Last week I went to a talk given by the leader of the Supernova Factory collaboration at LBNL. What is SN factory? This is an ambitious project to study supernovae like never before. I mentioned this project briefly in a previous post , now that they are so close to releasing their results I want to discuss it a bit more.

The main idea of this project is to study several hundred nearby supernovae using an instrument known as the Supernova Integral Field Spectrograph, or SNIFS. This type of instrument is essentially a blend between a traditional imaging camera and a spectrograph.

The resolution in an integral field spectrograph is defined in spaxels instead of the pixels that have become all too familiar with the advent of digital cameras. A spaxel is quite similar to a pixel, there aren't nearly as many and each one carries at least a 1000 times as much information.

In your digital camera, the light passes through the lens and directly onto the CCD. Each pixel on the CCD counts the number of photons in the red, the blue, and the green. Typically, there are millions of pixels, each counting photons from a slightly different region of the subject of your photograph.

Now imagine that instead of just counting red, green, and blue, that each pixel counts the entire rainbow of light from your subject. Now you have a spaxel. In an intregral field unit, the light passes through an array of microlenses and prisms before landing on the detector. We would call each set of microlenses and prisms a spaxel. The resulting image carries information about every wavelength of light from every region of your target.

Spectrum of the first SN observed with SNIFSThe advantage to an integral field spectrograph like SNIFS is that you gain a lot more information than either an imager or spectrograph alone. With an integral field spectrograph you can basically identify and organize every photon that reaches the telescope.

Specifically designed to observe supernovae, SNIFS is being operated at the 88-inch telescope on Mauna Kea. Spaxels are quite expensive – this particular instrument has only 225. However, this is more than enough to observe the entirety of a galaxy, a supernova, and the background.

The members of the SN Factory have now observed over 100 SNe using this new camera. Last Thursday, I saw the data from the first 25 well-calibrated supernovae and was very impressed. The data showed the evolution of each supernova and the properties of the host galaxy in great detail. I'm sure the supernova community will be equally impressed when they first see these new results.

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.

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Julien Guy: supernova cosmologist

I spent the last week at a conference in the Italian Alps with about 200 skier/cosmologists. Mornings were spent in the conference hall watching 15 or 25 minute presentations. Afternoons were for the slopes. Evenings were back in the conference hall.

The conference started with supernova talks – I was fourth on the list. Being in the field, I had heard most of the results that were presented in the other talks. Ditto the other attendees' perspectives on my talk. However, there were some new and very promising results from the Supernova Factory.

The supernova factory is a LBNL-based research group that focuses on "nearby supernovae". By nearby, I mean only a few hundred million light years away. These supernovae occur in galaxies that are distant enough to be free of the gravity of the Milky Way and our neighboring galaxies but close enough to observe with smaller telescopes.

The supernovae observed by the SN factory are very bright compared to the supernovae I observe with the Hubble Space Telescope. The supernovae are bright enough to make very precise measurements at each wavelength of the supernova spectrum. Just like my earlier post on spectroscopy, the supernova light is imaged after passing through a prism. These images provide very detailed information about the molecules and atoms that are present in the supernova explosion.

The spectroscopic observations also tell us how one supernova may differ from another. The small variations in type Ia supernovae have been a mystery for quite some time. If we can learn the causes of these variations, these supernovae could be come even more useful for measuring distances in space.

There are several models and theories to explain the differences, but none has been extensively tested. A large number of bright nearby supernovae is required to test these models. Hopefully, a project like the supernova factory will provide that sample. In this conference, they only showed a handful of supernovae. All but one of these supernovae was well-behaved, fitting our current models. The last one differed enormously from the others, but the detailed spectroscopic observations lent evidence as to why this may be the case. The data is still being examined, but I am encouraged by the progress necessary if supernovae are to be used to explain the cosmology of our universe.

The presentations over the next five days covered a very large range of topics. Some conference attendees presented ideas that had never occurred to me. One that I found very interesting was an experiment to model the orbital paths of stars around the black hole at the center of the Milky Way. For those patient enough to watch these stars for 15 years, it should be possible to measure the properties of gravity and the black hole itself by looking for deviations in the stars orbits from our current models.

While the talks were very interesting and well-attended, I can't help but comment on the other important side of this conference. That would of course be the skiing. The Europeans really have it right – they chose the site and the schedule with the perfect balance for leisure time. We were only ten miles from the tallest mountain in Europe, within site of the Matterhorn, had perfect snow all week, and had just enough time to enjoy it. I even had a chance to practice my amateur photography on the slopes. Now the next challenge will be to organize a conference in Tahiti!

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.