Variable Stars
When astronomers talk about variable stars they are refering to stars
that significantly change in brightness over the course of a relatively short
period of time. The reasons behind this change in brightness can be many fold.
Some common examples are:
- Pulsating stars: Example: RR Lyraes and Cepheids.
These stars actually change in intrisic radius and brightness due their
internal structure.
- Eclipsers: Example: Eclipsing Binaries. This kind of object changes
in brightness because one star is passing in front of its companion.
- Cataclysmic Variables: Example: Novae and Supernovae. In these
kinds of objects accretion of material from a companion star causes a run away
nuclear reaction.
Star Clusters
One way of studying variable stars is to look at objects that hold them.
Stars form from giant dust clouds. Very often stars form in groups and these
groups are called clusters.
- Open Clusters: This is a loose collection of stars that were born
from the same dust cloud. The stars in these clusters have approximately the
same age and chemical composition. Due to their low density, most open
clusters break apart quickly, with few lasting to a billion years.
- Globular Clusters: These kinds of clusters are very dense
collections of 10,000 to a million stars. Like open clusters, the stars
share the same age and chemical composition. Unlike open clusters, globulars
tend to be old objects and thus show us a much more evolved state.
Current Projects
I'm currently working on two projects primarily concerned with two types of
intrinsic variables: RR Lyrae and Cepheids. Both of these projects use the
shape of the lightcurve (change in brightness with time). The first of these
projetcs involves trying to determine the amount of metals (in astronomy
this means all elements heavier than helium) in these variables by looking at
the shape of the
lightcurve of RR Lyrae Stars. The second project,
Type II Cepheid Project, looks at how the periods
of Cepheid stars in globular clusters change over the course of many years.
This tells us about how these stars evolve with time. A third project that
looks at variables, but is more concerned with their immediate environmet
involves looking at RR Lyrae stars in the globular cluster
NGC 6304.
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