41 research outputs found
Discovery of a New Dusty B[e] Star in the Small Magellanic Cloud
We present new optical spectroscopic and archival Spitzer IRAC photometric
observations of a B-type star in the SMC cluster NGC 346, NGC 346:KWBBe 200. We
detect numerous Fe II, [O I], and [Fe II] lines, as well as strong P-Cygni
profile H I emission lines in its optical spectrum. The star's near-IR color
and optical to IR SED clearly indicate the presence of an infrared excess,
consistent with the presence of gas and warm, T ~800 K, circumstellar dust.
Based on a crude estimate of the star's luminosity and the observed
spectroscopic line profile morphologies, we find that the star is likely to be
a B-type supergiant. We suggest that NGC 346:KWBBe 200 is a newly discovered
B[e] supergiant star, and represents the fifth such object to be identified in
the SMC.Comment: 12 pages, accepted by Ap
The Dynamical Evolution of Be star disks
We present a novel theoretical tool to analyze the dynamical behaviour of a
Be disk fed by non-constant decretion rates. It is mainly based on the computer
code HDUST, a fully three-dimensional radiative transfer code that has been
successfully applied to study several Be systems so far, and the SINGLEBE code
that solves the 1D viscous diffusion problem. We have computed models of the
temporal evolution of different types of Be star disks for different dynamical
scenarios. By showing the behaviour of a large number of observables
(interferometry, polarization, photometry and spectral line profiles), we show
how it is possible to infer from observations some key dynamical parameters of
the disk.Comment: IAU 272 symposium proceedings, 3 pages, 1 figur
Disk-Loss and Disk Renewal Phases in Classical Be Stars II. Detailed Analysis of Spectropolarimetric Data
In Wisniewski et al. 2010, paper I, we analyzed 15 years of spectroscopic and
spectropolarimetric data from the Ritter and Pine Bluff Observatories of 2 Be
stars, 60 Cygni and {\pi} Aquarii, when a transition from Be to B star
occurred. Here we anaylize the intrinsic polarization, where we observe
loop-like structures caused by the rise and fall of the polarization Balmer
Jump and continuum V-band polarization being mismatched temporally with
polarimetric outbursts. We also see polarization angle deviations from the
mean, reported in paper I, which may be indicative of warps in the disk, blobs
injected at an inclined orbit, or spiral density waves. We show our ongoing
efforts to model time dependent behavior of the disk to constrain the
phenomena, using 3D Monte Carlo radiative transfer codes.Comment: 2 pages, 6 figures, IAU Symposium 27
Disk Loss and Disk Renewal Phases in Classical Be Stars I: Analysis of Long-Term Spectropolarimetric Data
(Abridged) Classical Be stars occasionally transition from having a gaseous
circumstellar disk (''Be phase'') to a state in which all observational
evidence for the presence of these disks disappears (''normal B-star phase'').
We present one of the most comprehensive spectropolarimetric views to date of
such a transition for two Be stars, pi Aquarii and 60 Cygni. 60 Cyg's disk loss
episode was characterized by a monotonic decrease in emission strength over a
time-scale of 1000 days, consistent with the viscous time-scale of the disk,
assuming alpha is 0.14. pi Aqr's disk loss was episodic in nature and occurred
over a time-scale of 2440 days. An observed time lag between the behavior of
the polarization and H-alpha in both stars indicates the disk clearing
proceeded in an ''inside-out'' manner. We determine the position angle of the
intrinsic polarization to be 166.7 +/- 0.1 degrees for pi Aqr and 107.7 +/- 0.4
degrees for 60 Cyg, and model the observed polarization during the quiescent
diskless phase of each star to determine the interstellar polarization along
the line of sight. Minor outbursts observed during the quiescent phase of each
star shared similar lifetimes as those previously reported for mu Cen,
suggesting that the outbursts represent the injection and subsequent viscous
dissipation of individual blobs of material into the inner circumstellar
environments of these stars. We also observe deviations from the mean intrinsic
polarization position angle during polarization outbursts in each star,
indicating deviations from axisymmetry. We propose that these deviations might
be indicative of the injection (and subsequent circularization) of new blobs
into the inner disk, either in the plane of the bulk of the disk material or in
a slightly inclined (non-coplanar) orbit.Comment: 30 pages, 14 figures; accepted in Ap
Monte Carlo Simulations of Polarimetric and Light Variability from Corotating Interaction Regions in Hot Stellar Winds
We use a 3D Monte Carlo radiative transfer code to study the polarimetric and
photometric variability from stationary corotating interaction regions (CIR) in
the wind of massive stars. Our CIRs are approximated by Archimedean spirals of
higher (or lower) density formed in a spherical wind originating from the star
and we also made allowance for a bright gaussian spot at the base of the CIR.
Comparing results from our code to previous analytical calculations in the
optically thin case, we find differences which we attribute mainly to a better
estimation of the total unpolarized flux reaching the observer. In the
optically thick case, the differences with the analytical calculations are much
larger, as multiple scattering introduces extra complexities including
occultation effects. The addition of a gaussian spot does not alter the shape
of the polarization curve significantly but does create a small excess in
polarization. On the other hand, the effect can be larger on the light curve
and can become dominant over the resulting CIR, depending on the spot
parameters and density of the wind.Comment: 16 pages, 17 figure