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NIRC-2 News | |
Over the past 1-2 years, the NIRC2 slit stage has faulted on several occasions when driven to locations near its negative limit. For this reason, we are restricting use of that stage to exclude use of the fine pin-hole mask. All other positions for that mask (slits 10-through-160 for spectroscopy, coronagraphic spots 100 through 2000, and the coarse pin-hole mask) are available for use. We will continue to investigate this issue and apologize for the inconvenience.
Observers using vertical angle mode, who are intending a fixed pupil, for example users of aperture masking or angular differential imaging (ADI), should be aware that a tracking shift in the pupil plane of order 0.4 degrees occurs when an object being observed in vertical angle mode transits near zenith. This effect is likely related to the difference between true vertical and the as-built telescope Y axis, as the offset is equal to the difference between PARANG and PARANTEL. A correction equal to that difference must also be applied to recover absolute astrometry. This plot characterizes the jump.
A problem with the NIRC2 detector readout system occurred on Wednesday night, June 18th, 2008. The root cause was traced to a failed transputer board in the detector system electronics rack. That board has been replaced and since that repair mission, NIRC2 has been in use on five science nights without a recurrence of the problem. Several efforts are underway to improve our preparedness should a similar problem occur in the future, including the configuration of a hot-swappable host computer system.
An Image Quality comparion page has been been generated for collecting observers' before and after experiences with NIRC2 since the upgrade of the AO Wave Front Controller.
As of April 24, 2008, an LGS mode which allows for differential motion between the laser and the tip-tilt reference is available for shared risk. Limiting rates and magnitudes for this new mode, as well as all other nonsidereal AO modes, are provided in a summary table. Contact Randy or Al for details.
The Astrometry Page has been revised, including new information related to the NIRC2 position angle.
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The procedure for observing M15 for astrometric calibration
has been added to the
Astrometry Page. If you use the procedure, please consider contributing your calibration frames to the Observatory (via your Support Astronomer) for general use by the community. |
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Since the commissioning of NGWFC, many have wondered: Under what conditions is it better to use NGS over LGS? Please see KAON 489 figure 14 for details, but the short answer is "When brighter than 14th and closer than 10 arcseconds, use NGS." |
The IDL code to remove geometric distortion (graciously provided by Brian Cameron) has been added to the NIRC2 web page. Go to the Dewarp Utility Page.
Strehl-vs-magnitude and related performance statistics for the upgraded AO system have been characterized.
The NIRC2 Adaptive Optics feed has been upgraded. Performance improvement is still being quantified, but in the mean time, check out this snapshot of improved performance at J from Mike Liu's April 3rd SSC presentation.
At the CfAO Retreat held in Santa Cruz March 26th, an informal meeting was held by NIRC2 observers interested in precise astrometry. The collaboration has resulted in a report, recommended calibration fields, and a dewarp application. Once these are finalized they will appear on this page. In the mean time, email aconrad@keck.hawaii.edu if you desire preliminary versions of this material.
Please check out the new NIRC2 home page. It is a work in progress, but comments are welcome.
Based on photometric data gathered in April of 2004 the zero points have been updated. The values are included in the list of filters and in the NIRC2 manual. There was improvement in both the zero points and the background levels from the initial commissioning measurements, likely the result of cleaner optics on the AO bench.
The three mirrors in the AO rotator were recoated with silver (2 of the 3 surfaces were previously Al.) and reinstalled in March 04. The rotator, which is often referred to as the K mirror, was subsequently realigned to the optical axis of the telescope and to the pupil of the optical system. One requirement of the realignment effort was to minimize the pupil nutation as a function of rotator angle, which has been a significant problem in the past. The realignment effort met the requirements and was deemed successful with the pupil nutation now only 10cm on the primary (peak to valley). These changes will have several likely benefits to NIRC2 observers,
An accurate and consistent method of measuring image quality on NIRC2 has been developed by Marcos van Dam, WMKO AO Scientist. The tool is available from the NIRC2 user interface menu and users are encouraged to give it a try. Instructions for its use are available as a web document.
The NIRC2 dewar was warmed to ambient temperature and opened in late August of 2003, the first time since being delivered to WMKO in June of 2001. The primary purpose of the service mission was to install recently procured narrow-band filters. The successful effort was led by PI, Keith Mathews of CalTech. One prerequisite to going forth with the service efforts was the development of the Keck II AO enclosure into a clean "ish" room. The clean room project was led by Craig Nance . He and the summit facilities group worked hard to enable this important work on NIRC2 to be accomplished.
Preliminary characterization has produced filter wavelength information that is now available on the NIRC2 filter page. Full characterization of the transmission profiles is yet to be completed.
A bug in the software was found that was hard-wiring the pixel scale to that of the wide-field camera. This has been fixed, so that the plate scale gets properly read from the FITS image keyword. Telescope movement in all three cameras was confirmed, and moving the telescope using an image from one camera while a different camera was currently in use was also verified.
You can still, of course, use one of the other telescope move commands, including "mov", "pxy", etc.
Currently the tint value is set with full precision, and the tint command prints it out to 4 decimal places.
Like NIRSPEC's version, the NIRC-2 "Move Tel" command does not work reliably. We have added debugging lines to the code to try to track down this problem, but meanwhile you may want to rely on the command-line command "mov" to move a target from one (x,y) position to another.
Update, 2002-Dec-25: A bug causing failure of the "Move Tel" command was found and fixed during December engineering. (see above.)
Work on the Strehl calculator proceeds. It now gets the pixel scale and filter bandpass information from the image headers, rather then requiring the observer to type this in each time. We will be adding better theoretical PSFs in the future, using the correct NIRC-2 pupil mask where appropriate.
The tool is available on-line using ION, IDL On the Net , which was recently installed on the Keck public web server. Please report any problems or suggestions associated with using this tool. .
Because NIRC-2 currently has a somewhat limited inventory of filters,
observers may wish to know what may be in store for the future. We are
providing a list of filters that have been
ordered, and will hopefully make their way into the NIRC-2 filter wheels.
Note, however, that there is no guarantee that all of these filters will
get successfully made and delivered to the NIRC-2 team at Caltech.
The "n=#" argument can be placed anywhere, e.g. "bxy5 n=3 1.3" will take three exposures at each of five dither positions in a 1.3 x 1.3 arcsec box. ("1.3" is the step size, not the size of the entire pattern.) Similarly, "bxy4 1.2 2.7 n=4" will take four exposures in each of four positions in a 2.4 x 5.4 arcsec rectangular pattern.
Commissioning is still not complete, and not all observing modes have been adequately tested. Also, Keck staff are still receiving training on the instrument. Thus, the early shared risk use of NIRC2 will have limitations applied. The spectroscopy mode of instrument is not fully tested and will not be supported in 2001B, especially since those planning spectroscopy programs will likely choose to stick with NIRSPEC. The coronography modes will also not be available during the pre-commissioned use of NIRC2. With it's three cameras, NIRC2 offers field of view advantages over the NIRSPEC SCAM detector with choices of 10, 20, and 40 arcsec FOV. NIRC2 has fewer optics in the path and is expected to have better sensitivity in most situations. Please see NIRC2 specifications and a comparison of NIRC2 to NIRSPAO for more information on the trade-offs between the two instruments.
M8 in JHK Neptune in K
NIRC-2 being lowered into Keck II AO enclosure.
PI Keith Matthew's of CalTech prepares NIRC-2 for placement, Bob Goodrich assists.
NIRC2 workers imaged at K (2.2 microns) with NIRC2's pupil imaging capability.
Perhaps it is the first use of a 10 meter telescope to image human beings.
From left to right, Randy Campbell, Keith Matthews, Eiichi Egami, James
Larkin.
