Context.
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.
Aims.
We aim to improve the orbits of VIs and eliminate their status by data mining the existing image archives.
Methods.
Within the European Near Earth Asteroids Research (EURONEAR) project, we developed the Virtual Impactor search using Mega-Precovery (VIMP) software, which is 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.
Results.
We applied VIMP to mine the data of 451,914
Blanco
/DECam images observed between 12 September 2012 and 11 July 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 4,000 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 ten objects. Most eliminated VIs (70%) had short initial arcs of less than five 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.
Conclusions.
Large etendue imaging archives represent great assets to search for serendipitous encounters of faint asteroids and VIs.
Context. Dynamical and albedo properties suggest that asteroids in cometary orbits (ACOs) are dormant or extinct comets. Their study provides new insights for understanding the end-states of comets ...and the size of the comet population. Aims. We intend to study the visible and near-infrared (NIR) spectral properties of different ACO populations and compare them to the independently determined properties of comets. Methods. We select our ACOs sample based on published dynamical criteria and present our own observational results obtained using the 10.4 m Gran Telescopio Canarias (GTC), the 4.2 m William Herschel Telescope (WHT), the 3.56 m Telescopio Nazionale Galileo (TNG), and the 2.5 m Isaac Newton Telescope (INT), all located at the El Roque de los Muchachos Observatory (La Palma, Spain), and the 3.0 m NASA Infrared Telescope Facility (IRTF), located at the Mauna Kea Observatory, in Hawaii. We include in the analysis the spectra of ACOs obtained from the literature. We derive the spectral class and the visible and NIR spectral slopes. We also study the presence of hydrated minerals by studying the 0.7 μm band and the UV-drop below 0.5 μm associated with phyllosilicates. Results. We present new observations of 17 ACOs, 11 of them observed in the visible, 2 in the NIR and 4 in the visible and NIR. We also discuss the spectra of 12 ACOs obtained from the literature. All but two ACOs have a primitive-like class spectrum (X or D-type). Almost 100% of the ACOs in long-period cometary orbits (Damocloids) are D-types. Those in Jupiter family comet orbits (JFC-ACOs) are ∼60% D-types and ∼40% X-types. The mean spectral slope S′ of JFC-ACOs is 9.7 ± 4.6%/1000 Å and for the Damocloids this is 12.2 ± 2.0%/1000 Å. No evidence of hydration on the surface of ACOs is found from their visible spectra. The spectral slope and spectral class distribution of ACOs is similar to that of comets. Conclusions. The spectral taxonomical classification and the spectral slope distribution of ACOs, and the lack of spectral features indicative of the presence of hydrated minerals on their surface, strongly suggest that ACOs are likely dormant or extinct comets.
ABSTRACT
The near-Earth objects with low-Jovian Tisserand invariant (TJ) represent about 9 per cent of the known objects orbiting in the near-Earth space, being subject of numerous planetary ...encounters and large temperature variations. We aim to make a spectral characterization for a large sample of NEOs with TJ ≤ 3.1. Consequently, we can estimate the fraction of bodies with a cometary origin. We report new spectral observations for 26 low-TJ NEOs. The additional spectra, retrieved from different public data bases, allowed us to perform the analysis over a catalogue of 150 objects. We classified them with respect to Bus-DeMeo taxonomic system. The results are discussed regarding their orbital parameters. The taxonomic distribution of low-TJ NEOs differs from the entire NEOs population. Consequently, TJ ∼ 3 can act as a composition border too. We found that 56.2 per cent of low-TJ NEOs have comet-like spectra and they become abundant (79.7 per cent) for TJ ≤ 2.8. 16 D-type objects have been identified in this population, distributed on orbits with an average TJ = 2.65 ± 0.6. Using two dynamical criteria, together with the comet-like spectral classification as an identification method and by applying an observational bias correction, we estimate that the fraction of NEOs with a cometary nature and H ∈ (14, 21) mag has the lower and upper bounds (1.5 ± 0.15) and (10.4 ± 2.2) per cent. Additionally, our observations show that all extreme cases of low-perihelion asteroids (q ≤ 0.3 au) belong to S-complex.
Context. We continue to study star formation in dwarf galaxies located in nearby clusters. Aims. Known physical and chemical relations outlining the formation and evolution of dwarfs is compared in ...different environments, including the Local Volume (LV) and some nearby clusters studied previously. Methods. We used the TNG telescope for four nights in 2010 to acquire deep near-infrared imaging in K′ of 45 star forming dwarf galaxies located in the Abell 779, Abell 1367, Abell 1656 (Coma), and Abell 2151 (Hercules) clusters. Results. Surface photometry was approached based on past experience by using the sech law to account for the outer old stellar contribution plus a Gaussian component to model the inner starburst, proving the blue compact dwarf (BCD) classification of most targets. Sech central surface brightness, semimajor axis, sech, and total apparent magnitude were measured, allowing to estimate size, absolute luminosity and mass for all targets. Conclusions. The physical correlations between size, central brightness, and NIR luminosity appear to hold, but previously known linear fits break above MSK = − 19 for Abell 779, Abell 1367 and especially for Hercules, while the dwarf fundamental plane (FP) is probed by only half cluster members, suggesting harassment by the denser cluster environments. Nevertheless, the chemical relations between the oxygen abundance, luminosity, gas mass, baryonic mass, and gas fraction in a closed box model are probed by most members of the four studied clusters, and the starburst grows linearly with the K′ luminosity.
Variable x-ray and γ-ray emission is characteristic of the most extreme physical processes in the universe. We present multiwavelength observations of a unique γ-ray—selected transient detected by ...the Swift satellite, accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z = 0.3534. Its high-energy emission has lasted much longer than any γ-ray burst, whereas its peak luminosity was ∼100 times higher than bright active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a rare mechanism involving the massive black hole in the nucleus of that galaxy.
ABSTRACT
NASA’s Transiting Exoplanet Survey Satellite (TESS) is performing a homogeneous survey of the sky from space in search of transiting exoplanets. The collected data are also being used for ...detecting passing Solar system objects, including 17 new outer Solar system body candidates located at geocentric distances in the range 80–200 au, that need follow-up observations with ground-based telescope resources for confirmation. Here, we present results of a proof-of-concept mini-survey aimed at recovering two of these candidates that was carried out with the 4.2-m William Herschel Telescope and a QHY600L CMOS camera mounted at its prime focus. For each candidate attempted, we surveyed a square of over 1○ × 1○ around its expected coordinates in Sloan r′. The same patch of sky was revisited in five consecutive or nearly consecutive nights, reaching S/N > 4 at $r^{\prime }\, \lt $23 mag. We focused on the areas of sky around the circumpolar TESS candidates located at (07h:00m:15s, +86○:55′:19″), 202.8 au from Earth, and (06h:39m:47s, +83○:43′:54″) at 162.1 au, but we could not recover either of them at $r^{\prime }\, \le$23 mag. Based on the detailed analysis of the acquired images, we confirm that either both candidates are much fainter than predicted or that they are false positives.
Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently. Backward integrations of their orbits indicated that they separated gently with low relative ...velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process may explain their formation-critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primary's spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
The first known asteroid with the orbit inside that of Venus is 2020 AV2. 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 AV2 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 AV2 in the 0.5–1.5-μm wavelength interval. These were performed with the Nordic Optical Telescope and the William Herschel Telescope. Based on the obtained spectra, we classify 2020 AV2 as a Sa-type asteroid. We estimate the diameter of this Vatira to be $1.50_{-0.65}^{+1.10}$ km by considering the average albedo of A-type and S-complex asteroids ($p_V=0.23_{-0.08}^{+0.11}$), and the absolute magnitude (H = 16.40 ± 0.78 mag). The wide spectral band around 1 μm shows the signature of an olivine-rich composition. The estimated band centre BIC = 1.08 ± 0.02 μm corresponds to a ferroan olivine mineralogy similar to that of brachinite meteorites.
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