#eclipsing binary

There is a class of stars called Eclipsing Binary stars, where a star can go in front of another star periodically and block out a portion of its light. The most famous of these is Algol in Perseus.

Recently a Triple eclipsing binary has been discovered, TIC 29574134. Two close together sun-like stars are orbited by a red giant star such that, when the red giant star goes behind the sunlike stars, the sunlike stars block some of the red giant's light, in steps.

You can read the paper on the ArXiv here:

Chapters: 2/2 Fandom: Danny Phantom

Summary:

An eclipsing binary consists of two close stars moving in an orbit so placed in space in relation to Earth that the light of one can at times be hidden behind the other. Binary star systems are very important in astrophysics because calculations of their orbits allow the masses of their component stars to be directly determined, which in turn allows other stellar parameters, such as radius and density, to be indirectly estimated.

(or: Danny is not quite a ghost in much the same way as he is not quite a human; it follows that the pretenses of one would be just as hard to keep up as those of the other.)

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A truly fascinating event may be in the offing this month. Picture two distant burning embers (candles, light bulbs, LEDs, what have you) circling each other in the distance... 

Many stars in the night sky are double or multiple in number; our Sun is unusual in that it's a single-star system. Sometimes the appearance of a "double" star is by chance, where two stars actually very far apart from each other in space coincidentally appear close together in our line of sight. But many doubles are true "binaries", where the two stars are locked in a gravitational pas de deux around each other.

Most binaries stars are in compact orbits around each other, taking only hours to days to make a complete revolution. In certain cases, their orbital planes match our line of sight and we periodically see one star "eclipse" the other, causing the light of the combined system to decrease. Here's an artist's impression of such a system:

For reasons that aren't well-understood, some "eclipsing binaries" have very long periods, ranging from years to decades. These stars are in very wide orbits, comparable to the size of our solar system. One such eclipsing binary, Epsilon Aurigae, takes 27 years to complete an orbit; its last eclipse was observed in 2009-11 and the next won't begin until 2036! With very few such systems known, understanding them better is important.

Not far behind Epsilon Aurigae in terms of long periods is another suspected eclipsing system: Alpha Coma Berenices, called "Diadem". It is known to be a double star with a period of about 26 years, and the two components appear very close together during the orbit -- close enough that it is suspected that they undergo a slight eclipse. At the last close approach, in February 1989, no eclipse was seen. But there are many more observers paying attention now, and we understand the orbit of these stars much better than we did in 1989. And the next eclipse may be only days away. 

Based on that understanding, the next eclipse has been predicted for a window of time from 22-26 January 2015, during which the combined light of the system may drop by as much as about 0.8 magnitude -- enough to be noticeable to the naked eye. 

That's right: those without any equipment at all can make scientifically-useful observations of Alpha Coma Berenices that will help improve astronomers' knowledge of these rare, "long period eclipsing binary" systems. Information on how you can help is available in this Alert Notice from the American Association of Variable Star Observers (AAVSO). Happy hunting!