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In 1910 Hans Oswald Rosenberg published a diagram plotting the apparent magnitude of stars in the Pleiades cluster against the strengths of the calcium K line and two hydrogen Balmer lines. [3] These spectral lines serve as a proxy for the temperature of the star, an early form of spectral classification.
Star clusters are large groups of stars held together by self-gravitation. Two main types of star clusters can be distinguished. ... Then, when similar diagram is ...
HR diagrams for two open clusters, M67 and NGC 188, showing the main sequence turn-off at different ages. The turnoff point for a star refers to the point on the Hertzsprung–Russell diagram where it leaves the main sequence after its main fuel is exhausted – the main sequence turnoff.
The path which the star follows across the HR diagram is called an evolutionary track. [57] H–R diagram for two open clusters: NGC 188 (blue) is older and shows a lower turn off from the main sequence than M67 (yellow). The dots outside the two sequences are mostly foreground and background stars with no relation to the clusters.
Ages for star clusters may be estimated by comparing the Hertzsprung–Russell diagram for the cluster with theoretical models of stellar evolution. Using this technique, ages for the Pleiades of between 75 and 150 million years have been estimated.
Hertzsprung–Russell diagram with the Hertzsprung Gap visible as an area containing few stars between the main sequence and red-giant branch. The Hertzsprung gap is a feature of the Hertzsprung–Russell diagram for a star cluster. This diagram is a plot of effective temperature versus luminosity for a
The first known globular cluster, now called M 22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. [4] [5] [6] The cluster Omega Centauri, easily visible in the southern sky with the naked eye, was known to ancient astronomers like Ptolemy as a star, but was reclassified as a nebula by Edmond Halley in 1677, [7] then finally as a globular cluster in the early 19th century ...
The remaining population of confirmed cluster members includes numerous bright stars of spectral types A (at least 21), F (about 60), and G (about 50). [1] [28] All these star types are concentrated much more densely within the tidal radius of the Hyades than within an equivalent 10-parsec radius of the Earth. By comparison, our local 10-parsec ...