Solar conjunction, 2010
This weekend marks both the 66th anniversary of D-Day, and the annual closest approach of the Sun to epsilon Aurigae - a scant 28 degree separation. If you've been attempting observations from anywhere in the northern hemisphere, you've seen how low the star is after sunset and how bright the lingering twilight has remained.
A fine screenshot shared by Thierry Garrel is appended, showing the cumulative effect over the past days, of the increasing twilight (scattering solar spectrum photons) on attempts to acquire spectrum of epsilon Aurigae (in this case, near the H-alpha line). Despite this, he and Robin Leadbeater appears to be able to extract consistent data (see image two). My thanks to these stalwart observers for sharing their findings.
For these reasons, it's a good thing we at Denver have an extreme high altitude observatory, atop Mt.Evans Colorado (14,148 ft, 4303 meters) where we have a chance to obtain daytime observations of epsilon Aurigae this summer. Given expectations about mid-eclipse brightening and contradictory data reports (as bright as 3.4 mag, as faint as 3.8 mag), any independent check from earth (or from orbit) may be decisive during this solar conjunction interval. Brian K and I are heading up soon, to see what information we can capture. Stay tuned. [ p.s. Attached is a new image we managed to obtain at 948pm MDT 6/6/2010 from the 11,000 ft level above tree line, at Mt.Evans, suggesting epsilon remains similar to zeta.]
A comment about bright sky observing - never trivial but feasible if you can get enough data to perform a clear calibration. For instance, in Thierry's data, with enough signal to noise, one could hope to subtract the foreground sky (solar) spectrum and recover the stellar signal. By the way, in the infrared, the sky is always very bright because the atmosphere glows like a 200K source, contributing greatly to multi-micron observations, but hardly affecting nighttime visual brightness.
For the hearty among us, epsilon Aurigae and the comparison stars will begin making their appearance as morning stars beginning this week. Go out, and see for yourself if the mid-eclipse brightening is happening. Comparison with zeta Aur (3.7) should provide an indication. Happy hunting!