SJAA Ephemeris December 2008 | SJAA Home | Contents | Previous | Next

December General Meeting

Robert Sabin

David Smith


Our December general meeting speaker, Robert Sabin, graduated from UC Santa Cruz in May 2008 with an astronomy major. He will speak on the subject, “Comparison of Stellar Characteristics of Red Giant Stars and their Evolutionary Path.” This presentation is based on his senior thesis, which he conducted with guidance from his advisor, Dr. Graeme Smith. Robert is a local product. A graduate of Leigh High School, he resides in west San Jose, near where he grew up. He currently works for Kaiser Permanente, and is looking for an opportunity for employment in astronomy. Robert’s abstract is as follows:

A star spends most of its life fusing hydrogen, H, into helium, He, within its core. This stage is known as the main sequence phase. Once a star’s core is depleted of H it is rendered dormant for a time until there is a significant enough increase in temperature for He to fuse into carbon, C. With all fusion stopped in the core, there is a shell surrounding the core that continues to fuse H into He. During this time a star goes through many changes both physically and chemically as observed from Earth; the star grows in size, the effective temperature goes down, the star becomes brighter and the chemical composition of the star’s outer envelope changes. The star will continue along this path until the core becomes hot enough, through contractions, for what astronomers call the “helium flash”, which marks the beginning of fusion of He into C within the core.

Stars that are between the main sequence phase of evolution and the helium flash are known as red giants and are the focus of this thesis. During this time there is a lowering of the 12-carbon to 13-carbon isotope ratio, 12C/13C ratio, that is caused from a low ratio of 12-Carbon to 13- Carbon being brought from the interior to the surface, while a high ratio of 12-Carbon to 13-Carbon is brought from the surface into the interior. This lowering of the 12C/13C ratio at the surface of the star is analyzed along with several stellar characteristics to see if any relationships exist that can identify how far along the red giant phase of evolution a star is, and when some of these changes happen. The results yielded possible connections while discounting others.


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