Table 3: VLBA rms astrometric errors (in $\mu $as) for a relative source separation $(\alpha -\alpha _0)\cos\delta_0 = 1\hbox{$^\circ$ }$. Individual astrometric error contributions from calibrator position, Earth orientation parameter, station coordinate, and dry and wet troposphere uncertainties are given separately, while the last two lines indicate the total astrometric errors when all model parameters are perturbed together.
    Declination of source  
    $-25\hbox {$^\circ $ }$   $0\hbox{$^\circ$ }$   $25\hbox{$^\circ$ }$   $50\hbox {$^\circ $ }$   $75\hbox{$^\circ$ }$   $85\hbox {$^\circ $ }$
Error component   $\Delta\alpha \cos\delta \hfil$ $\Delta \delta $   $\Delta\alpha \cos\delta \hfil$ $\Delta \delta $   $\Delta\alpha \cos\delta \hfil$ $\Delta \delta $   $\Delta\alpha \cos\delta \hfil$ $\Delta \delta $   $\Delta\alpha \cos\delta \hfil$ $\Delta \delta $   $\Delta\alpha \cos\delta \hfil$ $\Delta \delta $
Calibrator position (1 mas error)    8   7    1  9    8 16   20 26    59  68   196 193
Calibrator position (0.25 mas error)    2   7    1  3    2  5    3  5    12  11    49  50
Earth orientation    1   8    1  5    1  6    1  5     1   4     1   4
Antenna position    2   8    2  4    2  4    2  3     2   3     2   3
Dry troposphere   15  45    9 16    7  9   10 11    18  23    14  16
Wet troposphere (mean)   53 182   34 57   33 28   31 45    54  72    79  88
Wet troposphere (max)   87 219   46 66   42 38   49 56    65  78    81  91
Total (mean wtrp)   60 175   36 50   33 32   37 53    87 103   227 258
Total (max wtrp)   85 217   43 74   42 44   46 66   100 117   226 240


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