CFHT is hot! (and cold) Kevin Ho, Derrick Salmon, Steve Bauman CFHT is hot! And cold at the same time. As part of the IQ improvement initiative, we wanted to look at the thermal environment in and around the observatory. Back in March of this year, we borrowed a thermal IR camera from John Tonry at IFA. We first looked at heat sources in dome and in the crawl space under the telescope and then looked at the thermal signatures of the dome exterior and the surrounding area. 2010 Dec 13 CFHT 2010 BOD Meeting

Take a tour inside the observatory then outside. In this talk I’ll just take you on a tour of the inside of the observatory and show you some of the heat sources that we discovered and how we plan to mitigate the problem. Then I’ll show you aerial images of the dome taken from a Piper Cub and images taken from the Gemini stairway. Used FLIR camera -7.5 – 13 um wavelength. 2010 Dec 13 CFHT 2010 BOD Meeting

Heat is mainly due to the detector controller electronics being constantly on. Taken care of by powering down the system when not in use. But problem still remains when the instrument is on the telescope. Most likely solution is to beef up the heat exchange system. WIRCam in storage. 2010 Dec 13 CFHT 2010 BOD Meeting

MegaPrime PLC electronic boxes. MegaCam PLC junction boxes on the north pier which control the camera cooling, filter and shutter systems. The cryo PLC needs to be constantly on to cool the camera but the others could be turned off when not in use. MegaPrime PLC electronic boxes. 2010 Dec 13 CFHT 2010 BOD Meeting

Heat from the 4th floor crawl space is leaking into the 5th environment. New seals were installed to reduce the heat flow. North telescope pier. 2010 Dec 13 CFHT 2010 BOD Meeting

Same as the previous. The pipes are the hydraulic lines. South telescope pier. 2010 Dec 13 CFHT 2010 BOD Meeting

Control Station 5 on the south side Caisson Centrale. The heat sources are mainly linear power supplies powering the various electronic equipment. Could replace them with more efficient switching power supplies to reduce the heat load or put the electronics in a thermal enclosure. Control Station 5 on the south side Caisson Centrale. 2010 Dec 13 CFHT 2010 BOD Meeting

Control Station 5 on the north side Caisson Centrale. Can see some the heat leaking through the enclosure when the doors are closed. Control Station 5 on the north side Caisson Centrale. 2010 Dec 13 CFHT 2010 BOD Meeting

Control Station 6 on the north side Caisson Centrale. Same on the north side control station 6 although it’s not as problematic as control station 5. Lot less stuff in it. Control Station 6 on the north side Caisson Centrale. 2010 Dec 13 CFHT 2010 BOD Meeting

Control Station 6 on the north side. See the heat leaking through the cover. Control Station 6 on the north side. 2010 Dec 13 CFHT 2010 BOD Meeting

Dome skin. Can see the print through of the bulkier dome structure. 2010 Dec 13 CFHT 2010 BOD Meeting

Back in Oct we were finally able fly over Mauna Kea Back in Oct we were finally able fly over Mauna Kea. We took thermal images of our observatory as well as the others on the mountain. What’s quite visible in the image is the bow wave around the observatory which is created by the relatively warmer ambient air streaming around the observatory warming the radiatively cooled terrain. View from the west showing the bow-wave created by relatively warmer ambient air streaming around the observatory and mixing with the radiatively cooled terrain. The hot spot on the left is the building heat exhaust. 2010 Dec 13 CFHT 2010 BOD Meeting

Close view from the east Close view from the east. Can see the dome skin is much colder than the inside since it radiatively cools to the night sky. The temperatures on the dome are not quite accurate since you see some reflection of the night sky. Later I have a slides comparing the dome skin temperature along the backside of the slit taken with thermo probes and measurements taken with the IR camera. Ambient air emperature was about .9C during this period. View from the east. 2010 Dec 13 CFHT 2010 BOD Meeting

This is a close view from the east side This is a close view from the east side. There are couple of noticeable heat sources – a electrical transformer box to the left and exhaust outlet from the building on the bottom. View from the east. The hot spot on the left is an electrical transformer box. 2010 Dec 13 CFHT 2010 BOD Meeting

This image gives you a sense of the temperature differences of the terrain on the summit. The terrain temperatures around the observatory. It is mostly smoothed cinder around the observatories and rough a’a lava on the eastern slope. The terrain radiatively cools and is 4-8 deg colder than the ambient air. The terrain around the observatory is mostly smoothed cinder, quite different than the rough a’a lava on the eastern slope. 2010 Dec 13 CFHT 2010 BOD Meeting

IRCam Therm D -10.1 -5.4 -4.7 -9.9 -5.6 -4.3 -9.1 -5.3 -3.8 2010 Dec 07 20:30 IRCam Therm D -10.1 -5.4 -4.7 -9.9 -5.6 -4.3 -9.1 -5.3 -3.8 -8.8 XXX XXX -8.8 -4.9 -3.9 -8.7 -4.6 -4.1 -8.7 -4.5 -4.2 -7.6 -4.0 -3.6 -6.5 -3.0 -3.5 Last week I installed 10 remote thermistor buttons along the backside of the slit. I wanted to get a crude comparison of the temperatures recorded by the thermal IR camera with an external device. You can actually see them in the image. These buttons were stuck onto the dome with some heat sink compound, covered with foam and then taped over with AL tape. Took measurements every minute. I set the thermal IR camera on the Gemini stairway and recorded images for an hour or so. This is a snapshot of the temperatures at 8:30 pm. The IR measurements are about 3-5 deg lower than the those measured with thermistors. The camera is probably seeing some reflection of the night sky. 2010 Dec 13 CFHT 2010 BOD Meeting

I plotted the dome skin temperatures against the ambient air temperatures from the weather tower and from the top of the dome over a period of a day from 3pm to 3 pm. Once the sun sets the dome skin temperature drops quite a bit –somewhere between 7-10 degrees below the ambient air temperature. Ideally one would like to keep the temperature difference to 0 to minimize the air turbulence. 2010 Dec 13 CFHT 2010 BOD Meeting

Enclosure coatings UKIRT - reflective bare aluminum UH - TiO2-based white paint GEMINI - Al-based Lo-Mit paint CFHT - TiO2-based white paint IRTF - reflective aluminum foil KECK - TiO2-based white paint SUBARU - reflective Alclad siding A few years back Derrick and company looked at various enclosure coatings used at the different observatories. UH, Keck and CFHT use a TiO2 based paint, Gemini uses a AL based Lo-emissivity paint and UKIRT and Subaru use some a AL reflective cladding. Courtesy of D. Salmon 2010 Dec 13 CFHT 2010 BOD Meeting

They compared the CFHT, IRTF and Gemini enclosure coating and found that the IRTF aluminum foil performed the best at tracking the ambient air while the TiO2 was the worst. That’s surely one type of enclosure coating to consider in the overall desire to improve image IQ. Courtesy of D. Salmon 2010 Dec 13 CFHT 2010 BOD Meeting

Courtesy of D. Salmon 2010 Dec 13 CFHT 2010 BOD Meeting

Last I have a short time lapse movie of the images taken from the Gemini stairway last week. 2010 Dec 13 CFHT 2010 BOD Meeting