Microlensing Halo Models with Abundant Brown Dwarfs

All previous attempts to understand the microlensing results towards the Large Magellanic Cloud (LMC) have assumed homogeneous present day mass functions (PDMFs) for the lensing populations. Here, we present an investigation into the microlensing characteristics of haloes with spatially varying PDMFs and anisotropic velocity dispersion tensors. One attractive possibility -- suggested by baryonic dark cluster formation in pregalactic and protogalactic cooling flows -- is that the inner halo is dominated by stellar mass objects, whereas low mass brown dwarfs become more prevalent on moving outwards. The contribution to the microlensing rate must be dominated by dark remnants (of about 0.5 solar masses) to recover the observed timescales of the microlensing experiments. But, even though stellar remnants control the rate, they do not dominate the mass of the baryonic halo, and so the well-known enrichment and mass budget problems are much less severe. Using a simple ansatz for the spatial variation of the PDMF, models are constructed in which the contribution of brown dwarfs to the mass of the baryonic halo is 55 % and to the total halo is 30 %. An unusual property of the models is that they predict that the average timescale of events towards M31 is shorter than the average timescale towards the LMC. This is because the longer line of sight towards M31 probes more of the far halo where brown dwarfs are the most common constituent.Comment: 17 pages, 1 figure, in press at The Astrophysical Journal (Letters

New Venture Opportunity Cost of Capital and Financial Contracting

Investments in new ventures involve financial contracts between an entrepreneur and outside investors. Investors, such as venture capital firms, represent well-diversified investors. In contrast, the entrepreneur must commit a substantial fraction of human and financial capital to the venture. Consequently, the entrepreneur's required rate of return depends on total risk, in the context of the entrepreneur’s other assets. In this paper, we use the Capital Asset Pricing Model as an approximation of the asset pricing model used by well-diversified investors. Accordingly, the entrepreneur faces the risk-return tradeoff of the CAPM as the opportunity cost of holding an under-diversified portfolio that includes investment in the venture. We model the required rate of return of the entrepreneur, assuming investment in the venture is one of two assets in the portfolio and that the other is the market portfolio. We explore opportunities for value creation when the parties to a financial contract have different costs of bearing risk. We also present empirical data on factors relevant to new venture cost of capital estimation.

A Phenomenology of the Job-Related Experiences of Early Career Catholic Elementary School Principals

This qualitative phenomenology investigated the job-related experiences of early career Catholic elementary school principals (N = 13) in the Mideastern region of the United States. Data were collected from an introductory survey, semi-structured interviews, two focus groups, and a participant designed plan for professional development. The findings indicated that Catholic elementary principals in their early career are motivated by a calling to a vocation in Catholic school leadership as well as the ability to develop and implement a vision for their school. Principals reported being challenged by limited resources, balancing the demands of the position, and navigating relationships. Finally, principals believed they are supported by diocesan administrators in the areas of human resources and student issues, particularly if the concerns have legal implications

New Venture Opportunity Cost of Capital and Financial Contracting

Investments in new ventures involve financial contracts between an entrepreneur and outside investors. Investors, such as venture capital firms, represent well-diversified investors. In contrast, the entrepreneur must commit a substantial fraction of human and financial capital to the venture. Consequently, the entrepreneur's required rate of return depends on total risk, in the context of the entrepreneur's other assets. In this paper, we use the Capital Asset Pricing Model as an approximation of the asset pricing model used by well-diversified investors. Accordingly, the entrepreneur faces the risk-return tradeoff of the CAPM as the opportunity cost of holding an under-diversified portfolio that includes investment in the venture. We model the required rate of return of the entrepreneur, assuming investment in the venture is one of two assets in the portfolio and that the other is the market portfolio. We explore opportunities for value creation when the parties to a financial contract have different costs of bearing risk. We also present empirical data on factors relevant to new venture cost of capital estimation

The Origin of Primordial Dwarf Stars and Baryonic Dark Matter

I present a scenario for the production of low mass, degenerate dwarfs of mass $>0.1 M_{\odot}$ via the mechanism of Lenzuni, Chernoff & Salpeter (1992). Such objects meet the mass limit requirements for halo dark matter from microlensing surveys while circumventing the chemical evolution constraints on normal white dwarf stars. I describe methods to observationally constrain this scenario and suggest that such objects may originate in small clusters formed from the thermal instability of shocked, heated gas in dark matter haloes, such as suggested by Fall & Rees (1985) for globular clusters.Comment: TeX, 4 pages plus 2 postscript figures. To appear in Astrophysical Journal Letter

Gamma ray astronomy and baryonic dark matter

Recently, Dixon et al. have re-analyzed the EGRET data, finding a statistically significant diffuse $\gamma$-ray emission from the galactic halo. We show that this emission can naturally be explained within a previously-proposed model for baryonic dark matter, in which $\gamma$-rays are produced through the interaction of high-energy cosmic-ray protons with cold $H_2$ clouds clumped into dark clusters - these dark clusters supposedly populate the outer galactic halo and can show up in microlensing observations. Our estimate for the halo $\gamma$-ray flux turns out to be in remarkably good agreement with the discovery by Dixon et al. We also address future prospects to test our predictions.Comment: 9 pages, 1 figure included, to appear in ApJ 510, L103 (1999

Indigenous Cultural and Natural Resource Management Futures

This paper has a specific focus on lessons we have learnt from working with Indigenous peoples engaged in cultural and natural resource management projects in northern Australia and New South Wales. It is based on action research currently being undertaken under the five-year research project People on Country, Healthy Landscapes and Indigenous Economic Futures (PoC) and a related three-year project investigating the socioeconomic benefits of Aboriginal people being involved in the sustainable management of their country in NSW

Search for exoplanets in M31 with pixel-lensing and the PA-99-N2 event revisited

Several exoplanets have been detected towards the Galactic bulge with the microlensing technique. We show that exoplanets in M31 may also be detected with the pixel-lensing method, if telescopes making high cadence observations of an ongoing microlensing event are used. Using a Monte Carlo approach we find that the mean mass for detectable planetary systems is about $2 M_{\rm {J}}$. However, even small mass exoplanets ($M_{\rm P} < 20 M_{\oplus}$) can cause significant deviations, which are observable with large telescopes. We reanalysed the POINT-AGAPE microlensing event PA-99-N2. First, we test the robustness of the binary lens conclusion for this light curve. Second, we show that for such long duration and bright microlensing events, the efficiency for finding planetary-like deviations is strongly enhanced with respect to that evaluated for all planetary detectable events.Comment: 14 pages, 8 figures. Paper presented at the "II Italian-Pakistani Workshop on Relativistic Astrophysics, Pescara, July 8-10, 2009. To be published in a special issue of General Relativity and Gravitation (eds. F. De Paolis, G.F.R. Ellis, A. Qadir and R. Ruffini

Towards A Census of Earth-mass Exo-planets with Gravitational Microlensing

Thirteen exo-planets have been discovered using the gravitational microlensing technique (out of which 7 have been published). These planets already demonstrate that super-Earths (with mass up to ~10 Earth masses) beyond the snow line are common and multiple planet systems are not rare. In this White Paper we introduce the basic concepts of the gravitational microlensing technique, summarise the current mode of discovery and outline future steps towards a complete census of planets including Earth-mass planets. In the near-term (over the next 5 years) we advocate a strategy of automated follow-up with existing and upgraded telescopes which will significantly increase the current planet detection efficiency. In the medium 5-10 year term, we envision an international network of wide-field 2m class telescopes to discover Earth-mass and free-floating exo-planets. In the long (10-15 year) term, we strongly advocate a space microlensing telescope which, when combined with Kepler, will provide a complete census of planets down to Earth mass at almost all separations. Such a survey could be undertaken as a science programme on Euclid, a dark energy probe with a wide-field imager which has been proposed to ESA's Cosmic Vision Programme.Comment: 10 pages. White Paper submission to the ESA Exo-Planet Roadmap Advisory Team. See also "Inferring statistics of planet populations by means of automated microlensing searches" by M. Dominik et al. (arXiv:0808.0004