MACHO Alert 95-30 : First Real-Time Observation of Extended Source Effects in Gravitational Microlensing

We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event towards the Galactic bulge whose peak magnification departs significantly from the standard point-source microlensing model. Alert 95-30 was observed in real-time by the Global Microlensing Alert Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout the event. We interpret the light-curve ``fine structure'' as indicating transit of the lens across the extended face of the source star. This signifies resolution of a star several kpc distant. We find a lens angular impact parameter theta_{min}/theta_{source} = 0.715 +/- 0.003. This information, along with the radius and distance of the source, provides an additional constraint on the lensing system. Spectroscopic and photometric data indicate the source is an M4 III star of radius 61 +/- 12 Rsun, located on the far side of the bulge at 9 kpc. We derive a lens angular velocity, relative to the source, of 21.5 +/- 4.9 km/s/kpc, where the error is dominated by uncertainty in the source radius. Likelihood analysis yields a median lens mass of 0.67{+2.53}{-0.46} Msun, located with 80% probability in the Galactic bulge at a distance of 6.93{+1.56}{-2.25} kpc. If the lens is a main-sequence star, we can include constraints on the lens luminosity. This modifies our estimates to M_lens = 0.53{+0.52}{-0.35} Msun and D_lens = 6.57{+0.99}{-2.25} kpc. Spectra taken during the event show that the absorption line equivalent widths of H alpha and the TiO bands near 6700 A vary, as predicted for microlensing of an extended source. This is most likely due to center-to-limb variation in the stellar spectral lines. These data demonstrate the feasibility of using microlensing limb crossings as a tool to probe stellar atmospheres directly.Comment: 32 pages including 6 tables, and 15 figures; Uses AASTeX 4.0; submitted to The Astrophysical Journa

Remediable institutional alignment and water service reform: Beyond rational choice

A growing body of empirical evidence fails to support rational choice expectations of superior private sector efficiency in the urban water sector. Drawing on Oliver Williamson’s work on comparative institutional analysis, I suggest that institutional adaptability explains the efficiency and effectiveness of the public sector relative to the private sector. Under private sector participation, lowly remediable institutional adaptability favours the deployment of asymmetric power and the production of outcomes unaligned to reform objectives. Conversely, institutions supporting public operations are designed to facilitate the achievement of collective goals. This makes the alignment of individual attitudes, resources and institutions under in-house service provision less resilient to sustainability-oriented change. Remediable institutional alignment undergirds the comparative advantage of public water operations, as more ample opportunities are provided for compliance, allocative efficiency and adaptive performance. I thus call for a critical realist account of the outcomes of water service reform, free of rational choice dogma

Binary Microlensing Events from the MACHO Project

This article presents the light curves of 21 gravitational microlensing events from the first six years of the MACHO Project gravitational microlensing survey that are likely examples of lensing by binary systems