4 The results and discussion

We present our results in Table 3. The first two columns contain the coordinates of the primaries for epoch 2000. Next column contains the Durchmusterung designation of the primaries as listed in WDS (Worley & Douglass 1984). The next two columns contain the observed instrumental magnitude difference between the two components of the binary and its accuracy, $\Delta V$ and $\sigma_{_{\Delta V}}$.The following four columns contain angular separation $\rho''$, its accuracy $\sigma_{\rho''}$ in arcseconds, and the position angle $\theta$ with its accuracy $\sigma_{\theta}$ in degrees. All accuracies of the mean values always refer to four consecutive exposures of the same binary. The last column contains the epoch of the observation in years after 1900.0.

  

Table 3: Common proper motion binaries in our sample

The histogram of Fig. 4

  

Figure 4: Absolute values of differences in angular separations since the detection of the binary

  

Figure 5: Absolute values of differences in position angle since the detection of the binary

shows that 33% of the 83 observed binaries have an angular separation different by less than $0\hbox{$.\!\!^{\prime\prime}$}1$ or 5% of the initially observed -at the epoch of the detection of the binary- angular separation several decades ago. Additional 29% show changes in the range of 5% to 10%. ($0\hbox{$.\!\!^{\prime\prime}$}1 - 0\hbox{$.\!\!^{\prime\prime}$}2$). Most of them (73 or 88%) show $\vert\rho_{\rm detection}-\rho_{1998.5}\vert \le 0\hbox{$.\!\!^{\prime\prime}$}5$.Taken into account that WDS lists $\rho_{\rm detection}$ with a precision of 0.1 arcseconds and that the first double star observation is several decades old or even from last century -thus less accurate due to the technology used-, most of our targets show practically even now the same angular separation as at the epoch of their detection.

Similarly, Fig. 5 shows that 36% of them change their position angle less than $1.0\hbox{$^\circ$}$ (the precision of the position angle listed in WDS) in all these decades since their detection. Furthermore, 57 of them (or 70%) show $\vert\theta_{\rm detection}-\theta_{1998.5}\vert \le 5\hbox{$^\circ$}$.

Table 2 shows 12 double stars in the sample which show almost the same relative positions as at the epoch of their detection. The first column contains the BD number of the primary, columns two and four the angular separation and the position angle of the components at the epoch of the detection as listed in WDS. This epoch is shown in column six. Finally, corresponding relative positions of the present work are listed in columns three and five respectively.

Since the epoch of double star detection listed in column six is usually many decades ago, these double stars must be common proper motion double stars and thus very strong candidates to be physical binaries. More astrophysical data should be gathered on them; we will be able to execute a photometric programme to this purpose thanks to the availability of the Kryonerion telescope.

Acknowledgements

This research was partially carried out in the framework of the project "Pôles d' Attraction Interuniversitaires'' P4/05, initiated and financed by the Belgian Federal Scientific Services (DWTC/SSTC).