465 research outputs found
A Lighthouse Effect in Eta Carinae
We present a new model for the behavior of scattered time-dependent,
asymmetric near-UV emission from the nearby ejecta of {\eta} Car. Using a 3-D
hydrodynamical simulation of {\eta} Car's binary colliding winds, we show that
the 3-D binary orientation derived by Madura et al. (2012) is capable of
explaining the asymmetric near-UV variability observed in the Hubble Space
Telescope Advanced Camera for Surveys/High Resolution Camera (HST ACS/HRC)
F220W images of Smith et al. (2004b). Models assuming a binary orientation with
i ~ 130 to 145 degrees, {\omega} ~ 230 to 315 degrees, PAz ~ 302 to 327 degrees
are consistent with the observed F220W near-UV images. We find that the hot
binary companion does not significantly contribute to the near-UV excess
observed in the F220W images. Rather, we suggest that a bore-hole effect and
the reduction of Fe II optical depths inside the wind-wind collision cavity
carved in the extended photosphere of the primary star lead to the
time-dependent directional illumination of circum-binary material as the
companion moves about in its highly elliptical orbit.Comment: 14 pages, 4 figures, 1 table. Accepted for publication in ApJ
3D Radiative Transfer in Carinae: Application of the SimpleX Algorithm to 3D SPH Simulations of Binary Colliding Winds
Eta Carinae is an ideal astrophysical laboratory for studying massive binary
interactions and evolution, and stellar wind-wind collisions. Recent
three-dimensional (3D) simulations set the stage for understanding the highly
complex 3D flows in Car. Observations of different broad high- and
low-ionization forbidden emission lines provide an excellent tool to constrain
the orientation of the system, the primary's mass-loss rate, and the ionizing
flux of the hot secondary. In this work we present the first steps towards
generating synthetic observations to compare with available and future HST/STIS
data. We present initial results from full 3D radiative transfer simulations of
the interacting winds in Car. We use the SimpleX algorithm to
post-process the output from 3D SPH simulations and obtain the ionization
fractions of hydrogen and helium assuming three different mass-loss rates for
the primary star. The resultant ionization maps of both species constrain the
regions where the observed forbidden emission lines can form. Including
collisional ionization is necessary to achieve a better description of the
ionization states, especially in the areas shielded from the secondary's
radiation. We find that reducing the primary's mass-loss rate increases the
volume of ionized gas, creating larger areas where the forbidden emission lines
can form. We conclude that post processing 3D SPH data with SimpleX is a viable
tool to create ionization maps for Car.Comment: 18 pages, 11 figures, accepted for publication in MNRA
Multi-Wavelength Implications of the Companion Star in Eta Carinae
Eta Carinae is considered to be a massive colliding wind binary system with a
highly eccentric (e \sim 0.9), 5.54-yr orbit. However, the companion star
continues to evade direct detection as the primary dwarfs its emission at most
wavelengths. Using three-dimensional (3-D) SPH simulations of Eta Car's
colliding winds and radiative transfer codes, we are able to compute synthetic
observables across multiple wavebands for comparison to the observations. The
models show that the presence of a companion star has a profound influence on
the observed HST/STIS UV spectrum and H-alpha line profiles, as well as the
ground-based photometric monitoring. Here, we focus on the Bore Hole effect,
wherein the fast wind from the hot secondary star carves a cavity in the dense
primary wind, allowing increased escape of radiation from the hotter/deeper
layers of the primary's extended wind photosphere. The results have important
implications for interpretations of Eta Car's observables at multiple
wavelengths.Comment: 5 pages, 4 figures, To be published in the proceedings of the meeting
'Four Decades of Research on Massive Stars' in honor of Tony Moffat, 11-15
July 2011, Saint-Michel-des-Saints, Quebe
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
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 Technique to Address Peritoneal Dialysis Catheter Malfunction
Malpositioned peritoneal dialysis catheters may be repositioned laparoscopically with a testicular prosthesis used as an anchoring weight
On the influence of the companion star in Eta Carinae: 2D radiative transfer modeling of the ultraviolet and optical spectra
We present 2D radiative transfer modeling of the Eta Carinae binary system
accounting for the presence of a wind-wind collision (WWC) cavity carved in the
optically-thick wind of the primary star. By comparing synthetic line profiles
with HST/STIS spectra obtained near apastron, we show that the WWC cavity has a
strong influence on multi-wavelength diagnostics. This influence is regulated
by the modification of the optical depth in the continuum and spectral lines.
We find that H-alpha, H-beta, and Fe II lines are the most affected by the WWC
cavity, since they form over a large volume of the primary wind. These spectral
lines depend on latitude and azimuth since, according to the orientation of the
cavity, different velocity regions of a spectral line are affected. For 2D
models with orientation corresponding to orbital inclination angle 110deg < i <
140deg and longitude of periastron 210deg < omega < 330deg, the blueshifted and
zero-velocity regions of the line profiles are the most affected. These orbital
orientations are required to simultaneously fit the UV and optical spectrum of
Eta Car, for a half-opening angle of the cavity in the range 50-70deg. We find
that the excess P-Cygni absorption seen in H-alpha, H-beta and optical Fe II
lines in spherical models becomes much weaker or absent in the 2D models, in
agreement with the observations. The observed UV spectrum of Eta Car, dominated
by Fe II absorption lines, is superbly reproduced by our 2D cavity models.
Small discrepancies still remain, as H-gamma and H-delta absorptions are
overestimated by our models. We suggest that photoionization of the wind of the
primary by the hot companion star is responsible for the weak absorption seen
in these lines. Our CMFGEN models indicate that the primary star has a
mass-loss rate of 8.5x10e-4 Msun/yr and wind terminal velocity of 420 km/s
around the 2000 apastron.Comment: 20 pages, 14 figures, accepted for publication in MNRA
The Applied Meteorology Unit: Nineteen Years Successfully Transitioning Research Into Operations for America's Space Program
The Applied Meteorology Unit (AMU) provides technology development and transition services to improve operational weather support to America's space program . The AMU was founded in 1991 and operates under a triagency Memorandum of Understanding (MOU) between the National Aeronautics and Space Administration (NASA), the United States Air Force (USAF) and the National Weather Service (NWS) (Ernst and Merceret, 1995). It is colocated with the 45th Weather Squadron (45WS) at Cape Canaveral Air Force Station (CCAFS) and funded by the Space Shuttle Program . Its primary customers are the 45WS, the Spaceflight Meteorology Group (SMG) operated for NASA by the NWS at the Johnson Space Center (JSC) in Houston, TX, and the NWS forecast office in Melbourne, FL (MLB). The gap between research and operations is well known. All too frequently, the process of transitioning research to operations fails for various reasons. The mission of the AMU is in essence to bridge this gap for America's space program
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