Eclipse

Hi, all. The second year of Citizen Sky has just begun. Here are some of the things we have afoot...

The first year of the project was dedicated to training to observe the star and report your observations. We also worked on the site infrastructure. Since the funding came through late, we had to push a lot of what we originally had planned for years 1 and 2 - into year 1 alone. This meant it was a hectic year, but it now means years 2-3 can be at a more leisurely , natural pace.
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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

Despite a spring blizzard, we made it to our 28 inch f/21 RC telescope at Mt.Evans Observatory in Colorado (14,148 ft elev) and visually inspected epsilon, zeta and eta at low airmass mid-day Tues 6/15/2010.  Brian K and I agreed that eps and zeta were of comparable brightness, after several iterations.  I think eps is slightly fainter than zeta when color differences are taken into account, but that gets subjective under bright sky conditions.  Thus, we report no indication that epsilon Aur is brighter than zeta Aur at this time.  Hence, no evidence for mid-eclipse brightening at this time, but further reports to follow.

With mid-eclipse forecast for early August 2010 and mid-eclipse brightening supposedly lasting +/- 30 to 45 days around that point, we should either begin to see evidence for it soon, or redefine the mid-eclipse light curve.Read more

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.Read more

During the past week, careful observers have been struggling with the low horizon angle presented by epsilon Aurigae and its friends, due to approaching solar conjunction in early June.  Despite this, credible reports are being received that epsilon Aurigae may be as much as 0.1 mag brighter than it was during early May.  If you have a clear NW horizon and patience, try finding The Kids below Capella after sunset, and see if you can provide a brightness estimate during these challenging weeks of late spring.Read more

If you've tried to observe epsilon Aurigae lately, it is quickly sinking into the northwest at dusk, along with Orion and other winter constellations.  The star is at solar conjunction during early June, making observations more challenging over the coming several months.  To stretch the game analogy, it's essentially half-time - in terms off the eclipse schedule.  Naturally, this is just when the fabled mid-eclipse brightening is forecast to happen, suggestive of a central clearing in the midst of the dark disk.  Given the developments of the past months and the coming half-time show, it seems timely to review what's been learned, and outline some of the outstanding questions that further observations can help address. 

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Eyjafjallajokull may sound like a word lifted from Finnegans Wake (a novel by James Joyce), but the Icelandic volcano has grabbed worldwide attention by producing a dense ash cloud that threatens jet aviation over much of northern Europe again this week.  In this third blog exploration of the implication of direct detection of the disk in epsilon Aurigae, via interferometric imaging, I want to explore with you how terrestrial volcanic ash provides some analogies with the dusty material that scientists believe make up "debris disks" seen around a surprising percentage of normal stars. Read more

The set of images published in Nature on April 8th 2010 represent only a few nights of observing, mainly during ingress phases of this eclipse.  Brian and I will, in tag team form, blog about a number of facets about the observation and its implication, and provide a sense of what's next in this process.

First, this direct detection of the disk is a wonderful demonstration of the scientific method: long theorized to be there, and at long last it is observationally confirmed.

You might ask: The disk must be large, but how large? And how massive? How far is the companion from Epsilon Aurigae?

How large?  It's big - nearly reaching the orbit of Jupiter around the Sun if we moved it into our solar system, and as thick as earth's orbit in the vertical dimension.   This dimensional estimate is dependent on distance assumptions, but we'll come back to that.Read more

We are pleased to announce that images of the disk occulting the F star were obtained interferometrically during ingress (autumn 2009).  Details of this will appear in this week's issue of NATURE journal, April 8th edition.  Watch this space later in the week for more discussion about those pictures and what they tell us.

It's been a long road to get those images that confirm the disk explanation for the epsilon Aurigae eclipses.  Previous blogs and many online sources help explain the method, but its application to epsilon Aurigae has only really become practical this decade with the improvements in "closure phase" imaging made possible with the NSF-sponsored Michigan IR Combiner (MIRC) instrument, at the CHARA array atop Mt. Wilson.Read more

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