Abstract
Two high resolution spectra of the supergiant stars HR 4912 and HD 74180, obtained in 2001 and 2003, respectively, have been analyzed. These spectra were obtained with a CCD coupled to the HERCULES spectrograph, attached to the 1 m reflector telescope of the University of Canterbury, New Zealand. The spectrum of HR 4912, covers the region λ ∼ 4550 - 7150 Å, with a resolving power of 41000 and dispersion of ∼ 2 Å/mm. On the other hand, the spectrum of HD 74180 covers the region λ ∼ 4300 - 7100 Å, with a resolving power of R=82000 and the same dispersion of ∼ 2 Å/mm. A total of 439 photospheric lines have been identified in the spectrum of HR 4912, but only 347 were selected to derive its radial velocity, whose value is ∼ -24,5 + 0,1 km s^{-1]. Also, Hα y H{β were identified with a radial velocity of -28,4 km s^{-1} and -20,7 km s^{-1}, respectively. These values are comparable with the result obtained for the rest of the photospheric lines derived in the present work. With respect to the spectrum of HD 74180, a total of 390 photospheric lines were identified, but only 208 were selected to derive its radial velocity. From these, a value of ∼ 26,2+/-0,1 km s^{-1} was obtained for the radial velocity. Among the observations performed for this star during 100 years, the result obtained in this work is within the variability range obtained by other authors. Also, the Hβ line was identified and its radial velocity is 45,3 km s^{-1}. This value indicates a relative instability in the atmosphere of HD 74180.
