Metallic line doubling in the spectra of the variable RR Lyrae star

Abstract

We present the observation of line doubling absorption in the spectra of the RR Lyrae variable star on the metal lines of FeII (λ = 4923.921Å) as well as of D1 and D2 lines of sodium. For the emission, we observed the lines of hydrogen Hα and Hβ with a very high intensity and the two lines of HeI (λ = 5875.66 Å and λ = 6678.15Å). This transmission/helium I remission [1, 2] is directly related to the intensity of the shock wave through the atmosphere of the star during the phase of maximum Blazhko cycle [3]. During the expansion phase of the photosphere of the star and during the passage of the shock wave we witnessed a disappearance of the absorption lines of neutral FeI (λ = 4934.006Å and λ = 4920.503Å) and their reappearance in phase 1.00. These observations were made with a spectrograph resolution scale of about 12,000 installed on the C14 telescope at the Oukaimeden observatory (J43) during the different star pulsation cycle. We noticed that some of them almost coincide with the maximum Blazhko cycle. The doubling line were interpreted by Schwarzschild [4] on the basis of a two-layer atmosphere. This interpretation could measure the speed of the shock wave derived from the difference between the two red and blue spectral components on Hα hydrogen lines, D3 helium, D1 and D2 lines of sodium and FeII during the observed doubling of lines. At phase 1.00, the shock wave reached the maximum speed of 160 km.s−1 confirming the hypersonic regime occur during this maximum Blazhko cycle.