2016MNRAS.456.1424A

Emission-line stars are typically surrounded by dense circumstellar material, often in form of rings or disc-like structures. Line emission from forbidden transitions trace a diversity of density and temperature regimes. Of particular interest are the forbidden lines of [Oi] λλ6300, 6364 and [CaII] λλ7291, 7324. They arise in complementary, high-density environments, such as the inner-disc regions around B[e] supergiants. To study physical conditions traced by these lines and to investigate how common they are, we initiated a survey of emission-line stars. Here, we focus on a sample of nine B[e] stars in different evolutionary phases. Emission of the [Oi] lines is one of the characteristics of B[e] stars. We find that four of the objects display [CaII] line emission: for the B[e] supergiants V1478 Cyg and 3 Pup, the kinematics obtained from the [Oi] and [CaII] line profiles agrees with a Keplerian rotating disc scenario; the forbidden lines of the compact planetary nebula OY Gem display no kinematical broadening beyond spectral resolution; the luminous blue variable candidate V1429 Aql shows no [Oi] lines, but the profile of its [CaII] lines suggests that the emission originates in its hot, ionized circumbinary disc. As none of the B[e] stars of lower mass displays [CaII] line emission, we conclude that these lines are more likely observable in massive stars with dense discs, supporting and strengthening the suggestion that their appearance requires high-density environments.