The Kinematics of Kepler's Supernova Remnant as revealed by Chandra

I determine the expansion of the supernova remnant of SN1604 (Kepler's supernova) based on archival Chandra ACIS-S observations made in 2000 and 2006. The measurements were done in several distinct energy bands, and were made for the remnant as a whole, and for six individual sectors. The average expansion parameter indicates that the remnant expands as $r \propto t^{0.5}$, but there are significant differences in different parts of the remnant: the bright northwestern part expands as $r \propto t^{0.35}$, whereas the rest of the remnant's expansion shows an expansion $r \propto t^{0.6}$. The latter is consistent with an explosion in which the outer part of the ejecta has a negative power law slope for density ($\rho \propto v^{-n}$) of $n=7$, or with an exponential density profile($\rho \propto \exp(-v/v_e)$). The expansion parameter in the southern region, in conjunction with the shock radius, indicate a rather low value (<5E50 erg) for the explosion energy of SN1604 for a distance of 4 kpc. An higher explosion energy is consistent with the results, if the distance is larger. The filament in the eastern part of the remnant, which is dominated by X-ray synchrotron radiation seems to mark a region with a fast shock speed $r \propto t^{0.7}$, corresponding to a shock velocity of v= 4200 km/s, for a distance to SN1604 of 4 kpc. This is consistent with the idea that X-ray synchrotron emission requires shock velocities in excess of ~2000 km/s. The X-ray based expansion measurements reported are consistent with results based on optical and radio measurements, but disagree with previous X-ray measurements based on ROSAT and Einstein observations.Comment: Accepted for publication in ApJ. This new version is the accepted version, which differs mainly in the discussion sectio

Simulation and theory of fluid demixing and interfacial tension of mixtures of colloids and non-ideal polymers

An extension of the Asakura-Oosawa-Vrij model of hard sphere colloids and non-adsorbing polymers, that takes polymer non-ideality into account through a repulsive stepfunction pair potential between polymers, is studied with grand canonical Monte Carlo simulations and density functional theory. Simulation results validate previous theoretical findings for the shift of the bulk fluid demixing binodal upon increasing strength of polymer-polymer repulsion, promoting the tendency to mix. For increasing strength of the polymer-polymer repulsion, simulation and theory consistently predict the interfacial tension of the free colloidal liquid-gas interface to decrease significantly for fixed colloid density difference in the coexisting phases, and to increase for fixed polymer reservoir packing fraction.Comment: 10 pages, 4 figure

Proper Motions of H-alpha filaments in the Supernova Remnant RCW 86

We present a proper motion study of the eastern shock-region of the supernova remnant RCW 86 (MSH 14-63, G315.4-2.3), based on optical observations carried out with VLT/FORS2 in 2007 and 2010. For both the northeastern and southeastern regions, we measure an average proper motion of H-alpha filaments of 0.10 +/- 0.02 arcsec/yr, corresponding to 1200 +/- 200 km/s at 2.5kpc. There is substantial variation in the derived proper motions, indicating shock velocities ranging from just below 700 km/s to above 2200 km/s. The optical proper motion is lower than the previously measured X-ray proper motion of northeastern region. The new measurements are consistent with the previously measured proton temperature of 2.3 +/- 0.3 keV, assuming no cosmic-ray acceleration. However, within the uncertainties, moderately efficient (< 27 per cent) shock acceleration is still possible. The combination of optical proper motion and proton temperature rule out the possibility that RCW 86 has a distance less than 1.5kpc. The similarity of the proper motions in the northeast and southeast is peculiar, given the different densities and X-ray emission properties of the regions. The northeastern region has lower densities and the X-ray emission is synchrotron dominated, suggesting that the shock velocities should be higher than in the southeastern, thermal X-ray dominated, region. A possible solution is that the H-alpha emitting filaments are biased toward denser regions, with lower shock velocities. Alternatively, in the northeast the shock velocity may have decreased rapidly during the past 200yr, and the X-ray synchrotron emission is an afterglow from a period when the shock velocity was higher.Comment: Accepted for publication in MNRA

Advances in mass-loss predictions

We present the results of Monte Carlo mass-loss predictions for massive stars covering a wide range of stellar parameters. We critically test our predictions against a range of observed mass-loss rates -- in light of the recent discussions on wind clumping. We also present a model to compute the clumping-induced polarimetric variability of hot stars and we compare this with observations of Luminous Blue Variables, for which polarimetric variability is larger than for O and Wolf-Rayet stars. Luminous Blue Variables comprise an ideal testbed for studies of wind clumping and wind geometry, as well as for wind strength calculations, and we propose they may be direct supernova progenitors.Comment: 3 pages, 3 figures, to appear in the proceedings of workshop 'Clumping in Hot Star Winds', eds. W.-R. Hamann, A. Feldmeier, & L. Oskinov

The Becklin-Neugebauer Object as a Runaway B Star, Ejected 4000 years ago from the theta^1C system

We attempt to explain the properties of the Becklin-Neugebauer (BN) object as a runaway B star, as originally proposed by Plambeck et al. (1995). This is one of the best-studied bright infrared sources, located in the Orion Nebula Cluster -- an important testing ground for massive star formation theories. From radio observations of BN's proper motion, we trace its trajectory back to Trapezium star theta^1C, the most massive (45 Msun) in the cluster and a relatively tight (17 AU) visual binary with a B star secondary. This origin would be the most recent known runaway B star ejection event, occurring only \~4000 yr ago and providing a unique test of models of ejection from multiple systems of massive stars. Although highly obscured, we can constrain BN's mass (~7 Msun) from both its bolometric luminosity and the recoil of theta^1C. Interaction of a runaway B star with dense ambient gas should produce a compact wind bow shock. We suggest that X-ray emission from this shocked gas may have been seen by Chandra: the offset from the radio position is ~300 AU in the direction of BN's motion. Given this model, we constrain the ambient density, wind mass-loss rate and wind velocity. BN made closest approach to the massive protostar, source ``I'', 500 yr ago. This may have triggered enhanced accretion and thus outflow, consistent with previous interpretations of the outflow being a recent (~10^3 yr) "explosive" event.Comment: 6 pages, accepted to ApJ Letter

Now is the time for a comfort congress

When buying a bed, a chair or a car, taking the train, holding a hand tool or flying across the ocean, comfort comes into play. Users interact with products and rate their experience. Therefore, designers and manufacturers of products such as seats, cars, beds, hand tools, and production lines strive for optimal comfort. If we look at some trends like “attention to health”, “ageing workforce (and population)”, “environmental awareness and sustainability” and “attention to well-being”, (dis)comfort is an important consideration (Vink & Hallbeck, 2012). This means that in our daily lives we are confronted with comfort

Naar een oplossing voor onbekend wortelrot in lelie : praktijkproef

In lelies komt er al jaren een vorm van wortelrot voor waarvan de veroorzaker onbekend is. Net als bij een aantasting door wortellesie-aaltjes leidt een aantasting door het onbekende wortelrot tot opbrengstderving en kwaliteitsverlies. De symptomen van onbekend wortelrot ontstaan op de bolwortels en zien eruit als insnoeringen en ingezonken bruine plekjes. Soms lijkt het alsof er hapjes uit de wortels zijn genomen. De wortels rotten op dergelijke plaatsen geheel door waarna bruine wortelpunten ontstaan en de wortels zich sterk gaan vertakken. In dit project werd onderzocht of grondstructuur (verdichting) en het gebruik van GFT al dan niet in combinatie met grondgebonden pathogene schimmels een rol spelen in het optreden van onbekend wortelrot in lelie. Ook werd onderzocht of het vochtig of juist droog houden van de grond na planten van invloed is op de mate van onbekend wortelrot. Ten slotte werd de werking van de middelen Amistar en Monam tegen onbekend wortelrot onderzocht. In dit onderzoek werd 15 l/ha Amistar gebruikt i.p.v. de 6 l/ha die is toegestaan, terwijl voor Monam de gebruikelijke concentratie van 500 l/ha werd toegepast. Het onderzoek werd uitgevoerd op een praktijkperceel waar in 2007 lelies werden geteeld waarin volop onbekend wortelrot was waargenomen. Onder praktijkomstandigheden werd onderzocht of combinaties van genoemde factoren mogelijk een rol spelen bij het ontstaan van onbekend wortelrot

Trichodorideaaltjes en bodemschimmels lijken veroorzakers onbekend wortelrot

Onderzoek van PPO en BAB naar de mogelijke oorzaken en maatregelen om problemen met onbekend wortelrot in leli

Accelerated Electrons in Cassiopeia A: An Explanation for the Hard X-ray Tail

We propose a model for the hard X-ray (> 10 keV) emission observed from the supernova remnant Cas A. Lower hybrid waves are generated in strong (mG) magnetic fields, generally believed to reside in this remnant, by shocks reflected from density inhomogeneities. These then accelerate electrons to energies of several tens of keV. Around 4% of the x-ray emitting plasma electrons need to be in this accelerated distribution, which extends up to electron velocities of order the electron Alfven speed, and is directled along magnetic field lines. Bremsstrahlung from these electrons produces the observed hard x-ray emission. Such waves and accelerated electrons have been observed in situ at Comet Halley, and we discuss the viability of the extrapolation from this case to the parameters relevant to Cas A.Comment: 20 pages, 3 figures, aasTeX502, accepted in Ap

First-order phase transitions in two-dimensional off-lattice liquid crystals

We consider an off-lattice liquid crystal pair potential in strictly two dimensions. The potential is purely repulsive and short-ranged. Nevertheless, by means of a single parameter in the potential, the system is shown to undergo a first-order phase transition. The transition is studied using mean-field density functional theory, and shown to be of the isotropic-to-nematic kind. In addition, the theory predicts a large density gap between the two coexisting phases. The first-order nature of the transition is confirmed using computer simulation and finite-size scaling. Also presented is an analysis of the interface between the coexisting domains, including estimates of the line tension, as well as an investigation of anchoring effects.Comment: 12 pages, 17 figures, submitted to J. Phys.: Condens. Matte