Star_Clusters - Star Clusters Observational Testbeds of...

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Unformatted text preview: Star Clusters Observational Testbeds of Stellar Evolution Question If stars exist for billions of years but mortals live less than a century, How are we able to study, derive, and understand Stellar Evolution? Background Astronomy is unlike all other sciences in that experiments cannot be performed in a laboratory. Telescopes obtain data that reveal basic characteristics of the observed objects and monitor pertinent events, such as eruptions or pulsations. Using the laws of physics, computers model these phenomena. The human brain develops scenarios to explain the data and models and to offer new observational avenues to pursue. Astronomical Insight Iterative Process Involving Acquisition of Data Development of Models Refinement of Theories Astronomical Tools Determine the Brightness of Stars Magnitudes Colors Astronomical Tools Analyze the Spectra of Stars Chemical Composition Surface Temperatures Radii Astronomical Tools Measure the Movement of Stars Proper Motions Radial Velocities Astronomical Tools Get Masses from Binaries Get Distances from Parallaxes Statistical Results Photometry Spectroscopy Astrometry Masses Distances Relationships L M4 Lifetime = ( Total Energy ) / ( Rate Energy is Used ) E/L E M So E / L = M / M4 1 / M3 Example 1 / M3 Main Sequence lifetime of the Sun = 10 x 109 years Let M = 2 solar masses Then = ( 1 / 23 ) 10 x 109 = 1.25 x 109 years The HR Diagram Intrinsic Brightness Surface Temperature Mass Radii Age Evolution Stars have a Birth, Life, and Death Star Clusters have a Birth, Life, and Death Advantages of Star Clusters 1. All members have the Same Distance 2. All members have the Same Age 3. All members have the Same Chemical Composition Types of Star Clusters Open Clusters 1100 Clusters Spiral Arms 50 to 1000 Stars 10 pc Diameter Types of Star Clusters Globular Clusters 150 Clusters Halo 10,000+ Stars 100 pc Diameter Features to Note on CM Diagrams The Top of the Main Sequence The Shape of the Main Sequence The Other Populated Areas Combined Tracks PRS Question 1. The main general features that make clusters of stars useful to astronomers are that the stars all have a. the same distance from Earth, the same temperature, and joined the cluster at various times b. the same apparent magnitude, the same temperature, and the same size c. the same intrinsic brightness, differing only in size and temperature d. the same distance from Earth, the same age, and the same chemical composition e. the same mass and size Summary Star Clusters are Valuable Tools for the Study of Stellar Evolution (birth, life, and death). Just like their individual members, though, clusters also evolve. Open Clusters are eventually ripped apart by galactic rotation, and all of the stars disperse. The Globular Clusters have sufficient internal gravity to prevent dissipation, but they lack interstellar gas and dust to form a new generation of stars. The Open Clusters, however, have returned enriched material to the spiral arms of the Galaxy, and with time, there will be a re-birth of stars and the cycle will continue. ...
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This note was uploaded on 03/04/2012 for the course PHYS 2022 taught by Professor Jarrio during the Spring '12 term at Central GA Tech.

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