The Importance of Star Clusters

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The Importance of Star Clusters 1) All stars in a cluster lie at about the same distance from the Earth. 2) All the stars in the cluster were formed at about the same time (within a few million years of each other) Color-magnitude diagrams of clusters allow us to determine their relative ages, and also their relative distances. We can confirm the notion of different main sequence lifetime lengths by looking at the color-magnitude diagrams of star clusters of different ages. Open star clusters such as this one are not very old. Only their most massive stars have evolved to become giant stars. Once a star has exhausted its core hydrogen, its radius and luminosity will change. With a different intrinsic brightness and size, it will no longer be located on the main sequence in the Hertzsprung-Russell Diagram. Globular clusters such as M5 are old. Only the lower mass stars are still main sequence stars. We assume that main sequence stars of various spectral types are essentially the same, no matter what cluster they form in. Their compositions may differ slightly, but for a given mass, a main sequence star has a very predictable temperature and intrinsic luminosity. Thus, if we can determine how many magnitudes fainter the main sequence stars are in one cluster compared to another, we can determine the relative distances of the clusters. The HIPPARCOS satellite (launched 1989) was able to determine the trigonometric parallaxes of the stars in the Hyades star cluster. Main sequence fitting allows us to derive the distances of other star clusters using the Hyades distance as reference. Thus, with a two step calibration we can determine the true distances (not just the relative distances) of star clusters..

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Star Clusters
Star Clusters • Eventually, photons and stellar winds clear out the remaining gas and dust and leave behind the stars. • Reflection nebulae provide evidence for remaining dust on the far side of the Pleiades Star Clusters • It may be that all stars are born in clusters. • A good question is therefore why are most stars we see in the Galaxy not members of obvious clusters? • The answer is that the majority of newly-formed clusters are very weakly gravitationally bound. Perturbations from passing molecular clouds, spiral arms or mass loss from the cluster stars `unbind’ most clusters. Star Cluster Ages • We can use the H-R Diagram of the stars in a cluster to determine the age of the cluster. • A cluster starts off with stars along the full main sequence. • Because stars with larger mass evolve more quickly, the hot, luminous end of the main sequence becomes depleted with time. • The `main-sequence turnoff’ moves to progressively lower mass, L and T with time. • Young clusters contain short-lived, massive stars in their main sequence • Other clusters are missing the high-mass MSTO stars and we can infer the cluster age is the main-sequence lifetime of the highest mass star still on the main- sequence. 25Mo 3million years 104 3Mo 500Myrs 102 1M 10Gyr L o 1 0.5Mo 200Gyr 10-2 30000 15000 7500 3750 Temperature Star Clusters Sidetrip • There are two basic types of clusters in the Galaxy. • Globular Clusters are mostly in the halo of the Galaxy, contain >100,000 stars and are very ancient. • Open clusters are in the disk, contain between several and a few thousand stars and range in age from 0 to 10Gyr Galaxy Ages • Deriving galaxy ages is much harder because most galaxies have a star formation history rather than a single-age population of stars.
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Hyades Star Cluster and the New Comets Abstract. We Examined The
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Page 9 S C I E N C E H I G H L I G H T S
STAR CLUSTER KINEMATICS WITH changed in the last few years, when a number of new AAOMEGA instruments came online (Hectospec/Hectoechelle at SCIENCE HIGHLIGHTS Lszl L. Kiss (Univ. of Sydney), Zoltn MMT, FLAMES at VLT, DEIMOS at Keck, AAOmega at Balog (Univ. of Arizona), Gyula M. Szab AAT, etc.), delivering thousands of spectra at a speed (Univ. of Szeged, Hungary), Quentin A. and sensitivity never seen before. Parker (Macquarie Uni. & AAO), David J. Radial velocities tell a different story to the colour- Frew (Perth Observatory) magnitude diagram: velocity dispersion is linked to the total mass of the cluster, hence indicating the presence Introduction or absence of invisible matter; the dispersion as a The high-resolution setup of the AAOmega spectrograph function of radius is a tell-tale indicator of the underlying makes the instrument a unique stellar radial velocity mass profile, whereas systemic rotation can be revealed machine, with which measuring Doppler shifts through an analysis of angular distribution of the to /1.3 km s -1 for 16 magnitude stars within an hour of velocities. Coupled with proper motion measurements, net integration has become a reality. The 1700D grating velocities can also be used to derive a kinematic with its spectral resolution of l/Dl =10000 in the near- distance (assuming energy equipartition for the member infrared calcium triplet (CaT) range between stars). A completely new avenue opens up with the full 8400M8800 Å is particularly well suited for late-type stars, spectral analysis, when atmospheric parameters such whose spectral energy distribution peaks exactly in this as effective temperature, surface gravity and metallicity, range and whose spectra are dominated by the strong are determined for each star.
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The Stellar Life Cycle in This Final Class We'll Begin to Put Stars In
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Spatially Resolved X-Ray Study of Supernova Remnants That Host Magnetars
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Star Clusters E NCYCLOPEDIA of a STRONOMY and a STROPHYSICS
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