Stellar Spectroscopy

Spectroscopy is a branch of science concerned with the study of spectra produced when matter interacts with or emits electromagnetic radiation field.  On Earth, spectroscopy has a wide variety of applications: from medicine to geophysics. Spectroscopy is also a very powerful method to infer the structure of astronomical objects. 

Our Research Group applies spectroscopy in the study of stellar populations in the Milky Way and other galaxies. We observe stars on large ground-based telescopes and use the observed spectra along with theoretical radiative transfer models to infer the structure and physical properties of stellar atmospheres. These low-density outer gaseous shells display a variety of complex phenomena, including convective mixing, turbulence, and non-equilibrium matter-light interaction, just like the Earth's atmosphere. The thermodynamic structure of a stellar atmosphere, furthermore, depends on its chemical composition and on the interior structure of a star: its temperature, mass, and radius. This means that simple laws that relate the properties of matter to those of observed spectral lines, which are applicable in laboratories on Earth, are not useful for stellar surfaces. Instead, we have to solve a complex physical and chemical problem that describes radiation transfer in the extended outer layers of stars. 

It is the combination of observed data and models of stellar atmospheres that yields the parameters of a major scientific value. Through the comphensive analysis of the observed spectra, detailed abundances of elements and of their isotopes in stellar atmospheres can be determined. These abundances reflect self-pollution of stars and  nucleosynthesis yields of prior stellar generations, which, in return depend on the physics of Galaxy formation, nuclear physics, and evolution of stars from birth to explosion and/or merger (if a star is in a binary system). We use the chemical abudances to study a diversity of astrophysical phenomena: nucleosynthesis of heavy elements, secular stellar evolution, coupled evolution of stars and their accretion disks, and ultimately the chemical evolution of our Milky Way and large star-forming galaxies like it.

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