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Identification of Uncharted Star Clusters
Dilyana Mihaylova , Joyce Wu, Advisor: Dr. Wen-Ping Chen
Abstract
The purpose of this project is to
search for uncharted clusters by
measuring the density and
distribution of stars when given their
position.
Background Information
Star Clusters :
- A group of gravitationally bound stars
formed out of the same cloud, at the same
time, and at the same distance from us.
- They are ideal laboratories to study
stellar evolution, and to probe the
Galactic formation and evolutionary
history
Globular Clusters
Creating the star field and cluster
Creating the cluster
Examples:
:
field (N=500) and cluster N=250)
Field only (N=750)
xc=rho*rho*cos(theta/180*!pi)*cdia + ccenx
yc=rho*rho*sin(theta/180*!pi)*cdia + cceny
Generating a star field
xf=RANDOMU(seed, nfield)
yf=RANDOMU(seed, nfield)
Analyzing the field by stellar density
The output is a contour of the density of the
stellar field in which the cluster is clearly visible
Examples
Field N=2000, cluster N=500
Two Point Correlation Function
- 12Gyr old and no longer forming in the
Milky Way Galaxy
- Not possible to study their formation
Galactic open clusters
- 1Myr to 1Gyr
- Born of molecular clouds
- Makes them harder to study
Procedure
Analyzing actual data
We analyzed data from NGC 752, an open
cluster in the constellation Andromeda
The graph on the left shows a cluster of 500 stars centered at (.7,.2) with a
background of 2000 stars. The graph on the right is the corresponding
density graph in which the cluster is visible
1.Write an IDL code that creates
a background field of stars and a
star cluster
2.Write a code that searches for
this star cluster based on :
Two point correlation
- Finding an over-density region
(where it is, how large it is, etc.
- How stars are distributed by
analysis of the two-point correlation
function
- Measures how the separation of data pairs is
distributed.
W ( )  ( Ns( ) / Nr ( ))  1
- Monte Carlo Estimator:
- Computes the number of pairs for each separation,
and compares that with a random field
Position of each star
Analyzing the field
Contour Plot
Two point correlation function
Currently the above two point correlation
curve is not an accurate representation
of the data.
Conclusion
We were able to write a code that:
Counts the number of stars and outputs a contour of the star
density and Calculates the two point correlation function
Future work:
Use the methods described to search for uncharted star clusters
and calculate their size and density