We Have the Technology: Week 4

Welcome back, everyone! This week's post is going to be a bit shorter than previous weeks. Primarily, I plan to explain the technology and instruments that we have used in the gathering, reduction, and analysis of the supernova data we have. Some of what I actually do in the process will be explained.

A logical place to start would be with the telescopes that gather most of our data. Because Dr. Milne lives here in Tucson, most of our data comes from telescopes in the area. Dr. Milne most often receives observing time on Mt. Bigelow and Kitt Peak. The supernova data obtained from Mt. Bigelow comes from the 61-inch Kuiper telescope. The Kuiper is quite old, and was originally used to scope out a proper spot for the '69 moon landing, among other lunar missions. It's currently owned and operated by Steward Observatory, and is generally used for observing by astronomers from the 3 Arizona State schools (U of A, NAU, ASU).

The 61" Kuiper telescope. Courtesy Steward Observatory.

The Kuiper is equipped with the Mont4K CCD, which can take data in the Bessel-U, Harris-B, Harris-V, Harris-R, and Arizona-I filters. The filters correspond roughly as follows: U-ultraviolet, B-blue, V-green (visible), R-red, and I-infrared (near-infrared). About half our data has come from the Kuiper.

Much of the rest of our data was gathered on Kitt Peak, at the 90" (2.3m) Bok telescope. The Bok is the largest telescope owned solely by Steward Observatory, and was dedicated in 1969. In 1996 it was named in honor of then Steward Observatory head Professor Bart Bok.

The Bok 90" telescope. Courtesy Wikimedia Commons.

The Bok telescope has instruments that allow for both imaging and spectroscopy. The Bok telescope mainly uses 3 instruments; the 90prime, which does visual-range imaging, the B&C Spectrograph, which does visual spectroscopy, and the Steward 256x256 NIR camera, for infrared observations. Our data comes primarily from the 90prime instrument, although in future observing runs we hope to obtain some spectroscopy data for a relatively recent light-echo candidate supernova. Most of the other half of our data has originated from the Bok telescope.

We have a small amount of data from the Large Binocular Telescope, or LBT, on Mt. Graham. The LBT is one of the world's most advanced optical telescopes, making use of two 27-foot mirrors which together give it the light gathering capability of a single 39-foot mirror and the optical clarity of a 75-foot mirror.

The Large Binocular Telescope. Courtesy Wikimedia Commons.

Although not very much of our data has originated from the LBT due to considerable difficulty in getting observing time on the telescope, the data we do have from there are of unusually high quality.

The last of our data has come from the Holy Grail of telescopes, the Hubble. The data were not, in fact, taken by Dr. Milne but rather in a number of surveys conducted primarily by Nobel Laureate Dr. Adam Riess in searching for cepheids in other galaxies to get a better understanding of the expansion rate of the universe. A few data points are from the HST images, while the other images were primarily used in subtraction.

I have been observing with Dr. Milne at both the Kuiper and Bok telescopes, though our observing targets were not the supernovae that my research focuses on.

In addition to giving an overview of these telescopes, I would also like to briefly introduce the software that Dr. Milne and I have been using for image analysis. It's called IRAF (image reduction and analysis facility), and is a collection of many software components written by the National Optical Astronomy Observatory (NOAO). There are many packages and tasks that IRAF can perform. My roles primarily include fixing bad pixel strips, combining raw data images into stacked, usable data, performing subtraction on images to remove the background field from the supernovae, obtaining useful information about how bright objects are, and plotting the results. Each step involves quite a bit of code and user input, so this analysis is very time consuming. The results, however, tell us all of the information about the light echo I've mentioned previously; brightness, angular size, distance, color, and all the rest. In the past week, I have primarily been focused on stacking the raw images of our 2009 supernova, with some effort being put into subtraction on these same images.

That's all I have for you this week. I hope it wasn't too boring! Thanks for reading, everyone, and tune in next week for another post.