By: Mike Malatesta Introduction to Open Clusters

goals  Study the formation, composition and classifications of open clusters  Take pictures of open clusters using techmaun telescopes to become familiar with the scopes

Formation of Open Clusters - Dust and gas clouds (giant molecular cloud many thousands times the mass of the Sun) -Cloud too big to collapse into one star -stars are the same chemical composition -stars are approximately the same age - Many different sizes of stars from solar masses - Cloud can collapse because of shock waves from nearby supernovae. - Approx. 1 is born every 1000 years forms in the Milky Way

Characteristics of Open Clusters  All stars in the cluster are the same distance from Earth because their distances from each other are small when compared.  Usually is a dense core surrounded by smaller stars.  The core is typically 3-4 light years across  Stars can extend up to 20 light years from the center  1.5 stars per cubic light year

Classification  Tumpler scheme  3 part designation  I-IV (strong or weak concentration)  Aribic numeral 1-3 (from small to large range in brightness of members)  p,m,r (poor, medium, or rich in stars)

NGC 6705 Clear 600 sec 12/20/2010 AP 180 New Mexico

Full color

NGC 637 color 1x1 zoom

NGC 637 color 2x2

The H II Region  Cloud of excess molecular hydrogen gas surrounding recently formed stars  K  Stars massive enough heat and ionize the H II  Creates an ionization front radial outward from the center  Front begins at supersonic speed but slows to subsonic as its distance from the center increases  Pressure from the ionized gas causes ionized volume to expand  It is eventually overcome by the shockwave caused by the nebula expansion  Radiation pressure from young stars drives the gas and dust away

distribution  H II regions are mostly found in spiral and irregular galaxies  In spirals they are located primarily in the spiral arms  Density waves cause slowing and condensing of matter

H-alpha filter 10 min. Fsq 106 New Mexico 10/10/2010 IC 5146

IC 5146 Cocoon Nebula 10 min. Clear Barnard 168 Fsq 106 New Mexico 10/10/2010

Dark Nebulae  Dark nebulae are defined as clumps or clouds of dust grains that absorb light and create dark patches on the brighter background of the milky way  Mostly irregular formation  No definite outer boundary  Sometimes convoluted shapes  Neutral H2 in outer layer  Darker and colder towards center  C+ is converted to neutral carbon and then to CO  Stability of CO outweighs the rest and is major component of dark areas

Structure collapse  HCN converted to HNC  HNC preferred for chemical equilibrium  The center of the dark nebula receives less than 1/1000 the light than the space surrounding  Heating is done by cosmic rays  Cooling is done by transitions of internal electrons of CO  Gravitational forces work against collisional and magnetic field forces  Gravitational energy is released through contraction  Gas temperature increases  Pressure increases preventing further collapse  Dust grains emit infrared radiation which cools the nebula  ½ gravitational energy is put towards cooling  ½ gravitational energy is put towards contraction

Star formation  Small jumbles of dust and gas are attracted by gravity “protostar”  Each protostar is one stellar system  Most < 1 solar mass  Very few get up to 100 solar masses. These play a large role in the formation of the nebula  The stars collapse very rapidly  Initial protostar is 30 times the diameter of sun  Surrounding dust becomes “protoplanet”  Star contracts until heat is produced by converting H to He  If the star is hot enough it ionizes the dark nebula into a bright nebula

Summary: This project introduces the physical properties of open star clusters. They are described as a dense group of massive stars surrounded by less massive stars. These clusters begin as a giant molecular cloud that collapses. The excess molecular hydrogen that surrounds the recently formed stars is called the H II region. A combination of an ionization front caused by the hot, central stars and a shockwave caused the nebula expansion causes the H II region to be repelled from the stars. Sometimes there are large amounts of excess dust grains from the giant molecular cloud that absorb brightness causing a dark patch on a bright milky way background. At the center of these dark nebulae there is not enough light to produce necessary reactions for chemical equilibrium. Heating is thus done by cosmic rays and cooling is done by internal electron transitions. Because the dust grains emit infrared radiation that cools the gas, the gravitational force is able to overcome the force of pressure from the physical properties of gas. The small clumps of dust contract into protostars with protoplanets that ( if hot enough) can ionize the dark nebula into a bright nebula.

Sources  Frommert, Hartmut. "Open Cluster Stars." SEDS. SEDS, Web. 6 Oct  "H II Region." Wikipedia, the Free Encyclopedia. Web. 06 Oct  "Chandra :: Educational Materials :: Stellar Evolution - Cycles of Formation and Destruction." The Chandra X-ray Observatory Center :: Gateway to the Universe of X-ray Astronomy! Web. 06 Oct  Stecker, Michael A. "Barnard-168 and Cocoon Nebula." Michael A. Stecker. Web. 13 Oct  Davis, Tom V. "The Cosmic Cocoon: IC 5146 by Tom V. Davis." Universe Today. 07 July Web. 13 Oct  Schombert, James. "Dark Nebula." University of Oregon Department of Physics. Web. 13 Oct