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One of the most intriguing spectral features of WR binary stars is the presence of time-dependent line profiles. Long term observations of several systems revealed the periodicity of this variability, synchronized with the orbital movement.…
The luminous unstable star (star system) eta Carinae is surrounded by an optically bright bipolar nebula, the Homunculus and a fainter but much larger nebula, the so-called outer ejecta. As images from the EINSTEIN and ROSAT satellites have…
We have obtained X-ray observations of the bipolar planetary nebulae (PNe) NGC 2346 and NGC 7026 with XMM-Newton. These observations detected diffuse X-ray emission from NGC 7026 but not from NGC 2346. The X-ray emission from NGC 7026…
After having reported the detection of X-rays emitted by the peculiar system HD5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first…
We review some of the ways that X-ray observations provide unique information on radio galaxies. Thermal bremsstrahlung X-ray emission provides detailed data on ambient densities and temperatures. These parameters in turn can be used for…
Jets (fast collimated outflows) are claimed to be the main shaping agent of the most asymmetric planetary nebula (PNe) as they impinge on the circumstellar material at late stages of the asymptotic giant branch (AGB) phase. The first jet…
We present in this paper a first step toward a semi-analytical treatment of the accretion process in wind-fed neutron star supergiant X-ray binaries with eccentric orbits. We consider the case of a spherically symmetric wind for the…
We present an overview of the initial results from the Chandra Planetary Nebula Survey (ChanPlaNS), the first systematic (volume-limited) Chandra X-ray Observatory survey of planetary nebulae (PNe) in the solar neighborhood. The first phase…
We explore the possibility that neutron stars accreting from the winds of main-sequence stellar companions account for a significant fraction of low-luminosity, hard X-ray sources (L_X <~ 10^35 ergs/s; 1-10 keV) in the Galaxy. This work was…
Energetic pulsars power winds of relativistic leptons which produce photon nebulae (so- called pulsar wind nebulae, PWNe). Their spectral energy distribution has a double-humped structure: the first hump lies in the X-ray regime, the second…
To understand how the circumstellar environments of post-AGB stars develop into planetary nebulae, we initiate a systematic study of 2D axisymmetric hydrodynamic simulations of protoplanetary nebula (pPN) with a modified ZEUS code. The aim…
We present observations of the eccentric gamma-ray binary B1259-63/LS2883 with the Chandra X-ray Observatory. The images reveal a variable, extended about 4'', or about 1000 times the binary orbit size) structure, which appears to be moving…
We have detected an x-ray nebula around the binary millisecond pulsar B1957+20. A narrow tail, corresponding to the shocked pulsar wind, is seen interior to the known H-alpha bow shock and proves the long-held assumption that the rotational…
Galactic winds shape the stellar, gas, and metal content of galaxies. To quantify their impact, we must understand their physics. We review potential wind-driving mechanisms and observed wind properties, with a focus on the warm ionized and…
The dynamics, energetics and evolution of pulsar wind nebulae (PWNe) and supernova remnants (SNRs), are strongly affected by their magnetic field strength and distribution. They are usually strong, extended, sources of non-thermal X-ray…
X-ray emission line profiles provide the most direct insight into the dynamics and spatial distribution of the hot, X-ray-emitting plasma above the surfaces of OB stars. The O supergiant zeta Puppis shows broad, blueshifted, and asymmetric…
Approximately 1/4-1/2 of short duration Gamma-Ray Bursts are followed by variable X-ray emission lasting ~ 100 s with a fluence comparable or exceeding that of the initial burst itself. The long duration and significant energy of this…
The powerful wind-wind collision in massive star binaries creates a region of high temperature plasma and accelerates particles to relativistic energies. I briefly summarize the hydrodynamics of the wind-wind interaction and the…
X-rays give direct evidence of instabilities, time-variable structure, and shock heating in the winds of O stars. The observed broad X-ray emission lines provide information about the kinematics of shock-heated wind plasma, enabling us to…
Photospheric radius expansion during X-ray bursts can be used to measure neutron star radii and help constrain the equation of state of neutron star matter. Understanding the stellar wind dynamics is important for interpreting observations.…