Dr.Bob's blog posts

...or not. 
We are entering into a very special 2 month interval centered on predicted mid-eclipse, 4 August 2010 (JD 2,455,413 +/- 2 weeks).  Some expect a "mid-eclipse brightening" - as much as several tenths of a magnitude - which would demonstrate a substantial central clearing in the dark disk. 

Based on what we know from the initial round of interferometric imaging, the disk is so close to edge on, that seeing the "hole in the doughnut" is improbable.  However, there are some clues that surprises may await the persistent observer:

- the B star at the center of the disk is a significant source of ultraviolet photons, capable of vaporizing dust, possibly enlarging the central opening;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

Given that few ancient Greek or Roman astronomers are around today to help us with correct pronunciation, I'm happy to report a little gem has surface, published in 1942 by Adler Planetarium, that might help settle matters.  The pamphlet is called Report of a committee of the American Astronomical Society on Preferred Spellings and Pronunciations - see attached.  Therein, the Latin genitive (possessive) for constellation Auriga = Aurigae and is marked "o - ri - jee" - as in the concatenation of ORIon and GEE, O-RI-GEE.  However, unless you meet an ancient Greek or Roman, we'll probably know to what you refer, no matter your preferred pronunciation.

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

3/23/2010-- As reported by Hoard, Howell and Stencel...
(2010 to appear in the Astrophysical Journal), data have become available that span a wide spectral range, from the far-ultraviolet, through the visible range and out into the far-infrared. Because of calibration efforts, it has proven possible to combine these well calibrated data into a complete and self-consistent picture of the sources of light in epsilon Aurigae. Key to understanding this result is that interlocking requirements of distance and other constraints on F star diameter drive us to these self-consistent conclusions.

The full paper is available, free, at website:
http://arxiv.org/pdf/1003.3694v1

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