931 research outputs found
Astrometry with MCAO: HST-GeMS proper motions in the globular cluster NGC 6681
Aims: for the first time the astrometric capabilities of the Multi-Conjugate
Adaptive Optics (MCAO) facility GeMS with the GSAOI camera on Gemini-South are
tested to quantify the accuracy in determining stellar proper motions in the
Galactic globular cluster NGC 6681. Methods: proper motions from HST/ACS for a
sample of its stars are already available, and this allows us to construct a
distortion-free reference at the epoch of GeMS observations that is used to
measure and correct the temporally changing distortions for each GeMS exposure.
In this way, we are able to compare the corrected GeMS images with a
first-epoch of HST/ACS images to recover the relative proper motion of the
Sagittarius dwarf spheroidal galaxy with respect to NGC 6681. Results: we find
this to be (\mu_{\alpha}cos\delta, \mu_{\delta}) = (4.09,-3.41) mas/yr, which
matches previous HST/ACS measurements with a very good accuracy of 0.03 mas/yr
and with a comparable precision (r.m.s of 0.43 mas/yr). Conclusions: this study
successfully demonstrates that high-quality proper motions can be measured for
quite large fields of view (85 arcsec X 85 arcsec) with MCAO-assisted,
ground-based cameras and provides a first, successful test of the performances
of GeMS on multi-epoch data.Comment: 5 pages, 4 figures. Accepted for publication by A&A Letter
Proper motion in lensed radio jets at redshift 3:A possible dual super-massive black hole system in the early Universe
In this paper, we exploit the gravitational lensing effect to detect proper
motion in the highly magnified gravitationally lensed source MG B2016+112. We
find positional shifts up to 6 mas in the lensed images by comparing two Very
Long Baseline Interferometric (VLBI) radio observations at 1.7 GHz that are
separated by 14.359 years, and provide an astrometric accuracy of the order of
tens of as. From lens modelling, we exclude a shift in the lensing galaxy
as the cause of the positional change of the lensed images, and we assign it to
the background source. The source consists of four sub-components separated by
pc, with proper motion of the order of tens as yr for
the two components at highest magnification () and of the order of
a few mas yr for the two components at lower magnification ().
We propose single AGN and dual AGN scenarios to explain the source plane.
Although, the latter interpretation is supported by the archival
multi-wavelength properties of the object. In this case, MG B2016+112 would
represent the highest redshift dual radio-loud AGN system discovered thus far,
and would support the merger interpretation for such systems. Also, given the
low probability () of detecting a dual AGN system that is also
gravitationally lensed, if confirmed, this would suggest that such dual AGN
systems must be more abundant in the early Universe than currently thought.Comment: 11 pages, 4 figures; accepted for publication by Astronomy and
Astrophysic
Weak Galactic Halo--Fornax dSph Connection from RR Lyrae Stars
For the first time accurate pulsation properties of the ancient variable
stars of the Fornax dwarf spheroidal galaxy (dSph) are discussed in the broad
context of galaxy formation and evolution. Homogeneous multi-band optical
photometry of spanning {\it twenty} years has allowed us to identify and
characterize more than 1400 RR Lyrae stars (RRLs) in this galaxy. Roughly 70\%
are new discoveries. We investigate the period-amplitude distribution and find
that Fornax shows a lack of High Amplitude (A_V\gsim0.75 mag) Short Period
fundamental-mode RRLs (P\lsim0.48 d, HASPs). These objects occur in stellar
populations more metal-rich than [Fe/H]-1.5 and they are common in the
Galactic halo (Halo) and in globulars. This evidence suggests that old (age
older than 10 Gyr) Fornax stars are relatively metal-poor.
A detailed statistical analysis of the role of the present-day Fornax dSph in
reproducing the Halo period distribution shows that it can account for only a
few to 20\% of the Halo when combined with RRLs in massive dwarf galaxies
(Sagittarius dSph, Large Magellanic Cloud). This finding indicates that
Fornax-like systems played a minor role in building up the Halo when compared
with massive dwarfs. We also discuss the occurrence of HASPs in connection with
the luminosity and the early chemical composition of nearby dwarf galaxies. We
find that, independently of their individual star formation histories, bright
(M_V\lsim-13.5 mag) galaxies have HASPs, whereas faint ones (M_V\gsim-11
mag) do not. Interestingly enough, Fornax belongs to a luminosity range
(--11M--13.5 mag) in which the occurrence of HASPs appears to be
correlated with the early star formation and chemical enrichment of the host
galaxy.Comment: 7 pages, 5 figures, A&A, accepte
Successful application of PSF-R techniques to the case of the globular cluster NGC 6121 (M 4)
Context. Precise photometric and astrometric measurements on astronomical images require an accurate knowledge of the point spread function (PSF). When the PSF cannot be modelled directly from the image, PSF-reconstruction techniques become the only viable solution. So far, however, their performance on real observations has rarely been quantified.
Aims. In this Letter, we test the performance of a novel hybrid technique, called PRIME, on Adaptive Optics-assisted SPHERE/ZIMPOL observations of the Galactic globular cluster NGC 6121.
Methods. PRIME couples PSF-reconstruction techniques, based on control-loop data and direct image fitting performed on the only bright point-like source available in the field of view of the ZIMPOL exposures, with the aim of building the PSF model.
Results. By exploiting this model, the magnitudes and positions of the stars in the field can be measured with an unprecedented precision, which surpasses that obtained by more standard methods by at least a factor of four for on-axis stars and by up to a factor of two on fainter, off-axis stars.
Conclusions. Our results demonstrate the power of PRIME in recovering precise magnitudes and positions when the information directly coming from astronomical images is limited to only a few point-like sources and, thus, paving the way for a proper analysis of future Extremely Large Telescope observations of sparse stellar fields or individual extragalactic objects
The MICADO first light imager for ELT: its astrometric performance
We report on our ongoing efforts to ensure that the MICADO NIR imager reaches
differential absolute (often abbreviated: relative) astrometric performance
limited by the SNR of typical observations. The exceptional 39m diameter
collecting area in combination with a powerful multi-conjugate adaptive optics
system (called MAORY) brings the nominal centroiding error, which scales as
FWHM/SNR, down to a few 10 uas. Here we show that an exceptional effort is
needed to provide a system which delivers adequate and calibrateable
astrometric performance over the full field of view (up to 53 arcsec diameter).Comment: 5 pages, submitted to SPIE 2018 Astronomical Telescopes +
Instrumentatio
Dense Building Instrumentation Application for City-Wide Structural Health Monitoring
The Community Seismic Network (CSN) has partnered with the NASA Jet Propulsion Laboratory (JPL) to initiate a campus-wide structural monitoring program of all buildings on the premises. The JPL campus serves as a proxy for a densely instrumented urban city with localized vibration measurements collected throughout the free-field and built environment. Instrumenting the entire campus provides dense measurements in a horizontal geospatial sense for soil response; in addition five buildings have been instrumented on every floor of the structure. Each building has a unique structural system as well as varied amounts of structural information via structural drawings, making several levels of assessment and evaluation possible. Computational studies with focus on damage detection applied to the campus structural network are demonstrated for a collection of buildings. For campus-wide real-time and post-event evaluation, ground and building response products using CSN data are illustrating the usefulness of higher spatial resolution compared to what was previously typical with sparser instrumentation
Sequential behavior of broiler chickens in enriched environments under varying thermal conditions using the generalized sequential pattern algorithm: a proof of concept.
This study investigated the behavior sequences of broiler chickens housed in enriched environments subjected to thermal comfort and heat stress using the Generalized Sequential Pattern (GSP) data mining algorithm
Cardio-respiratory monitoring in archery using a smart textile based on flexible fiber bragg grating sensors
In precision sports, the control of breathing and heart rate is crucial to help the body to remain stable in the shooting position. To improve stability, archers try to adopt similar breathing patterns and to have a low heartbeat during each shot. We proposed an easy-to-use and unobtrusive smart textile (ST) which is able to detect chest wall excursions due to breathing and heart beating. The sensing part is based on two FBGs housed into a soft polymer matrix to optimize the adherence to the chest wall and the system robustness. The ST was assessed on volunteers to figure out its performance in the estimation of respiratory frequency (fR) and heart rate (HR). Then, the system was tested on two archers during four shooting sessions. This is the first study to monitor cardio-respiratory activity on archers during shooting. The good performance of the ST is supported by the low mean absolute percentage error for fR and HR estimation (â€1.97% and â€5.74%, respectively), calculated with respect to reference signals (flow sensor for fR, photopletismography sensor for HR). Moreover, results showed the capability of the ST to estimate fR and HR during different phases of shooting action. The promising results motivate future investigations to speculate about the influence of fR and HR on archersâ performance
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