stellar jewel box

The Jewel Box cluster (NGC 4755), in the constellation Crux, is one of the youngest known open clusters. Thought to be just 7 million years old, it is dominated by hot blue B-type stars, with one red supergiant.

a common recipe for some types of variable stars.

Often, the stars in a multiple system are so close together that they cannot be separated by even the most powerful telescope. However, such systems can still give themselves away if their planes lie in the same direction as Earth and they form eclipsing variables (see p.72). In other cases, the only clue to a multiple system may be the presence of "double" absorption lines in the spectrum of an apparently "single" star.

stellar pairings

Albireo, or Beta (b) Cygni, is one of the most colorful binary stars in the sky. It consists of an evolved yellow giant and a less massive blue-green star that is still on the main sequence.

weighing multiple stars

Multiple stars offer astronomers their only way to measure the relative masses of stars. All the stars in a system will orbit a common center of mass, known as the barycenter. If the stars are of equal mass, the barycenter will be midway between them, but if one is more massive, then it will be closer to the barycenter.

both members share same orbit, barycenter more massive star has tighter orbit and shorter orbital period,

Binary system of equal mass stars more massive star has tighter orbit and shorter orbital period,

Binary system of unequal mass stars

Binary system of unequal mass stars

open and globular clusters

Open clusters are found close to the Milky Way, while globulars are mostly found above and below the plane of the galaxy. Magnitudes given are estimated from the combined effect of all the member stars.



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