Examples of Open Clusters

1
Examples of Open Clusters

• The following Open Clusters are all young (less
  than a couple of hundred million years old) star
  clusters.
• The luminosity is dominated by very hot Main
  Sequence stars (B or A).
• There are many more cool Main Sequence stars that
  are not visible because their luminosity is so
  low.
• On occasion, a post-Main Sequence red giant star
  may be visible

2
Stellar Content of Open Clusters

• The following three slides illustrate the typical
  stellar content of Open Clusters at three
  different ages.
• Cluster Age 1 Myrs
• Cluster Age 10 Myrs
• Cluster Age 100 Myrs

3
O
B
A
F
K
M
G
4
O
B
A
F
K
M
G
5
O
B
A
F
K
M
G
6
What stars do we see in Open Clusters?

• The brightness of a star follows an inverse
  square law with distance (like the strength of
  Gravity).
• A Main Sequence A5 star has an absolute Magnitude
  of 2.0. Thus at 10 parsecs (33 lyrs) it would
  appear as a star with apparent magnitude of 2.
• The same star at 100 pcs (330 lyrs) would be 100
  times fainter and appear as a magnitude 7 star,
  invisible to the naked eye. At 1,000 pcs, the
  same star would appear as a magnitude 12 star.
• Most Open Clusters are between 100 pc and a few
  thousand parsecs away. Thus, we can only see
  the most luminous members of the cluster at these
  large distances. There are many more stars that
  simply do not appear, even on photographs, due to
  their very low luminosity.

7
Jewel Box Open Cluster
8
The Pleiades Open Cluster
9
Butterfly Open Cluster
10
M103 Open Cluster
11
M7 Open Cluster
12
NGC 3293 Open Cluster
13
M50 Open Cluster
14
Wild Duck Open Cluster
15
NGC 2266 Open Cluster
16
NGC 6791 Open Cluster
17
NGC 7789 Open Cluster
18
NGC 869 NGC 884 A Double Open Cluster
19
The Quintuplet Open Cluster