134 research outputs found
Ionization structure in the winds of B[e] supergiants: I. Ionization equilibrium calculations in a H plus He wind
The non-spherically symmetric winds of B[e] supergiants are investigated. An
empirical density distribution is chosen that accounts for the density
concentrations and ratios derived from observations, and our model winds are
assumed to contain only hydrogen and helium. We first calculate the approximate
ionization radii for H and He and compare the results with the ionization
fractions calculated from the more accurate ionization balance equations. We
find that winds with a r^-2 density distribution turn out to reach a constant
ionization fraction as long as the wind density is low, i.e. in polar
direction. For the high density equatorial regions, however, we find that the
winds become neutral just above the stellar surface of the hot and massive B[e]
supergiants forming a disk-like neutral region. In such a disk molecules and
dust can form even very near the hot central star.Comment: 11 pages, 8 figures, accepted for publication in A&
The Structure of the Homunculus. III. Forming a Disk and Bipolar Lobes in a Rotating Surface Explosion
We present a semi-analytic model for shaping the nebula around eta Carinae
that accounts for the simultaneous production of bipolar lobes and an
equatorial disk through a rotating surface explosion. Material is launched
normal to the surface of an oblate rotating star with an initial kick velocity
that scales approximately with the local escape speed. Thereafter, ejecta
follow ballistic orbital trajectories, feeling only a central force
corresponding to a radiatively reduced gravity. Our model is conceptually
similar to the wind-compressed disk model of Bjorkman & Cassinelli, but we
modify it to an explosion instead of a steady line-driven wind, we include a
rotationally-distorted star, and we treat the dynamics somewhat differently.
Continuum-driving avoids the disk inhibition that normally operates in
line-driven winds. Our model provides a simple method by which rotating hot
stars can simultaneously produce intrinsically bipolar and equatorial mass
ejections, without an aspherical environment or magnetic fields. Although
motivated by eta Carinae, the model may have generic application to other LBVs,
B[e] stars, or SN1987A's nebula. When near-Eddington radiative driving is less
influential, our model generalizes to produce bipolar morphologies without
disks, as seen in many PNe.Comment: ApJ accepted, 9 page
And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae
We report the discovery of two new circumstellar ring nebulae in the western
Carina Nebula. The brighter object, SBW1, resembles a lidless staring eye and
encircles a B1.5 Iab supergiant. Its size is identical to the inner ring around
SN1987A, but SBW1's low N abundance indicates that the star didn't pass through
a RSG phase. The fainter object, SBW2, is a more distorted ring, is N-rich, and
has a central star that seems to be invisible. We discuss these two new nebulae
in context with rings around SN1987A, Sher25, HD168625, RY Scuti, WeBo1, SuWt2,
and others. The ring bearers fall into two groups: Five rings surround hot
supergiants, and all except for the one known binary are carbon copies of the
ring around SN1987A. We propose a link between these rings and B[e]
supergiants, where the rings derive from the same material in an earlier B[e]
phase. The remaining four rings surround evolved intermediate-mass stars; all
members of this ring fellowship are close binaries, hinting that binary
interactions govern the forging of such rings. We estimate that there may be
several thousand more dark rings in the Galaxy, but we are scarcely aware of
their existence due to selection effects. The lower-mass objects might be the
equatorial density enhancements often invoked to bind the waists of bipolar
PNe.Comment: AJ accepted, 27 page
A 3-Dimensional study of the Local Environment of Bright IRAS Galaxies: The AGN/Starburst connection
We present a 3-dimensional study of the local ( kpc) and the
large scale ( 1 Mpc) environment of Bright IRAS Galaxies
(BIRGs). For this purpose we use 87 BIRGs located at high galactic latitudes
(with 0.0080.018) as well as a control sample of non-active
galaxies having the same morphological, redshift and diameter size
distributions as the corresponding BIRG sample. Using the Center for
Astrophysics (CfA2) and Southern Sky Redshift Survey (SSRS) galaxy catalogues
()as well as our own spectroscopic observations
() for a subsample of the original BIRG sample, we find that
the fraction of BIRGs with a close neighbor is significantly higher than that
of their control sample. Comparing with a related analysis of Sy1 and Sy2
galaxies of Koulouridis et al. (2006) we find that BIRGs have a similar
environment as Sy2s, although the fraction of BIRGs with a bright close
neighbor is even higher than that of Sy2 galaxies. An additional analysis of
the relation between FIR colors and the type of activity of each BIRG shows a
significant difference between the colors of strongly-interacting and
non-interacting starbursts and a resemblance between the colors of
non-interacting starbursts and Sy2s. Our results support the view where close
interactions can drive molecular clouds towards the galactic center, triggering
starburst activity and obscuring the nuclear activity. When the close neighbor
moves away, starburst activity is reduced with the simultaneous appearance of
an obscured (type 2) AGN. Finally, the complete disentanglement of the pair
gives birth to an unobscured (type 1) AGN.Comment: Accepted for publication in The Astrophysical Journal,10 pages, 4
figure
Shakhbazian compact galaxy groups. II. Photometric and spectroscopic study of ShCG 376
The results of the redshift measurements and of the detailed surface
photometry in BVR of the compact group ShCG 376 are presented. The radial
velocity dispersion, the virial mass, the total luminosity, the M/L ratio, and
the crossing time of the group are estimated. The group consists of eight
accordant redshift spiral galaxies. Four (or possibly five) of the group
members have emission-line spectra. Such morphological content and the number
of emission-line galaxies are very atypical for compact galaxy groups. There
are signs of interaction between some members of the group. It is suggested
that the irregular shape of the brightest galaxy No. 4 is probably due to
interaction with other members of the group, particularly, the emission line
galaxy No. 6 with a discordant redshift (Delta v = 2600 km/s). It is speculated
that the latter galaxy may be a infalling intruder to the group.Comment: accepted A&A, 7 pages, 6 figures are in separate file
The New AM Her System RX J0704.2+6203. Northern Twin of BL Hyi
We report here on the identification and study of the optical counterpart of
the ROSAT source RX J0704.2+6203. Extensive spectral and photometric
observation showed that the object belongs to the class of magnetic Cataclysmic
Variables. We determined the orbital period of the system to be 97.27m and
estimated the strength of its magnetic field to be on the order of 20 MG. The
system was observed in both high and low states, common for its class. Other
parameters of the magnetic close binary system were estimated. The spectral and
photometric behavior of the object is similar to that of the well studied polar
BL Hyi.Comment: 9 pages, 9 figures, accepted in A&
Supernova 1987A: Rotation and a Binary Companion
In this paper we provide a possible link between the structure of the bipolar
nebula surrounding SN1987A and the properties of its progenitor star. A Wind
Blwon Bubble (WBB) scenario is emplyed, in which a fast, tenuous wind from a
Blue Supergiant expands into a slow, dense wind, expelled during an earlier Red
Supergiant phase. The bipolar shapre develops due to a pole-to-equator density
contrast in the slow wind (ie, the slow wind forms a slow torus). We use the
Wind Compressed Disk (WCD) model of Bjorkman & Cassinelli (1992) to determine
the shape of the slow torus. In the WCD scenario, the shape of the torus is
determined by the rotation of the progenitor star. We then use a self-similar
semi-analytical method for wind blown bubble evolution to determine the shape
of the resulting bipolar nebula.
We find that the union of the wind-compressed-disk and bipolar-wind-blown-
bubble models allows us to recover the salient properties of SN1987A's
circumstellar nebula. In particular, the size, speed and density of SN1987A's
inner ring are easily reproduced in our calculations. An exploration of
parameter space shows the the red supergiant progenitor must be been rotating
at > 0.3 of its breakup speed. We conclude that the progenitor was most likely
spun up by a merger with a binary companion. Using a simple model for the
binary merger we find that the companion is likely to have had a mass > 0.5
M_sun.Comment: 30 pages, 4 figure
Bispectrum speckle interferometry of the B[e] star MWC 349A
We present the results of bispectrum speckle interferometry of the B[e] star
MWC 349A obtained with the SAO 6m telescope. Our diffraction-limited J-, H-,
and K-band images (resolutions 43--74 mas) suggest the star is surrounded by a
circumstellar disk seen almost edge-on. The observed visibility shape is
consistent with a two-component elliptical disk model, probably corresponding
to the gaseous and dusty components of the disk. We show that the
classification of the object as a pre-main-sequence star or a young planetary
nebula is problematic. An analysis of the uncertainties in the basic parameter
determination lead us to the conclusion that MWC 349A is probably either a B[e]
supergiant or a binary system, in which the B[e]-companion dominates the
observed properties.Comment: 8 pages, 16 figures, accepted for publication in A&
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