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The Location Of Cepheids In The Galaxy And On The H-R Diagram The Two Types Of Cepheid Variable Cepheids In Our Galaxy And The Magellanic Clouds Exercise-Determine The Type Of Cepheid DISCOVERY & THE PL LAW DISTANCE TO NGC 7331 ------------------------------------ THE H-R DIAGRAM TYPES OF CEPHEID OUR GALAXY,LMC,SMC DETERMINE THE CEPHEID ------------------------------------ PHYSICS OF CEPHEIDS THE K-MECHANISM RADIUS OF CEPHEIDS RADIUS OF ETA AQUILAE ------------------------------------ CEPHEIDS FOR AMATEURS OBSERVING DELTA CEPHEI OBSERVING ETA AQUILAE CEPHEIDS IN OUR GALAXY AND THE MAGELLANIC CLOUDS Classical Cepheids These make up the Population I stars in our galaxy. 90% of them are situated at less than 100 parsecs from the galactic plane. There are non at all beyond a distance of 300 parsecs. The majority of them are young stars and many, especially the long period Cepheids, are associated with hydrogen clouds in the galactic arms. However the Classical Cepheids with the shorter periods tend to occur in large numbers in the outer regions of the galaxy, such as the Cassiopeia, Orion and the Canis Major-Puppis regions. The Classical Cepheids with longer periods occur more in the arms nearer the galactic center in areas such as the Carina-Centaurus, Vela and Sagittarius regions. Short period Classical Cepheids are often associated with galactic clusters, for example, U Sgr is in the cluster Messier 25. Some long period Classical Cepheids belong to O associations and so are very young stars, this is the case with U Car. Photograph showing U Sgr CW Cepheids These make up the Population II stars. The short period CW Cepheids are found towards the galactic longitude of 180 degrees, whereas the long period stars are found in the direction of the galactic center. Some CW Cepheids are found in globular clusters but their light curves are similar to those found in the galactic halo.   Cepheids In The Small Magellanic Cloud Like our galaxy, there are two peaks on the histogram for the Small Magellanic Cloud, one between 1.5 and 2 days, the other between 2.5 and 4 days. The periods then are much shorter than they are in our galaxy. The SMC comprises of both Population I and II stars with the short period Cepheids near the outside, much like they are in our own galaxy, and the longer period stars concentrated near the central regions. Histogram showing the statistics for Cepheids in the SMC. Photograph of the SMC.   Cepheids In The Large Magellanic Cloud The histogram for the Large Magellanic Cloud is much different to the Small Magellanic Cloud. There is only one peak at around 3 to 4 days. The LMC comprises of mainly Population I stars, so those on the diagram below are mostly Classical Cepheids. There are many short period stars in the central region, whereas the longer period stars tend to lie in the outskirts. Histogram showing the statistics for Cepheids in the LMC. Photograph of the LMC.  Exercise-Determine The Type Of Cepheid

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