138 research outputs found
Supernova Kicks and Misaligned Be Star Binaries
Be stars are rapidly spinning B stars surrounded by an outflowing disc of gas
in Keplerian rotation. Be star/X-ray binary systems contain a Be star and a
neutron star. They are found to have non-zero eccentricities and there is
evidence that some systems have a misalignment between the spin axis of the
star and the spin axis of the binary orbit. The eccentricities in these systems
are thought to be caused by a kick to the neutron star during the supernova
that formed it. Such kicks would also give rise to misalignments. In this paper
we investigate the extent to which the same kick distribution can give rise to
both the observed eccentricity distribution and the observed misalignments. We
find that a Maxwellian distribution of velocity kicks with a low velocity
dispersion, , is consistent with the observed
eccentricity distribution but is hard to reconcile with the observed
misalignments, typically . Alternatively a higher velocity kick
distribution, , is consistent with the observed
misalignments but not with the observed eccentricities, unless post-supernova
circularisation of the binary orbits has taken place. We discuss briefly how
this might be achieved.Comment: Accepted for publication in MNRA
Radial Velocities of Six OB Stars
We present new results from a radial velocity study of six bright OB stars
with little or no prior measurements. One of these, HD 45314, may be a
long-period binary, but the velocity variations of this Be star may be related
to changes in its circumstellar disk. Significant velocity variations were also
found for HD 60848 (possibly related to nonradial pulsations) and HD 61827
(related to wind variations). The other three targets, HD 46150, HD 54879, and
HD 206183, are constant velocity objects, but we note that HD 54879 has
H emission that may originate from a binary companion. We illustrate
the average red spectrum of each target.Comment: Accepted for publication in PASP July 2007 issu
The Full Spectrum Galactic Terrarium: MHz to TeV Observations of Various Critters
Multi-wavelength studies at radio, infrared, optical, X-ray, and TeV
wavelengths have discovered probable counterparts to many Galactic sources of
GeV emission detected by EGRET. These include pulsar wind nebulae, high mass
X-ray binaries, and mixed morphology supernova remnants. Here we provide an
overview of the observational properties of Galactic sources which emit across
19 orders of magnitude in energy. We also present new observations of several
sources.Comment: 4 pages, 5 figures, Proceedings of the The 4th Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy, eds. Aharonian,
Hofmann, Riege
Runaway Massive Binaries and Cluster Ejection Scenarios
The production of runaway massive binaries offers key insights into the
evolution of close binary stars and open clusters. The stars HD 14633 and HD
15137 are rare examples of such runaway systems, and in this work we
investigate the mechanism by which they were ejected from their parent open
cluster, NGC 654. We discuss observational characteristics that can be used to
distinguish supernova ejected systems from those ejected by dynamical
interactions, and we present the results of a new radio pulsar search of these
systems as well as estimates of their predicted X-ray flux assuming that each
binary contains a compact object. Since neither pulsars nor X-ray emission are
observed in these systems, we cannot conclude that these binaries contain
compact companions. We also consider whether they may have been ejected by
dynamical interactions in the dense environment where they formed, and our
simulations of four-body interactions suggest that a dynamical origin is
possible but unlikely. We recommend further X-ray observations that will
conclusively identify whether HD 14633 or HD 15137 contain neutron stars.Comment: Accepted to ApJ, 11 page
Spectral Energy Distributions of Be and Other Massive Stars
We present spectrophotometric data from 0.4 to 4.2 microns for bright,
northern sky, Be stars and several other types of massive stars. Our goal is to
use these data with ongoing, high angular resolution, interferometric
observations to model the density structure and sky orientation of the gas
surrounding these stars. We also present a montage of the H-alpha and
near-infrared emission lines that form in Be star disks. We find that a
simplified measurement of the IR excess flux appears to be correlated with the
strength of emission lines from high level transitions of hydrogen. This
suggests that the near-IR continuum and upper level line fluxes both form in
the inner part of the disk, close to the star.Comment: 2010, PASP, 122, 37
The Long Period, Massive Binaries HD 37366 and HD 54662: Potential Targets for Long Baseline Optical Interferometry
We present the results from an optical spectroscopic analysis of the massive
stars HD 37366 and HD 54662. We find that HD 37366 is a double-lined
spectroscopic binary with a period of 31.8187 +/- 0.0004 days, and HD 54662 is
also a double lined binary with a much longer period of 557.8 +/- 0.3 days. The
primary of HD 37366 is classified as O9.5 V, and it contributes approximately
two-thirds of the optical flux. The less luminous secondary is a broad-lined,
early B-type main-sequence star. Tomographic reconstruction of the individual
spectra of HD 37366 reveals absorption lines present in each component,
enabling us to constrain the nature of the secondary and physical
characteristics of both stars. Tomographic reconstruction was not possible for
HD 54662; however, we do present mean spectra from our observations that show
that the secondary component is approximately half as bright as the primary.
The observed spectral energy distributions (SEDs) were fit with model SEDs and
galactic reddening curves to determine the angular sizes of the stars. By
assuming radii appropriate for their classifications, we determine distance
ranges of 1.4 - 1.9 and 1.2 - 1.5 kpc for HD 37366 and HD 54662, respectively.Comment: 27 pages, 8 figures, Accepted for publication in Ap
Spectral and spatial imaging of the Be+sdO binary phi Persei
The rapidly rotating Be star phi Persei was spun up by mass and angular
momentum transfer from a now stripped-down, hot subdwarf companion. Here we
present the first high angular resolution images of phi Persei made possible by
new capabilities in longbaseline interferometry at near-IR and visible
wavelengths. We observed phi Persei with the MIRC and VEGA instruments of the
CHARA Array. Additional MIRC-only observations were performed to track the
orbital motion of the companion, and these were fit together with new and
existing radial velocity measurements of both stars to derive the complete
orbital elements and distance. The hot subdwarf companion is clearly detected
in the near-IR data at each epoch of observation with a flux contribution of
1.5% in the H band, and restricted fits indicate that its flux contribution
rises to 3.3% in the visible. A new binary orbital solution is determined by
combining the astrometric and radial velocity measurements. The derived stellar
masses are 9.6+-0.3Msol and 1.2+-0.2Msol for the Be primary and subdwarf
secondary, respectively. The inferred distance (186 +- 3 pc), kinematical
properties, and evolutionary state are consistent with membership of phi Persei
in the alpha Per cluster. From the cluster age we deduce significant
constraints on the initial masses and evolutionary mass transfer processes that
transformed the phi Persei binary system. The interferometric data place strong
constraints on the Be disk elongation, orientation, and kinematics, and the
disk angular momentum vector is coaligned with and has the same sense of
rotation as the orbital angular momentum vector. The VEGA visible continuum
data indicate an elongated shape for the Be star itself, due to the combined
effects of rapid rotation, partial obscuration of the photosphere by the
circumstellar disk, and flux from the bright inner disk.Comment: 16 pages, 6 figures, 1 Anne
A Spectroscopic Study of Mass Outflows in the Interacting Binary RY Scuti
The massive interacting binary RY Scuti is an important representative of an
active mass-transferring system that is changing before our eyes and which may
be an example of the formation of a Wolf-Rayet star through tidal stripping.
Utilizing new and previously published spectra, we present examples of how a
number of illustrative absorption and emission features vary during the binary
orbit. We identify spectral features associated with each component, calculate
a new, double-lined spectroscopic binary orbit, and find masses of 7.1 +/- 1.2
M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the hidden massive
companion. Through tomographic reconstruction of the component spectra from the
composite spectra, we confirm the O9.7 Ibpe spectral class of the bright
supergiant and discover a B0.5 I spectrum associated with the hidden massive
companion; however, we suggest that the latter is actually the spectrum of the
photosphere of the accretion torus immediately surrounding the massive
companion. We describe the complex nature of the mass loss flows from the
system in the context of recent hydrodynamical models for beta Lyr, leading us
to conclude RY Scuti has matter leaving the system in two ways: 1) a bipolar
outflow from winds generated by the hidden massive companion, and 2) mass from
the bright O9.7 Ibpe supergiant flowing from the region near the L2 point to
fill out a large, dense circumbinary disk. This circumbinary disk (radius ~ 1
AU) may feed the surrounding double-toroidal nebula (radius ~ 2000 AU).Comment: 41 pages with 7 tables and 11 figures, accepted to Ap
Now you see it, now you don't - the circumstellar disk in the GRO J1008--57 system
Multiwavelength observations are reported here of the Be/X-ray binary pulsar
system GRO J1008-57. Over ten years worth of data are gathered together to show
that the periodic X-ray outbursts are dependant on both the binary motion and
the size of the circumstellar disk. In the first instance an accurate orbital
solution is determined from pulse periods, and in the second case the strength
and shape of the Halpha emission line is shown to be a valuable indicator of
disk size and its behaviour. Furthermore, the shape of the emission line
permits a direct determination of the disk size which is in good agreement with
theoretical estimates. A detailed study of the pulse period variations during
outbursts determined the binary period to be 247.8, in good agreement with the
period determined from the recurrence of the outbursts.Comment: Accepted for publication in MNRA
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