tokens: based on the Lick indices and the abundance ratios. In Section 4 , our results are summarized and discussed. In Section 5 , conclusions are given. 2 OBSERVATIONS AND DATA REDUCTION Our sample consists of 37 galaxies, the full spectroscopic sample of the SMAKCED project. For each of them, we obtained data suitable for a detailed stellar population study, with relatively high spectral resolution and high S/N ratio. Two galaxies in the sample (VCC1684 and VCC2083) were not included, since no ages could be determined because of lack of observed Balmer lines. The spectroscopic data were obtained at three different telescopes. A total of 26 dEs were observed at the 4.2-m William Herschel Telescope (WHT) using the double-arm ISIS spectrograph, of which the blue-arm covered the wavelength range 4200–5000 Å and the red-arm covered the wavelength range 5500–6700 Å. A total of 10 dEs were observed at the 2.5-m Isaac-Newton Telescope (INT), using the IDS spectrograph covering the wavelength range 4600–5600 Å, whereas the remaining three dEs were observed at the 8-m Very Large Telescope (VLT), using the FORS2 spectrograph that covers the wavelength range 4500–5600 Å. Table 1 summarizes the main properties of these 37 dEs (see also T14 ). Table 1. Properties of the SMAKCED dEs. Column 1: galaxy name. Columns 2 and 3: right ascension and declination in J2000, respectively. Columns 4 and 5: r -band magnitude (in the AB system) and half-light radius by Janz Lisker ( 2008 , 2009 ), respectively. Column 6: velocity dispersion. The data were reduced following the standard procedure for long-slit spectra using the package reduceme (Cardiel 1999 ). Details on sample selection, observations, and data reduction are presented in T14 . 2.1 Line-strength measurements Observed spectral data can be studied either by fitting the full spectrum or by focusing on selected line indices. In this work, we study selected line indices. We measured Lick indices (Worthey et al. 1994 ) in the Line Index System (LIS)-5 Å flux calibrated system (Vazdekis et al. 2010 ). The new LIS has numerous advantages over the Lick system. It is defined at three different resolutions, namely 5.0 Å, 8.4 Å, and 14.0 Å. As such, it is particularly useful for analysing small galaxies and globular clusters. As the resolution of the Lick/IDS library (FWHM ∼ 8–11 Å) is much lower than what is available with our high resolution spectra, we broadened the spectra to the LIS-5 Å system. The LIS-5 Å system choice expresses a factor of 2 improvement in resolution over Lick/IDS system. Also, the fact that the LIS system is flux calibrated makes it easier to reproduce data from other authors. The spectra were broadened to the LIS-5 Å system, taking into account the velocity dispersion of the spectra. This ensures that every galaxy spectrum has the same spectral resolution, which is important and necessary to compare them with each other. We measured a total of 23 Lick indices (Faber et al. 1985 ; Gorgas et al.
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