This page serves as an informal repository for collecting NIRC2 imaging results to help observers choose optimal NIRC2 settings, in particular the choice of filter, to achieve the best angular resolution with Keck AO.
In particular, since the commissioning of the Next Generation Wave Front Contoller (NGWFC) in March of 2007, there has been a general feeling that, for bright objects, comparable Strehl can be achieved, under average conditions, with H as with Kp; making the former preferable given the approximately 40 mas resolution element size, versus 50 with Kp.
This page intends to provide evidence to either support or debunk this claim. Similar observations taken before and after the upgrade are ideal.
We encourage observing teams to support any results they can share in this area. All submissions are voluntary and users of this page should not consider this to be published information that can be cited in publications.
As reported in KAON 489 figure 3, a bright star provided H and Kp Strehls of 0.41 and 0.62, respectively. This document also contains a before and after J-band images of a binary (figure 11).
We observed similar Main Belt asteroids in both the H and Kp filters before and after the NGWFC upgrade. These two objects each subtend approximately one quarter arcsecond (approximately 5 resolution elements at Kp).
Preliminary analysis indicates that Strehl ratios for both H and Kp improved dramatically following the NGWFC upgrade. Moreover, these preliminary results indicate that the Strehl achievable with H is now (given its lower diffraction limit) sufficiently high to make it preferable to Kp on nights of average to good seeing.
As a result, the Resolved Asteroid Program (RAP) team has changed their observing strategy to always begin observing with H on nights of good to average seeing.
The figure below provides Strehl values from data taken before and after the upgrade. Note that the Strehl values provided here were computed using a technique that differs from the standard method. For these extended sources, we took the Strehls of the perfect Lorentzians extracted from a fit. We have found that these do not differ substantially from Strehls measured on point sources appearing in the same field. Therefore, we believe that these Strehls are valid for this before-and-after comparison,