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ii peg is one of the very active rs cvn stars and it is the brightest x - ray star with 50pc of the sun .
rs cvn stars are closely detached binaries where the more massive component is a g - k giant or subgiant and the secondary a subgiant or dwarf of spectral class g to m. because of the low luminosity of the secondary many rs cvn systems appear as single - line binaries which are suitable for spectral analysis ( berdyugina et al .
1998a ) . in close binaries
the rapid rotation is maintained by tidal forces due to the close companion .
large amplitude brightness variation of rs cvn stars imply the presence of enormous star spots on their surfaces covering up to 50% of the visible disk .
also coronal x - ray and microwave emissions , strong flares in the optical , uv , radio and x - ray are seen .
cool spots on the stellar surface will locally alter the photospheric absorption lines and continuum intensities .
previous investigations on the temperature distribution over the surface of ii peg include the study of berdyugina et al .
( 1998b ) , who presented surface temperature maps for 1992 - 1996 , and bergyugina et al .
( 1999c ) with surface maps for 1996 - 1999 , both studies were based on observations with the sofin - spectrograph at not .
gu et al . (
2003 ) presented surface images of ii peg for 1999 - 2001 based on observations with the coude echelle spectrograph at the xinglong station of the national astronomical observatories , china , but the spectral lines used for inversions were different to that of sofin observations .
photometric light curve variations of the object were analysed by berdyugina & tuominen ( 1998c ) , and by rodon et al .
the results of berdyugina et al .
( 1998a , b , 1999a , b , c ) and berdyugina & tuominen ( 1998c ) consistently show that there are two active longitudes separated approximately by 180@xmath0 , migrating in the orbital reference frame , and that a switch of activity level occurs periodically with a period of 4.65 years . in the surface images of gu et al .
( 2003 ) the general spot pattern was quite similar , but the drift with respect of the orbital frame was less obvious , and the switch of the activity level appeared to occur earlier than predicted by berdyugina et al ( 1999c ) .
rodon et al .
( 2000 ) found a much more complicated spot pattern from their analysis of photometry : they report on the existence of a longitudinally uniformly distributed component together with three active longitudes , with complicated cyclic behavior .
carroll et al .
( 2009 ) have also applied a zeeman doppler imaging technique to derive the magnetic field configuration on the surface of ii peg during 2007 using spectropolarimetric ( stokes i and v ) observations with sofin .
their maps show a very similar spot pattern as found by berdyugina et al .
( 1998b , 1999c ) ; moreover , the radial field direction is opposite on different active longitudes .
.summary of the observations . [ cols="<,^,^,^,<,^,^,^ " , ]     when a star rotates rapidly star spots modify the observed spectral line profiles .
as the star rotates , these bumps will move across the absorption line profiles ( hackman et al .
( 2001 ) ; kurster , m. ( 1993 ) ) .
the surface imaging techique is basically to trace these distortions and create a surface map of the star .
we use the surface imaging technique developed by piskunov ( the code invers7 , piskunov et al .
( 1990 ) ; piskunov ( 1991 ) ) .
we use the stellar model atmospheres of kurucz ( 1993 ) for local line profile calculations for a set of temperatures and limb angles .
this table is then used for the disk integration of a given surface temperature distribution .
the surface imaging problem can be solved by searching for a such surface temperature distribution that minimizes the discrepancy function between the observations and the calculated line profiles ( hackman et al .
( 2001 ) ) .
high resolution spectra of ii peg were measured in july - august 1999 , september 1999 , august 2001 , august 2002 and november 2002 .
all the observations were made using the sofin high resolution echelle spectrograph at the 2.6 m nordic optical telescope ( not ) , la palma , spain .
the data were acquired with the 2nd camera equipped with a ccd detector of 1152@xmath1298 pixels , and the spectral region @xmath2was chosen for surface imaging .
the observations are summarized in table 1 .
the spectral observations were reduced with the 4a software system ( ilyin 2000 ) .
bias , cosmic ray , flat field and scattered light corrections , wavelength calibration and normalization were included in the reduction process .
the stellar parameters used in the inversions were chosen according to berdyugina et al .
( 1998a ) , and read @xmath3=4600 k , @xmath4 kms@xmath5 , @xmath6=3.5 kms@xmath5 , @xmath7=6.724333 d , @xmath8=22.6 kms@xmath5 , @xmath9 .
the following spectral lines were used in the surface temperature inversions : fe i 6173  , ni i 6175  , ni i 6177  , and fe i 6180  .
spectral line parameters were obtained from the vienna atomic line database ( kupka et al .
1999 ) ; the @xmath10 values of the two included ni i lines were modified from the standard value of @xmath11 to @xmath12 as the standard values were found to produce much weaker absorption lines than the actually observed ones .
this is equivalent to an increase in the ni abundancy , which is probably the real reason for the observed strong ni lines .
figures 1 - 5 show the results of the inversions . during july - august 1999 ( fig .
1 ) only one spot is seen approximately at latitude 40@xmath0 .
the minimum temperature inside the spot was measured to occur at the approximate longitude of 170@xmath0 or phase 0.47 .
our image is quite different from the one obtained by gu et al .
( 2003 ) for almost a simultaneous observing period , but a different spectral region .
their inversions gave much larger , longitudinally extended , spot structures around 170 - 290@xmath0 at roughly 60@xmath0 of latitude .    in september 1999
our inversions also show only one strong spot that has barely moved in the orbital reference frame ( latitude 44@xmath0 and longitude 160@xmath0 or phase 0.44 ) .
there is a weaker , longitudinally extended feature visible between 220 - 270@xmath0 or phase 0.61 - 0.75 .
almost two years later , in august 2001 ( fig .
3 ) , the star exhibits much more surface structures : three spots are visible in our image ( longitudes 70@xmath0 , 140@xmath0 , and 200@xmath0 or phases 0.19 , 0.39 and 0.56 ) at an approximate latitude of 40@xmath0 .
the inversions of gu et al .
( 2003 ) for an observing run 5 months later show much less structure , and the maximal activity seems to have moved roughly to the other side of the star than what was seen in their images during 1999 and 2000 .
one year later , in august 2002 ( fig .
4 ) our maps show one strong spot at the latitude 40@xmath0 and longitude 80@xmath0 or phase 0.22 , and a weaker one at 300@xmath0 or phase 0.83 . in november 2002 ( fig .
5 ) only the stronger spot is seen approximately at the same location . comparing the surface temperature distribution during the observing seasons 1999 and 2002
, the maximal spot activity seems to have moved by roughly 100@xmath0 in the orbital reference frame , while very little drift of the spots can be seen during the consequtive observing runs during 1999 and 2002 . in between these
two states of only one strong spot at different location on the surface , a much more complex distribution could be seen during august 2001 .
our images give some support to the conclusion of gu et al .
( 2003 ) of a significant change of the longitudinal spot distribution having occured sometime during 2001 ( fig .
we plan to continue to study the spot evolution on ii peg by analysing photometric and spectropolarimetric observations of the object , both to invert the surface temperature distribution , but also the magnetic field configuration of the object .
1998a , _ a&a _ , 340 , 437
the active rs cvn star ii peg has been spectroscopically monitored for almost 18 years with the sofin spectrograph at not , la palma , spain . in this paper 
 we present five new surface temperature maps of the object for the years 1999 ( two maps ) , 2001 ( one map ) and 2002 ( two maps ) .