Extended shells around B[e] stars

Implications for B[e] star evolution

¹ ESA/ESAC, Villafranca del Castillo, 28080 Madrid, Spain e-mail: tmarston@sciops.esa.int
² Spitzer Science Center, IPAC, Caltech, Pasadena, CA 91125, USA e-mail: mccollum@ipac.caltech.edu

Received: 21 July 2006
Accepted: 15 October 2007

Abstract

Aims.The position of B[e] stars in the upper left part of the Hertzsprung-Russell diagram creates a quandary. Are these stars young stars evolving onto the main sequence or old stars that are evolving off of it? Spectral characteristics suggest that B[e] stars can be placed into five subclasses and are not a homogeneous set. Such sub-classification is believed to coincide with varying origins and different evolutions. However, the evolutionary connection of B[e] stars – and notably sgB[e] – to other stars is unclear, particularly to evolved massive stars. We attempt to provide insight into the evolutionary past of B[e] stars.

Methods.We performed an Hα narrow-band CCD imaging survey of B[e] stars, in the northern hemisphere. Prior to the current work, no emission-line survey of B[e] stars had yet been made, while only two B[e] stars appeared to have a shell nebula as seen in the Digital Sky Survey. Of nebulae around B[e] stars, only the ring nebula around MWC 137 has been previously observed extensively.

Results.In this presentation we report the findings from our narrow-band optical imaging survey of the environments of 25 B[e] stars. Of the objects surveyed, 7 show bipolar or uni- polar structures up to 15′ across; 5 show faint, large, or filamentary shells; and 2 are compact planetary nebula-type systems. The most spectacular system observed is a large bipolar structure associated with MWC 314.

Conclusions.The possible links between B[e] stars and other evolved stars, implied by our observations, are investigated.