Planning Observations with Subaru AO36It is a bit complicated to plan observations with AO. If you wish to observe optically faint targets (e.g., distant galaxies, brown dwarfs) or extended sources (e.g., nearby galaxies), you have to find an AO guide star close to your target. If you wish to observe diffuse nebulousity associated with a very bright star (e.g., a circumstellar disk), you may want to observe a PSF reference star to subtract contaminated emission from the star. Also, we need some overheads to optimize AO for each target, and we cannot achieve good AO correction if you targets are at low elevations.
Read this page carefully if you apply for observing time. Check all the information in Section 1 before submitting your proposal. If technical details described in your proposal are incomplete, it may be rejected even if your science case is great!
Information you have to describe in your proposal
The following should be clearly stated in Section 9, 13, 14 of the proposal form.
Selecting AO guide starsGuide stars/objects for AO correction should be selected with the criteria listed below. The target itself or a non-sidereal object can be used if it satisfies these criteria.
Selecting PSF reference stars
You may observe a PSF reference star if the AO guide star cannot be used as a reference. The PSF reference stars should be observed at a condition as similar as possible to that of your targets, i.e., the same instrumental configuration, at a similar airmass and just before/after observing your target (as the PSF can vary with time). For this reason, you may select a PSF reference star as close as possible to your target.
To let PSFs similar to each other, the R-band flux to the wavefront sensor (WFS) should also be nearly the same between the AO guide star/object and PSF reference star. To adjust the flux of the PSF reference star, a number of neutral density (ND) filters are installed in WFS. The table below shows a list of ND filters available. Using one of these filters, you can use a PSF guide star with a R-magnitude of 0-11 brighter than your target.
Planning dates of observationsEvaluate possible dates of your observations based on the following tips:-
OverheadsWe usually need 10-15 minutes for overheads of each target. These include acquisition of the AO guide star, optimization of AO, and acquisition of the target. In addition to these, we need up to 12 minutes to slew the telescope to your target. Here are some tips for reducing overheads.
Flexible change between AO/no-AO modesAt the telescope you may find that AO correction does not work well due to poor seeing. In this case you may want use CIAO without AO as its warm optics significantly increases thermal background (about 40 %). In another case, AO correction may not be mandatory for your project but you may want to use AO if it provides a better point-spread function or S/N. Such a change between AO/no-AO modes can be easily performed by inserting/retracting a pick-up mirror for the AO optics. The plate scale for these two modes are the same as each other.
If you want to try `flexible' AO correction in a way describe above, state this in your proposal . This is mandatory to assign an AO instrument operator and the support astronomer to your observing run.
Subaru is a visitor-mode telescope. Satisfactory AO correction is
not achieved under a poor seeing condition, say, > 1''. The
observers should thus prepare a backup program for such an occasion.
7 February 2007