2002MNRAS.335.1133S

Photometry and low- to high-resolution spectroscopy have been obtained throughout the 1998 decline of V854 Centauri. This is the most complete coverage of a decline of this star. Various emission lines which are typical of an RCB decline have been observed. Their evolution is consistent with the classification into three groups according to the E₁/E₂/BL line-region model. However, some of the line characteristics indicate a different origin from that suggested by the model. The low-excitation sharp emission lines (E₂group), visible throughout the whole decline, show a blueshift of about 3 km s ^–1 and a complex profile indicating a shell with its outer region expanding faster than the inner parts. The estimated position of this region is at about 3.5 R_*, assuming the dust cloud condensation occurs at about 2 R_*. The high-excitation lines of Ci, Oi and Mgi, classified as E₁, exhibit a redshift of a few km s ^–1 relative to the stellar velocity, indicating a possible photospheric origin. The broad lines (BL group) show a constant absolute flux throughout the decline phase and therefore the region of their origin does not seem to be affected or obscured by the dust cloud causing the decline. The high-velocity Nai D absorption components, at a velocity of about -400 km s ^–1, show a constantly increasing blueshift interpreted as an acceleration of the gas associated with the dust cloud formation.