662 research outputs found
Optimal Chandra/XMM-Newton Band-Passes for Detecting Low Temperature Groups and Clusters of Galaxies
In this short paper I present the results of a calculation which seeks the
maximum, or optimal, signal-to-noise energy band for galaxy group or cluster
X-ray emission detected by the Chandra and XMM-Newton observatories. Using a
background spectrum derived from observations and a grid of models I show that
the "classical" 0.5-2 keV band is indeed close to optimal for clusters with gas
temperatures >2 keV, and redshifts z<1. For cooler systems however, this band
is generally far from optimal. Sub-keV plasmas can suffer 20-60%
signal-to-noise loss compared to an optimal band, and worse for z>0. The
implication is that current and forthcoming surveys should be carefully
constructed in order to minimize bias against the low mass, low temperature end
of the cluster/group population.Comment: 9 pages, 4 postscript figures, uses AASTEX, accepted Ap
Exoplanet Transit Parallax
The timing and duration of exoplanet transits has a dependency on observer
position due to parallax. In the case of an Earth-bound observer with a 2 AU
baseline the dependency is typically small and slightly beyond the limits of
current timing precision capabilities. However, it can become an important
systematic effect in high-precision repeated transit measurements for long
period systems due to its relationship to secular perspective acceleration
phenomena. In this short paper we evaluate the magnitude and characteristics of
transit parallax in the case of exoplanets using simplified geometric examples.
We also discuss further implications of the effect, including its possible
exploitation to provide immediate confirmation of planetary transits and/or
unique constraints on orbital parameters and orientations.Comment: 12 Pages, 3 Figures, Accepted for publication in Ap
A possible dearth of hot gas in galaxy groups at intermediate redshift
We examine the X-ray luminosity of galaxy groups in the CNOC2 survey, at
redshifts 0.1 < z < 0.6. Previous work examining the gravitational lensing
signal of the CNOC2 groups has shown that they are likely to be genuine,
gravitationally bound objects. Of the 21 groups in the field of view of the
EPIC-PN camera on XMM-Newton, not one was visible in over 100 ksec of
observation, even though three of the them have velocity dispersions high
enough that they would easily be visible if their luminosities scaled with
their velocity dispersions in the same way as nearby groups' luminosities
scale. We consider the possibility that this is due to the reported velocity
dispersions being erroneously high, and conclude that this is unlikely. We
therefore find tentative evidence that groups at intermediate redshift are
underluminous relative to their local cousins.Comment: 16 pages, 5 figures, reference added in section 1, typos corrected,
published in Ap
Habitable Climates
According to the standard liquid-water definition, the Earth is only
partially habitable. We reconsider planetary habitability in the framework of
energy-balance models, the simplest seasonal models in physical climatology, to
assess the spatial and temporal habitability of Earth-like planets. We quantify
the degree of climatic habitability of our models with several metrics of
fractional habitability. Previous evaluations of habitable zones may have
omitted important climatic conditions by focusing on close Solar System
analogies. For example, we find that model pseudo-Earths with different
rotation rates or different land-ocean fractions have fractional habitabilities
that differ significantly from that of the Earth itself. Furthermore, the
stability of a planet's climate against albedo-feedback snowball events
strongly impacts its habitability. Therefore, issues of climate dynamics may be
central in assessing the habitability of discovered terrestrial exoplanets,
especially if astronomical forcing conditions are different from the moderate
Solar System cases.Comment: Accepted by ApJ. Several references added. 41 pages, 11 figures, 2
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