4,360 research outputs found
Modeling the RXTE light curve of Carinae from a 3-D SPH simulation of its binary wind collision
The very massive star system Carinae exhibits regular 5.54-year
(2024-day) period disruptive events in wavebands ranging from the radio to
X-ray. There is a growing consensus that these events likely stem from
periastron passage of an (as yet) unseen companion in a highly eccentric
() orbit. This paper presents three-dimensional (3-D)
Smoothed Particle Hydrodynamics (SPH) simulations of the orbital variation of
the binary wind-wind collision, and applies these to modeling the X-ray light
curve observed by the Rossi X-ray Timing Explorer (RXTE). By providing a global
3-D model of the phase variation of the density of the interacting winds, the
simulations allow computation of the associated variation in X-ray absorption,
presumed here to originate from near the apex of the wind-wind interaction
cone. We find that the observed RXTE light curve can be readily fit if the
observer's line of sight is within this cone along the general direction of
apastron. Specifically, the data are well fit by an assumed inclination for the orbit's polar axis, which is thus consistent with orbital
angular momentum being along the inferred polar axis of the Homunculus nebula.
The fits also constrain the position angle that an orbital-plane
projection makes with the apastron side of the semi-major axis, strongly
excluding positions along or to the retrograde side of the
axis, with the best fit position given by . Overall the
results demonstrate the utility of a fully 3-D dynamical model for constraining
the geometric and physical properties of this complex colliding-wind binary
system.Comment: 5 pages, 4 figures, accepted to MNRAS Letter
3-D SPH simulations of colliding winds in eta Carinae
We study colliding winds in the superluminous binary eta Carinae by
performing three-dimensional, Smoothed Particle Hydrodynamics (SPH)
simulations. For simplicity, we assume both winds to be isothermal. We also
assume that wind particles coast without any net external forces. We find that
the lower density, faster wind from the secondary carves out a spiral cavity in
the higher density, slower wind from the primary. Because of the
phase-dependent orbital motion, the cavity is very thin on the periastron side,
whereas it occupies a large volume on the apastron side. The model X-ray light
curve using the simulated density structure fits very well with the observed
light curve for a viewing angle of i=54 degrees and phi=36 degrees, where i is
the inclination angle and phi is the azimuth from apastron.Comment: 6 pages, 3 figures, To be published in Proceedings of IAU Symposium
250: Massive Stars as Cosmic Engines, held in Kauai, Hawaii, USA, Dec 2007,
edited by F. Bresolin, P.A. Crowther & J. Puls (Cambridge University Press
X-ray Modeling of \eta\ Carinae and WR140 from SPH Simulations
The colliding wind binary (CWB) systems \eta\ Carinae and WR140 provide
unique laboratories for X-ray astrophysics. Their wind-wind collisions produce
hard X-rays that have been monitored extensively by several X-ray telescopes,
including RXTE. To interpret these RXTE X-ray light curves, we model the
wind-wind collision using 3D smoothed particle hydrodynamics (SPH) simulations.
Adiabatic simulations that account for the absorption of X-rays from an assumed
point source at the apex of the wind-collision shock cone by the distorted
winds can closely match the observed 2-10keV RXTE light curves of both \eta\
Car and WR140. This point-source model can also explain the early recovery of
\eta\ Car's X-ray light curve from the 2009.0 minimum by a factor of 2-4
reduction in the mass loss rate of \eta\ Car. Our more recent models relax the
point-source approximation and account for the spatially extended emission
along the wind-wind interaction shock front. For WR140, the computed X-ray
light curve again matches the RXTE observations quite well. But for \eta\ Car,
a hot, post-periastron bubble leads to an emission level that does not match
the extended X-ray minimum observed by RXTE. Initial results from incorporating
radiative cooling and radiatively-driven wind acceleration via a new
anti-gravity approach into the SPH code are also discussed.Comment: 5 pages, 3 figures, Proceedings of the 39th Li\'ege Astrophysical
Colloquium, held in Li\`ege 12-16 July 2010, edited by G. Rauw, M. De Becker,
Y. Naz\'e, J.-M. Vreux, P. William
The Molecular Gas Environment around Two Herbig Ae/Be Stars: Resolving the Outflows of LkHa 198 and LkHa 225S
Observations of outflows associated with pre-main-sequence stars reveal
details about morphology, binarity and evolutionary states of young stellar
objects. We present molecular line data from the Berkeley-Illinois-Maryland
Association array and Five Colleges Radio Astronomical Observatory toward the
regions containing the Herbig Ae/Be stars LkHa 198 and LkHa 225S. Single dish
observations of 12CO 1-0, 13CO 1-0, N2H+ 1-0 and CS 2-1 were made over a field
of 4.3' x 4.3' for each species. 12CO data from FCRAO were combined with high
resolution BIMA array data to achieve a naturally-weighted synthesized beam of
6.75'' x 5.5'' toward LkHa 198 and 5.7'' x 3.95'' toward LkHa 225S,
representing resolution improvements of factors of approximately 10 and 5 over
existing data. By using uniform weighting, we achieved another factor of two
improvement. The outflow around LkHa 198 resolves into at least four outflows,
none of which are centered on LkHa 198-IR, but even at our resolution, we
cannot exclude the possibility of an outflow associated with this source. In
the LkHa 225S region, we find evidence for two outflows associated with LkHa
225S itself and a third outflow is likely driven by this source. Identification
of the driving sources is still resolution-limited and is also complicated by
the presence of three clouds along the line of sight toward the Cygnus
molecular cloud. 13CO is present in the environments of both stars along with
cold, dense gas as traced by CS and (in LkHa 225S) N2H+. No 2.6 mm continuum is
detected in either region in relatively shallow maps compared to existing
continuum observations.Comment: 14 pages, 10 figures (5 color), accepted for publication in Ap
Quasiparticles in the vortex state of V3Si
Low-energy quasiparticle excitations in the vortex state of the superconductor V3Si have been investigated using the de Haas-van Alphen effect. Quantum oscillations persist to surprisingly low values of B0/B(c2) is similar to 0.6 and T/T(c) is similar to 0.001. The superconducting state introduces a field-dependent quasiparticle damping which has a value HBAR tau-1 almost-equal-to 0.25 DELTA at the lowest fields investigated, considerably less than the superconducting gap DELTA. Quantum oscillations are attributed to the presence of a gapless excitation spectrum and may be a universal characteristic of superconductors in the vortex state
Suzaku monitoring of hard X-ray emission from η carinae over a single binary orbital cycle
The Suzaku X-ray observatory monitored the supermassive binary system η Carinae 10 times during the whole 5.5 yr orbital cycle between 2005 and 2011. This series of observations presents the first long-term monitoring of this enigmatic system in the extremely hard X-ray band between 15 and 40 keV. During most of the orbit, the 15-25 keV emission varied similarly to the 2-10 keV emission, indicating an origin in the hard energy tail of the kT ∼ 4 keV wind-wind collision (WWC) plasma. However, the 15-25 keV emission declined only by a factor of three around periastron when the 2-10 keV emission dropped by two orders of magnitude due probably to an eclipse of the WWC plasma. The observed minimum in the 15-25 keV emission occurred after the 2-10 keV flux had already recovered by a factor of ∼3. This may mean that the WWC activity was strong, but hidden behind the thick primary stellar wind during the eclipse. The 25-40 keV flux was rather constant through the orbital cycle, at the level measured with INTEGRAL in 2004. This result may suggest a connection of this flux component to the γ-ray source detected in this field. The helium-like Fe Kα line complex at ∼6.7 keV became strongly distorted toward periastron as seen in the previous cycle. The 5-9 keV spectra can be reproduced well with a two-component spectral model, which includes plasma in collision equilibrium and a plasma in non-equilibrium ionization (NEI) with τ ∼ 1011 cm-3 s-1. The NEI plasma increases in importance toward periastron
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