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Epsilon Aurigae Mystery and Opportunity. Your Name Your Affiliation Month, Date. How Do You Say Epsilon Aurigae?. Ep’ si lon Au ry’ gee. Where is Epsilon Aurigae?. Courtesy Jerry Lodriguss www.astropix.com. Eclipsing Binaries. Eclipsing binary light curves.
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Epsilon AurigaeMystery and Opportunity Your Name Your Affiliation Month, Date
How Do You Say Epsilon Aurigae? Ep’ si lon Au ry’ gee
Where is Epsilon Aurigae? Courtesy Jerry Lodriguss www.astropix.com
Eclipsing binary light curves • A brightness versus time plot for a variable star is known as light curve. For close binary systems, time is usually expressed as phase, for which one unit of time is the orbital period. • Measured light curves for periodic variable stars are usually "folded", which means that successive cycles are plotted atop one another. • The shape of the light curve for an eclipsing binary star system depends mostly on the relative brightness and size of the two stars as well as their orbital inclination as seen from Earth.
What can we learn from eclipsing binaries? • p = Period • i = Orbital Inclination • M1, M2 = Masses of the Stars • L1, L2 = Luminosities of the Stars • R1, R2 = Radii of the Stars
Epsilon AurigaeThe History of the Mystery • Johann Fritsch was the first to note the variability of epsilon Aurigae in early 1821, when the star was likely in the midst of a deep eclipse. • The German astronomers Argelander and Heis both began "regular" observing once every few years around 1842-1843, and the data from both men showed that the star became significantly fainter around 1847. • Observers later in the 19th Century recorded another dimming event in 1874-1875, and another in 1901-1902.
Massive Mystery • Although they didn't know it at the time, what they had observed was an extremely long-period eclipsing binary, and one that was interacting as well. • In 1928, Harlow Shapley correctly concluded the secondary was as massive as the primary, an F0 supergiant star. The companion should be as bright as the primary. • But the spectrum of the system showed no light from the companion at all. • The primary was being eclipsed by a massive, invisible secondary!
Pieces to the puzzle • A 1937 paper by three of the greats of observational astronomy,Gerard Kuiper, Otto Struve, and Bengt Strömgren,suggested the system was an eclipsing binary composed of an F2 star and an extremely cool and tenuous star that they described as "semitransparent". • According to this model, the F star was being eclipsed by this ‘transparent shell star’, and its light was scattered by the extremely thin atmosphere of the eclipsing star.
Observation leads to new ideas • A 1965 paper by Su-Shu Huang introduced the suggestion of an edge-on thick disk as the eclipsing body. • In 1971, Robert Wilson introduced a tilted, thin disk with a central opening, suggesting that this model could most easily describe all of the observed effects of the eclipses, particularly the mid-eclipse re-brightening.
Moving Target • There is a slight brightening during mid-eclipse, suggesting the disk has a hole in it which the F star shines through. • The central brightening was stronger in 1954-56 than in earlier eclipses. Was the hole growing? • The time of minimum light lengthened by about 64 days. • The overall duration of the eclipse had decreased by 44 days!
The last eclipse • During the 1982-84 eclipse the central brightening was the brightest ever. • The duration of minimum was the longest, and the fading and brightening happened fastest. • The F star’s companion is changing on timescales of decades. • From 1901 to 1983 the time of minimum has increased from 313 to 445 days. • The overall eclipse duration has declined from 727 to 640 days.
As if that weren’t enough… • Precise measurements out of eclipse revealed a quasi-periodic low amplitude variation of 96 days from 1984-87. • During the 2003-2004 observing season this variation had sped up to 71 days. • In 2007-2008 the period became 65 days.
The scale of the system is astronomical! The primary is 300 times the diameter of the Sun. The secondary orbits at the distance of Uranus from the Sun. Both components are 14-15 solar masses.
The Center of Controversy • What is the nature of the object or objects at the center of the disk? • It could be two B type stars in a tight orbit. This would account for the mass. • A pair of stars would act as a gravitational eggbeater, keeping the center clear.
Is there a giant planet involved? • One or more proto-hot-Jupiters would affect the distribution of matter in the disk. • A hot Jupiter spiraling inward to meet its death might account for the low amplitude variations and their decreasing periodicity.
IYA 2009 • International Year of Astronomy • Celebrating the 400th anniversary of Galileo turning a telescope to the heavens • AAVSO Citizen Science Project- Citizen Sky Project
Citizen Science What are citizen scientists? • Volunteers, many of whom have no prior scientific training, who work with trained scientific researchers to answer real-world questions. • This means YOU!
AAVSO Citizen Sky Project www.citizensky.org • We need you to help us collect data so that we can better understand this star. • Because the star is very bright, it can be observed by anyone regardless of background, training, or equipment. • With just good eyesight and a finder chart, you can monitor this eclipse.
We will guide you through the process. • How to observe the star- (Ten Star Training program for beginners) • How to send us your observations of the star • How to see your results and analyze them • And even publish them in a scientific journal! • We hope that this will be the largest citizen science project in modern history that involves real, active research!
Workshops • A 3-day workshop, focused on observing and education/public outreach, will be held at the Adler Planetarium in Chicago, August 5-7, 2009. The workshop will occur just days before the eclipse of epsilon Aurigae is predicted to begin. • Video of talks at the workshops will be placed online and available via DVD upon request. • It is very likely that we will have travel grants available for workshop participants. Stay tuned to www.citizensky.org for workshop/grant application instructions.
Visual Observers • At 3rd magnitude, epsilon Aurigae is bright enough to be seen from most urban areas. This makes it an ideal target for those interested in learning how to observe variable stars. • No equipment is needed. • By following the Ten Star Tutorial, a new observer will be trained in the technique needed to make and report a variable star estimate.
Data Analysis • All data collected by observers will be available to the public as it is submitted. • AAVSO is developing data analysis software. • This software will come with tutorials to help train participants in the basics of astronomical data analysis. • A special edition of the peer-reviewed Journal of the AAVSO will be dedicated to papers written about epsilon Aurigae by amateur astronomers.
Education and Public Outreach • The brightness of the star provides a rare opportunity to engage the general public in citizen science. • Participants are needed to help write newsletter and newspaper articles, prepare talks and slide shows, develop artwork, to give talks and participate in other forms of community outreach. • Teams of interested participants with complementary skill sets are being assembled right now, and will continue to be assembled throughout the project.
What are the science questions? • Is the F star a massive supergiant or an early post-asymptotic giant branch star? • What is at the center of the eclipsing disk? • Is the disk tilted or warped? • How massive is the disk?
Time Line • Eclipse begins Aug. 11, 2009 • Minimum light begins Dec. 19, 2009 • Mid-eclipse Aug. 4, 2010 • Minimum light ends Mar.19, 2011 • Eclipse ends May 13, 2011 • All dates are approximate
You can follow updates on Twitter http://twitter.com/epsilon_Aurigae
