Binary populations and stellar dynamics in young clusters

We first summarize work that has been done on the effects of binaries on theoretical population synthesis of stars and stellar phenomena. Next, we highlight the influence of stellar dynamics in young clusters by discussing a few candidate UFOs (unconventionally formed objects) like intermediate mass black holes, Eta Carinae, Zeta Puppis, Gamma Velorum and WR 140.Comment: Contributed paper IAU 250: Massive Stars as Cosmic Engine

The formation and evolution of very massive stars in dense stellar systems

The early evolution of dense stellar systems is governed by massive single star and binary evolution. Core collapse of dense massive star clusters can lead to the formation of very massive objects through stellar collisions ($M\geq$ 1000 \msun). Stellar wind mass loss determines the evolution and final fate of these objects, and decides upon whether they form black holes (with stellar or intermediate mass) or explode as pair instability supernovae, leaving no remnant. We present a computationaly inexpensive evolutionary scheme for very massive stars that can readily be implemented in an N-body code. Using our new N-body code 'Youngbody' which includes a detailed treatment of massive stars as well as this new scheme for very massive stars, we discuss the formation of intermediate mass and stellar mass black holes in young starburst regions. A more detailed account of these results can be found in Belkus et al. 2007.Comment: 2 pages, 2 figures. To appear in conference proceedings for IAUS246, 200

On the X-ray Emission from Massive Star Clusters and their Evolving Superbubbles

The X-ray emission properties from the hot thermalized plasma that results from the collisions of individual stellar winds and supernovae ejecta within rich and compact star clusters are discussed. We propose a simple analytical way of estimating the X-ray emission generated by super star clusters and derive an expression that indicates how this X-ray emission depends on the main cluster parameters. Our model predicts that the X-ray luminosity from the star cluster region is highly dependent on the star cluster wind terminal speed, a quantity related to the temperature of the thermalized ejecta.We have also compared the X-ray luminosity from the SSC plasma with the luminosity of the interstellar bubbles generated from the mechanical interaction of the high velocity star cluster winds with the ISM.We found that the hard (2.0 keV - 8.0 keV) X-ray emission is usually dominated by the hotter SSC plasma whereas the soft (0.3 keV - 2.0 keV) component is dominated by the bubble plasma. This implies that compact and massive star clusters should be detected as point-like hard X-ray sources embedded into extended regions of soft diffuse X-ray emission. We also compared our results with predictions from the population synthesis models that take into consideration binary systems and found that in the case of young,massive and compact super star clusters the X-ray emission from the thermalized star cluster plasma may be comparable or even larger than that expected from the HMXB population.Comment: 24 pages, 8 figures, Accepted for publication in The Astrophysical Journa

Young Crab-like pulsars and luminous X-ray sources in starbursts and optically dull galaxies

Recent Chandra observations of nearby galaxies have revealed a number of ultraluminous X-ray sources (ULXs) with super-Eddington luminosities, away from the central regions of non-active galaxies. The nature of these sources is still debated. We argue that a fraction of them could be young, Crab-like pulsars, the X-ray luminosity of which is powered by rotation. We use the pulsar birth parameters estimated from radio pulsar data to compute the steady-state pulsar X-ray luminosity distribution as a function of the star formation rate (SFR) in the galaxy. We find that ~10% of optically dull galaxies are expected to have a source with L_x >~ 10^{39} erg/s, while starbursts galaxies should each have several of these sources. We estimate that the X-ray luminosity of a few percents of galaxies is dominated by a single bright pulsar with L_x >~10^{39} erg/s, roughly independently of its SFR. We discuss observational diagnostics that can help distinguish the young pulsar population in ULXs.Comment: 17 pages, 4 figures, accepted to Ap

Differential sensitivity of atrial and ventricular KATP channels to metabolic inhibition

Objective: The aim is to compare the activation of ATP-sensitive potassium channels (KATP channels) in intact and metabolically impaired atrial and ventricular myocytes. Methods: The KATP channel current is measured by whole cell and gramicidin-perforated patch clamp recordings in 164 cultured neonate rat cardiomyocytes. Results: In whole cell recordings with 84 μmol/l ADP in pipette, spontaneous activity is significantly higher in atrium than ventricle, and EC50 for the KATP channel opener diazoxide is 0.13 μmol/l (atrium) versus 3.1 μmol/l (ventricle). With an ATP-regenerating system in pipette, EC50 for diazoxide is 19.7 μmol/l (atrium) versus 54.9 μmol/l (ventricle). In gramicidin-perforated patch recordings, atrial myocytes respond significantly to 100 nmol/l of the mitochondrial protonophore CCCP, while ventricular myocytes do not. EC50 for diazoxide is 129 μmol/l (atrium) versus <2500 μmol/l (ventricle) for myocytes exposed to CCCP, and 676 versus <2500 μmol/l, respectively, without CCCP. Conclusions: (1) KATP channels are significantly more sensitive to metabolic inhibition in atrial than ventricular myocytes. (2) Sensitivity of atrium versus ventricle to the channel opener diazoxide increases from 3:1 to ≥24:1 with ADP or metabolic inhibition. If extended to intact hearts, the results would predict a higher atrial sensitivity to ischemia, and a high sensitivity of the ischemic atrium to KATP channel opener

The evolution of very massive stars

Publisher's version/PDFCore collapse of dense massive star clusters is unavoidable, and this leads to the formation of massive objects, with masses of up to 1000 M[circled dot] and even larger. When these objects become stars, stellar wind mass loss determines their evolution and final fate, and decides on whether they form black holes (with normal mass or with intermediate mass) or explode as a pair-instability supernova. In this paper we discuss the evolution of very massive stars and present a convenient evolution recipe that can be implemented in a gravitational N-body code to study the dynamics of dense massive clusters

An estimate of the SN kick velocities for High Mass X-ray Binaries in the SMC

This work investigates the possible supernova kick velocities imposed on HMXB systems in the Small Magellanic Cloud. Comparisons are made between the location of such systems and the locations of young, stellar clusters on the premise that these may represent the birthplace of many of these systems. Measurements of the separation of clusters and HMXBs,and an estimate of the typical lifetimes of these systems, leads to a minimum average space velocity 30 km/s. This value is compared to theoretical estimates.Comment: Accepted for publication in MNRA

Investigation of groundwater salinity using geophysical and geochemical approaches: Heuningnes catchment coastal aquifer. Western Cape Province, South Africa

Seawater intrusion is recognised as a major factor affecting the quality of groundwater in coastal aquifers around the world. To determine the occurrence and extent of saline groundwater intrusion prevailing in the Heuningnes Catchment, a 2D resistivity imaging survey was carried out in three sites within the catchment. Eleven resistivity profile lines were conducted using the multi-electrode ABEM SAS resistivity meter system, employing the Wenner Array to map the extent of saline groundwater. A 2D resistivity image was acquired for these resistivity profile lines and the data were processed using Res2DINV software to produce the 2D inverse resistivity models. The interpretation of the resistivity models revealed three resistivity zones. The first zone is characterised by low resistivity (1–3 Ω.m); this represents an aquifer filled with saline water. The second resistivity zone has values ranging from (3–30 Ω.m); this represents a brackish saturated formation. The third resistivity zone denotes a sandy layer/sandstone saturated with freshwater having high resistivity values above 30 Ω.m. Geochemical analysis results of water samples at 11 locations along the electrical resistivity profile lines also suggest high salinity, indicated by high levels of Cl−, Na+, Total Dissolved Solids, and Electrical Conductivity

Clustering between high-mass X-ray binaries and OB associations in the Milky Way

We present the first direct measurement of the spatial cross-correlation function of high-mass X-ray binaries (HMXBs) and active OB star-forming complexes in the Milky Way. This result relied on a sample containing 79 hard X-ray selected HMXBs and 458 OB associations. Clustering between the two populations is detected with a significance above 7-sigmas for distances < 1 kpc. Thus, HMXBs closely trace the underlying distribution of the massive star-forming regions that are expected to produce the progenitor stars of HMXBs. The average offset of 0.4+-0.2 kpc between HMXBs and OB associations is consistent with being due to natal kicks at velocities of the order of 100+-50 km/s. The characteristic scale of the correlation function suggests an average kinematical age (since the supernova phase) of ~4 Myr for the HMXB population. Despite being derived from a global view of our Galaxy, these signatures of HMXB evolution are consistent with theoretical expectations as well as observations of individual objects.Comment: 18 pages, 10 figures, 3 tables, accepted for publication in Ap