68 research outputs found
The Gaia Data Release 1 parallaxes and the distance scale of Galactic planetary nebulae
In this paper we gauge the potentiality of Gaia in the distance scale
calibration of planetary nebulae (PNe) by assessing the impact of DR1
parallaxes of central stars of Galactic PNe (CSPNe) against known physical
relations. For selected PNe targets with state-of-the-art data on angular sizes
and fluxes, we derive the distance-dependent parameters of the classical
distance scales, i.e., physical radii and ionized masses, from DR1 parallaxes;
we propagate the uncertainties in the estimated quantities and evaluate their
statistical properties in the presence of large relative parallax errors; we
populate the statistical distance scale diagrams with this sample and discuss
its significance in light of existing data and current calibrations.
We glean from DR1 parallaxes 8 CSPNe with S/N1. We show that this set of
potential calibrators doubles the number of extant trigonometric parallaxes
(from HST and ground-based), and increases by two orders of magnitude the
domain of physical parameters probed previously. We then use the combined
sample of suitable trigonometric parallaxes to fit the
physical-radius-to-surface-brightness relation. This distance scale
calibration, although preliminary, appears solid on statistical grounds, and
suggestive of new PNe physics.
With the tenfold improvement in PNe number statistics and astrometric
accuracy expected from future Gaia releases the new distance scale, already
very intriguing, will be definitively constrained.Comment: New Astronomy, in pres
A test of Gaia Data Release 1 parallaxes: implications for the local distance scale
We present a comparison of Gaia Data Release 1 (DR1) parallaxes with
photometric parallaxes for a sample of 212 Galactic Cepheids at a median
distance of 2~kpc, and explore their implications on the distance scale and the
local value of the Hubble constant H_0. The Cepheid distances are estimated
from a recent calibration of the near-infrared Period-Luminosity P-L relation.
The comparison is carried out in parallax space, where the DR1 parallax errors,
with a median value of half the median parallax, are expected to be
well-behaved. With the exception of one outlier, the DR1 parallaxes are in
remarkably good global agreement with the predictions, and the published errors
may be conservatively overestimated by about 20%. The parallaxes of 9 Cepheids
brighter than G = 6 may be systematically underestimated, trigonometric
parallaxes measured with the HST FGS for three of these objects confirm this
trend. If interpreted as an independent calibration of the Cepheid luminosities
and assumed to be otherwise free of systematic uncertainties, DR1 parallaxes
would imply a decrease of 0.3% in the current estimate of the local Hubble
constant, well within their statistical uncertainty, and corresponding to a
value 2.5 sigma (3.5 sigma if the errors are scaled) higher than the value
inferred from Planck CMB data used in conjunction with Lambda-CDM. We also test
for a zeropoint error in Gaia parallaxes and find none to a precision of ~20
muas. We caution however that with this early release, the complete systematic
properties of the measurements may not be fully understood at the statistical
level of the Cepheid sample mean, a level an order of magnitude below the
individual uncertainties. The early results from DR1 demonstrate again the
enormous impact that the full mission will likely have on fundamental questions
in astrophysics and cosmology.Comment: A&A, submitted, 6 pages, 3 figure
The Global sphere reconstruction (GSR) - Demonstrating an independent implementation of the astrometric core solution for Gaia
Context. The Gaia ESA mission will estimate the astrometric and physical data
of more than one billion objects, providing the largest and most precise
catalog of absolute astrometry in the history of Astronomy. The core of this
process, the so-called global sphere reconstruction, is represented by the
reduction of a subset of these objects which will be used to define the
celestial reference frame. As the Hipparcos mission showed, and as is inherent
to all kinds of absolute measurements, possible errors in the data reduction
can hardly be identified from the catalog, thus potentially introducing
systematic errors in all derived work. Aims. Following up on the lessons
learned from Hipparcos, our aim is thus to develop an independent sphere
reconstruction method that contributes to guarantee the quality of the
astrometric results without fully reproducing the main processing chain.
Methods. Indeed, given the unfeasibility of a complete replica of the data
reduction pipeline, an astrometric verification unit (AVU) was instituted by
the Gaia Data Processing and Analysis Consortium (DPAC). One of its jobs is to
implement and operate an independent global sphere reconstruction (GSR),
parallel to the baseline one (AGIS, namely Astrometric Global Iterative
Solution) but limited to the primary stars and for validation purposes, to
compare the two results, and to report on any significant differences. Results.
Tests performed on simulated data show that GSR is able to reproduce at the
sub-as level the results of the AGIS demonstration run presented in
Lindegren et al. (2012). Conclusions. Further development is ongoing to improve
on the treatment of real data and on the software modules that compare the AGIS
and GSR solutions to identify possible discrepancies above the tolerance level
set by the accuracy of the Gaia catalog.Comment: Accepted for publication on Astronomy & Astrophysic
POSSIBLE ASTRONOMICAL MEANINGS OF SOME EL MOLLE RELICS NEAR THE ESO OBSERVATORY AT LA SILLA
Abstact: This paper describes a peculiar, man-made circular stone structure, associated with the ancient rock engravings that are around the site of La Silla in Chile close to the European Southern Observatory, and are attributed to the El Molle Culture. Three stones of the circle, different from all the others, were likely to pinpoint the alignment of three bright stars close to the horizon, as seen from a specific vantage point inside the structure. The El Molle was the only period in which this alignment occurred significantly close to the horizon, moreover it was only in this epoch that it could also be associated with the transition from the warm to the cold season, a period of the year which was quite important for a society that supported itself by herding and farming
Updates from FOTOSS: Highlights and Statistics from the OATo Photographic Plate Archive
This is a progress report of the on-going work related to the FOTOSS project (Valorizzazione scientifica dell’archivio di osservazioni FOTOgrafiche del Secolo Scorso di patrimonio dell’OATo). First, we give an up-to-date account of the status of the FOTOSS project, including preliminary informations on the number and characteristics of the digitized plate images; we then present a detailed explanation of the content and usage of the latest realization of the Master Plate Catalog (MPC), along with some general statistics based on the observations recorded in the MPC
Differential astrometric framework for the Jupiter relativistic experiment with Gaia
We employ differential astrometric methods to establish a small field reference frame stable at the microarcsecond (μas) level on short time-scales using high-cadence simulated observations taken by Gaia in 2017 February of a bright star close to the limb of Jupiter, as part of the relativistic experiment on Jupiter's quadrupole. We achieve subμas-level precision along scan through a suitable transformation of the field angles into a small-field tangent plane and a least-squares fit over several overlapping frames for estimating the plate and geometric calibration parameters with tens of reference stars that lie within ∼0.5 deg from the target star, assuming perfect knowledge of stellar proper motions and parallaxes. Furthermore, we study the effects of unmodelled astrometric parameters on the residuals and find that proper motions have a stronger effect than unmodelled parallaxes, e.g. unmodelled Gaia DR2 proper motions introduce extra residuals of ∼23 μas (AL) and 69 μas (AC) versus the ∼5 μas (AL) and 17 μas (AC) due to unmodelled parallaxes. On the other hand, assuming catalogue errors in the proper motions and parallaxes such as those from Gaia DR2 has a minimal impact on the stability introducing subμas and μas level residuals in the along and across scanning direction, respectively. Finally, the effect of a coarse knowledge in the satellite velocity components (with time-dependent errors of 10 μas s-1) is capable of enlarging the size of the residuals to roughly 0.2 mas
Some aspects of Relativistic Astrometry from within the Solar System
In this article we outline the structure of a general relativistic
astrometric model which has been developed to deduce the position and proper
motion of stars from 1-microarcsecond optical observations made by an
astrometric satellite orbiting around the Sun. The basic assumption of our
model is that the Solar System is the only source of gravity, hence we show how
we modeled the satellite observations in a many-body perturbative approach
limiting ourselves to the order of accuracy of . The microarcsecond
observing scenario outlined is that for the GAIA astrometric mission.Comment: 11 pages, 2 figures, accepted by Cel. Me
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