979 research outputs found
The Gaia Astrometric Survey
In its all-sky survey, the ESA global astrometry mission Gaia will perform
high-precision astrometry and photometry for 1 billion stars down to
mag. The data collected in the Gaia catalogue, to be published by the end of
the next decade, will likely revolutionize our understanding of many aspects of
stellar and Galactic astrophysics. One of the relevant areas in which the Gaia
observations will have great impact is the astrophysics of planetary systems.
This summary focuses on a) the complex technical problems related to and
challenges inherent in correctly modelling the signals of planetary systems
present in measurements collected with a space-borne observatory poised to
carry out precision astrometry at the micro-arcsecond (as) level, and b)
on the potential of Gaia as astrometry for important contributions to the
astrophysics of planetary systems.Comment: 2 pages. Summary of an invited talk given at Special Session 6
(Planetary Systems as Potential Sites for Life) of the XXVIIth IAU General
Assembly held in Rio de Janeiro (Brazil). To appear in IAU Highlights of
Astronomy 15 (2010
Optimal Galaxy Shape Measurements for Weak Lensing Applications Using the Hubble Space Telescope Advanced Camera for Surveys
We present three-epoch multiband (, , )
measurements of galaxy shapes using the ``polar shapelet'' or
Laguerre-expansions method with the Hubble Space Telescope () Advanced
Camera for Surveys (ACS) data, obtained as part of the {\it Great Observatories
Origin Deep Survey} (GOODS). We take advantage of the unique features of the
GOODS/ACS Fields to test the reliability of this relatively new method of
galaxy shape measurement for weak lensing analysis and to quantify the impact
of the ACS Point Spread Function (PSF) on /ACS data. We estimate the bias
introduced by the sharp PSF of the ACS on shape measurement. We show that the
bias in the tangential shear due to galaxy-galaxy lensing can be safely
neglected provided only well-resolved galaxies are used, while it would be
comparable to the signal level (1--3%) for cosmic shear measurements. These
results should of be general utility in planning and analyzing weak lensing
measurements with /ACS data.Comment: 12 pages, 3 figures. Accepted for ApJ
Detection and measurement of planetary systems with GAIA
We use detailed numerical simulations and the Andromedae,
planetary system as a template to evaluate the capability of the ESA
Cornerstone Mission GAIA in detecting and measuring multiple planets around
solar-type stars in the neighborhood of the Solar System. For the outer two
planets of the Andromedae, system, GAIA high-precision global
astrometric measurements would provide estimates of the full set of orbital
elements and masses accurate to better than 1--10%, and would be capable of
addressing the coplanarity issue by determining the true geometry of the system
with uncertainties of order of a few degrees. Finally, we discuss the
generalization to a variety of configurations of potential planetary systems in
the solar neighborhood for which GAIA could provide accurate measurements of
unique value for the science of extra-solar planets.Comment: 4 pages, 2 pictures, accepted for publication in A&A Letter
Narrow-Angle Astrometry with the Space Interferometry Mission: The Search for Extra-Solar Planets. II. Detection and Characterization of Planetary Systems
(Abridged) The probability of detecting additional companions is essentially
unchanged with respect to the single-planet configurations, but after fitting
and subtraction of orbits with astrometric signal-to-noise ratio
the false detection rates can be enhanced by up to a
factor 2; the periodogram approach results in robust multiple-planet detection
for systems with periods shorter than the SIM mission length, even at low
values of , while the least squares technique combined with
Fourier series expansions is arguably preferable in the long-period regime. The
accuracy on multiple-planet orbit reconstruction and mass determination suffers
a typical degradation of 30-40% with respect to single-planet solutions; mass
and orbital inclination can be measured to better than 10% for periods as short
as 0.1 yr, and for as low as , while
is required in order to measure with similar
accuracy systems harboring objects with periods as long as three times the
mission duration. For systems with all components producing
or greater, quasi-coplanarity can be reliably
established with uncertainties of a few degrees, for periods in the range
yr; in systems where at least one component has
, coplanarity measurements are compromised, with typical
uncertainties on the mutual inclinations of order of . Our
findings are illustrative of the importance of the contribution SIM will make
to the fields of formation and evolution of planetary systems.Comment: 61 pages, 14 figures, 5 tables, to appear in the September 2003 Issue
of the Publications of the Astronomical Society of the Pacifi
Perceiving the Vertigo: The Fall of the Heroine in Four New Zealand Writers
In this study I analyse the role of the heroine in the work of four New Zealand writers, Katherine Mansfield, Robin Hyde, Janet Frame and Keri Hulme, starting from the assumption that such a role is influenced by the notion of the fall
and by the perception of the vertigo entailed in it. In order to prove this I turn to the texts of four New Zealand writers dedicating one chapter to each.
In the first chapter a few of Katherine Mansfield's short stories are analysed
from the vantage point of the fall, investigated both in the construction of the
character's subjectivity and in the construction of the narration. In the second
chapter a link is established between Katherine Mansfield and Robin Hyde. A
particular emphasis is put on the notion of subjectivity in relationship developed by
the two writers, highlighting the link between this kind of subjectivity and the
notion of the fall. In the third chapter the focus is subsequently shifted to Robin
Hyde's work, in particular one of her novels, Wednesday's Children, which is read in the context of Mikhail Bakhtin's theory of the carnivalistic. In the fourth chapter the notion of the fall is analysed in the fiction of Janet Frame, which is related to the treatment of the notion of the fall present in Keri Hulme's The Bone People. The
fifth chapter is dedicated to the analysis of The Bone People as in the novel the
notion of the fall and the vertigo perception find their fullest expression, whilst in the sixth chapter a significant parallel is drawn between Janet Frame's Scented Gardens for the Blind and Keri Hulme's The Bone People and links are established with their predecessors.
Finally in the seventh chapter the critical perspective is broadened to comprise those common elements in the writing of Katherine Mansfield, Robin Hyde, Janet Frame and Keri Hulme that have been neglected by focusing uniquely on the notion of the fall, and thus to contribute to a more complete overall picture of the comparison presented in this study
Testing Planet Formation Models with Gaia as Astrometry
In this paper, we first summarize the results of a large-scale double-blind
tests campaign carried out for the realistic estimation of the Gaia potential
in detecting and measuring planetary systems. Then, we put the identified
capabilities in context by highlighting the unique contribution that the Gaia
exoplanet discoveries will be able to bring to the science of extrasolar
planets during the next decade.Comment: 4 pages, 1 figure. To appear in the proceedings of "IAU Symposium 248
- A Giant Step: from Milli- to Micro-arcsecond Astrometry", held in Shanghai,
China, 15-19 Oct. 200
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