About two months ago I contacted Eric Jensen at Swarthmore College, the home of the Sproul Observatory with a simple question and shortly thereafter I ended up with three folders containing a slice of astronomical history.
Before we get to the good parts, I should give a little background. Back in November 2010 I wrote a blog post that discussed one of the fundamental problems with studying epsilon Auriage, the distance estimates are all over the map. The most modern distance estimate is from Hipparcos. It puts the F-star at 625 +/- 581 pc. With such a large uncertainty, coming up with any absolute scale for the system is a futile act. There are, however, other distance estimates that have much lower uncertainties.
The late Dr. Van de Kamp provides one of these estimates from a series of astrometric observations of eps Aur using the Sproul Observatory's 24” (61cm) refractor. The data were taken on photographic plates starting in 1938 and ending in the mid 1970's and cover about 1.3 orbits of the system. Among the astrometric solution, Van de Kamp's paper also featured an apparent orbit for eps Aur on the sky (see the small inset in the center of the image below)
After working out a preliminary orbital solution for the system from interferometric observations, one thing became clear, the inclinations didn't agree:
About two months ago I set out to figure out why the two sets of observations were so dissimilar. I contacted Eric Jensen at Swarthmore College (the home of Sproul) to ask if he had any information that might help me in my quest. He dug around in the basement of Sproul in which there is a whole drawer of plates labeled “eps Aur”
along with stacks of printouts. I met up with him at the Seattle AAS meeting and he provided me with three folders that amount to a historical goldmine: three folders of notes, printouts, and charts used in the publication of Van de Kamp's paper.
Aside from raw values from the plate measuring machine, there are two items that top the cake:
A Print from a photographic plate taken in 1938 showing eps Aur (marked with the greek symbol pi) (click to enlarge).
Van de Kamp's hand-drawn orbital solution (click to enlarge). Note, North is Down, East is to the Right
So, what do I hope to gleen from this information? I noticed some of his reference stars were moving in different directions than were assumed when the orbital solution was calculated (interestingly enough the erroneous motion is mostly in declination which could explain why the inclination was so low). Furthermore Van de Kamp used a method of dependencies to solve for the position of stars on the plates. With the help of local astrometrist, Paul Hemenway, I hope to digitize all of the raw data and compute a new orbital solution. With any luck, this will be congruent with the interferometric observations, but there is still a chance that the resulting solution may not. Only by doing the experiment can we find out. Read more