How the Images Were Obtained: Observing at Subaru
The images that we show on Comet Hunters come form the Subaru Telescope and currently the Suprime-Cam wide-field imager, which Charles described in the last blog post. We are using images primarily taken for other purposes that serendipitously have known asteroids in the images. Since most of the science cases that prompted those observations were likely about other things outside our the Solar System, most of these asteroids have gone unnoticed and never been looked at for cometary activity.
Subaru is mostly a classical observing telescope, which means you apply for time on the telescope and if the Time Allocation Committee (TAC) awards your proposal time on the telescope you have to go to Hawaii or to a remote observing station and take the observations. Of course this is not completely on your own you have help from the telescope operator who’s job it is to run and drive the telescope. On my observing runs at Subaru there has also been an observatory staff scientist who is an expert on Suprime-Cam there for additional support. It is the visiting astronomers’ jobs to decide where the telescope is pointing, how long the camera should be imaging, and what filter should be on the imager. The visiting astronomers are also checking the image quality and determining if it is good enough for their science requirements. If it isn’t they can ask for the telescope to be refocused to try and improve the crispness of the stars in image (or the size and shape of the point spread function).
Although there are remote observing stations in Japan and in Hilo, Hawaii most observations are taken at the telescope. Well in reality right next door to the telescope near the top of Mauna Kea. Telescope is housed in one building with the telescope control room in the building next door connected by a tunnel. Mauna Kea reaches 14,000 feet above sea level where it is possible to get altitude sickness, which can be very serious. Observers from the summit are barred from deep sea diving right afterwards and vice versa because it would cause ‘the bends’ or decompression sickness.
You can definitely feel the lack of oxygen and the dryness of the air when observing there. I was eating a sandwich once while observing on Subaru, and a glitch happened with the camera. I put my sandwich down to help deal with the issue and make sure we were imaging the observation that screwed up after we power-cycled (aka rebooted) the Suprime-Cam. It took about 20 minutes until everything was back running smoothly. By the time I got back to my computer and my night lunch, the bread had given all its water to the air and was stale!
At such high altitudes, there is actually a rule that anyone working at the summit of Mauna Kea cannot stay up longer there longer than 14 hours, before they need to descend to mid-altitude for safety and health precautions. The astronomers, operators, and observatory support staff working on the telescopes at Mauna Kea sleep at the mid-altitude site known as Hale Pohaku (which means ‘stone house’ in Hawaiian), dubbed HP for short by many. Shortly before sunset, the night crews and visiting observers drive up to the telescopes at the summit. At sunrise, or shortly after depending on what wavelength you are observing in, the domes empty out and people descend to mid-altitude for sleep and maybe breakfast. The day crews take over with the engineers and observatory staff scientists perform maintenance, test the telescope and instruments, and prepare the observatory for the next night of observing. One of the moments I look forward to after a few nights observing on Mauna Kea is coming down after a good night of observing to HP and having a warm breakfast while tired and groggy before trying to catch some sleep before the start of the the next night.
Mauna Kea is one of the best astronomical observing sites in the world, and I would say every observational astronomer dreams of one day observing with the telescopes there. We’re all grateful for the privilege and opportunity to use these telescopes on such a special place in the world. In a way, with Comet Hunters we’re extending the scientific legacy of the Subaru Telescope and these observations by searching them for new main-belt comets that might have been hiding in plain sight.
I’ll leave you with some photos below of Subaru and Mauna Kea from my fairly cloudy observing run this past June.