S 235 B explained: An accreting Herbig Be star surrounded by reflection nebulosity

Abstract

The intent of this study is to determine the nature of the star and associated nebulosity S 235 B, which are located in a region of active star formation still heavily obscured by the parent molecular cloud. Low-resolution (R = 400) long-slit spectra of the star and nebulosity, and medium- (R = 1800) and high-resolution (R = 60 000) spectra of the central star are presented along with the results of Fabry-Perot interferometric imaging of the entire region. Based on the long-slit and Fabry-Perot observations, the nebulosity appears to be entirely reflective in nature, with the stellar component S 235 B providing most of the illuminating flux. The stellar source itself is classified here as a B1V star, with emission-line profiles indicative of an accretion disc. S 235 B thus belongs to the relatively rare class of early-type Hebrig Be stars. Based on the intensity of the reflected component, it is concluded that the accretion disc must be viewed nearly edge-on. Estimates of the accretion rate of S 235 B from the width of the Hα profile at 10 per cent of maximum intensity, a method which has been used lately for T Tauri stars and Brown Dwarfs, appear to be inconsistent with the mass outflow rate and accretion rate implied from previous infrared observations by Felli et al., suggesting this empirical law does not extend to higher masses. © 2009 RAS.