1,323 research outputs found
Detection of the compressed primary stellar wind in eta Carinae
A series of three HST/STIS spectroscopic mappings, spaced approximately one
year apart, reveal three partial arcs in [Fe II] and [Ni II] emissions moving
outward from eta Carinae. We identify these arcs with the shell-like
structures, seen in the 3D hydrodynamical simulations, formed by compression of
the primary wind by the secondary wind during periastron passages.Comment: Accepted for publication in the Astrophysical Journal Letter
The three-dimensional structure of the Eta Carinae Homunculus
We investigate, using the modeling code SHAPE, the three-dimensional
structure of the bipolar Homunculus nebula surrounding Eta Carinae, as mapped
by new ESO VLT/X-Shooter observations of the H2 micron
emission line. Our results reveal for the first time important deviations from
the axisymmetric bipolar morphology: 1) circumpolar trenches in each lobe
positioned point-symmetrically from the center and 2) off-planar protrusions in
the equatorial region from each lobe at longitudinal (~55 degrees) and
latitudinal (10-20 degrees) distances from the projected apastron direction of
the binary orbit. The angular distance between the protrusions (~110 degrees)
is similar to the angular extent of each polar trench (~130 degrees) and nearly
equal to the opening angle of the wind-wind collision cavity (~110 degrees). As
in previous studies, we confirm a hole near the centre of each polar lobe and
no detectable near-IR H2 emission from the thin optical skirt seen prominently
in visible imagery. We conclude that the interaction between the outflows
and/or radiation from the central binary stars and their orientation in space
has had, and possibly still has, a strong influence on the Homunculus. This
implies that prevailing theoretical models of the Homunculus are incomplete as
most assume a single star origin that produces an axisymmetric nebula. We
discuss how the newly found features might be related to the Homunculus
ejection, the central binary and the interacting stellar winds. We also include
a 3D printable version of our Homunculus model.Comment: 14 pages, 7 color figures, 1 interactive 3D figure (Figure 5,
requires Adobe Reader), published in MNRAS. A 3D printable version of our
Homunculus model can be downloaded from
http://svs.gsfc.nasa.gov/vis/a010000/a011500/a011568/Eta_Car_Homunuculus_3D_model.zip
or from the 'Supporting Information' link in the electronic version of the
MNRAS articl
Discovery of Extremely Embedded X-ray Sources in the R Coronae Australis Star Forming Core
With the XMM-Newton and Chandra observatories, we detected two extremely
embedded X-ray sources in the R Corona Australis (R CrA) star forming core,
near IRS 7. These sources, designated as XB and XA, have X-ray absorption
columns of ~3e23 cm-2 equivalent to AV ~180 mag. They are associated with the
VLA centimeter radio sources 10E and 10W, respectively. XA is the counterpart
of the near-infrared source IRS 7, whereas XB has no K-band counterpart above
19.4 mag. This indicates that XB is younger than typical Class I protostars,
probably a Class 0 protostar or in an intermediate phase between Class 0 and
Class I. The X-ray luminosity of XB varied between 29<log LX <31.2 ergs s-1 on
timescales of 3-30 months. XB also showed a monotonic increase in X-ray
brightness by a factor of two in 30 ksec during an XMM-Newton observation. The
XMM-Newton spectra indicate emission from a hot plasma with kT ~3-4 keV and
also show fluorescent emission from cold iron. Though the X-ray spectrum from
XB is similar to flare spectra from Class I protostars in luminosity and
temperature, the light curve does not resemble the lightcurves of magnetically
generated X-ray flares because the variability timescale of XB is too long and
because variations in X-ray count rate were not accompanied by variations in
spectral hardness. The short-term variation of XB may be caused by the partial
blocking of the X-ray plasma, while the month-long flux enhancement may be
driven by mass accretion.Comment: 26 pages, 8 figures, To be published in ApJ in April 200
Constraints on decreases in Eta Carinae's mass loss from 3D hydrodynamic simulations of its binary colliding winds
Recent work suggests that the mass-loss rate of the primary star (Eta A) in
the massive colliding wind binary Eta Carinae dropped by a factor of 2-3
between 1999 and 2010. We present results from large- (r=1545au) and small-
(r=155au) domain, 3D smoothed particle hydrodynamic (SPH) simulations of Eta
Car's colliding winds for 3 Eta A mass-loss rates (2.4, 4.8, and 8.5 x 10^-4
M_sun/yr), investigating the effects on the dynamics of the binary wind-wind
collision (WWC). These simulations include orbital motion, optically thin
radiative cooling, and radiative forces. We find that Eta A's mass-loss rate
greatly affects the time-dependent hydrodynamics at all spatial scales
investigated. The simulations also show that the post-shock wind of the
companion star (Eta B) switches from the adiabatic to the radiative-cooling
regime during periastron passage. The SPH simulations together with 1D
radiative transfer models of Eta A's spectra reveal that a factor of 2 or more
drop in Eta A's mass-loss rate should lead to substantial changes in numerous
multiwavelength observables. Recent observations are not fully consistent with
the model predictions, indicating that any drop in Eta A's mass-loss rate was
likely by a factor < 2 and occurred after 2004. We speculate that most of the
recent observed changes in Eta Car are due to a small increase in the WWC
opening angle that produces significant effects because our line-of-sight to
the system lies close to the dense walls of the WWC zone. A modest decrease in
Eta A's mass-loss rate may be responsible, but changes in the wind/stellar
parameters of Eta B cannot yet be fully ruled out. We suggest observations
during Eta Car's next periastron in 2014 to further test for decreases in Eta
A's mass-loss rate. If Eta A's mass-loss rate is declining and continues to do
so, the 2014 X-ray minimum should be even shorter than that of 2009.Comment: 38 pages, 25 figures, 1 table. Accepted for publication in MNRA
A Definitive Signal of Multiple Supersymmetry Breaking
If the lightest observable-sector supersymmetric particle (LOSP) is charged
and long-lived, then it may be possible to indirectly measure the Planck mass
at the LHC and provide a spectacular confirmation of supergravity as a symmetry
of nature. Unfortunately, this proposal is only feasible if the gravitino is
heavy enough to be measured at colliders, and this condition is in direct
conflict with constraints from big bang nucleosynthesis (BBN). In this work, we
show that the BBN bound can be naturally evaded in the presence of multiple
sectors which independently break supersymmetry, since there is a new decay
channel of the LOSP to a goldstino. Certain regions of parameter space allow
for a direct measurement of LOSP decays into both the goldstino and the
gravitino at the LHC. If the goldstino/gravitino mass ratio is measured to be
2, as suggested by theory, then this would provide dramatic verification of the
existence of multiple supersymmetry breaking and sequestering. A variety of
consistent cosmological scenarios are obtained within this framework. In
particular, if an R symmetry is imposed, then the gauge-gaugino-goldstino
interaction vertices can be forbidden. In this case, there is no bound on the
reheating temperature from goldstino overproduction, and thermal leptogenesis
can be accommodated consistently with gravitino dark matter.Comment: 10 pages, 5 figures, title changed to match the version published in
JHE
First-order Raman spectra of double perovskites AB''{1/2}O3
First principles computations of Raman intensities were performed for
perovskite-family compound CaAlNbO (CAN). This compound
features 1:1 (NaCl-type) ordering of Al and Nb superimposed onto the
octahedral tilting. Raman tensor for CAN was computed using the package for
first-principles computations ABINIT (URL \underline {http://www.abinit.org}).
Computations performed for both untilted cubic () and tilted
monoclinic () CAN structures showed that the strongest Raman lines are
associated with the ordering of Al and Nb. The computed spectrum agreed
qualitatively with the experimental data measured on powder (CAN is available
in polycrystalline form only). The effect of cation disorder on the Raman
intensities was considered using phenomenological theory of light scattering in
the vicinity of a phase transition. We suggest that, for certain modes, the
corresponding Raman intensities depend primarily on the average long range
order while, for other modes, the intensities are determined by fluctuations of
the order parameter.Comment: 4 figures, submitte
Long-Lived Superheavy Particles in Dynamical Supersymmetry-Breaking Models in Supergravity
Superheavy particles of masses with lifetimes
are very interesting, since their decays may
account for the ultra-high energy (UHE) cosmic rays discovered beyond the
Greisen-Zatsepin-Kuzmin cut-off energy . We show
that the presence of such long-lived superheavy particles is a generic
prediction of QCD-like SU(N_c) gauge theories with N_f flavors of quarks and
antiquarks and the large number of colors N_c. We construct explicit models
based on supersymmetric SU(N_c) gauge theories and show that if the dynamical
scale and N_c = 6-10 the lightest
composite baryons have the desired masses and lifetimes to explain the UHE
cosmic rays. Interesting is that in these models the gaugino condensation
necessarily occurs and hence these models may play a role of so-called hidden
sector for supersymmetry breaking in supergravity.Comment: 13 pages, Late
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