Institute of Astronomy

Open cluster spectroscopy with the HERMES multi-object spectrograph

SpeakerTalk DateTalk Series
Carlos Bacigalupo28 July 2014Across HR 2014 Posters


HERMES, the new spectrograph at the Anglo Australian Telescope, is designed to observe ~400 simultaneous targets at R~28000. Spectra collected from open clusters allow asteroseimology analysis of giant stars and the search for hot jupiters around main sequence stars. This provides the advantage of sampling several members of the same cluster, allowing us to determine stellar properties by association and derive results with higher precision than those obtainable from individual stars. Using a physically motivated wavelength scale model, we tested this proof of concept in two open clusters, M67 and NGC2477. The custom built addition to the standard analysis pipeline allows us to increase the radial velocity precision measurements beyond the values yielded by the standard data reduction process. Although our pilot observations yielded only 2 clear nights, simulations of radial velocity fluctuations in giant stars show that 4 nights are required to obtain a 2.5% precision measurement of the frequency of the largest amplitude oscillation in ~1.4 solar mass stars. This can be obtained by extracting inf ormation from a minimum of 30 stars. Using calibrations from Kepler and calculating the stellar temperatures from individual stellar spectra, we can determine stellar masses in the cluster with an 8% precision, or the differential mass between the first ascent giant branch and the red clump to at least 4% precision. This technique can potentially allow us to identify red giants from horizontal branch stars.