October 23, 2017

AstroEvent: When will Epsilon Aurigae Brighten?

One of the strangest variable stars is worth watching this spring.  Back in 2009, we alerted viewers to monitor the curious variable Epsilon Aurigae. Once every 27.06 years, this star dips nearly a magnitude in brightness down to about +3.8, markedly discernable to the naked eye. This drop lasts for over a year before Epsilon Aurigae returns to its former self. This spring should witness such an occurrence.

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25.04.10-First Extra-solar Magnetic Loop Recorded.

 

(Credit: Peterson, NRAO/NSF).

(Credit: Peterson, NRAO/NSF).

Artist’s conception of the radio flare superimposed over the Algol system.

   Radio-Interferometry has really shown its stuff as of late. Recently, astronomers have used a collaboration of radio telescopes based planet-wide to study a familiar variable star; Algol in the constellation Perseus. Known since Arabic times as “The Demon Star,” Algol is an eclipsing binary, where two stars are locked in a 5.8 million mile embrace and “eclipse” each other from our vantage point. This explanation has been known since 1889, but radio astronomers have added another unique feature to the pair; a long pair of magnetic loops connecting the two stars. “This is the first time we’ve seen a feature like this in the magnetic field of any star other than the Sun,” stated William Peterson of the University of Iowa. The scopes linked included the NSF’s Very Long Baseline Array, Green Bank, and the Effelsburg Radio telescope based in Germany.  Collectively, the setup is known as the High Sensitivity Array. Algol is about 93 light years distant, and is a variable star that can be easily monitored by even beginning amateurs with the naked eye.

08.04.10-Epsilon Aurigae Update.

   We couldn’t resist shooting this one out there today, as it contains some fairly mind-blowing imagery. Late last year, we put a shout-out to observe the eclipsing binary star Epsilon Aurigae, a bright naked eye star that undergoes periodic diming once every 27 years. For over 190 years, this star has stubbornly not only refused to match stellar evolutionary models, but sometimes threatened to overthrow them, to boot. Now, scientists have solved the case of the disappearing star, and it’s a strange one, indeed. The variation in brightness appears to be the result of three factors; a bright type F supergiant, orbited by a hot type B star about 1,000 times dimmer shrouded in a massive dust disk. The entire system passes along our line of sight and obscures the host for an 18 month period. The grouping is about 2,000 light years distant. In fact, if Epsilon Aurigae were tipped away even 10 degrees more from our line of sight, we wouldn’t see anything unusual at all! This model of the systems’ total luminous output matches the observed brightness curve from the recent dimming. (see above) [Read more...]

16.03.10:Relativity Triumphant over Bizarre Binary.

The unique dance of DI Herculis. (Credit: Simon Albrect/MIT).

The unique dance of DI Herculis. (Credit: Simon Albrect/MIT).

 

   For years, a unique binary system has plagued Einsteinian physics. DI Herculis (DI Her) is a seemingly innocuous binary star about 2,000 light years distant. Type B stars each about five times the mass of our Sun, these stars are in a mutual orbital embrace about 0.2 A.U. apart. Visually, the system is at magnitude +8.5, and the orbit is inclined along our line of sight so that mutual eclipses occur every 10.55 days. First recorded in 1900, this feature allows the systems’ mass, luminosity and orbital characteristics to be known to a high degree of precession. For the past several decades, however, astronomer Ed Guinan at Villanova University couldn’t shake an odd effect; namely, periastron of the two stars is advancing at a rate of only ¼ what’s predicted by Einstein’s theory of general relativity. Is an unseen companion lurking in the DI Her system, or is it Albert himself who was wrong? Prediction of such anomalies as the precession of the perihelion of Mercury is one of the great cornerstones of relativity.  In a massive system such as DI Her, this effect should be even more pronounced. Like the Pioneer anomaly, several would-be theorists have pointed to this discrepancy as a potential chink in the relativistic armor…

 Enter Simon Albrecht of MIT. Using a 1.93-meter telescope to obtain a high-resolution spectrograph of the two suns, a bizarre fact has become apparent; both stars are tipped on their rotational axes, giving them an orbital “kick” at their closest approach. This configuration adequately accounts for the relativistic anomaly. Apparently, DI Her underwent a close passage of another star or massive object sometime in its history. Guinan is relieved, but will no doubt continue to receive a flood of email from alternate-gravity theorists!

AstroEvent of the Week: 27.04.09: Epsilon Aurigae.

The American Association of Variable Star Observers wants you to help gather data on a very enigmatic astronomical object; the variable star Epsilon Aurigae. This seemingly ordinary star varies in a very peculiar way. The primary is a type F0 super-giant star, and what is known is that every 27.06 years an unseen mass dims its light from its usual +3.0 magnitude to about +3.8 for about a year.

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AstroEvent for the week of June 30th-July 7th, 2008.

And now for a difficult challenge…

I give you a New England Occultation.

First up, I’d like to apologize for the short notice on this week’s featured event, which occurs seconds before midnight tonight June 30th over New England and the Canadian Maritimes. [Read more...]