Dr.Bob's blog posts

Bounce during totality: have you noticed that epsilon is a bit brighter this month compared to last?  Totality is with us, but the Out of Eclipse variations continue.  We anticipate a significant brightening starting next month as the central opening in the disk begins crossing in front of the F star...

It's been a pleasure to attend the 5 year science review meeting of the CHARA collaboration (http://www.chara.gsu.edu/CHARA/ ) an amazing group that runs the interferometer atop Mt. Wilson, CA.  This 300 meter baseline telescope is capable of delivering milli-arcsecond imaging that has made the details of the epsilon Aur eclipse much more obvious, as has been reported in recent popular articles in Sky & Telescope, Astronomy and Astronomy Now. Read more

Observers are beginning to report a sea change.  Totality is upon us and the center of the dark turbulent disk is just about to make its presence felt atop the beacon of light that is the F star in epsilon Aurigae.

Photometrically, bumps and wiggles have persisted, a mix of out of eclipse variations and the stately progression of the eclipse itself.

Spectroscopically, the enhanced absorption of shell lines has been waxing and waning as though disk substructure is coming increasingly into view.  What we've been seeing is the "morning side" of the disk - the portion that has been facing cold space and is just starting to rotate toward the hot glare of the F star (7750K). As soon as we reduce this week's IRTF spectra, we'll share any info about changes detected in the near-infrared.Read more

It's official - we passed into totality during January, perhaps a few days later than predicted.  Nonetheless, you can enjoy the view of epsilon fainter than eta or zeta in the Kids asterism, all winter long (between snowstorms).
There is exciting news to announce soon, once publishers accept some epsilon Aurigae results that have been submitted.  Stay tuned and keep up the observing reports!Read more

Predictions suggested the total eclipse phase of epsilon Aurigae should have arrived as early as mid-December [JD 2,455,190], but observers are still reporting a slow fade even now in late January [JD 2,455,220]!  What's going on? 
The answer includes the notorious "out of eclipse" variations -OOE- which are still lurking in the eclipse light curve.  These have amplitude of one-tenth magnitude (or more) and a quasi period of two or more months.  By using a 5 to 10 day mean in plotting the visual light curve data, you can see evidence for at least one local maximum around JD 2,455,160.  The excursion from a straight line during ingress is only ~0.05 mag, but it takes only a small size variation or an even smaller temperature variation in the F star to cause that kind of variation.Read more

Observers are reporting signs that epsilon Aurigae's light has plateau'd during the past week or so, suggestive that second contact was reached - that is, the dark disk now stretches across the nearly 1.5 astronomical unit diameter F star.   Exact time of second contact  can only be determined in hindsight, but the  change in the rate of decline is noteworthy.  Comparison with last eclipse is informative, although the data density is somewhat less.  In part, second contact was not the final, minimum brightness for the system.  Rather, another drop of 0.03 mags happened about a month after the initial minimum, then a slow decline over several months until so-called mid-eclipse brightening started around mid-eclipse (and the seasonal close approach of sunlight made those observations very difficult).Read more

This morning, Donald Hoard (Spitzer Science Center) reported on an analysis of a large set of multi-wavelength measurements (ultraviolet, optical and infrared) that provide important insight into the components that comprise the epsilon Aurigae system.  Dr.Hoard spoke about this work at the Adler meeting of Citizen Sky August 2009 and you can find the video of his talk on the website.Read more

Did you observe the palindromic date this weekend, 01- 02- 20 10 ? 
If you have been observing the steady decline of the light of epsilon Aurigae this autumn, you might wonder if it too will be palindromic - that is, the brightness symmetricaly rising during egress early in 2011, as steadily as it declined during ingress autumn 2009.  Short answer, probably not.  Among the many wonderful conundrums surrounding epsilon Aurigae is that the eclipse is asymmetrical - egress tending to be fast than ingress. 
This difference is thought to be due to asymmetries in the disk - somewhat less well defined on the trailing edge that we'll see later in 2010 and during early 2011 as eclipse ends, relative to the leading edge this past few months.Read more

The end of the calendar year marks an end and a beginning for many cycles, among them the annual bird count conducted by the Audubon Society - this year being their 110th census, making it the longest-running volunteer or citizen science effort.  Results of the Christmas Bird Count are being used to gauge climate change effects, among many other purposes.  Many birders are also avid astronomers, sharing a love of observing and recording data.  AAVSO - the American Association of Variable Star Observers - comes in a close second at 98 years, for conducting one of the longest running citizen science activities as well.  The millions of observations reported to AAVSO are useful for all kinds of astrophysical studies, including this focus on epsilon Aurigae.Read more

For the Northern Hemisphere of Earth, we have arrived at the winter solstice and the light has faded.  For us in the north, spring is only 3 months away.  For all of Earth, however, we will remain in the shadow of the disk in the epsilon Aurigae system for the next 12 months and then some - until nearly spring of 2011.  Thus, we will be deprived of some of the warming photons coming to us from the F star in the system, while the dark disk intrudes and lingers in the line of sight.Read more

It's December 8th evening, Julian Date (J.D.) 2,455,175 and we are only a few days from predicted time of Second Contact when total eclipse starts.

The words "1st, 2nd, 3rd, 4th contact" refer to moments when objects in eclipsing systems overlap partially and totally.  Consider a small circle crossing in front of a bigger circle: first, just the outsides touch (1st contact); then the small circle just gets fully inside the larger (2nd contact); later, the smaller circle begins to exit from inside the larger circle (3rd contact), and at the end, the circles stop touching at their edges, before separating (4th contact).Read more