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proper interpretation of the results from precision rv studies of gk - giants requires a detailed knowledge of their physical parameters .
effective temperatures and gravitational accelerations are needed to obtain luminosities , and , with the additional knowledge of metallicities , estimates of stellar masses and ages can be derived by means of the isochrone fitting . together with estimates of stellar radii and rotation periods , these data allow one to address the influence of stellar surface inhomogeneities ( spots ) on the observed rv variations .
all alternative sources of rv variations in gk - giants have to be ruled out before substellar companion interpretation becomes acceptable .
unfortunately , the long period variations , if present , can not usually be studied using data other than the existing photometry ( usually of moderate quality ) , or the data collected from the rv survey .
therefore , the detailed activity discussion is usually based on the indicators defined on the basis of the same spectra as those used for the rv measurements . in this paper
, we illustrate our methodology of the determination of stellar parameters and activity analysis based on the case of the k - giant psu - tcfa 18 , a potential planet hosting star .
observations were made with the hobby - eberly telescope ( het ) and the high resolution spectrograph ( hrs ) .
the hrs was used in the r=60,000 resolution mode with a gas cell ( @xmath1 ) inserted into the optical path , and it was fed with a 2 arcsec fiber .
typically , the signal - to - noise ratio per resolution element ( at 594 nm ) was @xmath2200 for the stellar spectra taken with the gas cell , and @xmath3250 for the templates .
the atmospheric parameters of the program stars were obtained with the spectroscopic method ( ( * ? ? ? * ; * ? ? ?
* takeda  2005a , b ) ) , which is based on analysis of fe  i and fe  ii lines and relies on conditions resulting from the assumption of the lte .
typically , over 200 fei and about 25 feii lines were measured for every star .
we tested a reliability of our determinations with the ( * ? ? ?
* takeda  _ et  al . _
( 2005a ) ) tgvit code by applying it to 8 stars , for which the parameters have been published by ( * ? ? ?
* butler  ( 2006 ) ) .
a comparison of the results shows that @xmath4 values agree to within 49 k , and that the same is true for @xmath5 to within 0.11 dex and @xmath6 $ ] to within 0.11 dex , respectively .
stellar masses were derived by comparing the positions of stars in the hr diagram with the theoretical evolutionary tracks of ( * ? ? ?
* girardi  ( 2000 ) ) and ( * ? ? ?
* salasnich  ( 2000 ) ) for a given metallicity . for stars for which the parallax determinations are precise enough
, the metallicity may introduce a significant uncertainty in mass because of the choice of an evolutionary track .
we assume that for an average red giant with a known parallax , the mass may be estimated to within @xmath7 .
we also note that for stars in the red giant clump , which are in the fast evolution phase with mass - loss , the derived masses are probably the upper limits .
stellar radii were determined using the calibration given in ( * ? ? ?
* alonso  ( 2000 ) ) .
stellar ages are usually estimated with the aid of the theoretical stellar isochrones .    in the case of the psu - tcfa  18 star , we have measured equivalent widths of up to 195 fe  i and 11 fe  ii lines for further analysis . for this star ,
the basic physical parameters are @xmath8 , @xmath9 , @xmath10 , @xmath6 = 0.11 $ ] , @xmath11 , and @xmath12 .
intrinsic uncertainties of our determinations are @xmath13 , @xmath14 , @xmath15 and @xmath16 = 0.06 $ ] .
rotation periods represent a parameter of particular importance in searches for planetary companions to red giants .
as the rotation periods of these stars are very similar to expected orbital periods , their knowledge is critical for an unambiguous interpretation of observations .
any correlation of stellar activity indicators variations with the rotation period make a substellar companion hypothesis unlikely . to estimate rotation periods from our spectra
we have used the cross - correlation technique , as described in ( * ? ? ?
* benz & mayor ( 1984 ) ) .
we have computed the ccfs by cross correlating the high s / n blue spectra with a numerical mask . to measure @xmath17
we have worked out a @xmath17 calibration for the het / hrs . to determine the @xmath18 vs. @xmath19 relationship ,
we have used 16 slow rotators with accurately known projected rotational velocities , preferably from ( * ? ? ?
* gray ( 1989 ) ) , ( * ? ? ?
* fekel ( 1997 ) ) and ( * ? ? ?
* de medeiros & mayor ( 1999 ) ) . for these stars
we have determined @xmath18 using the formula from ( * ? ? ?
* benz & mayor ( 1984 ) ) ( @xmath20 ) and assuming the constant @xmath21 following the ( * ? ? ?
* queloz  ( 1998 ) ) and ( * ? ? ?
* melo  ( 2001 ) ) .
we have carried out a least - squares fit to the data of the analytical function @xmath22 , which yields the following calibration : @xmath23 .    using this calibration
we have obtained @xmath24 for our star . adopting the radius for this star
as determined above , we have estimated its rotational period to be 220 - 950 days .
the large uncertainty in the rotation period is caused by uncertainties related to the determination of the radius and @xmath17 .
one of possible sources of the observed rv variations in gk - giants is due to their pulsations .
therefore , photometric data that span long periods of time are needed for the interpretation of the results of our survey . because we do not conduct our own parallel photometric observations ,
we must rely on the existing photometric databases like _
hipparcos _ or _ nsvs _ ( ( * ? ? ?
* woniak et al . 2004 ) ) .
these moderate quality data provide time - series , which are long enough to be useful in searches for long - term periodicities .
however , these measurements were usually performed many years prior to our rv survey . in the particular case of the psu - tcfa 18 star ,
no detectable variability is present in the existing photometric data .
the basic tool to study the origin of rv variations derived from the stellar spectra is the analysis of the shapes of spectral lines via line bisectors ( ( * ? ? ?
* gray 1983 ) ) .
we have computed line bisectors for 5 strong , unblended spectral features of a moderate intensity , which were located close to the center of echelle orders : cr i 663.003 nm , ni i
664.638 nm , ca i 671.77 nm , fe i 675.02 nm , and ni i 676.784 nm .
all these lines show well defined bisectors .
the changes in the spectral line bisectors were quantified using the bisector velocity span ( @xmath25 ) parameter , which is simply the velocity difference between the upper and the lower points of the line bisector ( @xmath26 ) , and the bisector curvature ( @xmath27 ) , which is the difference of the velocity span of the upper half of the bisector and its lower half ( @xmath28 ) .
it is important to examine both @xmath25 and @xmath27 , because it is possible for a star to show variations in one of these parameters only . in choosing the span points
, it is important to avoid the wings and cores of the spectral line , where the errors in the bisector measurements are large . for our span measurements we chose @xmath29 , @xmath30 , and @xmath31 in terms of the line depth at the line core . using the bisector measurements of all 5 spectral lines
we have computed the average velocity span and curvature after subtracting the mean value for each spectral line .    in figure[fig1 ] , we present the mean bisector velocity span ( @xmath32)and the mean bisector curvature ( @xmath33 ) for our star , as a function of rv . uncertainties in the derived values of @xmath32 and @xmath33 were estimated as standard deviations of the mean .
the correlation coefficients were found to be @xmath34 for @xmath32 and @xmath35 for @xmath33 .
it is clear that they are not correlated with radial velocities which supports the planetary mass companion hypothesis .
the available rv measurements are not uniformly distributed over the estimated period , which is visible in fig . 1 as a scatter varying with rv .
more observations are needed to confirm the apparent lack of correlation .     for psu - tcfa 18 as a function of radial velocity.,width=182 ]      since our spectra start at 407.6 nm we can not investigate the variation of the ca ii k emission line ( 393.4 nm ) .
also the infrared caii triplet lines 849.8 - 854.2 are outside the range of our spectra .
therefoer , we use h@xmath0 line ( 656.28 nm ) as a chromospheric activity indicator .
the ew measurements of the @xmath36 line can be made in our spectra with a typical precision of a few percent . in the case of our star ,
the measurements give a mean value of @xmath37 .
the rms value of @xmath38 corresponds to 2 % variation in the ew . in figure [ fig1 ]
we present ew measurements for @xmath36 as a function of rv .
the correlation coefficient of @xmath39 shows marginal relationship ( probably resulting from the non - uniform rv coverage ) which again supports the planetary hypothesis .
a detailed knowledge of stellar parametres of red giants is very important for interpretation of their rv variations . to rule out stellar activity as the source of such variations
, one needs precise rotation periods and several other indicators to be measured at many epochs .
an & gn acknowledge the financial support from the mnisw through grant 1p03d 007 30 .
gn is a recipient of a graduate stipend of the chairman of the polish academy of sciences .
pz was supported by mnisw grant spb 104e-3376 .
the hobby - eberly telescope ( het ) is a joint project of the university of texas at austin , the pennsylvania state university , stanford university , ludwig - maximilians - universitt mnchen , and georg - august - universitt gttingen .
the het is named in honor of its principal benefactors , william p. hobby and robert e. eberly .
the main objective of the penn state / toru centre for astronomy search for planets around evolved stars is the detection of planetary systems around massive , evolved stars . 
 we are also interested in the evolution of these systems on stellar evolution timescales . in this paper 
 we present our approach to determine the basic physical parameters of our targets gk - giants . 
 we also discuss the stellar activity indicators used in our survey : line bisector and curvature , and h@xmath0 variability .