Projekt G

PEPSI Deep Spectrum Project

Dr. Matthias Steffen (AIP, advisor) and Prof. Dr. Klaus G. Strassmeier (AIP, co-advisor)

Background: The project shall primarily address the properties of stellar surface convection as a function of atmospheric depth by measuring the subtle asymmetries of selected spectral line profiles. This kind of information is essential for our understanding of the nature of »turbulence« in stellar atmospheres and for the validation of current hydrodynamical models of stellar convection.

Aims: The idea of a PEPSI »deep spectrum« [29] is to provide the highest quality optical spectra ever obtained for any star other than the Sun. Thus, we intend to find evidence for non-radiative heating processes by comparing average line profiles from strong and weak lines, preferably iron lines, and try to quantify these. The accurate determination of chemical abundances and isotope ratios is a fundamental building block of our knowledge about stellar nucleosynthesis and the chemical evolution of the Galaxy. Detecting 6Li in solar-metallicity stars might indicate the existence of an extra-solar planetary system, part of which has been accreted onto the star and thus contaminated its atmosphere with 6Li-rich material [30].

Methods: We plan to employ the new PEPSI spectrograph [31] at the 2 × 8.4-meter LBT in southern Arizona to obtain a spectrum with a signal-to-noise ratio of about 5000:1 at a spectral resolution of 1 km/s covering the entire optical spectrum from 380–910 nm. State-of-the-art hydrodynamical models will be computed tailored to the deep-spectrum target(s) with our in-house 3-D code CO5BOLD [32]. The search for the 6Li line in the deep spectrum down to the 1 mÅ equivalent-width level shall be compared to the best solar spectra and the model predictions. Also, the determination of an accurate 12C / 13C ratio allows a Lithium-related age estimation of the star but may even reveal parts of the galactic evolution history of the target in question. Data for the PEPSI deep spectrum would be taken already during the commissioning phase of PEPSI in mid-2013. Finally, the spectrum shall be made available to the entire astronomical community via a web interface in due time.