document: one surprising result that has come out of the more than 200 extrasolar planet discoveries to date is the wide range of eccentricities observed . unlike our own solar system 
   , many of the extrasolar planets which are not tidally locked to their host stars have moderate eccentricities ( @xmath1 ) , and 15 planets have high eccentricities ( @xmath0 ) . 
   these observations have spawned several theories as to the origin of highly eccentric extrasolar planets . 
   one such method , planet - planet scattering , occurs when multiple jovian planets form several astronomical units ( au ) from the host star and then interact , leaving one in an eccentric orbit and often ejecting the other @xcite . 
   this method has been proposed to explain the architecture of the @xmath2 and planetary system @xcite , which contains a hot jupiter as well as two jovian planets in moderately eccentric orbits . 
   @xcite suggested a merger scenario in which inner protoplanets perturb each other and merge to form a single massive , eccentric planet with @xmath3 and @xmath4 au . 
   interactions with stellar companions are another possible way to boost a planet s eccentricity . 
   of the 15 stars hosting a planet with @xmath0 , six are also known to possess stellar - mass companions in wide binary orbits : hd  3651 @xcite , hd  20782 @xcite , hd  80606 , hd  89744 @xcite , 16  cyg  b , and hd  222582 @xcite . 
   if the inclination angle between the planetary orbit and a stellar companion is large , the kozai mechanism @xcite can induce large - amplitude oscillations in the eccentricity of the planet ( e.g.  malmberg et al . 
   these oscillations can be damped by general relativistic effects and by interaction with other planets , and hence are most effective in systems with a single planet in an orbit @xmath51  au from the host star @xcite . 
   the kozai mechanism has been suggested to explain the high eccentricity of 16  cyg  bb @xcite and hd  80606b @xcite . 
   @xcite found the inclination of 16  cyg  b orbiting the system barycenter to lie between 100 and 160 degrees , where 90 degrees is an edge - on orientation . 
   however , it is the difference in inclination between the orbital planes of the planetary and stellar companion that is critical in determining the importance of the kozai mechanism , and the inclination of the planet s orbit is generally not known for non - transiting systems .    of the 192 known planetary systems , 23 ( 12% ) 
   are multi - planet systems . 
   recent discoveries of additional objects in systems known to host at least one planet @xcite suggest that multiple - planet systems are common . 
   of particular interest are systems which host a jovian planet and a low - mass `` hot neptune , '' e.g.  55  cnc ( = hd  75732 ) , gj  876 , @xmath6 arae ( = hd  160691 ) , gl  777a ( = hd  190360 ) . motivated by the discoveries of hot neptunes in known planetary systems , we have undertaken an intensive survey of selected single - planet systems to search for additional low - mass companions . 
   three of the planetary systems discussed in this paper ( hd  3651 , hd  80606 , hd  89744 ) are part of this campaign . 
   the excellent radial - velocity precision of the high resolution spectrograph on the hobby - eberly telescope ( het ) , combined with queue - scheduling , allow us to time the observations in such a way as to minimize phase gaps in the orbit of the known planet , and also to act quickly on potential new planet candidates . 
   the use of the het in this manner is discussed further in @xcite with regard to the discovery of hd  37605b .    in this work 
   , we aim to combine observational limits on additional planets in known planetary systems with dynamical constraints obtained by n - body simulations . 
   the observations address the question : what additional planets are ( or are not ) in these systems ? 
   the dynamical simulations can answer the question : where are additional planets possible ? 
   section  2 describes the observations and the test particle simulations for six highly eccentric planetary systems : hd  3651 , hd  37605 , hd  45350 , hd  80606 , hd  89744 , and 16 
   cyg  b. we have chosen these systems based on two criteria : ( 1 ) each hosts a planet with @xmath0 , and ( 2 ) each has been observed by the planet search programs at mcdonald observatory . in  3 , we present and discuss the results of the updated orbital fits , dynamical simulations , and detection limit computations . 
   five of the six stars considered in this work have been observed with the mcdonald observatory 9.2  m hobby - eberly telescope ( het ) using its high resolution spectrograph ( hrs ) @xcite . 
   a full description of the het planet search program is given in @xcite . 
   for 16  cyg  b , observations from mcdonald observatory were obtained only with the 2.7  m harlan j.  smith ( hjs ) telescope ; the long - term planet search program on this telescope is described in @xcite . 
   all available published data on these systems were combined with our data from mcdonald observatory in the orbit fitting procedures .      to place constraints on the architecture of planetary systems , we would like to know where additional objects can remain in stable orbits in the presence of the known planet(s ) . 
   we performed test particle simulations using swifthal / swift.html . ] 
   @xcite to investigate the dynamical possibility of additional low - mass planets in each of the six systems considered here . 
   low - mass planets can be treated as test particles since the exchange of angular momentum with jovian planets is small . 
   we chose the regularized mixed - variable symplectic integrator ( rmvs3 ) version of swift for its ability to handle close approaches between massless , non - interacting test particles and planets . 
   particles are removed if they are ( 1 ) closer than 1 hill radius to the planet , ( 2 ) closer than 0.05  au to the star , or ( 3 ) farther than 10  au from the star . 
   since the purpose of these simulations is to determine the regions in which additional planets could remain in stable orbits , we set this outer boundary because the current repository of radial - velocity data can not detect objects at such distances . 
   the test particle simulations were set up following the methods used in @xcite , with the exception that only initially circular orbits are considered in this work . for each planetary system , 
   test particles were placed in initially circular orbits spaced every 0.002  au in the region between 0.05 - 2.0  au . 
   we have chosen to focus on this region because the duration of our high - precision het data is currently only 2 - 4 years for the objects in this study . 
   the test particles were coplanar with the existing planet , which had the effect of confining the simulation to two dimensions . 
   input physical parameters for the known planet in each system were obtained from our keplerian orbit fits described in   3.1 , and from recent literature for 16  cyg  b @xcite and hd  45350 @xcite . 
   the planetary masses were taken to be their minimum values ( sin  @xmath7 ) . 
   the systems were integrated for @xmath8 yr , following @xcite and allowing completion of the computations in a reasonable time . 
   we observed that nearly all of the test - particle removals occurred within the first @xmath9 yr ; after this time , the simulations had essentially stabilized to their final configurations . 
   we present updated keplerian orbital solutions for hd  3651b , hd  37605b , hd  80606b , and hd  89744b in table  1 . 
   a summary of the data used in our analysis is given in table  2 , and the het radial velocities are given in tables  3 - 6 . 
   the velocity uncertainties given for the het data represent internal errors only , and do not include any external sources of error such as stellar `` jitter . '' 
   the parameters for the remaining two planets , hd  45350b and 16  cyg  bb , are taken from @xcite and @xcite , respectively . 
   radial velocity measurements from the het are given for hd  45350 in @xcite , and velocities for 16  cyg  b from the hjs telescope are given in @xcite . 
   as in @xcite , all available published data were combined with those from mcdonald , and the known planet in each system was fit with a keplerian orbit using gaussfit @xcite , allowing the velocity offset between each data set to be a free parameter . 
   examination of the residuals to our keplerian orbit fits revealed no evidence for additional objects in any of the six systems in this study . 
   the saturn - mass ( m  sin  @xmath10 ) planet hd  3651b was discovered by @xcite using observations from lick and keck . 
   we fit these data , which were updated in @xcite , in combination with observations from the hjs and het at mcdonald observatory . 
   the het data , which consist of multiple exposures per visit , were binned using the inverse - variance weighted mean value of the velocities in each visit . 
   the standard error of the mean was added in quadrature to the weighted rms about the mean velocity to generate the error bar of each binned point ( n=29 ) . 
   the rms about the combined fit for each dataset is : lick & keck6.6 , het9.4 , hjs12.2 . 
   the fitted orbital parameters for hd  3651b are of comparable precision to those reported in @xcite , and agree within 2@xmath11 . 
   the recent discovery of a t dwarf companion to hd  3651 @xcite prompts an interesting exercise : can the radial - velocity trend due to this object be detected in the residuals after removing the planet ? 
   we detect a slope of @xmath12  yr@xmath13 , indicating that we are indeed able to discern a trend which is possibly due to the binary companion . 
   however , the reduced @xmath14 of the orbital solution is not significantly improved by the inclusion of a linear trend ( @xmath15=0.18 ) . 
   the parameters given in table  1 were obtained from the fit which did not include a trend . 
   we present 23 new het observations for hd  37605 obtained since its announcement by @xcite . 
   the data now span a total of 1065  days . 
   the best fit is obtained by including an acceleration of @xmath16  yr@xmath13 , indicating a distant orbiting body . 
   such a finding would lend support to the hypothesis that very eccentric single - planet systems originate by interactions within a wide binary system . 
   the shortest period that this outer companion could have and still remain consistent with the observed acceleration and its uncertainty over the timespan of the observations is about 40  yr , assuming a circular orbit . 
   this object would then have a minimum mass in the brown dwarf range 
   .    the planet orbiting hd  80606 , first announced by @xcite , is the most eccentric extrasolar planet known , with @xmath17 ( table  1 ) . 
   we have fit the coralie data in combination with the keck data given in @xcite and 23 observations from het . 
   the extreme velocity variations induced by this planet greatly increase the sensitivity of orbit fits to the weighting of individual measurements . since the uncertainties of the het velocities given in tables  3 - 6 represent internal errors only , we experimented with adding 1 - 7 of radial - velocity `` jitter '' in quadrature before fitting the data for hd  80606 . 
   for all of these jitter values , the fitted parameters remained the same within their uncertainties . 
   table  1 gives the parameters derived from a fit which added 3.5  of jitter @xcite to the het data . 
   the rms about the combined fit is : coralie18.7 , het7.5 , keck5.6 . 
   @xcite noted that the eccentricity @xmath18 and the argument of periastron @xmath19 had to be held fixed in their fit to the keck data alone . 
   however , the large number of measurements included in this work allowed gaussfit to converge with all parameters free .    for hd  89744b , we combine data from the het with 6 measurements from the hjs telescope and lick data from @xcite . 
   the het data were binned in the same manner as for hd  3651 , resulting in n=33 independent visits . 
   the rms about the combined fit for each dataset is : lick17.1 , het10.7 , hjs9.5 . as with hd  3651b , 
   our derived parameters agree with those of @xcite within 2@xmath11 . 
   the scatter about our fit remains large , most likely due to the star s early spectral type ( f7v ) , which hinders precision radial - velocity measurements due to the smaller number of spectral lines . 
   for example , the f7v star hd  221287 was recently found to host a planet @xcite ; despite the superb instrumental precision of the harps spectrograph , that orbital solution has a residual rms of 8.5 . 
   the results of the dynamical simulations are shown in figures  1 - 3 . 
   the survival time of the test particles is plotted against their initial semimajor axis . 
   as shown in figure  1 , the short - period planets hd  3651 and hd  37605 sweep clean the region inside of about 0.5  au . in both of these systems , however , a small number of test particles remained in low - eccentricity orbits near the known planet s apastron distance , near the 1:2 mean - motion resonance ( mmr ) . in the hd  3651 system , particles remained stable beyond about 0.6  au , which is not surprising given the low mass of the planet . for hd  37605 , 
   two distinct strips of stability are seen in fig .  1 , corresponding to the 1:2 and 1:3 mmrs . 
   the eccentricity of the test particles in the region of the 1:2 mmr oscillated between 0.00 and 0.06 . 
   particles in 1:3 mmr oscillated in eccentricity with a larger range , up to @xmath20 , which is expected due to secular forcing . as with hd  3651 , the region beyond about 0.8  au 
   was essentially unaffected by the planet . 
   figure  2 shows the results for the hd  45350 and hd  80606 systems . 
   the long period ( 963.6 days ) and relatively large mass ( m  sin  @xmath21=1.8 ) of hd  45350b restricted stable orbits to the innermost 0.2  au . 
   these test particles oscillated in eccentricity up to @xmath22 . 
   the 4  planet orbiting hd  80606 removed all test particles to a distance of about 1.5  au , and only beyond 1.75  au did test particles remain in stable orbits for the duration of the simulation ( @xmath8 yr ) . 
   a region of instability is evident at 1.9  au due to the 8:1 mmr . 
   figure  3 shows that hd  89744b eliminated all test particles except for a narrow region near the 8:3 resonance . 
   for the 16  cyg  b system , only particles inside of about 0.3  au remained stable , leaving open the possibility of short - period planets . 
   the surviving particles oscillated in eccentricity up to @xmath23 , but these simulations treat the star as a point mass , and hence tidal damping of the eccentricity is not included 
   . our results are consistent with those of @xcite , who investigated dynamical stability in extrasolar planetary systems and found that no test particles survived in the habitable zones of the hd  80606 , hd  89744 , and 16  cyg  b systems . 
   three of these systems ( hd  3651 , hd  80606 , hd  89744 ) were monitored intensely with the het as part of a larger effort to search for low - mass , short period planets . 
   no evidence was found for any such objects in these or any of the six systems in this work . 
   we then asked what limits can be set on additional planets using the high - precision het data we have obtained . 
   the procedure for determining companion limits was identical to the method described in @xcite , except that in this work , the best - fit keplerian orbit for the known planet ( see   3.1 ) was removed before performing the limits computations . in this way 
   , we determined the radial - velocity amplitude @xmath24 for which 99% of planets would have been detected in the residuals . 
   the eccentricity of the injected test signals was chosen to be the mean eccentricity of the surviving particles from the simulations described in   3.2 . only the regions in which test particles survived were considered in these limits computations . 
   the results of these computations were highly varied , reflecting the differing observing strategies employed for these six objects . 
   in particular , hd  3651 , hd  80606 , and hd  89744 were monitored intensely with the het as part of a search for short - period objects , whereas hd  37605 and hd  45350 were only observed sporadically after the known planet orbits were defined and published @xcite , and 16  cyg  b has only been observed with the hjs telescope at a frequency of at most once per month . 
   the companion limits are shown in figures  4 - 6 ; planets with masses above the solid line can be ruled out by the data with 99% confidence . 
   not surprisingly , the tightest limits were obtained for hd  3651 ( figure  4 ) , which had a total of 195 measurements , including 29 independent het visits . 
   for periods less than about 1  year , we can exclude planets with m  sin  @xmath21  2 neptune masses . 
   similar results were obtained for 16  cyg  b ( n=161 ) , where the limits approach a neptune mass ( figure  6 ) . 
   since the detection limits generally improve with the addition of more data and with higher - quality data , we can define a quantity to measure the goodness of the limits . 
   a simple choice would be @xmath25 , where @xmath26 is the total number of observations , and @xmath27 is the mean uncertainty of the radial - velocity measurements . 
   the values of @xmath26 and @xmath27 are given in table  2 .    in the hd  45350 system , the results of the dynamical simulations complement those of the detection limit determinations . 
   very tight limits are obtained in close orbits ( @xmath280.2  au ) . in this region , 
   test particles were stable ( fig .  2 ) and our observations can exclude planets with m  sin  _ i _ between about 1 and 4 neptune masses . 
   similar results were obtained for the 16  cyg  b system , in which test particles remained stable inward of @xmath29  0.3  au . in that region , 
   planets of 1 - 3 neptune masses can be excluded by our limits determinations ( fig . 
   6 ) . in most of the limits determinations 
   , there are multiple `` blind spots '' evident where the periodogram method failed to significantly recover the injected signals . 
   typically this occurs at certain trial periods for which the phase coverage of the observational data is poor , and often at the 1-month and 1-year windows .    for none of hd  37605 ( fig .  4 ) , hd  80606 ( fig .  5 ) , or hd  89744 ( fig . 
   6 ) could additional companions be ruled out below about 0.7 , and for most orbital periods tested , the limits were substantially worse . 
   one possible explanation for this result is that the sampling of the observations was poorly distributed in phase for many of the injected test signals , making significant recovery by the periodogram method difficult . 
   this is evidenced by the `` jagged '' regions in the plots . 
   also , the intrinsic scatter for those three systems was too large to permit tight limits determination . 
   this is certainly reasonable for the f7 star hd  89744 . 
   the three systems with the best limits ( hd  3651 , hd  45350 , and 16  cyg  b ) also had the lowest rms scatter about their orbital solutions ( mean=@xmath30 ; table  1 ) . 
   in contrast , the mean rms for the remaining three systems was @xmath31 . 
   additional factors such as a paucity of data ( hd  37605 ) and short time baselines ( hd  80606 , hd  89744 ) made the determination of useful companion limits challenging for some of the planetary systems in this study . 
   we have shown that for a sample of six highly eccentric extrasolar planetary systems , there is no evidence for additional planets . 
   test particle simulations show that there are regions detectable by current surveys ( i.e.  for @xmath32 au ) where additional objects can exist . for hd  3651 and hd  37605 
   , we find that protected resonances are also present . 
   combining these simulations with detection limits computed using new high - precision het data combined with all available published data is particularly effective for the hd  3651 and hd  45350 systems . 
   additional short - period planets can be ruled out down to a few neptune masses in the dynamically stable regions in these systems . 
   this material is based upon work supported by the national aeronautics and space administration under grant nos . 
   nng04g141 g and nng05g107 g issued through the terrestrial planet finder foundation science program . 
   we are grateful to the het tac for their generous allocation of telescope time for this project . 
   we also would like to thank barbara mcarthur for her assistance with gaussfit software . 
   we thank the referee , greg laughlin , for his careful review of this manuscript . 
   this research has made use of nasa s astrophysics data system ( ads ) , and the simbad database , operated at cds , strasbourg , france . 
   the hobby - eberly telescope ( het ) is a joint project of the university of texas at austin , the pennsylvania state university , stanford university , ludwig - maximilians - universit " at mnchen , and georg - august - universit " at g " ottingen the het is named in honor of its principal benefactors , william p.  hobby and robert e.  eberly . 
   lllllllll hd 3651 b & 62.197@xmath330.012 & 53932.2@xmath330.4 & 0.630@xmath330.046 & 250.7@xmath336.3 & 15.6@xmath331.1 & 0.20@xmath330.01 & 0.280@xmath330.006 & 7.1 + hd 37605 b & 55.027@xmath330.009 & 52992.8@xmath330.1 & 0.677@xmath330.009 & 218.4@xmath331.7 & 201.5@xmath333.9 & 2.39@xmath330.12 & 0.263@xmath330.006 & 13.0 + hd 45350 b & 963.6@xmath333.4 & 51825.3@xmath337.1 & 0.778@xmath330.009 & 343.4@xmath332.3 & 58.0@xmath331.7 & 1.79@xmath330.14 & 1.92@xmath330.07 & 9.1 + hd 80606 b & 111.428@xmath330.002 & 53421.928@xmath330.004 & 0.933@xmath330.001 & 300.4@xmath330.3 & 470.2@xmath332.5 & 4.10@xmath330.12 & 0.460@xmath330.007 & 13.5 + hd 89744 b & 256.78@xmath330.05 & 53816.1@xmath330.3 & 0.689@xmath330.006 & 194.1@xmath330.6 & 263.2@xmath333.9 & 7.92@xmath330.23 & 0.91@xmath330.01 & 14.4 + 16 cyg b b & 799.5@xmath330.6 & 50539.3@xmath331.6 & 0.689@xmath330.011 & 83.4@xmath332.1 & 51.2@xmath331.1 & 1.68@xmath330.07 & 1.68@xmath330.03 & 10.6 +    lllll hd 3651 & 163 & 3.4 & & @xcite + hd 3651 & 3 & 6.1 & & hjs + hd 3651 & 29 & 2.1 & & het + hd 3651 ( total ) & 195 & 3.2 & 7083 & + hd 37605 ( total ) & 43 & 2.9 & 1065 & het + hd 45350 & 38 & 2.8 & & @xcite + hd 45350 & 28 & 4.2 & & het + hd 45350 & 47 & 8.9 & & hjs + hd 45350 ( total ) & 113 & 5.7 & 2265 & + hd 80606 & 61 & 13.7 & & @xcite + hd 80606 & 46 & 5.1 & & @xcite + hd 80606 & 23 & 2.5 & & het + hd 80606 ( total ) & 130 & 8.7 & 2893 & + hd 89744 & 50 & 11.2 & & @xcite + hd 89744 & 33 & 3.2 & & het + hd 89744 & 6 & 9.4 & & hjs + hd 89744 ( total ) & 89 & 8.1 & 2687 & + 16 cyg b & 95 & 6.3 & & @xcite + 16 cyg b & 29 & 19.7 & & hjs phase ii + 16 cyg b & 37 & 7.4 & & hjs phase iii + 16 cyg b ( total ) & 161 & 9.0 & 6950 & +    lrr [ tbl-3 ] 53581.87326 & -19.1 & 2.9 + 53581.87586 & -19.4 & 2.7 + 53581.87846 & -20.7 & 2.7 + 53600.79669 & -11.5 & 2.4 + 53600.79860 & -15.5 & 3.0 + 53600.80050 & -22.8 & 2.9 + 53604.79166 & -15.8 & 1.9 + 53604.79356 & -18.8 & 2.1 + 53604.79548 & -21.3 & 2.1 + 53606.78169 & -19.3 & 1.8 + 53606.78360 & -14.8 & 2.1 + 53606.78551 & -24.0 & 1.8 + 53608.77236 & -18.8 & 1.9 + 53608.77426 & -18.0 & 1.9 + 53608.77617 & -18.8 & 1.8 + 53615.96280 & -28.0 & 2.6 + 53615.96471 & -31.9 & 2.4 + 53615.96662 & -37.8 & 2.5 + 53628.74050 & -6.8 & 2.2 + 53628.74240 & -14.5 & 2.4 + 53628.74431 & -5.5 & 2.2 + 53669.61012 & -18.2 & 2.1 + 53669.61203 & -19.2 & 2.2 + 53669.61394 & -17.7 & 2.4 + 53678.78954 & -10.6 & 2.4 + 53678.79141 & -8.6 & 2.3 + 53678.79332 & -2.3 & 2.1 + 53682.78423 & -15.4 & 2.2 + 53682.78609 & -15.0 & 2.3 + 53682.78801 & -11.9 & 2.3 + 53687.77684 & 11.3 & 2.2 + 53687.77875 & 8.7 & 2.2 + 53687.78066 & 15.9 & 2.2 + 53691.75967 & 9.6 & 2.2 + 53691.76158 & 20.3 & 2.1 + 53691.76349 & 15.9 & 2.0 + 53696.75837 & 16.1 & 1.8 + 53696.76028 & 18.6 & 1.8 + 53696.76220 & 20.0 & 2.0 + 53694.75275 & 18.0 & 1.9 + 53694.75466 & 15.1 & 2.0 + 53694.75656 & 17.8 & 2.0 + 53955.83401 & -0.5 & 1.9 + 53955.83593 & -1.2 & 2.0 + 53955.83785 & 1.3 & 1.9 + 53956.82850 & 0.4 & 2.0 + 53956.83046 & -1.0 & 2.0 + 53956.83236 & -5.4 & 2.2 + 53957.82201 & -2.1 & 2.0 + 53957.82392 & -1.3 & 2.0 + 53957.82583 & -3.6 & 2.0 + 53973.80721 & 9.8 & 7.3 + 53973.81020 & 3.5 & 2.3 + 53973.81200 & -3.5 & 2.0 + 53976.78393 & -10.4 & 2.4 + 53976.78586 & -5.4 & 2.1 + 53976.78778 & -6.7 & 2.3 + 53978.97197 & -3.8 & 2.6 + 53985.95886 & -9.0 & 2.3 + 53985.96079 & 4.3 & 3.3 + 53987.95335 & -8.3 & 2.2 + 53987.95527 & -8.0 & 2.2 + 53987.95719 & -12.0 & 2.3 + 53989.73817 & -13.2 & 2.2 + 53989.74009 & -13.2 & 2.1 + 53989.74203 & -18.6 & 2.1 + 54003.70719 & 2.0 & 2.2 + 54003.70915 & 4.7 & 2.4 + 54005.68297 & 7.0 & 2.5 + 54005.68488 & 11.1 & 2.0 + 54005.68690 & 10.2 & 2.1 + 54056.77919 & -7.5 & 2.2 + 54056.78110 & -11.5 & 2.1 + 54056.78302 & -9.6 & 2.3 + 54062.55119 & 20.1 & 1.8 + 54062.55312 & 21.9 & 2.0 + 54062.55505 & 20.9 & 2.0 + 54064.54710 & 12.8 & 2.0 + 54064.54902 & 16.7 & 2.1 + 54064.55094 & 16.6 & 2.1 + 54130.55316 & 19.1 & 2.4 + 54130.55508 & 16.9 & 2.5 + 54130.55701 & 17.6 & 2.5 +    lrr [ tbl-4 ] 53002.67151 & 487.6 & 3.8 + 53003.68525 & 495.5 & 3.0 + 53006.66205 & 496.2 & 3.0 + 53008.66407 & 501.3 & 2.9 + 53010.80477 & 499.8 & 2.9 + 53013.79399 & 482.1 & 2.6 + 53042.72797 & 269.7 & 2.8 + 53061.66756 & 489.0 & 2.6 + 53065.64684 & 479.0 & 2.8 + 53071.64383 & 463.8 & 2.6 + 53073.63819 & 460.4 & 2.6 + 53082.62372 & 422.8 & 2.5 + 53083.59536 & 422.2 & 2.8 + 53088.59378 & 418.6 & 4.0 + 53089.59576 & 379.1 & 2.2 + 53092.59799 & 343.7 & 2.5 + 53094.58658 & 323.2 & 2.4 + 53095.58642 & 302.1 & 2.4 + 53096.58744 & 302.1 & 3.2 + 53098.57625 & 193.8 & 2.7 + 53264.95137 & 164.9 & 3.0 + 53265.94744 & 112.9 & 3.0 + 53266.94598 & 113.2 & 3.7 + 53266.95948 & 74.6 & 3.6 + 53266.97396 & 119.2 & 8.0 + 53283.92241 & 471.6 & 2.7 + 53318.81927 & 213.3 & 3.0 + 53335.92181 & 496.9 & 2.6 + 53338.90602 & 493.9 & 2.6 + 53377.81941 & 109.1 & 2.7 + 53378.81189 & 214.6 & 2.7 + 53379.80225 & 338.3 & 2.6 + 53381.64429 & 436.1 & 2.7 + 53384.64654 & 482.9 & 2.8 + 53724.85584 & 468.2 & 2.6 + 53731.69723 & 435.4 & 2.7 + 53738.67472 & 404.3 & 2.6 + 53743.81020 & 400.5 & 2.6 + 53748.64724 & 348.4 & 2.7 + 54039.85015 & 272.5 & 3.1 + 54054.96457 & 437.4 & 2.7 + 54055.95279 & 422.0 & 2.9 + 54067.76282 & 376.4 & 2.6 +    lrr [ tbl-5 ] 53346.88103 & -20.8 & 3.0 + 53358.02089 & -49.5 & 2.7 + 53359.82400 & -60.4 & 3.0 + 53361.02985 & -64.7 & 2.5 + 53365.03079 & -77.4 & 2.4 + 53373.98282 & -88.4 & 3.0 + 53377.80112 & -105.5 & 2.4 + 53379.75230 & -109.3 & 2.7 + 53389.74170 & -115.3 & 2.5 + 53391.74400 & -129.4 & 2.4 + 53395.72763 & -146.4 & 2.3 + 53399.72518 & -158.4 & 2.5 + 53401.72497 & -174.7 & 2.7 + 53414.67819 & -219.8 & 3.0 + 53421.85529 & 261.0 & 2.2 + 53423.86650 & 322.1 & 2.0 + 53424.85231 & 245.9 & 2.1 + 53432.87120 & 87.5 & 1.9 + 53433.60628 & 70.0 & 2.1 + 53446.79322 & 4.5 & 1.9 + 54161.85400 & -109.5 & 2.8 + 54166.83797 & -119.3 & 2.4 + 54186.76189 & -184.2 & 2.3 +    lrr [ tbl-6 ] 53709.89685 & -184.5 & 2.3 + 53723.85188 & -238.6 & 2.2 + 53723.85367 & -238.2 & 2.5 + 53723.85546 & -227.7 & 2.3 + 53727.84394 & -238.9 & 2.5 + 53727.84573 & -244.9 & 2.4 + 53727.84752 & -242.9 & 2.6 + 53736.81887 & -257.6 & 2.5 + 53736.82100 & -248.2 & 2.9 + 53736.82315 & -253.4 & 2.4 + 53738.03261 & -246.7 & 2.8 + 53738.03441 & -243.3 & 2.4 + 53738.03620 & -236.0 & 2.5 + 53738.80860 & -240.5 & 2.6 + 53738.81040 & -258.9 & 2.4 + 53738.81219 & -249.3 & 2.5 + 53734.81795 & -242.8 & 2.6 + 53734.81973 & -243.9 & 2.8 + 53734.82152 & -248.5 & 2.4 + 53742.79119 & -252.0 & 2.8 + 53742.79299 & -257.2 & 2.8 + 53742.79479 & -239.7 & 2.8 + 53751.78199 & -257.4 & 2.9 + 53751.78378 & -263.1 & 2.5 + 53751.78558 & -268.0 & 2.3 + 53753.78155 & -273.1 & 2.5 + 53753.78381 & -278.7 & 2.5 + 53753.78607 & -266.4 & 2.4 + 53755.76038 & -286.6 & 2.3 + 53755.76218 & -266.5 & 2.6 + 53755.76397 & -274.9 & 2.7 + 53746.81506 & -257.1 & 1.9 + 53746.81778 & -250.9 & 2.1 + 53746.82051 & -245.2 & 2.3 + 53757.77002 & -277.6 & 2.4 + 53757.77181 & -280.3 & 2.4 + 53757.77360 & -288.7 & 2.2 + 53797.64609 & -439.8 & 3.1 + 53797.64834 & -462.6 & 2.8 + 53797.65059 & -452.5 & 2.9 + 53809.62428 & -658.6 & 2.4 + 53809.62700 & -658.8 & 2.5 + 53809.62972 & -659.2 & 2.3 + 53837.76359 & -304.3 & 3.0 + 53837.76670 & -324.0 & 2.9 + 53837.78731 & -308.6 & 2.7 + 53837.79077 & -285.2 & 2.6 + 53866.69987 & -215.9 & 1.7 + 53866.70329 & -228.3 & 1.7 + 53866.70670 & -220.4 & 1.8 + 53868.68349 & -251.6 & 3.8 + 53868.68562 & -208.6 & 2.9 + 53868.68777 & -247.4 & 9.7 + 53875.66956 & -215.7 & 1.6 + 53883.65565 & -213.8 & 1.8 + 53883.65837 & -209.2 & 1.7 + 53883.66109 & -200.4 & 1.7 + 53890.63776 & -203.4 & 1.7 + 53890.63954 & -202.6 & 1.9 + 53890.64134 & -203.2 & 1.9 + 53893.62959 & -193.8 & 2.0 + 53893.63139 & -189.3 & 1.9 + 53893.63318 & -189.7 & 1.8 + 54047.94811 & -375.2 & 4.8 + 54047.94991 & -353.2 & 4.5 + 54047.95172 & -362.6 & 4.4 + 54050.96248 & -415.0 & 2.6 + 54050.96453 & -423.0 & 2.5 + 54050.96657 & -420.1 & 2.4 + 54052.96488 & -426.8 & 2.3 + 54052.96762 & -437.1 & 2.5 + 54052.97035 & -447.6 & 2.5 + 54056.94606 & -468.0 & 3.0 + 54056.94786 & -466.4 & 2.6 + 54056.94964 & -479.4 & 2.8 + 54063.92981 & -599.1 & 2.1 + 54063.93166 & -594.8 & 2.3 + 54063.93348 & -592.3 & 2.4 + 54073.91213 & -685.8 & 2.8 + 54073.91476 & -688.7 & 2.9 + 54073.91739 & -704.4 & 2.7 + 54122.01039 & -220.8 & 2.5 + 54122.01243 & -219.1 & 2.6 + 54122.01447 & -218.4 & 2.8 + 54129.74214 & -215.7 & 2.6 + 54129.74491 & -224.4 & 3.0 + 54129.74768 & -223.7 & 3.1 + 54160.65850 & -189.5 & 3.2 + 54160.66031 & -181.8 & 2.7 + 54160.66212 & -204.8 & 3.2 + 54163.66458 & -213.9 & 3.1 + 54163.66643 & -200.8 & 2.9 + 54163.66828 & -208.0 & 3.2 + 54165.88148 & -208.5 & 2.7 +
summary: long time coverage and high radial velocity precision have allowed for the discovery of additional objects in known planetary systems . 
   many of the extrasolar planets detected have highly eccentric orbits , which raises the question of how likely those systems are to host additional planets . 
   we investigate six systems which contain a very eccentric ( @xmath0 ) planet : hd  3651 , hd  37605 , hd  45350 , hd  80606 , hd  89744 , and 16 
   cyg  b. we present updated radial - velocity observations and orbital solutions , search for additional planets , and perform test particle simulations to find regions of dynamical stability . 
   the dynamical simulations show that short - period planets could exist in the hd  45350 and 16  cyg  b systems , and we use the observational data to set tight detection limits , which rule out additional planets down to a few neptune masses in the hd  3651 , hd  45350 , and 16  cyg  b systems .