| Abstract from DBPedia | A technetium star, or more properly a Tc-rich star, is a star whose stellar spectrum contains absorption lines of the light radioactive metal technetium. The most stable isotope of technetium is 98Tc with a half-life of 4.2 million years, which is too short a time to allow the metal to be material from before the star's formation. Therefore, the detection in 1952 of technetium in stellar spectra provided unambiguous proof of nucleosynthesis in stars, one of the more extreme cases being R Geminorum. Stars containing technetium belong to the class of asymptotic giant branch stars (AGB)—stars that are like red giants, but with a slightly higher luminosity, and which burn hydrogen in an inner shell. Members of this class of stars switch to helium shell burning with an interval of some 100,000 years, in "dredge-ups". Technetium stars belong to the classes M, MS, S, SC and C-N. They are most often variable stars of the long period variable types. Current research indicates that the presence of technetium in AGB stars occurs after some evolution and that a significant number of these stars do not exhibit the metal in their spectra. The presence of technetium seems to be related to the "third dredge-up" in the history of the stars. In between the thermal pulses of these RGB stars, heavy elements are formed in the region between the hydrogen and helium fusing shells via the slow neutron capture process; the s-process. The materials are then brought to the surface via deep convection events.テクネチウム星 (technetium star) は、スペクトル中にテクネチウムの吸収線を持つ恒星である。 最も安定なテクネチウムの同位体は98Tcであり、その半減期は420万年であるが、恒星の形成前から恒星の材料となるには短すぎる期間である。そのため、1952年にポール・メリルにより恒星スペクトル中にテクネチウムが検出されたことは、恒星内元素合成の存在の明確な証拠となった。 最も顕著な例としては、がある。 テクネチウム星は、いわゆる漸近巨星分枝に分類され、赤色巨星に似るがわずかに大きな光度を持ち、内殻で水素を燃やしている。テクネチウム星のスペクトル分類はM、MS、S、SC、C-Nとなり、そのほとんどは長周期変光星である。 (Source: http://dbpedia.org/resource/Technetium_star) |
