AO Reference Star Selection

The guide stars for an AO observation can be chosen normally, that is, the way we have been choosing them from the NOMAD catalog.

The AO reference star is viewed by the AO wavefront sensor through a dichroic filter. Because of this, if the target (the astronomical object of interest) is a point source object and it is bright enough, the target itself can be used as the AO reference star. If the target is not a point source, then you need an AO reference star which is very near the target. An arcminute is much too far away. 10 arcseconds is desirable. Doug says a separation of 20 arcseconds works only half as well as a separation of 10 arcseconds. Stars with Rmag = 9.0 to 12.0 or 13.0 are usable. At Rmag =9.0 AO can use 500 "modes." At 12.0 it will use about 300. More modes provide better AO correction. Doug says the wavefront sensor's spectral sensitivity is actually between the R and I bandpasses, but I think using R magnitude to select an AO star is usually close enough to get a good result.

In general you shouldn't use the guide star as the AO reference star because the guider needs to have the guide star be a few arcminutes away from the target, otherwise the guide probe will obscure the target. But you get better AO results if the AO reference star is very close to the target. So a star that is a good AO reference star is a bad choice to use as a guide star. A star that is a good guide star is a bad choice to use as an AO reference star.

Also, to be able to use AO, the object must have an elevation above 30 degrees. If it gets below 30 degrees, the thin shell will "rest itself", that is, it will stop changing shape.

So, how should the AO reference star be specified by the scriptor program? My suggestion would be to enter the position of the AO reference star manually, or, if the target is a point source and it is bright enough, have a check box that says to use the target itself as the AO reference star.

The telescope manager needs to supply the "list" of AO stars (a list just 1 element long) to the telescope service. Below I show the combinations of telescope service parameters needed to specify all three of the Adaptive Optics ACE telescope modes to the telescope service.

ADAPTIVEACE_TRACK requires
target position to be a TrackingPosition object and TelescopeParameters.activeOpticsMode = ACTIVE_OPTICS_OFF
TelescopeParameters.adaptiveOpticsMode = ADAPTIVE_OPTICS_ACE
There should be NO guide star list.
There should be an AO reference star list.

ADAPTIVEACE_GUIDE requires
The target position to be a GuidingPosition object and
TelescopeParameters.activeOpticsMode = ACTIVE_OPTICS_OFF
TelescopeParameters.adaptiveOpticsMode = ADAPTIVE_OPTICS_ACE
A guide star list must be provided.
There should be an AO reference star list.

ADAPTIVEACE_ACTIVE requires
the target position be a GuidingPosition object and
TelescopeParameters.activeOpticsMode = ACTIVE_OPTICS_ON
TelescopeParameters.adaptiveOpticsMode = ADAPTIVE_OPTICS_ACE
A guide star list must be provided.
There should be an AO reference star list.

The three AO telescope modes for tip/tilt (ADAPTIVETTM_TRACK, ADAPTIVETTM_GUIDE, ADAPTIVETTM_ACTIVE) have the same requirements as the 3 modes above, except that in all 3 cases the TelescopeParameters.adaptiveOpticsMode should be = ADAPTIVE_OPTICS_TTM instead of ADAPTIVE_OPTICS_ACE. But I doubt Jochen or Dave T. would want to use tip/tilt mode if th

-- %USERSIG{TomSargent - 2017-03-15}%

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This topic: Software > Software > InstrumentSoftwarePages > LUCIChoices > LUCIRedmineWiki > AOReferenceStars
Topic revision: 15 Mar 2017, TomSargent
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