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Dr.Bob's blog posts
Well folks, the end is near: third contact arguably arrived 2 weeks earlier than predicted - sometime during late Feb, early March**. We've seen a rise from V ~ 3.75 then, to V ~3.55 last night according to several observers. At this rate, ~50 milli-mag per week (0.050 mag/week), we will climb to out of eclipse level, V ~ 3.0, during April and May.
**Caution: there is a chance, albeit small, that we are being fooled by one of those out of eclipse variations that can add/subtract up to 0.1 mag to brigthness trends, so careful watch is still needed.Read more
Observers are reporting a slight increase in brightness during these final 2 weeks until PREDICTED "third contact" (March 19, 2011) - signaling the end of total phase of this long, long eclipse.
When two spherical stars of unequal size eclipse, there is a moment when one star is inside but in tangential contact - like the end of a total lunar eclipse, when the moon emerges from the darker part (umbra) of the earth's shadow. We can this moment the Third Contact - see attached figure.
However, epsilon Aurigae differs from the classical model in at least 2 respects:
1. the two "stars" aren't simple spheres - the eclipser is an elongated disk, and,
2. egress seems to happen twice as fast as ingress.Read more
this updated blog deals mainly with invited talks at the Seattle meeting in Jan. 2011, at the American Astronomical Society and commenting on the remaining weeks of eclipse. First, we report on a recent cyber-conversation between Edward Guinan (Prof. Astronomy, Villanova University) and Bradley Schaefer (Prof. Astronomy, Louisiana State University). Both have studied ancient star catalogs for years as part of their research into the lives of stars. Ed Guinan, in a 1990 conference paper reported the following records for visual estimates of epsilon Aurigae over time:
Era Visual mag. SourcesRead more
You might want to make the effort to get outside and estimate the visual brightness of epsilon Aurigae now, as it appears to be close to a minimum, about 3.75. This is possibly the faintest it will be this year and for years to come, if the end of eclipse begins in mid/late March as forecast. This assumes that the recent ~67 day in eclipse light variation behavior persists. In that event, we should see return to a local maximum, perhaps V ~ 3.65 in mid/late Feb, followed by a decline - until third contact.
As the year of total eclipse draws to a close, we are beginning to see hints of the end of eclipse, now only a matter of weeks away. OK, mid-March is 2+ months away, but have you noticed how the time flies by? So-called third contact is predicted for 19 March, when the light is anticipated to begin rising quickly. Previous eclipses have seen the time between third contact (end of totality) and fourth contact (end of eclipse) abbreviated to as little as 50-60 days, which would mean mid-May in this cycle. But these are merely predictions, and your continued observational effort will help tell the tale.
Since mid-eclipse in late July, a steady 60+ day light oscillation emerged, although the most recent observations suggest this has lengthened to ~80 days. Check out the visual data record to explore this.
December 2010 has been a busy month observationally, with the following large telescope observations obtained:Read more
November 2010 will be remembered for the final phases of totality, with hints of 3rd contact beginning to appear.
During the course of the month and since mid-eclipse in August 2010, a 63 day periodicity in the visual light curve has become more noticeable, as noticed by Thomas Karlsson. Recent minima occurred in late Aug and early Nov, and recent maxima in early Oct and presumably in early Dec 2010.
The latest CHARA+MIRC observations were obtained in late Oct (poor observing conditions) and again in early Nov (better conditions). While the data reduction remains challenging, these images show a hint of elongation of light toward the egress end of the disk. Our next chance to confirm this is with scheduled time Dec. 9+10, 2010.Read more
Suddenly the leaves are off the trees and carved pumpkin symbols abound - we've reached another "quarter-cross" day, which means half way between seasons. Halloween (or more properly, All Saint's Day during late Oct and early Nov mark the time half-way between the autumn equinox and winter solstice. You know other quarter-cross days as Groundhog's Day (Feb.2), May Day (May 1) and more causally, the Dog Days of early August (connected with the heliacal rising of Sirius).Read more
September 2010 featured a variety of observations possible with epsilon Aurigae rising earlier, nightly. The star brightened slightly during the month, somewhat at variance with post-mid-eclipse expectations of fading. Among other key observations made during the month were:
A Hubble Space Telescope far-UV spectrum obtained with the Cosmic Origins Spectrograph, on 9/1/2010. The analysis will help confirm the identification of the central star inside the dark disk, claimed by Hoard, Howell and Stencel to be a hot, B5V star.
Robin Leadbeater reported that the strength of neutral potassium once again started increasing after a several month plateau around mid-eclipse.
Next, a second CHARA interferometric imaging run of the fall season at Mt. Wilson resulted in images on the mornings of Sept.23/24. These images are being compiled in the PhD dissertation of Brian Kloppenborg at the University of Denver.Read more
Although we won't be able to confirm until later, that mid-eclipse occurred as predicted during the end of July - beginning of August, all the evidence strongly suggests it's so.
Despite solar conjunction at the start of summer, photometric monitoring continued, but little evidence for Mid-Eclipse Brightening has been produced thus far. In fact, a first minimum during totality was reached near RJD 55250 (V ~ 3.8), then slowly rising toward mid-eclipse values close to V ~ 3.6Read more
How the time flies. Seems like yesterday (actually 2005) when the first observing proposals* for monitoring epsilon Aurigae were being submitted - and suddenly we have arrived at predicted mid-eclipse. According to Jeff Hopkins, who has made a study of the light curves, he expected mid-eclipse to occur August 4th, 2010 = JD 2,455,413.
The light curve shows no strong evidence for "mid-eclipse brightening" thus far. Now that epsilon Aurigae is getting well separated from the sun, airmass corrections are less a problem, so more accurate photometry is possible. From Mt.Evans this week, we had an exceptional morning for J& H band work, very good signal to noise, but found the brightness was close to that reported during spring 2010 - well into totality.Read more