tokens: are needed to perform the analysis of cTTS. In this investigation we analyse rather weak spectral lines, with equivalent width (EW) of about 10 mÅ, so we need high-resolution, high S/N spectra of template stars of different spectral type. In order to minimize the errors of measurements, we prefer to use a grid of synthetic spectra. This way we avoid possible spectral peculiarities from the real stars that could affect our results. 3.1 Template synthetic spectra The synthetic spectra were produced by the software package Spectroscopy Made Easy (SME; Valenti Piskunov 1996 ). It was initially used to confirm the spectral type of each cTTS, with the estimation of T eff , as well as for the determination of v sin i and v rad . Two sets of synthetic spectra with spectral resolution R = 50 000 were produced. The first set corresponds to a grid of narrow-band spectra withseveral values of stellar parameters, which was used in the determination of spectral type, as well as v sin i and v rad . Then, specific spectra for each star in a wider wavelength band between 4500 and 7000 Å were produced. This second set of synthetic spectra corresponds to our templates and was used to measure EWs of hundreds of spectral lines for comparison with the same lines in the spectra of cTTS. The spectral type determination, described in detail in Sect. 3.2 , allowed us to gather information mainly about T eff . The usual criteria of surface gravity (log g ) can hardly be used in the case of highly veiled spectra with strong lines in emission. Due to that we are assuming the value log g = 3.75 dex for these stars (see Sect. 3.2 ). We also assume a priori a solar-like metallicity ([M/H] = 0.0). Besides the mentioned stellar parameters, SME also needs input information about the microturbulence velocity ( v mic ) and macroturbulence velocity ( v mac ), as well as the instrumental resolution. For the v mic parameter we assume a value that is typical for cool stars and wTTS (e.g. Padgett 1996 ; Rojas et al. 2008 ; James et al. 2006 ; Taguchi et al. 2009 ): v mic = 1.0 km s −1 . For the v mac value we assume a value based on the T eff value, as reported by Valenti Fischer (2005) . The three stars have spectral types between K1 and G5 corresponding to temperatures between 4900 and 5500 K for sub-giant stars ( Table 1 ). For this range of temperatures we assume a value of v mac = 2.8 km s −1 , consonant to an average T eff = 5000 K. To create the synthetic spectra we use the Kurucz grids of stellar atmospheric models, considering local thermodynamic equilibrium (LTE) conditions. The line list used by SME to create the synthetic spectra was extracted from the Vienna Atomic Line Database (VALD) database using the “Extract stellar” option ( Ryabchikova et al. 2015 ). Since we measured several hundred spectral lines, we did not apply any corrections to the log gf and Van der Waals damping parameters. 3.2 Spectral type determination The spectral types of our targets were determined
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