681 research outputs found
Towards Understanding The B[e] Phenomenon: IV. Modeling of IRAS 00470+6429
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 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.Comment: 11 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Short-term variability and mass loss in Be stars II. Physical taxonomy of photometric variability observed by the Kepler spacecraft
Context: [abbreviated]
Aims: Kepler data of three known Be stars are re-visited to establish their
pulsational nature and assess the properties of additional, non-pulsational
variations. The three program stars turned out to be one inactive Be star, one
active, continuously outbursting Be star, and one Be star transiting from a
non-outbursting into an outbursting phase, thus forming an excellent sample to
distill properties of Be stars in the various phases of their life-cycle.
Methods: [abbreviated]
Results: The short-term photometric variability of Be stars must be
disentangled into a stellar and a circumstellar part. The stellar part is on
the whole not different from what is seen in non-Be stars. However, some of the
observed phenomena might be to be due to resonant mode coupling, a mechanism
not typically considered for B-type stars. Short-term circumstellar variability
comes in the form of either a group of relatively well-defined, short-lived
frequencies during outbursts, which are called \v{S}tefl frequencies, and broad
bumps in the power spectra, indicating aperiodic variability on a time scale
similar to typical low-order -mode pulsation frequencies, rather than true
periodicity.
Conclusions: From a stellar pulsation perspective, Be stars are rapidly
rotating SPB stars, that is they pulsate in low order -modes, even if the
rapid rotation can project the observed frequencies into the traditional
high-order -mode regime above about 4 c/d. However, when a circumstellar
disk is present, Be star power spectra are complicated by both cyclic, or
periodic, and aperiodic circumstellar phenomena, possibly even dominating the
power spectrum.Comment: Accepted by Astronomy and Astrophysic
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