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

Integrating space-and time-scales of sediment-transport for Poverty Bay, New Zealand

Poverty Bay is a small embayment located in the middle of the Waipaoa River Sedimentary Dispersal System (WSS) on the eastern coast of the north island of New Zealand. Within this dispersal system, a large multidisciplinary study was focused on determining the sediment routing from the source within the headwaters to the locations of sediment accumulation on the continental shelf and slope. Poverty Bay acts as the land to sea transition area in the WSS, and as such significantly modifies the fluvial sedimentary signal before it is exported to the continental shelf. Until this study, little hydrodynamic or sediment-transport work had been conducted in Poverty Bay, however. This dissertation analyzed observation and numerical model results to characterize the hydrodynamics and sediment-transport within Poverty Bay. Three S4 current meters with pressure and temperature/salinity sensors, one upward looking ADCP, and one downward looking ADV were deployed in Poverty Bay for April--September, 2006. Hydrodynamics, sediment-transport, and waves were modeled using the Regional Ocean Modeling System (ROMS) fully coupled to the Simulated WAves Nearshore (SWAN) model. The 2006 winter wet season was modeled to overlap with the field observations, along with a ∼40 yr recurrence interval storm that occurred from 21--23 October, 2005. For these two meteorological conditions, four different model grid and sediment load configurations were modeled; (1) the modern Poverty Bay with the modern sediment load, (2) the modern Poverty Bay with the pre-anthropogenic (PA) sediment load, (3) the 2 kya Poverty Bay with the PA sediment load, and (4) the 7 kya Poverty Bay with the PA sediment load. Both the observation and modeling results showed significant quantities of fine sediment were ephemerally deposited within the shallow Poverty Bay during times of elevated river discharge and energetic waves and currents. The deposition of sediment within Poverty Bay during floods followed by the resuspension and export to the continental shelf during subsequent wave events created multiple pulses of sediment out of Poverty Bay. as the sediment underwent multiple resuspension episodes, the sedimentary signal initially supplied by the river, such as the timing of supply to the shelf and the grain size distribution, would be altered. Shoreward nearshore currents and a divergence in the currents seaward of the Waipaoa River mouth provided mechanisms for the segregation of the sand from the muddy sediment, with the coarse sediment preferentially moved shoreward and the fine sediment exported from Poverty Bay to deeper water. Model results also showed significant differences between the sedimentary signals supplied to the continental shelf based on the dispersal basin geometry and river mouth orientation. The model estimates showed that marine dispersal can influence the long-term trends of a slowing shoreline progradation rate and coarsening upward sequences on the continental shelf, without invoking climate change or changes to the sediment supply. This implies that the processes controlling marine and nearshore sediment dispersal must be considered when developing hypothesis based on sedimentological observations

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

Hypoxia forecasts as a tool for Chesapeake Bay fisheries

The Estuarine Hypoxia component of the U.S. Integrated Ocean Observing System Coastal and Ocean Modeling Testbed (COMT) is evaluating existing hydrodynamic and water quality models used, or likely to be used, for operations in the Chesapeake Bay. As a proof-of-concept, an implementation of the Regional Ocean Modeling System in the Chesapeake Bay (ChesROMS) is linked to a simple respiration model for hypoxia (Hypoxia_SRM). The modeling system is presently being used to produce real-time nowcasts and short-term (3-day) hypoxia forecasts for the Chesapeake Bay, which are currently available on the Virginia Institute of Marine Science (VIMS) website. Workshops with citizen stakeholders have explored potential applications of the estuarine hypoxia nowcast/forecast products in support of recreational and commercial fishing. Interest in this product is high, particularly by recreational fishermen and charter boat captains, since reduced catch per unit effort in the Bay is clearly associated with regions where dissolved oxygen is low. This presentation reviews the insights gained at these stakeholder workshops, including how these stakeholders might apply these products to improve the efficiency and success of their fishing activities and what forecast presentation formats are most useful. Future work involves transporting the hypoxia forecast tool to the Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS), and eventually linking the product with NOAA’s Chesapeake Bay Operational Forecasting System (CBOFS)