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Lick index system definition at the RSS/SALT

Lick index system definition at the RSS/SALT. A.Y. Kniazev (SALT/SAAO), O.K. Sil’chenko (SAI MSU). Lick index system is a tool to derive (mean) stellar population characteristics through the evolutionary synthesis of integrated spectra. Can be applied to galaxies and stellar clusters.

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Lick index system definition at the RSS/SALT

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  1. Lick index system definition at the RSS/SALT A.Y. Kniazev (SALT/SAAO), O.K. Sil’chenko (SAI MSU)

  2. Lick index system is a tool to derive (mean) stellar population characteristics through the evolutionary synthesis of integrated spectra. Can be applied to galaxies and stellar clusters.

  3. The problem of equivalent width measurements: an arbitrary continuum level • Typical galactic spectra, being of F-K spectral types, have NO spectral ranges free of absorption lines, to trace safely the continuum level.

  4. Lick indices: unified prescription of absorption line measurements • The borders of lines and continuum bands for integration are fixed! (Adopted to the Lick/IDS spectral resolution)‏ The description of some Lick indices: The central (`line’) band and two continuum bands

  5. The preference of Lick indices over the direct spectrum (SED) fitting: No problem with (unknown internal) dust: continuum interpolation onto the absorption line centers eliminates dust effect.

  6. The preference of Lick indices over the direct spectrum (SED) fitting: Even more important – independent determination of abundances of VARIOUS chemical elements Current stellar spectral libraries used in fitting contain stars with only SOLAR element abundance ratios for nearly solar metallicities (there are no other stars in the Sun vicinity), while in external galaxies a great variety of abundance ratios is observed.

  7. Massive elliptical galaxies are strongly magnesium overabundant (Worthey, Faber, Gonzalez 1992) Solid lines are SSP-models of two different ages with SOLAR Mg/Fe; the signs supplied by arrows present observed elliptical galaxies with the index radial gradients indicated

  8. Lick system calibration To calibrate the Lick system onto the particular spectrograph and spectral resolutions, 15 standard stars from the Worthey et al. (1994)’s list have been observed ~40 times with the RSS/SALT during commissioning period (2011). Two gratings, VPHG900 and VPHG1800, and two slit widths, 0.6 A and 1.25 A, have been probed.

  9. The Lick system for the VPHG900

  10. The index correction for the stellar velocity dispersion: the grating VPH900, the spectral resolution of 5.6 A

  11. The Lick system for the VPHG1800

  12. The index correction for the stellar velocity dispersion: the grating VPH1800, the spectral resolution of 2.5 A

  13. Comparison of the Lick index profiles measured in the lenticular galaxy NGC509 with the MPFS/BTA and RSS/SALT

  14. Relic rings in S0 galaxies with young bulges The kinematic profiles of NGC509 and NGC 516: the LOS velocities of the stellar component, and the stellar velocity dispersions. The SAURON LOS velocity field cut by the digital slit along the major axis is over-plotted for comparison (Krajnovic et al. 2011).

  15. Relic rings in S0 galaxies with young bulges The age diagnostic index-index diagrams for the disks and rings of NGC509 and NGC516. The stellar population models for [Mg/Fe]= 0.0 and five different ages, plotted by red curves and marked by log(Gyr), are plotted as the reference frame; the blue lines crossing the model metallicity sequences mark the metallicities of +0.67, +0.35, 0.00, –0.33 from right to left. Left panel: – The large-scale stellar disks, at R > 12′′ for NGC509 and at R > 7′′ for NGC516; Right panel: – the ‘relic rings’ zones, at R = 8′′ − 10′′ for NGC509 and at R = 6′′ − 7′′ for NGC516.

  16. Further statistics: elliptical galaxies are calcium-underabundant and carbon- and nitrogen-overabundant Proctor & Sansom 2002 Unnoticed feature: Fe5015 contains strong Ti lines, so the Ti/Fe ratio in elliptical galaxies is also non-solar

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