While the NAS was mounted on the telescope we took a quick set of readnoise measurements with the CCD39. Here are the results. The only major caveat is that the telescope was not tracking, so we didn’t test whether the drives have any impact. Otherwise, this is the most realistic set of RON measurements we have taken to date. We are very happy with the results, especially the 156kHz 3.8 electrons. This number essentially sets the limit to how faint our guide star can be, so keeping it low is important.
Pixel Rate (kHz)
Frame Rate (fps)
RON (e-)
156
80
3.8
400
197
5.8
900
893
8.4
2500
1053
10.2
Note: these are determined using the actual gains from Scimeasure, rather than assuming 0.5. This can cause as much as an 8% difference.
Meanwhile, back in Tucson… We interrupt the NAS Fitcheck program to bring you this update on the Clio2 infrared camera.
After the Pre-Ship Review for Clio2 in Amsterdam in July, we have been completing preparations to receive diffraction-limited near-IR to thermal-IR photons from MagAO. Yesterday and today we installed the new J-band filter, and the cold pupil stops sized for Magellan. This was done in a CAAO lab at Steward Observatory in Tucson, where Clio2 is undergoing its final testing before shipment.
Cold pupil stops: Clio2 used to be “Clio” and was installed on the MMT telescope in Arizona. The MMT, like Magellan, is a 6.5-m telescope, but the Magellan secondary is 0.85m while the MMT secondary is 0.7m. Therefore, because the pupil is different, we needed two new cold stops for Clio2 on Magellan. A cold stop is a cryogenically-cooled metal mask located at an image of the telescope pupil, and its purpose is to block stray light (heat sources in the dome cause a lot of background thermal light) from contaminating the infrared image. Here is a picture of the pupil wheel with the new cold stops:
We also added a new J-band filter, taking out the old 3-5um Janostech filter from filter-wheel 1:
Clockwise from the red arrow: J (new), Blocked (for darks), Open (home), MKO M', Barr M, Direct vision prism, 3.1um, Barr L'.
We updated the Clio2 user manual at http://zero.as.arizona.edu/groups/clio2usermanual/ so that we can repeat this in Chile if need be. Note the tools required: Most of the wrenches were found in a standard set of Allen keys, except for the 0.035” driver which is a special size.
Tools required for changing Clio2 filters: Phillips/flat head, 0.035, 5/64, 3/32, 7/64, and 9/64 inch Allen keys.
It took about 3 hours to take it apart and insert the new filter and pupil stops, including finding new spacers, etc. It took about 1 hour to put it all back together.
T.J. Rodigas (foreground) and Andy Skemer (background) helped take Clio2 apart.The box labeled 3 and 4 contains filter wheels 1 and 2. The box labeled 2 contains the cold pupil stops. We disconnected the wires and unscrewed the bellows (those keep the shafts straight at cryo temperatures) to access the filter and pupil wheels.The same view as the previous image, with the filter and pupil wheels removed.Opening the pupil box to put in the new cold stops, and also Phil put in a new home switch. (Otherwise we could have just inserted the new cold stops through the port and not had to open it all the way.)Oli Durney putting Clio2 back together
Jason finished assembling our new CCD (and shutter) cooling system in the mirror lab yesterday. After several tries, and finally replacing the threaded cap that wouldn’t hold pressure, the system passed a pressure and operational test. It’s on its way to Pasadena, and from there to Chile.
Here Jason is installing the drain valve on the tank outlet.These are our CCD cold plates, and the famous shutter, with coolant flowing through them.Just after pressurizing the system.And after about 10 minutes, with the pump running.
I have updated our VisAO filter curves to now include the effects of 3 reflections from Aluminum mirrors (important because Al has a feature at 0.8 microns), the Clio dichroic, the AR coated surfaces of the VisAO Optics, and the protected silver gimbal mirror in the VisAO camera. Most of these are small losses, but 3 Al reflections are fairly costly at only ~90% reflectance each. I have also convolved the resultant curves with the HST/STIS Vega spectrum to give the approximate photon flux in each filter from a 0 magnitude star. The only major thing not included in these calculations is the reflectance of the beam splitter, since it will vary depending on AO system setup.
On March 10, 2011 the MagAO secondary shell had its frontside successfully aluminized at the University of Arizona, Steward Observatory coating facility in Tucson by Richard Sosa and Gary Rosenbaum. This also took a lot of hard work by Jason Lewis and Victor Gasho.
The side of our freshly aluminized 850 mm diameter adaptive secondary for MagAO. This shell is just 1.5mm thick with 585 magnets glued on the back.The newly coated front of the secondary.Project Manager Victor Gasho reflected in the secondaryA relieved Principal Investigator Laird Close reflected in the secondary.
