6,916 research outputs found
Ground-based CCD astrometry with wide field imagers. IV. An improved Geometric Distortion Correction for the Blue prime-focus Camera at the LBT
High precision astrometry requires an accurate geometric distortion solution.
In this work, we present an average correction for the Blue Camera of the Large
Binocular Telescope which enables a relative astrometric precision of ~15 mas
for the B_Bessel and V_Bessel broad-band filters. The result of this effort is
used in two companion papers: the first to measure the absolute proper motion
of the open cluster M67 with respect to the background galaxies; the second to
decontaminate the color-magnitude diagram of M67 from field objects, enabling
the study of the end of its white dwarf cooling sequence. Many other
applications might find this distortion correction useful.Comment: 13 pages, 11 figures, 4 tables. accepted for publication on Astronomy
and Astrophysic
Astrometry and photometry with HST-WFC3. I. Geometric distortion corrections of F225W, F275W, F336W bands of the UVIS-channel
An accurate geometric distortion solution for the Hubble Space Telescope
UVIS-channel of Wide Field Camera 3 is the first step towards its use for high
precision astrometry. In this work we present an average correction that
enables a relative astrometric accuracy of ~1 mas (in each axis for well
exposed stars) in three broad-band ultraviolet filters (F225W, F275W, and
F336W). More data and a better understanding of the instrument are required to
constrain the solution to a higher level of accuracy.Comment: 20 pages, 7 figures (3 in low resolution), 3 tables. Accepted for
publication in PASP on October 16 200
Geometric back-reaction in pre-inflation from relativistic quantum geometry
The pre-inflationary evolution of the universe describes the beginning of the
expansion from a static initial state, such that the Hubble parameter is
initially zero, but increases to an asymptotic constant value, in which it
could achieve a de Sitter (inflationary) expansion. The expansion is driven by
a background phantom field. The back-reaction effects at this moment should
describe vacuum geometrical excitations, which are studied with detail in this
work using Relativistic Quantum Geometry.Comment: improved versio
Thermodynamical properties of metric fluctuations during inflation
I study a thermodynamical approach to scalar metric perturbations during the
inflationary stage. In the power-law expanding universe here studied, I find a
negative heat capacity as a manifestation of superexponential growing for the
number of states in super Hubble scales. The power spectrum depends on the
Gibbons-Hawking and Hagedorn temperatures.Comment: 7 pages, no figures (accepted to publication in General Relativity
and Gravitation
Charged and electromagnetic fields from relativistic quantum geometry
In the Relativistic Quantum Geometry (RQG) formalism recently introduced, was
explored the possibility that the variation of the tensor metric can be done in
a Weylian integrable manifold using a geometric displacement, from a Riemannian
to a Weylian integrable manifold, described by the dynamics of an auxiliary
geometrical scalar field , in order that the Einstein tensor (and the
Einstein equations) can be represented on a Weyl-like manifold. In this
framework we study jointly the dynamics of electromagnetic fields produced by
quantum complex vector fields, which describes charges without charges. We
demonstrate that complex fields act as a source of tetra-vector fields which
describe an extended Maxwell dynamics.Comment: improved versio
Ground-based astrometry with wide field imagers. V. Application to near-infrared detectors: HAWK-I@VLT/ESO
High-precision astrometry requires accurate point-spread function modeling
and accurate geometric-distortion corrections. This paper demonstrates that it
is possible to achieve both requirements with data collected at the high acuity
wide-field K-band imager (HAWK-I), a wide-field imager installed at the Nasmyth
focus of UT4/VLT ESO 8m telescope. Our final astrometric precision reaches ~3
mas per coordinate for a well-exposed star in a single image with a systematic
error less than 0.1 mas. We constructed calibrated astro-photometric catalogs
and atlases of seven fields: the Baade's Window, NGC 6656, NGC 6121, NGC 6822,
NGC 6388, NGC 104, and the James Webb Space Telescope calibration field in the
Large Magellanic Cloud. We make these catalogs and images electronically
available to the community. Furthermore, as a demonstration of the efficacy of
our approach, we combined archival material taken with the optical wide-field
imager at the MPI/ESO 2.2m with HAWK-I observations. We showed that we are able
to achieve an excellent separation between cluster members and field objects
for NGC 6656 and NGC 6121 with a time base-line of about 8 years. Using both
HST and HAWK-I data, we also study the radial distribution of the SGB
populations in NGC 6656 and conclude that the radial trend is flat within our
uncertainty. We also provide membership probabilities for most of the stars in
NGC 6656 and NGC 6121 catalogs and estimate membership for the published
variable stars in these two fields.Comment: 36 pages (included appendix), 13 tables, 35 figures (26 in low
resolution), accepted for publication in Astronomy and Astrophysics. Online
materials will be soon available on CDS. Meanwhile, online materials can be
requested directly to the first autho
Optimized Multimode Interference Fiber Based Refractometer in A Reflective Interrogation Scheme
A fiber based refractometer in a reflective interrogation scheme is investigated and optimized. A thin gold film was deposited on the tip of a coreless fiber section, which is spliced with a single mode fiber. The coreless fiber is a multimode waveguide, and the observed effects are due to multimode interference. To investigate and optimize the structure, the multimode part of the sensor is built with 3 different lengths: 58 mm, 29 mm and 17 mm. We use a broadband light source ranging from 1475 nm to 1650 nm and we test the sensors with liquids of varying refractive indices, from 1.333 to 1.438. Our results show that for a fixed wavelength, the sensor sensitivity is independent of the multimode fiber length, but we observed a sensitivity increase of approximately 0.7 nm/RIU for a one-nanometer increase in wavelength
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