Expected performance and applications

In the following we assume that Pueo has been upgraded to a 36-actuator system and we estimate its performance. It can be easily predicted from data recorded at the CFHT f/35 focus with the UH 36-actuator Hokupa`a system, and is summarized in Fig. 3. The gain in Strehl ratio is particularly important at short wavelengths. Under median seeing conditions, it is by a factor 1.7 in the J band and by a factor 2.7 in the I band. Note that there is no degradation in the limiting magnitude as one would expect from a sensor purely limited by photon shot noise.
 
  Fig. 3. Estimated performance for a 36-actuator Pue`o plus AO system. Strehl ratios are derived from real data recorded with the UH 36-actuator AO system on CFHT.

 

Regarding the potential applications of Pueo Nui, they will be best advocated by the current users of Pueo. We will give here only two examples. One is the application of Pueo Nui to planetary science. As noted above, the NASA IRTF is currently being equipped with a 36-actuator curvature AO system. This will give US astronomers a definite advantage over the CFHT planetary observers. Pueo Nui will easily outperform the ESO Adonis system and provide a competitive tool to the French planetary community. The benefits to planetary science are both an important increase in image contrast allowing the observer to detect finer details on the surface of asteroids and planetary satellites or finer structures in planetary atmospheres and rings, and the ability to observe these objects at shorter wavelengths. An example of planetary application is shown in Fig. 4.
 
 

Fig. 4. Infrared (1.7 µm) image of Neptune obtained with Hokupa`a on the CFHT. Image quality is comparable if not better than that of  Neptune's HST images obtained in the same wavelength range. Thanks to AO, it is now possible to monitor Neptune's atmospheric activity from  the ground.

The other example is the study of AGNs, quasars and starburst galaxies. Apart from improved correction on bright objects and at shorter wavelengths (which in itself would be sufficient to warrant such an upgrade), it is expected that the number of observable sources with substantial image quality improvement will also increase , even though the absolute limiting magnitude will not. This is is illustrated on Fig. 5which shows the number of AGNs as a function of their V magnitude. This curve is extracted from the Véron&Véron-Cetty catalogue, and even though details may vary, it gives a fair approximation. Super-imposed on this curve are Strehl ratio vs. magnitude plots for a 19 and a 36 elements system for the J band (at K band, we should obtain similar curves with higher absolute values of Strehl). The dashed horizontal line at a value of $\simeq$30% approximately indicates the diffraction limit. It can tehrefore be seen that the number of extragalactic objects for which diffraction limited imaging becomes possible increases dramatically. Coupled with instruments such as OASIS and GRiF, this upgrade would become a very powerful and unique tool in the study of the close environment of AGNs and quasars.
 
 

Fig. 5. The number of AGNs as a function of their V magnitude. Superimposed are curves of  Strehl ratio for a 19 and 36 element system at J band. The number of objects on which diffraction limited imaging can be achieved at such short wavelengths increases quite dramatically.