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The Astronomy Division is divided into two sections
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1. Astroimage index:
a photo gallery of some of my astrophotos
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2. Astronomy Home Page:
this page has information on the Cepheus Bubble and ancient star clusters

 
 Research papers can be found by searching for them at the
Astronomical Data Service:

 
The Cepheus Bubble (molecular cloud):
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The Cepheus Bubble  is a large molecular cloud in the northern constellation of Cepheus. It measures about 10 x 10 degrees or 120 parsecs in diameter, based on a distance from earth of 800 pc. This ring or bubble of infrared emission was discovered by Kun, et. al. in 1987. A similar structure appears in an older Hydrogen-alpha photographic atlas of Sivan in 1974. The region is seen in the visual spectrum to outline Sharpless H-alpha regions including nebulae IC 1396 (Sh2-131) and Sh2-140. The total gas mass is estimated at 400,000 solar masses. The bubble is thought to have been formed in 3 phases (Patel, 1998). Members of earlier generations of massive stars (which have since gone super nova) in NGC 7160 are responsible for the origin of the Cepheus Bubble. These stars created an expanding compressed shell of gas that became gravitationally unstable at an age of 7 million years. The members of the Cepheus OB2 association of stars comprise the second (intermediate) generation of stars in this region that formed as a consequence of this instability. Numerous IRAS point sources (current new star formation) represents the third and youngest generation of stars in this region. Consequently, evolution of the Cepheus Bubble and its stars is thought to result from sequential triggering. At present a major cause for star formation may be do to radiative implosion from hot stars on globules in this region. The image here is courtesy of N. Patel (Harvard-Smithsonian Center for Astrophysics). It shows Carbon Monoxide emission of the molecular cloud as yellow to white, atomic Hydrogen as green contour lines and B-type and O-type stars as blue and cyan star-shapes, respectively. The optically visible Sharpless emission nebulae are marked. IC 1396 is seen to form the southern border of the molecular cloud. Imaging was done using the 14 meter FCRAO dish telescope and the QUARRY receiver. North is up.
 
References:
1. Kun, M., et. al., Ap&SS, 134:211, 1987.
2. Sivan, J.P., A&AS, 16:163, 1974.
3. Patel, N., et. al., Origin and Evolution of the Cepheus Bubble, Astrophysical Journal, 507:241, 1998.
 
 
The Ancient Open Clusters
 Old open or galactic star clusters in our Milky Way galaxy serve as excellent probes of the structure and evolution of the galactic disk. Cluster spatial and age distribution help in understanding the processes of cluster formation and destruction that allow old clusters to survive. Old open clusters that span a large range in distance and age are used to define disk abundance gradients and the cluster age-metallicity relationship. They point to a complex history of chemical enrichment and mixing within the disk.  Old open clusters are richer and more concentrated than younger ones. They are thought to have survived because of their large mass, higher central concentration and their orbits that avoid the disruptive influence of large molecular clouds. Cluster age determination may be related to reddening, metallicity and morphology . James and Phelps (1994) developed a Morphologic Age Index (MAI) used for determining the age of these old clusters. The oldest known open cluster is Berkeley 17 in Auriga. Its age (MAI) of 12.6 billion years approaches that of some globular clusters. This estimate also slightly exceeds some of the younger estimates of the age of the universe !
  To my knowledge this image of Berkeley 17 is the first color one made.
 
References:
1. Friel,E.D., The Old Open Clusters of the Milky Way, Annu. Rev. Astron. Astrophys., 33:381, 1995.
2. James, K, and Phelps, R., Astron. J., 108:1773, 1994.

 
Table of some old open clusters
 
           Cluster's name                            Age (MAI) in billions
                                                                       of years
             Berkeley 17                                  12.6 (oldest known)
             NGC 6791                                     9.5                            
             CR 261                                          9.5
             NGC 188                                       7.2
             M67                                               6.3

 

 
All of the images and text on these pages are © Copyright 2000 by Michael A. Stecker, unless otherwise noted. All rights reserved. They may not be reproduced, published, copied or transmitted in any form, including electronically on the Internet or World Wide Web, without written permission of the author. Thank you for respecting my rights protected by the Copyright laws of the United States and new International Copyright treaty.