234 research outputs found
Astrometry with PRAIA
PRAIA - Package for the Reduction of Astronomical Images Automatically - is a
suite of astrometric and photometric tasks designed to cope with huge amounts
of heterogeneous observations with fast processing, no human intervention,
minimum parametrization and yet maximum possible accuracy and precision. It is
the main tool used to analyse astronomical observations by an international
collaboration involving Brazilian, French and Spanish researchers under the
Lucky Star umbrella for Solar System studies. In this paper, we focus on the
astrometric concepts underneath PRAIA, used in reference system works, natural
satellite and NEA astrometry for dynamical and ephemeris studies, and lately
for the precise prediction of stellar occultations by planetary satellites,
dwarf-planets, TNOs, Centaurs and Trojan asteroids. We highlight novelties
developed by us and never reported before in the literature, which
significantly enhance astrometry precision and automation. Such as the robust
object detection and aperture characterization (BOIA), which explains the long
standing empirical photometry/astrometry axiom that recommends using apertures
with 2 - 3 sigma (Gaussian width) radius. We give examples showing the
astrometry performance, discuss the advantages of PRAIA over other astrometry
packages and comment about future planed astrometry implementations. PRAIA
codes and input files are publicly available for the first time at:
https://ov.ufrj.br/en/PRAIA/. PRAIA astrometry is useful for Solar System as
well as astrophysical observations
Astrometry of mutual approximations between natural satellites. Application to the Galilean moons
Typically we can deliver astrometric positions of natural satellites with
errors in the 50-150 mas range. Apparent distances from mutual phenomena, have
much smaller errors, less than 10 mas. However, this method can only be applied
during the equinox of the planets. We developed a method that can provide
accurate astrometric data for natural satellites -- the mutual approximations.
The method can be applied when any two satellites pass close by each other in
the apparent sky plane. The fundamental parameter is the central instant
of the passage when the distances reach a minimum.
We applied the method for the Galilean moons. All observations were made with
a 0.6 m telescope with a narrow-band filter centred at 889 nm with width of 15
nm which attenuated Jupiter's scattered light. We obtained central instants for
14 mutual approximations observed in 2014-2015. We determined with an
average precision of 3.42 mas (10.43 km). For comparison, we also applied the
method for 5 occultations in the 2009 mutual phenomena campaign and for 22
occultations in the 2014-2015 campaign. The comparisons of determined by
our method with the results from mutual phenomena show an agreement by less
than 1-sigma error in , typically less than 10 mas. This new method is
particularly suitable for observations by small telescopes.Comment: 13 pages, 11 figures and 8 tables. Based on observations made at the
Laborat\'orio Nacional de Astrof\'isica (LNA), Itajub\'a-MG, Brazi
The Large Quasar Reference Frame (LQRF) - an optical representation of the ICRS
The large number and all-sky distribution of quasars from different surveys,
along with their presence in large, deep astrometric catalogs,enables the
building of an optical materialization of the ICRS following its defining
principles. Namely: that it is kinematically non-rotating with respect to the
ensemble of distant extragalactic objects; aligned with the mean equator and
dynamical equinox of J2000; and realized by a list of adopted coordinates of
extragalatic sources. Starting from the updated and presumably complete LQAC
list of QSOs, the initial optical positions of those quasars are found in the
USNO B1.0 and GSC2.3 catalogs, and from the SDSS DR5. The initial positions are
next placed onto UCAC2-based reference frames, following by an alignment with
the ICRF, to which were added the most precise sources from the VLBA calibrator
list and the VLA calibrator list - when reliable optical counterparts exist.
Finally, the LQRF axes are inspected through spherical harmonics, contemplating
to define right ascension, declination and magnitude terms. The LQRF contains
J2000 referred equatorial coordinates for 100,165 quasars, well represented
across the sky, from -83.5 to +88.5 degrees in declination, and with 10 arcmin
being the average distance between adjacent elements. The global alignment with
the ICRF is 1.5 mas, and the individual position accuracies are represented by
a Poisson distribution that peaks at 139 mas in right ascension and 130 mas in
declination. It is complemented by redshift and photometry information from the
LQAC. The LQRF is designed to be an astrometric frame, but it is also the basis
for the GAIA mission initial quasars' list, and can be used as a test bench for
quasars' space distribution and luminosity function studies.Comment: 23 pages, 23 figures, 6 tables Accepted for publication by Astronomy
& Astrophysics, on 25 May 200
Optical identification of the companion to PSR J1911-5958A, the pulsar binary in the outskirts of NGC 6752
We report on the identification of the optical counterpart of the binary
millisecond pulsar PSR J1911-5958A, located in the outskirts of the globular
cluster NGC 6752. At the position of the pulsar we find an object with V=22.08,
B-V=0.38, U-B=-0.49. The object is blue with respect to the cluster main
sequence by 0.8 magnitudes in B-V. We argue that the object is the white dwarf
companion of the pulsar. Comparison with white dwarf cooling models shows that
this magnitude and colors are consistent with a low-mass white dwarf at the
distance of NGC 6752. If associated with NGC 6752, the white dwarf is
relatively young, <2 Gyr, which sets constraints on the formation of the binary
and its ejection from the core of the globular cluster.Comment: Accepted for publication in A&A Letters (September 1st, 2003
Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations
The prediction of stellar occultations by Transneptunian objects and Centaurs
is a difficult challenge that requires accuracy both in the occulted star
position as for the object ephemeris. Until now, the most used method of
prediction involving tens of TNOs/Centaurs was to consider a constant offset
for the right ascension and for the declination with respect to a reference
ephemeris. This offset is determined as the difference between the most recent
observations of the TNO and the reference ephemeris. This method can be
successfully applied when the offset remains constant with time. This paper
presents an alternative method of prediction based on a new accurate orbit
determination procedure, which uses all the available positions of the TNO from
the Minor Planet Center database plus sets of new astrometric positions from
unpublished observations. The orbit determination is performed through a
numerical integration procedure (NIMA), in which we develop a specific
weighting scheme. The NIMA method was applied for 51 selected TNOs/Centaurs.
For this purpose, we have performed about 2900 new observations during
2007-2014. Using NIMA, we succeed in predicting the stellar occultations of 10
TNOs and 3 Centaurs between 2013 and 2015. By comparing the NIMA and JPL
ephemerides, we highlighted the variation of the offset between them with time.
Giving examples, we show that the constant offset method could not accurately
predict 6 out of the 13 observed positive occultations successfully predicted
by NIMA. The results indicate that NIMA is capable of efficiently refine the
orbits of these bodies. Finally, we show that the astrometric positions given
by positive occultations can help to further refine the orbit of the TNO and
consequently the future predictions. We also provide the unpublished
observations of the 51 selected TNOs and their ephemeris in a usable format by
the SPICE library.Comment: 12 pages, 9 figures, accepted in A&
Astrometry of the main satellites of Uranus: 18 years of observations
We determine accurate positions of the main satellites of Uranus: Miranda,
Ariel, Umbriel, Titania, and Oberon. Positions of Uranus, as derived from those
of these satellites, are also determined. The observational period spans from
1992 to 2011. All runs were made at the Pico dos Dias Observatory, Brazil.
We used the software called Platform for Reduction of Astronomical Images
Automatically (PRAIA) to minimise (digital coronography) the influence of the
scattered light of Uranus on the astrometric measurements and to determine
accurate positions of the main satellites. The positions of Uranus were then
indirectly determined by computing the mean differences between the observed
and ephemeris positions of these satellites. A series of numerical filters was
applied to filter out spurious data. These filters are mostly based on the
comparison between the positions of Oberon with those of the other satellites
and on the offsets as given by the differences between the observed and
ephemeris positions of all satellites.
We have, for the overall offsets of the five satellites, -29 (+/-63) mas in
right ascension and -27 (+/-46) mas in declination. For the overall difference
between the offsets of Oberon and those of the other satellites, we have +3
(+/-30) mas in right ascension and -2 (+/-28) mas in declination. Ephemeris
positions for the satellites were determined from DE432+ura111. Comparisons
using other modern ephemerides for the solar system -INPOP13c- and for the
motion of the satellites -NOE-7-2013- were also made. They confirm that the
largest contribution to the offsets we find comes from the motion of the
barycenter of the Uranus system around the barycenter of the solar system, as
given by the planetary ephemerides. Catalogues with the observed positions are
provided.Comment: 13 pages, 21 figure
Apparent close approaches between near-Earth asteroids and quasars. Precise astrometry and frame linking
Reproduced with permission. Copyright ESO. Article published by EDP Sciences and available at www.aanda.org.International audienceAims. We investigate the link between the International Celestial Reference Frame (ICRF) and the dynamical reference frame realized by the ephemerides of the Solar System bodies. Methods. We propose a procedure that implies a selection of events for asteroids with accurately determined orbits crossing the CCD field containing selected quasars. Using a Bulirsch-Stoer numerical integrator, we constructed 8-years (2010-2018) ephemerides for a set of 836 numbered near-Earth asteroids (NEAs). We searched for close encounters (within a typical field of view of groundbased telescopes) between our selected set of asteroids and quasars with high-accuracy astrometric positions extracted from the Large Quasars Astrometric Catalog (LQAC). Results. In the designated period (2010-2018), we found a number of 2924, 14 257, and 6972 close approaches (within 10') between asteroids with a minimum solar elongation value of 60◦and quasars from the ICRF-Ext2, the Very Large Baseline Array Calibrator Survey (VLBA-CS), and the Very Large Array (VLA), respectively. This large number of close encounters provides the observational basis needed to investigate the link between the dynamical reference frame and the ICRF
PRAIA - Platform for Reduction of Astronomical Images Automatically
4 p.International audiencePRAIA performs high precision differential photometry and astrometry on digitized images (CCD frames, Schmidt plate surveys, etc). The package main characteristics are automation, accuracy and processing speed. Written in FORTRAN 77, it can run in scripts and interact with any visualization and analysis software. PRAIA is in cope with the ever growing amount of observational data available from private and public sources, including data mining and next generation fast telescope all sky surveys, like SDSS, Pan-STARRS and others. PRAIA was officially assigned as the astrometric supporting tool for participants in the GAIA-FUNSSO activities and will be freely available for the astronomical community
Candidate stellar occultations by large trans-neptunian objects up to 2015
We study large trans-neptunian objects (TNOs) using stellar occultations. We
derive precise astrometric predictions for stellar occultations by Eris,
Haumea, Ixion, Makemake, Orcus, Quaoar, Sedna, Varuna, 2002 TX300, and 2003
AZ84 for 2011-2015. We construct local astrometric catalogs of stars in the
UCAC2 (Second US Naval Observatory CCD Astrograph Catalog) frame covering the
sky path of these objects. For that purpose, during 2007-2009, we carried out
an observational program at the ESO2p2/WFI (2.2 m Max-Planck ESO telescope with
the Wide Field Imager) instrument. Astrometric catalogs with proper motions
were produced for each TNO, containing more than 5.35 million stars covering
the sky paths with 30' width in declination. The magnitude completeness is
about R = 19 with a limit of about R = 21. We predicted 2717 stellar
occultation candidates for all targets. Ephemeris offsets with about from 50
mas to 100 mas precision were applied to each TNO orbit to improve the
predictions. They were obtained during 2007-2010 from a parallel observational
campaign carried out with from 0.6 m to 2.2 m in size telescopes. This extends
our previous work for the Pluto system to large TNOs, using the same
observational and astrometric procedures. The obtained astrometric catalogs are
useful for follow-up programs at small to large telescopes used to improve the
candidate star positions and TNO ephemeris. They also furnish valuable
photometric information for the field stars. For each TNO, updates on the
ephemeris offsets and candidate star positions (geometric conditions of
predictions and finding charts) are made available in the web by the group.Comment: 11 pages, 4 figures. Accepted for publication in the Astronomy &
Astrophysics in March 9th, 201
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