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Seminars at FGG

Atmospheric Stellar Parameters from Numerical CCFs with HARPS/HARPS-N

Speaker: Luca Malavolta (Universit√° degli Studi di Padova)

Date and time: 2013-09-25 11:30

We present a new technique for the determination of atmospheric stellar parameters for low signal-to-noise spectra, based on the determination of several numerical Cross Correlation Functions (CCFs). From a qualitative point of view it is well know that the shape of the CCF depends somehow by the characteristics of the spectrum under analysis, but the interplay between temperature, metallicity and gravity in line formation affects a direct determination from a single CCF. Taking inspiration by the well-experimented approach in temperature determination with equivalent widths, we use several CCFs to break the temperature-metallicity degeneracy by including lines selected according to their excitation potential. The use of neutral Iron lines ensures a reduced effected from gravity, which is in turn determined using ionized species. Atmosphere parameters as function of the CCFs properties are calibrated using a set of stars with equivalent width (EW)-derived parameters from high signal-to-noise spectra. The atmosphere parameters determined with our technique on individual observations are compared with the EW-based ones (on co-added spectra) as function of the Signal-To-Noise Ratio (SNR) for 1111 FGK stars. Preliminary results show a 1-sigma random error of 85 K in Temperature, 0.04 dex in [Fe/H] and 0.17 dex in log(g) at SNR=50. The aim of this technique is to provide a quick and reliable atmosphere parameters determination right after the first spectrum acquisition. In particular the project has started after the installation of HARPS-N at the Telescopio Nazionale Galileo for confirmation and follow-up of Kepler super-Earth and hot-Neptunes candidates.