Photometry of a Star Cluster

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Photometry of a Star Cluster
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Globular Clusters
M22 Magnitude 5.1 d 10,400 ly
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Globular Cluster Facts

• Circular formation
• Up to millions of stars
• Old stellar population
• redder
• Located in galactic
• halo

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Open Clusters
M6 The Butterfly Cluster Magnitude 4.2 d 4600
ly
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Open Cluster Facts

• Loose, random formation
• Up to several thousand stars
• Young stellar population blue
• Located in the galactic disk

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Open Cluster Formation

• Large cloud of gas and dust cools, collapses
• Group into smaller chunks
• Gas continues to collapse until stars turn on
  within smaller chunks -gt Clusters!
• Over time clusters disperse ... even the sun
  formed this way. Ask Professor Lada!

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Photometry

• Recall from Electronic Camera in Astronomy Lab,
  Photometry is the measurement of brightness of
  stars magnitude
• If one magnitude is known, can get ABSOLUTE
  magnitude rather than just APPARENT magnitude
• Even without absolute magnitude, observing a
  cluster tells us relative magnitudes of all the
  stars.
• In a cluster, these are related to the absolute
  magnitude simply by the distance scale because...
• All stars in a cluster are close together,
  approximately the same distance from Earth!

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h and chi Persei
Magnitude 4.3, 4.4 d 7000 ly separation 100 ly
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Procedure for Today

• Follow procedure in lab 5 Electronic Camera in
  Astronomy for the photometry only using CCDOpps
  on file in HCLUSTER folder
• Find star 843 and use as reference star
  magnitude 7.6
• Choose box size carefully
• Fill out sheet 10 stars, and answer questions
  on the back. For true values, use V0 column.
• Turn in when you finish. That's all!