25 research outputs found
Dozens of virtual impactor orbits eliminated by the EURONEAR VIMP DECam data mining project
Massive data mining of image archives observed with large etendue facilities
represents a great opportunity for orbital amelioration of poorly known virtual
impactor asteroids (VIs). There are more than 1000 VIs known today; most of
them have very short observed arcs and many are considered lost as they became
extremely faint soon after discovery. We aim to improve the orbits of VIs and
eliminate their status by data mining the existing image archives. Within the
European Near Earth Asteroids Research (EURONEAR) project, we developed the
Virtual Impactor search using Mega-Precovery (VIMP) software endowed with a
very effective (fast and accurate) algorithm to predict apparitions of
candidate pairs for subsequent guided human search. Considering a simple
geometric model, the VIMP algorithm searches for any possible intersection in
space and time between the positional uncertainty of any VI and the bounding
sky projection of any image archive. We applied VIMP to mine the data of 451914
Blanco/DECam images observed between 12 Sep 2012 and 11 Jul 2019, identifying
212 VIs that possibly fall into 1286 candidate images leading to either
precovery or recovery events. Following a careful search of candidate images,
we recovered and measured 54 VIs in 183 DECam images. About 4000 impact orbits
were eliminated from both lists, 27 VIs were removed from at least one list,
while 14 objects were eliminated from both lists. The faintest detections were
around V~24.0, while the majority fall between 21<V<23. The minimal orbital
intersection distances remains constant for 67% detections, increasing for
eight objects and decreasing for 10 objects. Most eliminated VIs had short
initial arcs of less than 5 days. Some unexpected photometric discovery has
emerged regarding the rotation period of 2018 DB, based on the close inspection
of longer trailed VIs and the measurement of their fluxes along the trails.Comment: Accepted for publication in Astronomy & Astrophysics (27 July 2020
Some notes on rayleigh distribution
In this paper, we emphasize some aspects concerning the Rayleigh distribution. After a brief presentation of the literature devoted to this variable, we give a characterization of the Rayleigh distribution by using a Gercbach idea (1967). Then, some properties are put into ligth and in the latter part of the work sequential tests are constructed in order to test a simple and a compound hypothesis concerning a Rayleigh parameter
Surface Morphology of Unused and Used HydromerR-Coated Intravenous Catheters
HydromerR-coated polyurethane (Erythroflex)R catheters, unused, or intravenously inserted for 2-20 days, were studied by scanning electron microscopy (SEM). Both unfixed and fixed (2% glutar-aldehyde in phosphate buffer), and air-or critical-point dried (CPD) specimens were investigated. The catheter segments were sputter-coated with approx. 20 nm gold and studied at an accelerating voltage of 20 kV. The specimens were examined for surface depositions, thickness and structure of the HydromerR layers, and occurrence of adhering and embedded bacteria.
The outer HydromerR layer showed, in the un-used specimens, scratches and fissures, as well as adhering foreign bodies. In used specimens, the layer was swollen, with cracks (like dried earth ), and, occasionally , amorphous substances and coccoid bacteria were seen adhering. Damage to the layer, or even its total disappearance was also noted in some specimens.
The inner (luminal) HydromerR layer was, in unused specimens, clean and slightly wavy. In used catheters, it was thicker, possibly swollen, with small, isolated or agglomerated protrusions, like a lunar landscape . Adhering platelets and amorphous substances were also occasionally seen.
The results suggest that the HydromerR is a fragile material in both its dry and wet forms. Thus, the HydromerR-coated catheters should neither be stored in flexible packs, nor inserted by the Seldinger technique. The findings do not support the belief that the HydromerR-coating can prevent either thrombus formation, or intraluminal occlusion of the in-situ catheters
Una vez más sobre la estimación de la desviación estándar
El propósito de este trabajo es hacer un recorrido por el tema de la estimación de la desviación estándar de uno población normal. Al final se propone un estimador lineal para σ basado en el rango muestral y se le compara con el estimador clásico basado en el rango. Se dan también tablas relacionadas con el dicho estimador para diferentes tamaños de la muestra
Physical characterization of 2020 AV2, the first known asteroid orbiting inside Venus orbit
The first known asteroid with the orbit inside that of Venus is
2020~AV. This may be the largest member of a new population of small
bodies with the aphelion smaller than 0.718~au, called Vatiras. The surface of
2020~AV is being constantly modified by the high temperature, by the
strong solar wind irradiation that characterizes the innermost region of the
Solar system, and by high-energy micrometeorite impacts. The study of its
physical properties represents an extreme test-case for the science of
near-Earth asteroids. Here, we report spectroscopic observations of
2020~AV in the 0.5-1.5~ wavelength interval. These were performed
with the Nordic Optical Telescope and the William Herschel Telescope. Based on
the obtained spectra, we classify 2020~AV as a Sa-type asteroid. We
estimate the diameter of this Vatira to be km by
considering the average albedo of A-type and S-complex asteroids
(), and the absolute magnitude (H=
mag). The wide spectral band around 1~ shows the signature of an olivine
rich composition. The estimated band centre
corresponds to a ferroan olivine mineralogy similar to that of brachinite
meteorites.Comment: Accepted for publication in MNRAS. 10 pages, 5 figures
Discovery and physical characterization as the first response to a potential asteroid collision: The case of 2023 DZ2
Near-Earth asteroids (NEAs) that may evolve into impactors deserve detailed
threat assessment studies. Early physical characterization of a would-be
impactor may help in optimizing impact mitigation plans. We first detected NEA
2023~DZ on 27--February--2023. After that, it was found to have a Minimum
Orbit Intersection Distance (MOID) with Earth of 0.00005~au as well as an
unusually high initial probability of becoming a near-term (in 2026) impactor.
We aim to perform a rapid but consistent dynamical and physical
characterization of 2023~DZ as an example of a key response to mitigate
the consequences of a potential impact. We use a multi-pronged approach,
drawing from various methods (observational/computational) and techniques
(spectroscopy/photometry from multiple instruments), and bringing the data
together to perform a rapid and robust threat assessment.} The visible
reflectance spectrum of 2023~DZ is consistent with that of an X-type
asteroid. Light curves of this object obtained on two different nights give a
rotation period =6.27430.0005 min with an amplitude
=0.570.14~mag. We confirm that although its MOID is among the smallest
known, 2023~DZ will not impact Earth in the foreseeable future as a
result of secular near-resonant behaviour. Our investigation shows that
coordinated observation and interpretation of disparate data provides a robust
approach from discovery to threat assessment when a virtual impactor is
identified. We prove that critical information can be obtained within a few
days after the announcement of the potential impactor.Comment: Accepted for publication in Astronomy and Astrophysics, 15 page
280 one-opposition near-Earth asteroids recovered by the EURONEAR with the <i>Isaac Newton</i> Telescope
Context. One-opposition near-Earth asteroids (NEAs) are growing in number, and they must be recovered to prevent loss and mismatch risk, and to improve their orbits, as they are likely to be too faint for detection in shallow surveys at future apparitions.
Aims. We aimed to recover more than half of the one-opposition NEAs recommended for observations by the Minor Planet Center (MPC) using the Isaac Newton Telescope (INT) in soft-override mode and some fractions of available D-nights. During about 130 h in total between 2013 and 2016, we targeted 368 NEAs, among which 56 potentially hazardous asteroids (PHAs), observing 437 INT Wide Field Camera (WFC) fields and recovering 280 NEAs (76% of all targets).
Methods. Engaging a core team of about ten students and amateurs, we used the THELI, Astrometrica, and the Find_Orb software to identify all moving objects using the blink and track-and-stack method for the faintest targets and plotting the positional uncertainty ellipse from NEODyS.
Results. Most targets and recovered objects had apparent magnitudes centered around V ~ 22.8 mag, with some becoming as faint as V ~ 24 mag. One hundred and three objects (representing 28% of all targets) were recovered by EURONEAR alone by Aug. 2017. Orbital arcs were prolonged typically from a few weeks to a few years; our oldest recoveries reach 16 years. The O−C residuals for our 1854 NEA astrometric positions show that most measurements cluster closely around the origin. In addition to the recovered NEAs, 22 000 positions of about 3500 known minor planets and another 10 000 observations of about 1500 unknown objects (mostly main-belt objects) were promptly reported to the MPC by our team. Four new NEAs were discovered serendipitously in the analyzed fields and were promptly secured with the INT and other telescopes, while two more NEAs were lost due to extremely fast motion and lack of rapid follow-up time. They increase the counting to nine NEAs discovered by the EURONEAR in 2014 and 2015.
Conclusions. Targeted projects to recover one-opposition NEAs are efficient in override access, especially using at least two-meter class and preferably larger field telescopes located in good sites, which appear even more efficient than the existing surveys
A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS measured from stellar occultations
This work aims at constraining the size, shape, and geometric albedo of the
dwarf planet candidate 2002 MS4 through the analysis of nine stellar
occultation events. Using multichord detection, we also studied the object's
topography by analyzing the obtained limb and the residuals between observed
chords and the best-fitted ellipse. We predicted and organized the
observational campaigns of nine stellar occultations by 2002 MS4 between 2019
and 2022, resulting in two single-chord events, four double-chord detections,
and three events with three to up to sixty-one positive chords. Using 13
selected chords from the 8 August 2020 event, we determined the global
elliptical limb of 2002 MS4. The best-fitted ellipse, combined with the
object's rotational information from the literature, constrains the object's
size, shape, and albedo. Additionally, we developed a new method to
characterize topography features on the object's limb. The global limb has a
semi-major axis of 412 10 km, a semi-minor axis of 385 17 km, and
the position angle of the minor axis is 121 16. From
this instantaneous limb, we obtained 2002 MS4's geometric albedo and the
projected area-equivalent diameter. Significant deviations from the fitted
ellipse in the northernmost limb are detected from multiple sites highlighting
three distinct topographic features: one 11 km depth depression followed by a
25 km height elevation next to a crater-like depression with an
extension of 322 39 km and 45.1 1.5 km deep. Our results present an
object that is 138 km smaller in diameter than derived from thermal
data, possibly indicating the presence of a so-far unknown satellite. However,
within the error bars, the geometric albedo in the V-band agrees with the
results published in the literature, even with the radiometric-derived albedo