![\begin{figure}
\par\includegraphics[width=8.8cm,clip]{H4312F1.eps}
\end{figure}](/articles/aa/full/2003/24/aah4312/img58.gif) |
Figure 1:
Example of SVD threshold selection for the case of 3NGS on a
circumference of
with DM2 conjugated to 4.7 km. The normalized
S rms curve corresponding to
is slightly displaced
upward so as not to be superimposed on the curve corresponding to
 .
Here we selected the thr3 curve as the one
with the best compromise between the highest S ratio value and the lowest S
rms. |
| Open with DEXTER | |
In the text
![\begin{figure}
\par\includegraphics[width=16.6cm,clip]{H4312F2.eps} \end{figure}](/articles/aa/full/2003/24/aah4312/img62.gif) |
Figure 2:
Strehl maps for several SVD threshold values in a reconstructed FoV
of
diameter with DM2 conjugated to 8.4 km and 3NGS
on a circumference of
radius. |
| Open with DEXTER | |
In the text
![\begin{figure}
\par\includegraphics[width=16.8cm,clip]{H4312F3.eps}
\end{figure}](/articles/aa/full/2003/24/aah4312/img63.gif) |
Figure 3:
Strehl maps for a reconstructed
 FoV for DM2 conjugated to 6.1 km and 10. km for a constellation of 3NGS on a
circumference of
radius. These maps correspond to the
best SVD case for each DM2 conjugation
altitude. |
| Open with DEXTER | |
In the text
![\begin{figure}
\par\includegraphics[angle=90,width=16.25cm,clip]{H4312F4.eps} \end{figure}](/articles/aa/full/2003/24/aah4312/img64.gif) |
Figure 4: Summary of simulation results. Top panels show the dependence of the MCAO average Strehl ratio on the conjugation altitude of DM2. The bottom panels give the normalized rms of the averaged Strehl ratio on the 83% radius annulus (see main text in Sect. 5 for further details). |
| Open with DEXTER | |
In the text
![\begin{figure}
\par\includegraphics[width=16.8cm,clip]{H4312F5.eps}
\end{figure}](/articles/aa/full/2003/24/aah4312/img65.gif) |
Figure 5:
Checking two constellation geometries employing 5 NGS. On the
left panel the Strehl map when the 5NGS are evenly arranged
on the vertices of a regular pentagon within a
FoV. On
the right panel the results when 4 NGSs are placed on the
vertices of a square and 1 NGS is placed on the FoV center. Both
panels correspond to having DM2 conjugated to 10 km above the
telescope pupil. |
| Open with DEXTER | |
In the text
![\begin{figure}
\par\includegraphics[width=16.8cm,clip]{H4312F6.eps} \end{figure}](/articles/aa/full/2003/24/aah4312/img66.gif) |
Figure 6:
Left panel shows the best SVD Strehl map in a reconstructed
FoV of
diameter with DM2 conjugated to 10 km and 4 LGS on a circumference of
radius plus one on-axis
bright NGS (i.e. wave-front sensing on the on-axis NGS is up
to the same order as with any LGS). Right panel is
the Strehl map corresponding to the reconstruction of a
diameter FoV with DM2 conjugated to 10 km and 5 LGS on a
circumference of
radius plus one on-axis bright
NGS. |
| Open with DEXTER | |
In the text
![\begin{figure}
\par\includegraphics[width=16cm,clip]{H4312F7.eps}
\end{figure}](/articles/aa/full/2003/24/aah4312/img77.gif) |
Figure 7:
Strehl maps for two LGS geometries employing the hybrid LGS
constellations. Panel a) corresponds to using 4 Na LGS at
90 km with an off-axis angle of
(in order to provide
a corrected
FoV) and an on-axis tip-tilt
NGS. Panel b) corresponds to using 5 Na LGS at 90 km with an
off-axis angle of
plus an on-axis Rayleigh LGS at
30 km and an on-axis tip-tilt NGS. Both cases consider DM2 conjugated to 10 km. Panels c) and d) are the
same as panels a) and b), respectively except that tip-tilt is
perfectly removed. This ideal exercise supports our interpretation on
the limited level of reconstruction being mainly caused by residual
tip-tilt modes. |
| Open with DEXTER | |
In the text