Saint Mary's University

About: Saint Mary's University is a education organization based out in Halifax, Nova Scotia, Canada. It is known for research contribution in the topics: Population & Stars. The organization has 1931 authors who have published 4993 publications receiving 143226 citations.

X-ray reverberation around accreting black holes

Abstract: Luminous accreting stellar mass and supermassive black holes produce power-law continuum X-ray emission from a compact central corona. Reverberation time lags occur due to light travel time-delays between changes in the direct coronal emission and corresponding variations in its reflection from the accretion flow. Reverberation is detectable using light curves made in different X-ray energy bands, since the direct and reflected components have different spectral shapes. Larger, lower frequency, lags are also seen and are identified with propagation of fluctuations through the accretion flow and associated corona. We review the evidence for X-ray reverberation in active galactic nuclei and black hole X-ray binaries, showing how it can be best measured and how it may be modelled. The timescales and energy-dependence of the high frequency reverberation lags show that much of the signal is originating from very close to the black hole in some objects, within a few gravitational radii of the event horizon. We consider how these signals can be studied in the future to carry out X-ray reverberation mapping of the regions closest to black holes.

Extending the Use of Games in Health Care

Abstract: Digital games have the ability to engage both children and adults alike. We are exploring the use of games for children with long term treatment regimes, where motivation for compliance is a key factor in the success of the treatment. In this paper, we describe the game framework we are building for this purpose. This framework is meant to support the long term use of a gaming world for children with three main goals: (a) provide easy and continual gaming access on a range of computing appliances including small screen devices; (b) offer games that can be personalized and are adaptable based on the child’s interests or specific illness; and (c) maintain novelty and interest in the treatment over time. This framework not only provides a benefit to the children involved, but also provides user data to the coaches, clinicians, and health researchers involved in the child’s treatment regime.

MOST space-based photometry of the transiting exoplanet system HD 189733: precise timing measurements for transits across an active star

Abstract: We have measured transit times for HD 189733b passing in front of its bright (V = 7.67), chromospherically active, and spotted parent star. Nearly continuous broadband optical photometry of this system was obtained with the Microvariability and Oscillations of Stars (MOST) space telescope during 21 days in 2006 August, monitoring 10 consecutive transits. We have used these data to search for deviations from a constant orbital period which can indicate the presence of additional planets in the system that are as yet undetected by Doppler searches. There are no transit timing variations above the level of ±45 s, ruling out super-Earths (of masses 1-4 M⊕) in the 1:2 and 2:3 inner resonances, and planets of 20 M⊕ in the 2:1 outer resonance of the known planet. We also discuss complications in measuring transit times for a planet that transits an active star with large starspots, and how the transits can help constrain and test spot models. This has implications for the large number of such systems expected to be discovered by the COROT and Kepler missions.

Measuring and Explaining Changes in REIT Liquidity: Moving Beyond the Bid–Ask Spread

Abstract: This paper investigates changes in REIT liquidity since the REIT boom of 1993. We use trade-by-trade data for REITs traded on the major U.S. exchanges to estimate and compare Kyle's (1985) measure of inverse liquidity for the 1993 and 1996 time periods. For our full sample of equity REITs, there is a significant increase in REIT liquidity in terms of the median price impact of trades. The increasing importance of the self-advised, self-managed organizational structure is found to be a major factor driving increased REIT liquidity. Our results imply a decline in the asymmetric information faced by market-makers. Our investigation of the changes in the size distribution and resulting price impacts of REIT trades over the 1993–1996 period yields evidence of increased importance of informed traders to REIT price dynamics. Our findings of increased liquidity indicate that the increase in adverse-selection costs due to the presence of more informed traders is more than offset by the increase in market thickness as a result of an increase in the number of uninformed (liquidity) traders.