TOWARD UNDERSTANDING THE B[e] PHENOMENON. IV. MODELING OF IRAS 00470+6429

Abstract

FS CMa type stars are a recently described group of objects with the B[e] phenomenon that exhibit strong emission-line spectra and strong IR excesses. In this paper we report the first attempt for a detailed modeling of IRAS 00470+6429, for which we have the best set of observations. Our modeling is based on two key assumptions: the star has a main-sequence luminosity for its spectral type (B2) and the circumstellar envelope is bimodal, composed of a slowly outflowing disk-like wind and a fast polar wind. Both outflows are assumed to be purely radial. We adopt a novel approach to describe the dust formation site in the wind that employs timescale arguments for grain condensation and a self-consistent solution for the dust destruction surface. With the above assumptions we were able to reproduce satisfactorily many observational properties of IRAS 00470+6429, including the H I line profiles and the overall shape of the spectral energy distribution. Our adopted recipe for dust formation proved successful in reproducing the correct amount of dust formed in the circumstellar envelope. Possible shortcomings of our model, as well as suggestions for future improvements, are discussed.

Fast ray-tracing algorithm for circumstellar structures (FRACS)

“…For the gas number density we adopt the bi-modal distribution used by Carciofi et al (2010) to study another B[e] star. Similar density distribution descriptions were adopted for Be stars (e.g.…”

“…Different approaches exist to define regions of dust formation (e.g. Carciofi et al 2010). Here we adopt the relatively simple assumption where dust is allowed to exist only within the disc opening angle, i.e., at co-latitudes between 90 • − 0.5Δθ d and 90…”

First detections of FS Canis Majoris stars in clusters

“…Subsequent observations (Miroshnichenko et al , 2009(Miroshnichenko et al , 2011aBorges Fernandes et al 2009Rodríguez et al 2012;Polster et al 2012;Liermann et al 2014) and modeling (Carciofi et al 2010;Borges Fernandes et al 2011) of FS CMa stars have not been capable of unraveling the enigmatic nature of these objects. One of the most puzzling issues refers to the observationally inferred mass-loss rates, which are 2-3 dex higher than predicted by wind theory for B-type main-sequence stars.…”

“…Miroshnichenko et al (2000) used the optical H i emission of the FS CMa star AS 78 to obtain a very crude estimate ofṀ ≈ 1.5 × 10 −6 M /yr. Later, Carciofi et al (2010) calculated a more accurate value ofṀ ≈ 2.7 × 10 −7 M /yr for the model of IRAS 00470+6429, taking into account the geometrical effects through a latitude-dependent mass-loss rate per solid angle, together with constraints in the latitudinal density profile that allowed dust formation in a disk. In contrast, the mass-loss theoretical recipe of Vink et al (2000Vink et al ( , 2001) yields 9 × 10 −9 and 2 × 10 −9 M /yr respectively for these two FS CMa stars, assuming solar metallicity.…”

The circumstellar environment of the FS CMa star IRAS 00470+6429

“…Therefore, the observed shape of the IR excess seems to firmly indicate that the CS dust grains of IRAS 00470+6429 are both very large and fluffy. This work is described in detail in a recently accepted paper to the Astrophysical Journal (Carciofi, Miroshnichenko & Bjorkman 2010).…”