----- Original Message -----
From: "Jeff Hopkins"
Sent: Tuesday, June 03, 2008 6:09 PM
Subject: Epsilon Aurigae Press Release
> Dear Colleagues,
>
> The following is a press release from this morning at the AAS meeting
> in St. Louis.
>
> ************************************************************************
> Tuesday June 3, 2008
>
> FOR RELEASE: 9:40 AM Central Daylight Time, June 3, 2008
>
> Contact information: Dr. Robert Stencel, Professor of Astronomy,
> University of Denver
> 303-871-2135 ;
rstencel@du.edu ;
http://www.du.edu/~rstencel
>
> ASTRONOMERS PREDICT NEARBY STELLAR FIREWORKS BY MID-CENTURY
>
> Astronomers are announcing today the prediction that the bright
> northern star called epsilon Aurigae is headed for a "doomsday event"
> within a few decades. The report is being presented by Dr. Robert
> Stencel of the University of Denver Observatories in a press
> conference at the American Astronomical Society meeting in St. Louis,
> Missouri. Observations over the coming three years, when the
> mysterious star undergoes a once-per-generation eclipse event, may
> hold the secret to the extreme changes detected during the past few
> decades.
>
> THE DETAILS:
>
> Science case:
> What could be simpler than an eclipsing binary star? As they
> orbit each other, it is relatively easy to measure brightness change
> and the duration of change, and, from simple geometric arguments, to
> obtain size and temperatures for each star in the binary. With the
> addition of Doppler spectroscopy, which measures orbital velocities,
> one can solve for mass of each star, using Kepler's third law.
>
> The classic example of this is the so-called Demon Star, Algol,
> which exhibits 2 hour eclipses every 2.87 days. With such eclipsing
> binary stars, astronomers can calibrate important parameters that
> describe a star's structure. The Vogt-Russell theorem says the mass,
> composition and age uniquely determine the stellar structure, when
> normal laws of physics are applied. This theorem appears largely
> true, except for epsilon Aurigae - the real "Demon star". It's
> behavior has "bedeviled" astronomers for centuries.
>
> The spectrum of epsilon Aurigae looks like a normal F supergiant
> star, estimated at about 12 to 15 times the mass of the Sun. The
> orbit data implies that the mass ratio in the binary is close to one,
> implying that the companion is about 12 to 14 solar masses as well.
> Epsilon Aurigae exhibits Algol-like eclipses every 27 years, which
> last for nearly 2 years. The next one starts in August 2009, and
> should run through May 2011.
>
> The problem? The 12 to 14 solar mass second "star" is largely
> INVISIBLE! The best model (Huang, 1965) says the secondary is a huge
> dark disk, not a sphere. Such a shape needs a massive central
> object(s) to stabilize it.
>
> Normal eclipsing binary star analysis suggests that the secondary
> is about 10 A.U. across (10 times the distance from the Earth to the
> Sun, or 930 million miles). It does not emit anywhere near the
> amount of light expected from a star of its size. Scientists are
> confident that it is not a black hole, because it hasn't been
> detected with X-ray observations (Einstein, Swift).
>
> Epsilon Aurigae shows low amplitude quasi-periodic light
> variations, similar to Cepheid variable stars. Cepheid variable
> stars are close relatives of epsilon Aurigae, being high mass yellow
> stars prone to pulsation - a useful property in terms of their
> Period-Luminosity relationship. Currently the light variations in
> epsilon Aurigae are on a 67 day cycle, but -KEY POINT- these were
> nearer to 100 days during the last two decades. Something is
> accelerating in this system! At this rate, variations will become
> very rapid within six decades, perhaps cataclysmically so. Much of
> the relevant photometric data has been obtained by Jeff Hopkins of
> Phoenix Observatory, Arizona
> (
http://www.hposoft.com/EAur09/EAur0307Plots.html ), Il-Seong Nha of
> the Yonsei University Observatory, Korea (
>
http://adsabs.harvard.edu/abs/1993ASPC...38..291N ) and other
> observers.
>
> But wait---there's more. Observations made during the last
> eclipse suggest that the F supergiant star may be shrinking by about
> 1/2 percent per year (noted in 1986 by Mamuro Saito and Masatoshi
> Kitamura at Tokyo Astronomical Observatory -
>
http://adsabs.harvard.edu/abs/1986Ap%26SS.122..387S ). The duration
> of total eclipse (during which the F star is partially covered by the
> disk shaped companion) has increased by about 25 percent between the
> 1956 and 1983 eclipses. Despite this, the overall length of the
> total plus partial phases of eclipse - especially the time where the
> F star moves out from the cover of its partner - has gotten shorter!
>
> If these trends continue, the F star will come out of eclipse
> (from totality) in only 1 or 2 weeks during 2011. BUT, it will still
> take 140 days or so to move from the beginning of the eclipse to
> totality next year, autumn.
>
> What is changing, and what do the variations mean? Is this binary
> system preparing for an energetic event?
>
> Is the light variation due to changes in the F supergiant star's
> radius or temperature? Using the well-known correlation among
> stellar luminosity, radius and temperature, a ten percent change in
> Luminosity can result from a 5 percent change in Radius, or a 2.5
> percent change in Temperature. At an estimated distance of 625 pc,
> and assuming the F supergiant star is close to the nominal 100 solar
> diameters appropriate for its type, then the implied angular diameter
> is 3 milli-arcseconds. Modern interferometers, like the Palomar
> Testbed Interferometer (PTI, San Diego County, CA), are capable of
> measuring down to fractions of one milli-arcsecond, close to that 5
> percent change anticipated, and these measurements are underway.
> These measurements would help confirm that the F star could be
> causing the accelerating light changes.
>
> What's a milli-arcsecond? Astronomers use angular measures much
> finer than degrees on a protractor. The arc-second is 1/3600 part of
> one degree, and a milli-arcsecond is 1000 times finer. A 25 cent US
> coin seen at a distance of 6,500 miles (10,000 km) subtends about one
> milli-arcsecond.
>
> The best model for the eclipsing object makes a clear, testable
> prediction that is suitable for interferometry: the F supergiant star
> should be BIFURCATED (cut in half) by the eclipse-causing disk, if
> indeed it is a disk. Next generation imaging interferometers like
> CHARA at Mt.Wilson and MROI at Socorro, should be easily able to
> monitor this set of changes. If the disk is causing the changes in
> the system, that should be seen with these measurements.
>
> Bonus points: Public participation!
> The epsilon Aurigae eclipse event is being promoted as one facet
> of the International Year of Astronomy, IYA2009:
>
http://astronomy2009.us/citizen_science/ . It is a bright star that
> can be seen despite light pollution, monitored both visually and with
> the simplest of digital camera equipment. One goal is to better
> define the eclipse duration and catch the mysterious central eclipse
> brightening. The observing activity is intended to promote citizen
> science in honor of the 400th anniversary of the telescope and
> Galileo's applications of it. JOIN US FOR THE 2PM SESSION #68 TODAY,
> ROOM 232: Citizen Science & IYA - Your role, and poster #35.02, Price
> et al.
>
> In summary, the bright northern star, epsilon Aurigae, is
> exhibiting rapid changes suggestive of dramatic events within one or
> two eclipse cycles, later this century. "These changes offer a
> chance to examine the dynamics of rapidly changing stellar disks on a
> human timescale, and an opportunity for the public to see for
> themselves that stars change."
>
> ==end of text==
>
> Lots of additional material available at webpage:
>
http://www.du.edu/~rstencel/epsaur.htm
>
> Artwork and illustrations, at webpage:
>
http://www.du.edu/~rstencel/epsaurnews.htm
>
> Forthcoming publication: Epsilon Aurigae - the Book (Hopkins and
> Stencel, 2008 summer).
>
> References:
> Disk Model, S.S. Huang 1965, Astrophysical Journal, vol. 141, p.976
> Epsilon Aurigae Star System Model, Sean Carroll, et al. 1991 Ap.J.
> 367: 278 [invited speaker, cosmology session,Wed. #94.01]
> Photometry, Jeff Hopkins, Phoenix AZ:
phxjeff@hposoft.com
>
> Artwork inspired by epsilon Aurigae: M.Carroll, D. Weeks, D. Egge.
> Contact info for artists:
> Michael Carroll -
cosmicart@stock-space-images.com
> Daniel Weeks -
ouiques@comcast.net - 717 264 8570
> D. Egge - not available.
>
> Interferometer websites:
> PTI -
http://pti.jpl.nasa.gov/index.html
> CHARA -
http://www.chara.gsu.edu/CHARA/array.html
> MROI -
http://www.mro.nmt.edu/
>
> Contact information:
> Dr. Robert Stencel, Professor of Astronomy, University of Denver
> 303-871-2135 ;
rstencel@du.edu ;
http://www.du.edu/~rstencel
>
> CALENDAR OF ECLIPSE EVENTS:
> 2009 Aug 6th - predicted start of eclipse (partial phase)
> 2009 Dec 21st - predicted start of totality
> 2010 Aug 1st - predicted, mid-eclipse
> 2011 March 12th - predicted end of totality
> 2011 May 15th - predicted end of eclipse
> ...
> 2036 - next eclipse starts in autumn 2036.
>
> Footnote regarding Cepheids:
> Recent paper on long-period galactic Cepheid RS Puppis by Kervella et
> al.
http://adsabs.harvard.edu/abs/2008A%26A...480..167K
> "The bright southern Cepheid RS Pup (P=41.4 d) is surrounded by a
> circumstellar nebula reflecting the light from the central star. The
> propagation of the light variations from the Cepheid inside the dusty
> nebula creates spectacular light echoes that can be observed up to
> large distances from the star itself. This phenomenon is currently
> unique in this class of stars..."
>
> [end]
> --
> Jeff Hopkins
> HPO SOFT
> Counting Photons
>
http://www.hposoft.com/Astro/astro.html
> Hopkins Phoenix Observatory
>
www.hposoft.com
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