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An Introduction to Hyper Suprime-Cam (HSC)

The Hyper Suprime-Cam  (HSC) is the next generation camera on the Subaru Telescope, replacing its’ predecessor  Suprime-cam that had been used for 18 years. The field of view (FOV) has been dramatically increased from 0.16 to 1.5 square degree (10 times!!!). The HSC has not only a large FOV but it is also mounted on one of the biggest telescopes in the world. The camera’s ability and efficiency are the mightiest in the current observatories. HSCs physical extent is larger than three meters. Its focal plane (60 cm in diameter) is paved with 116 CCDs (including focus and tracking chips), operating in -100 degrees centigrade. The diameter of the front lens is 82 cm, the length of the lens barrel is 165 cm. The total weight is 890 kg. Every exposure includes 870 million pixels.

(c) Subaru Telescope, NAOJ

Before the HSC era, most of the cameras with large sky coverage were installed on  medium or small telescopes (48-inch-a few meter telescopes), e.g. GigaPixelCamera on Pan-STARRS 1 (1.8m), MegaCam on the  Canada-France-Hawaii Telescope (3.6m) and Magellan(3.6m), Dark Energy Camera on the Blanco Telescope (4m). Although they can cover a few square degrees, the sensitivity is  25% less than what you can achieve on an 8-meter class telescope. In some astrometry topics, like micro-lensing and large structure in the universe, both large aperture and FOV are vital. The enough sample will lead astrometers to a significant and compact conclusion.

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(c) Subaru Telescope, NAOJ

The HSC Subaru Strategic Program (SSP) is most important and largest programs o the  Subaru Telescope in this decade. This survey started in 2014, finishing at 2019. This program will survey 1400 square degrees, using optical to near-infrared filters (g, r, i, z and y), reaching a 26.5 magnitudes in stacked images. The survey regions are fixed on the equator (Dec = 0) and cross with Ecliptic plane where are the locations including a lot of solar system bodies. Hence, beside cosmology science, this survey data is quite valuable for Solar System science. Now with the HSC Survey Search, you can search for cometary activity in asteroids imaged in the HSC survey on Comet Hunters.

Introducing the Hyper Suprime-Cam Survey Main-belt Comet Search

As of today, Comet Hunters has a new dataset and a new look. You’ll notice there’s now a button called ‘HSC Survey Search’ on the front page of the website.  We are thrilled to announce the incorporation of data from the Hyper Suprime-Cam Subaru Strategic Program. Hyper Suprime-Cam (HSC) is the largest field-of-view camera ever stuck on an 8-10-m class telescope. HSC covers nine times the size of the full moon in a single pointing!

What makes this so exciting is that the asteroid images you can review now on Comet Hunters from this survey are as from as close to right off the telescope as we can get. This means we can follow-up and try to catch the asteroid still in the act if Comet Hunters spots a tail. No one has ever looked at these images for main-belt comets before. Your eyes will be one of the first to view these images. Who knows what we’ll find!

The old Comet Hunters classification interface you know and love is still around. It’s now under the ‘Archival Data Search’ on the Comet Hunters front page. Looking for main-belt comets in the archival Suprime-Cam data is still extremely useful, and we’ll be keeping that classification interface going in parallel to the HSC Survey Search. You’ll notice the HSC images are a bit different than the Archival Data Search. There’s a tutorial and help buttons that will show you how find tails in the HSC images. You can also find more information on the Research and FAQ pages as well.

Dive into the HSC Survey data and help search for main-belt comets today!

Blends, Blends Blends

The science team is working on incorporating data from the Hyper Suprime-Cam (HSC) survey into Comet Hunters.  We started with the archival Suprime-Cam data first to get a better understanding of what are the false positives and challenges for identifying Main-Belt Comets (MBCs) in data from 8-10-m class telescopes. We’ll continue with both datasets as there’s more Suprime-Cam asteroids, but when we have the chance we’ll move to reviewing the new HSC observations hopefully a few days after they’re taken.Most previous asteroid detection surveys are using 1-3-m class telescopes, so there are bound to be surprises that we wanted to know about before we developed the decision tree for the HSC snapshots on to the site. So we launched Comet Hunters with the archival Suprime-Cam images first. Now that things are going smoothly, we can turn our attention to the HSC data.

We combined your classifications from the first batch of Suprime-Cam images and had 125 candidates in need of further vetting. Thanks to volunteer Tadeáš Cernohous who on Talk went through our list comparing repeat images of the asteroid at slightly different positions in the same batch of subjects. What we learned that all of the candidates are unfortunately blends with stationary background sources. There are lots of faint background blobs that the asteroid moves on top of overlapping in the images creating very tail-like features. All of these images the science team would have had said has a tail.

A few examples are below (all blends with faint background sources):

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Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.

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Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.

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Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.

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Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.

There’s a lot more blends than we had anticipated given some of the team’s past experience with 2-m asteroid survey data. It’s still very much worth digging into the rest of the Suprime-Cam archive to look for MBCs. There might be many blends, but there could still be undiscovered MBCs too! Knowing that the background blends rate is much higher  because of the increase in the photon collecting bucket is extremely useful. From the candidates, we could see the blends are faint blobby structures that would be likely hard to get a source extractor to pick up in all cases.  Because of the quality of the HSC data and the repeat observation cadence we can try and take this into account possibly by checking the image of the asteroid and the repeat image of the same position take later on in the same night (not all Suprime-Cam images will have that and are taken in all types of sky conditions).

Now the Comet Hunters team is thinking about how best to develop a classification interface for the HSC data to include this. In the meantime, there are new Suprime-Cam images in need of review at http://www.comethunters.org if you have a minute or two to spare.

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