8 research outputs found
The origin of the X-ray emitting plasma in the eastern edge of the Cygnus Loop
The Cygnus Loop is interacting with a protrusion of the cavity wall in its
eastern edge (the XA region), where the X-ray emission is very bright. The
complexity of the environment and the non-linear physical processes of the
shock-cloud interaction make the origin of the X-ray emission still not well
understood. Our purpose is to understand the physical origin of the X-ray
emission in the XA region, addressing, in particular, the role of thermal
conduction in the interaction process. We analyzed two XMM-Newton data sets,
performing image analysis and spatially resolved spectral analysis on a set of
homogeneous regions. We applied a recently developed diagnostic tool to compare
spectral analysis results with predictions of theoretical models, and to
estimate the efficiency of thermal conduction on the X-ray emitting shocked
plasma. We found that the inhomogeneous cavity wall contains both large clumps
(the protrusion) and small isolated clumps with different densities. A large
indentation bent over to the south is detected. The abundance of the
surrounding ISM is ~0.2 times solar value. We confirmed the important role of
thermal conduction in the evolution of X-ray emitting plasma during shock-cloud
interaction.Comment: 7 pages, 5 figures, MNRAS in pres
Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary gamma Velorum
We present XMM-Newton observations of gamma^2 Velorum (WR 11, WC8+O7.5III, P
= 78.53 d), a nearby Wolf-Ray binary system, at its X-ray high and low states.
At high state, emission from a hot collisional plasma dominates from about 1 to
8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasma
is identified with the shock zone between the winds of the primary Wolf-Rayet
star and the secondary O giant. The absorption at low state is interpreted as
photoelectric absorption in the Wolf-Rayet wind. This absorption allows us to
measure the absorbing column density and to derive a mass loss rate 8x10^{-6}
M_sun/yr for the WC8 star. This mass loss rate, in conjunction with a previous
Wolf-Rayet wind model, provides evidence for a clumped WR wind. A clumping
factor of 16 is required. The X-ray spectra below 1 keV (12 Ang) show no
absorption and are essentially similar in both states. There is a rather clear
separation in that emission from a plasma hotter than 5 MK is heavily absorbed
in low state while the cooler plasma is not. This cool plasma must come from a
much more extended region than the hot material. The Neon abundance in the
X-ray emitting material is 2.5 times the solar value. The unexpected detection
of CV (25.3 Ang) and CVI (31.6 Ang) radiative recombination continua at both
phases indicates the presence of a cool (~40,000 K) recombination region
located far out in the binary system.Comment: 16 page
Detection of accretion X-rays from QS Vir: cataclysmic or a lot of hot air?
An XMM-Newton observation of the nearby "pre-cataclysmic" short-period (P_orb
= 3.62 hr) binary QS Vir (EC 13471-1258) revealed regular narrow X-ray eclipses
when the white dwarf passed behind its M2-4 dwarf companion. The X-ray emission
provides a clear signature of mass transfer and accretion onto the white dwarf.
The low-resolution XMM-Newton EPIC spectra are consistent with a cooling flow
model and indicate an accretion rate of Mdot= 1.7\times10^-13M\odot/yr. At 48
pc distant, QS Vir is then the second nearest accreting cataclysmic variable
known, with one of the lowest accretion rates found to date for a non-magnetic
system. To feed this accretion through a wind would require a wind mass loss
rate of Mdot ~ 2 \times 10^-12M\odot/yr if the accretion efficiency is of the
order of 10%. Consideration of likely mass loss rates for M dwarfs suggests
this is improbably high and pure wind accretion unlikely. A lack of accretion
disk signatures also presents some difficulties for direct Roche lobe overflow.
We speculate that QS Vir is on the verge of Roche lobe overflow, and that the
observed mass transfer could be supplemented by upward chromospheric flows on
the M dwarf, analogous to spicules and mottles on the Sun, that escape the
Roche surface to be subsequently swept up into the white dwarf Roche lobe. If
so, QS Vir would be in a rare evolutionary phase lasting only a million years.
The X-ray luminosity of the M dwarf estimated during primary eclipse is L_X = 3
\times 10^28 erg/s, which is consistent with that of rapidly rotating
"saturated" K and M dwarfs.Comment: ApJ in pres
Human Engineered Heart Tissue as a Versatile Tool in Basic Research and Preclinical Toxicology
Human embryonic stem cell (hESC) progenies hold great promise as surrogates for human primary cells, particularly if the latter are not available as in the case of cardiomyocytes. However, high content experimental platforms are lacking that allow the function of hESC-derived cardiomyocytes to be studied under relatively physiological and standardized conditions. Here we describe a simple and robust protocol for the generation of fibrin-based human engineered heart tissue (hEHT) in a 24-well format using an unselected population of differentiated human embryonic stem cells containing 30â40% Îą-actinin-positive cardiac myocytes. Human EHTs started to show coherent contractions 5â10 days after casting, reached regular (mean 0.5 Hz) and strong (mean 100 ÂľN) contractions for up to 8 weeks. They displayed a dense network of longitudinally oriented, interconnected and cross-striated cardiomyocytes. Spontaneous hEHT contractions were analyzed by automated video-optical recording and showed chronotropic responses to calcium and the β-adrenergic agonist isoprenaline. The proarrhythmic compounds E-4031, quinidine, procainamide, cisapride, and sertindole exerted robust, concentration-dependent and reversible decreases in relaxation velocity and irregular beating at concentrations that recapitulate findings in hERG channel assays. In conclusion this study establishes hEHT as a simple in vitro model for heart research