384 research outputs found
The Galactic Exoplanet Survey Telescope (GEST)
The Galactic Exoplanet Survey Telescope (GEST) will observe a 2 square degree
field in the Galactic bulge to search for extra-solar planets using a
gravitational lensing technique. This gravitational lensing technique is the
only method employing currently available technology that can detect Earth-mass
planets at high signal-to-noise, and can measure the frequency of terrestrial
planets as a function of Galactic position. GEST's sensitivity extends down to
the mass of Mars, and it can detect hundreds of terrestrial planets with
semi-major axes ranging from 0.7 AU to infinity. GEST will be the first truly
comprehensive survey of the Galaxy for planets like those in our own Solar
System.Comment: 17 pages with 13 figures, to be published in Proc. SPIE vol 4854,
"Future EUV-UV and Visible Space Astrophysics Missions and Instrumentation
Improving the Prospects for Detecting Extrasolar Planets in Gravitational Microlensing in 2002
Gravitational microlensing events of high magnification have been shown to be
promising targets for detecting extrasolar planets. However, only a few events
of high magnification have been found using conventional survey techniques.
Here we demonstrate that high magnification events can be readily found in
microlensing surveys using a strategy that combines high frequency sampling of
target fields with online difference imaging analysis. We present 10
microlensing events with peak magnifications greater than 40 that were detected
in real-time towards the Galactic Bulge during 2001 by MOA. We show that Earth
mass planets can be detected in future events such as these through intensive
follow-up observations around the event peaks. We report this result with
urgency as a similar number of such events are expected in 2002.Comment: 11 pages, 3 embedded ps figures including 2 colour, revised version
accepted by MNRA
MOA 2003-BLG-37: A Bulge Jerk-Parallax Microlens Degeneracy
We analyze the Galactic bulge microlensing event MOA-2003-BLG-37. Although
the Einstein timescale is relatively short, t_e=43 days, the lightcurve
displays deviations consistent with parallax effects due to the Earth's
accelerated motion. We show that the chi^2 surface has four distinct local
minima that are induced by the ``jerk-parallax'' degeneracy, with pairs of
solutions having projected Einstein radii, \tilde r_e = 1.76 AU and 1.28 AU,
respectively. This is the second event displaying such a degeneracy and the
first toward the Galactic bulge. For both events, the jerk-parallax formalism
accurately describes the offsets between the different solutions, giving hope
that when extra solutions exist in future events, they can easily be found.
However, the morphologies of the chi^2 surfaces for the two events are quite
different, implying that much remains to be understood about this degeneracy.Comment: 19 pages, 3 figures, 1 table, ApJ, in press, 1 July 200
GRB 091029: At the limit of the fireball scenario
Using high-quality, broad-band afterglow data for GRB 091029, we test the
validity of the forward-shock model for gamma-ray burst afterglows. We used
multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND,
BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the
XRT onboard the Swift satellite. To explain the almost totally decoupled light
curves in the X-ray and optical/NIR domains, a two-component outflow is
proposed. Several models are tested, including continuous energy injection,
components with different electron energy indices and components in two
different stages of spectral evolution. Only the last model can explain both
the decoupled light curves with asynchronous peaks and the peculiar SED
evolution. However, this model has so many unknown free parameters that we are
unable to reliably confirm or disprove its validity, making the afterglow of
GRB 091029 difficult to explain in the framework of the simplest fireball
model.Comment: Accepted to A&
Design and conduct of 'Xtreme Alps' : a double-blind, randomised controlled study of the effects of dietary nitrate supplementation on acclimatisation to high altitude
The study of healthy human volunteers ascending to high altitude provides a robust model of the complex physiological interplay that emulates human adaptation to hypoxaemia in clinical conditions. Nitric oxide (NO) metabolism may play an important role in both adaptation to high altitude and response to hypoxaemia during critical illness at sea level. Circulating nitrate and nitrite concentrations can be augmented by dietary supplementation and this is associated with improved exercise performance and mitochondrial efficiency. We hypothesised that the administration of a dietary substance (beetroot juice) rich in nitrate would improve oxygen efficiency during exercise at high altitude by enhancing tissue microcirculatory blood flow and oxygenation. Furthermore, nitrate supplementation would lead to measurable increases in NO bioactivity throughout the body.
This methodological manuscript describes the design and conduct of the ‘Xtreme Alps’ expedition, a double-blind randomised controlled trial investigating the effects of dietary nitrate supplementation on acclimatisation to hypobaric hypoxia at high altitude in healthy human volunteers. The primary outcome measure was the change in oxygen efficiency during exercise at high altitude between participants allocated to receive nitrate supplementation and those receiving a placebo. A number of secondary measures were recorded, including exercise capacity, peripheral and microcirculatory blood flow and tissue oxygenation.
Results from this study will further elucidate the role of NO in adaption to hypoxaemia and guide clinical trials in critically ill patients. Improved understanding of hypoxaemia in critical illness may provide new therapeutic avenues for interventions that will improve survival in critically ill patients
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