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.

A possible sequential star formation in the giant molecular cloud G174+2.5

“…Sh2‐235A Cluster is a compact H ii region of ≈20 arcsec (0.17 pc) in diameter (Felli et al 1997). For Boley et al (2009), the exciting star of Sh2‐235B Cluster is an early‐type Herbig Be star of spectral type B1V. Hodapp (1994) found a cluster in Sh2‐235B Cluster, which was confirmed by Wang, Testi & Felli (1997), Allen et al (2005) and Kirsanova et al (2008).…”

Infrared photometric study of the massive star-forming region S235 using Spitzer-Infrared Array Camera and JHK observations

“…We also found that source S235B is associated with Brα emission due to the presence of an H ii region. Recently, using spectroscopy, Boley et al (2009) reported that S235B is a source that belongs to a rare class of early‐type Herbig Be stars. SED modelling of source S235B (see Table C8) shows that it is an intermediate‐mass young star and our model results are consistent with the Boley et al (2009) results.…”

“…Krassner et al (1982) found recombination lines of hydrogen and the polycyclic aromatic hydrocarbon (PAH) emission features at 3.3, 8.7 and 11.3 μm associated with S235B. Boley et al (2009) attributed the central star of S235B to a rare class of early‐type Herbig Be star.…”

Activity of Herbig Be stars and their environment

“…While most of these clumpy accretion diagnostics are observed in HAe stars, we can observe them also in few HBe stars (e.g. Boley et al 2009). Finkenzeller & Mundt (1984) have detected P Cygni profiles in the Hα and Mg ii h & k lines, in a large number of HAeBe stars.…”