Dr. Martin Asplund, a professor from Australian National University, visited NAOC on September 12, 2014 and gave a lecture about metallicity in the Sun. He explained that the Sun acts as reference for metalicity, since metallicity in other stars is expressed in terms of solar metallicity. However, defining precise values for solar metallicity is a difficult process, since values that are retrieved depend on what model of solar processes is used. Hence, in order to have good values of solar metallicity, it is necessary to develop as accurate of a model for processes that generate spectral lines on the solar surface as possible.
Dr. Asplund went on to explain that his research group has developed a very accurate three-dimensional computer model of the solar surface by including many processes known to happen, such as the rapid cooling that occurs within about 20 seconds as hot gas rises and is exposed to space. Including these processes into the model can generate accurate representations of spectral lines which can be compared to observed spectral lines. He continued by saying that his research group has published the first complete compilation of solar chemical compositions. The spectral lines generated by this compilation can act as a reference to compare with observed spectral lines in other stars in order to gauge metallicity values.
Dr. Asplund ended the lecture by describing how these new values for metallicity can be used in studying exoplanets. Some astronomers think that there is a threshold needed for the amount of refractory elements in a protostellar system to form planets, since the cores of the planets need to form first from solid materials. This area is still under active investigation, but insights provided by the new compilation of metallicities should further advance this field.