012 ) ) . in our case
we find around the four dominant frequencies first- and tentatively second - order side - lobes .
the amplitudes of the latter range from 6.7 to 20 ppm .
the average noise of the residuals after prewhitening is 1.8 ppm , which transforms to a s / n of 3.7 for the lowest - amplitude side - lobe .
the amplitudes of the lower - frequency side - lobes ( @xmath6 ) are systematically higher than those of the higher - frequency sidepeaks .
.frequencies , amplitudes and phases used for the determination of theoretical rv curve .
[ cols= " < , < , < , < , < , < , < , < , < , < , < , < , < , < , < " , ]         candidate frequencies for the second - order side peaks were found around the 4 dominant frequencies but no side - lobes were detected for the other frequencies .
the amplitudes of these second - order side peak candidates range from only 6.7 to 21 ppm .
we show that for low - amplitude pulsators ( highest amplitudes only @xmath7 2 mmag ) a noise level well below 1 ppm is required to recover the rv curve purely from photometry .
fig.[fig - freqmod ] shows the structure of side - lobes around the 4 dominant peaks , where the corresponding modulated frequency was subtracted and table[tab - freq - split ] lists the four dominant pulsation frequencies ( column f@xmath8 ) , the identified side - lobes ( f@xmath9 ) , the corresponding amplitudes ( a@xmath9 ) and phases ( @xmath10 , zero point : beginning of corot observations jd 2454784.565 ) .
the binary nature of this star was discovered in the eso lp185.d-0056 harps spectroscopy programme ( led by e. poretti ) .
the light curve clearly shows a recurring brightening event with a period of 33.498 days .
thus , a spectroscopic campaign was organised with a good phase coverage that confirmed this period as the binary orbit period .
these spectra include 19 hermes and 5 mcdonald spectra
.    the radial velocities ( rvs ) were determined by fitting synthetic spectra to the observations using the software binmag3 ( by o. kochukhov , www.astro.uu.ee/@xmath11oleg ) .
first , the  was determined by fitting synthetic spectra ( both with  = 6800k and  = 3.5 ) to the observations in which the lines of both components are well separated . in total 60 measurements were averaged and the mean values of  = 41.4@xmath12 1.5 and 41.7 @xmath12 1.7 respectively , were determined .
thus , keeping the  fixed for both components at 42  we determined the rv curves for all available spectra by using the same software .
for each spectrum 16 windows were selected to fit the rvs .
the standard deviations for the phases where the lines of the components are separated are 1.5  and for the phases where the lines are blended @xmath7 3 .
the theoretical rvs curves calculated from the frequencies ( tab . [ tab - freq - split ] ) are compared to the observed rvs in fig[fig - pincers ] .
for f@xmath3 the agreement is acceptable , while for f@xmath5 to f@xmath4 the agreement is poor . because the second order side lobes have extremely low amplitudes they are prone to significant relative errors .
hence , we estimate that a noise level of less than 1 ppm in the fourier domain is required to reconstruct the rv curve purely from photometry for such low - amplitude @xmath0 sct stars .
the brightening of the system is at maximum , when the rvs of the components are maximum .
thus , a tidal deformation and reflected light is likely to cause the brightening ( `` heartbeat effect '' ) .
and their errors are below 3kms , which is approximately of the order of the symbol size.,width=288 ]
m.h and m.p . acknowledge financial support of the esa pecs project 4000103541/11/ nl / kml .
m.h is grateful to j. benk and l. fosatti for valuable discussion .
we are grateful to the observers p. de cat , p. lampens , p. m. arenal , j. vos , and m. rainer for collecting the spectra .
the star hd 51844 was observed in corot lra02 as a seismo target which turned out to be an sb2 system . 
 the 117 days long light curve revealed @xmath0 scuti pulsation in the range of 6 to 15  where four frequencies have amplitudes larger than 1.4 mmag and a rich frequency spectrum with amplitudes lower than 0.6 mmag . additionally , the light curve exhibits a brightening event recurring every 33.5 days with a maximum of 3 mmag and a duration of about 5 days . 
 thus , this star can be considered as a heartbeat candidate . 
 the radial velocities from spectroscopy confirmed an eccentric binary system with nearly identical masses and physical parameters . 
 the brightening event of the light curve coincides with the maximum radial velocity separation showing that the brightening is in fact caused by tidal distortion and/or reflected light . 
 one component displays large line profile variations , while the other does not show significant variation . 
 the frequency analysis revealed a quintuplet structure of the four highest - amplitude frequencies , which is due to the orbital motion of the pulsating star .