Context. The rotation states of small asteroids are affected by a net torque arising from an anisotropic sunlight reflection and thermal radiation from the asteroids’ surfaces. On long timescales, ...this so-called YORP effect can change asteroid spin directions and their rotation periods. Aims. We analyzed lightcurves of four selected near-Earth asteroids with the aim of detecting secular changes in their rotation rates that are caused by YORP or at least of putting upper limits on such changes. Methods. We use the lightcurve inversion method to model the observed lightcurves and include the change in the rotation rate dω/ dt as a free parameter of optimization. To enlarge the time line of observations and to increase the sensitivity of the method, we collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used thermal infrared data from the WISE spacecraft and estimated their size and thermal inertia by means of a thermophysical model. We also used the currently available optical and radar astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. Results. We detected a YORP acceleration of dω/ dt = (1.9 ± 0.3) × 10-8 rad d-2 for asteroid Cacus. The current astrometric data set is not sufficient to provide detection of the Yarkovsky effect in this case. For Toro, we have a tentative (2σ) detection of YORP from a significant improvement of the lightcurve fit for a nonzero value of dω/ dt = 3.0 × 10-9 rad d-2. We note an excellent agreement between the observed secular change of the semimajor axis da/ dt and the theoretical expectation for densities in the 2–2.5 g cm-3 range. For asteroid Eger, we confirmed the previously published YORP detection with more data and updated the YORP value to (1.1 ± 0.5) × 10-8 rad d-2. We also updated the shape model of asteroid Ra-Shalom and put an upper limit for the change of the rotation rate to | dω/ dt | ≲ 1.5 × 10-8 rad d-2. Ra-Shalom has a greater than 3σ Yarkovsky detection with a theoretical value consistent with observations assuming its size and/or density is slightly larger than the nominally expected values. Using the convex shape models and spin parameters reconstructed from lightcurves, we computed theoretical YORP values and compared them with those measured. They agree with each other within the expected uncertainties of the model.
A description of the software designed for controlling robotic observatories is given. Its main features and functional capabilities are described. Special attention is paid to approaches to ...improving the utilization of the telescope observation time, which is its main resource. A solution for the automation of routine observational tasks the execution of which directly affects the efficiency of the entire system is proposed. It is shown that the use of the new software increased the total coverage of the celestial sphere during an observational night by 25–30%. The main discoveries and achievements of two remote robotic observatories controlled by this software are presented. During the operation of these observatories, more than half-a-million astrometric measurements of small bodies of the Solar System were made, more than hundred photometric light curves were obtained, and a number of near-Earth asteroids and comets were discovered. The optical component of the afterglow of gamma-ray bursts was observed.
•We determined the orbital vector with a substantially greater accuracy than before.•We found a quadratic drift of mean anomaly of the satellite consistent with zero.•The drift supports the theory of ...an equilibrium between BYORP and tidal torques.•We derived a product of rigidity and quality factor of μQ=1.3×107Pa.•The low value of μQ calls for a re-thinking of the tidal energy dissipation.
Using our photometric observations taken between April 1996 and January 2013 and other published data, we derived properties of the binary near-Earth Asteroid (175706) 1996 FG3 including new measurements constraining evolution of the mutual orbit with potential consequences for the entire binary asteroid population. We also refined previously determined values of parameters of both components, making 1996 FG3 one of the most well understood binary asteroid systems. With our 17-year long dataset, we determined the orbital vector with a substantially greater accuracy than before and we also placed constraints on a stability of the orbit. Specifically, the ecliptic longitude and latitude of the orbital pole are 266° and -83°, respectively, with the mean radius of the uncertainty area of 4°, and the orbital period is 16.1508±0.0002h (all quoted uncertainties correspond to 3σ). We looked for a quadratic drift of the mean anomaly of the satellite and obtained a value of 0.04±0.20deg/yr2, i.e., consistent with zero. The drift is substantially lower than predicted by the pure binary YORP (BYORP) theory of McMahon and Scheeres (McMahon, J., Scheeres, D. 2010. Icarus 209, 494–509) and it is consistent with the tigidity and quality factor of μQ=1.3×107Pa using the theory that assumes an elastic response of the asteroid material to the tidal forces. This very low value indicates that the primary of 1996 FG3 is a ‘rubble pile’, and it also calls for a re-thinking of the tidal energy dissipation in close asteroid binary systems.
The exploration and investigation of near-Earth outer space (NES) have highlighted attention to potential threats, namely the dangers posed by asteroids and the emergence of techno-genic pollution ...known as space debris (SD). To address these challenges, an international initiative known as the ISON Optical Observatories Global Network was established. The International Scientific Optical Network (ISON) volunteer project commenced in 2004 intending to serve as an open repository of scientific data related to NES objects. At its zenith, the project collaborated with 33 observatories across 17 countries, operating 100 telescopes. Currently, ISON conducts its research using approximately 50 optical telescopes situated in 23 observatories across Europe, Asia, the Far East, Africa, and North & South America. The network is coordinated in conjunction with the dedicated company Research and Development Institution ISON Orbital Dynamics (RD ISON-OD), which owns 32 telescopes, observation scheduling centers, and databases focusing on SD and asteroids. ISON actively monitors the entire Geostationary Earth Orbit (GEO) region, tracking objects at GEO, Geostationary transfer orbit (GTO), High Earth Orbit (HEO), and Low Earth Orbit (LEO), while also maintaining the orbits of around 10,000 space objects. The data collected by ISON on space debris contribute to validating space debris population models and conducting conjunction assessment analyses for satellites in high orbits. Additionally, ISON is developing technology for asteroid surveys using small telescopes, providing follow-up observations, and conducting regular photometry observations of near-Earth asteroids. The project has resulted in the discovery of approximately 1600 new asteroids, obtaining 1.25 million astrometry measurements, and acquiring around 700 light curves for 300 asteroids. Space debris represents a unique subject of study, as it intersects the interests of various industries, scientific institutions, and governmental agencies.
Context.
The rotation state of small asteroids is affected by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, which is a net torque caused by solar radiation directly reflected and thermally ...reemitted from the surface. Due to this effect, the rotation period slowly changes, which can be most easily measured in light curves because the shift in the rotation phase accumulates over time quadratically.
Aims.
By new photometric observations of selected near-Earth asteroids, we want to enlarge the sample of asteroids with a detected YORP effect.
Methods.
We collected archived light curves and carried out new photometric observations for asteroids (10115) 1992 SK, (1620) Geographos, and (1685) Toro. We applied the method of light curve inversion to fit observations with a convex shape model. The YORP effect was modeled as a linear change of the rotation frequency
υ
≡ d
ω
∕d
t
and optimized together with other spin and shape parameters.
Results.
We detected the acceleration
υ
= (8.3 ± 0.6) × 10
−8
rad d
−2
of the rotation for asteroid (10115) 1992 SK. This observed value agrees well with the theoretical value of YORP-induced spin-up computed for our shape and spin model. For (1685) Toro, we obtained
υ
= (3.3 ± 0.3) × 10
−9
rad d
−2
, which confirms an earlier tentative YORP detection. For (1620) Geographos, we confirmed the previously detected YORP acceleration and derived an updated value of
υ
with a smaller uncertainty. We also included the effect of solar precession into our inversion algorithm, and we show that there are hints of this effect in Geographos’ data.
Conclusions.
The detected change of the spin rate of (10115) 1992 SK has increased the total number of asteroids with YORP detection to ten. In all ten cases, the d
ω
∕d
t
value is positive, so the rotation of these asteroids is accelerated. It is unlikely to be just a statistical fluke, but it is probably a real feature that needs to be explained.
Context. The spin state of small asteroids can change on a long timescale by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises from anisotropically scattered ...sunlight and proper thermal radiation from an irregularly-shaped asteroid. The secular change in the rotation period caused by the YORP effect can be detected by analysis of asteroid photometric lightcurves. Aims. We analyzed photometric lightcurves of near-Earth asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible deviations from the constant rotation caused by the YORP effect. Methods. We carried out new photometric observations of the three asteroids, combined the new lightcurves with archived data, and used the lightcurve inversion method to model the asteroid shape, pole direction, and rotation rate. The YORP effect was modeled as a linear change in the rotation rate in time dω/dt. Values of dω/dt derived from observations were compared with the values predicted by theory. Results. We derived physical models for all three asteroids. We had to model Eger as a nonconvex body because the convex model failed to fit the lightcurves observed at high phase angles. We probably detected the acceleration of the rotation rate of Eger dω/dt = (1.4 ± 0.6) × 10-8 rad d-2 (3σ error), which corresponds to a decrease in the rotation period by 4.2 ms yr-1. The photometry of Cerberus and Ra-Shalom was consistent with a constant-period model, and no secular change in the spin rate was detected. We could only constrain maximum values of |dω/dt| < 8 × 10-9 rad d-2 for Cerberus, and |dω/dt| < 3 × 10-8 rad d-2 for Ra-Shalom.
Opposition effect of Trojan asteroids Shevchenko, V.G.; Belskaya, I.N.; Slyusarev, I.G. ...
Icarus (New York, N.Y. 1962),
2012, 2012-01-00, 20120101, Letnik:
217, Številka:
1
Journal Article
Recenzirano
► We have obtained detailed magnitude–phase relations for three Jupiter Trojans. ► The magnitude–phase relations are linear down to phase angle of 0.1–0.2°. ► We have not revealed any noticeable ...opposition brightening for the V and R bands. ► Such behavior is inherent for dark surfaces where single scattering plays main role.
CCD-photometry of three Jupiter Trojan asteroids were carried out to study their opposition effect. We obtained well-sampled magnitude–phase curves for (588) Achilles, (884) Priamus, and (1143) Odysseus in the maximal attainable phase angle range down to 0.1–0.2°. The magnitude–phase relations have a linear behavior in all observed range of phase angles and do not show any non-linear opposition brightening. We have not found any confident differences between phase slopes measured in B, V and R bands. The values of the measured phase slopes of Trojans are different from available data for Centaurs. They are within the range of phase slopes measured for some low-albedo main belt asteroids, also exhibit a linear behavior down to small phase angles. An absence of non-linear opposition brightening puts constraints on the surface properties of the studied objects, assuming very dark surfaces where single scattering plays dominating role.
We also determined the rotation periods, amplitudes, the values of color indexes B–V and V–R, and the absolute magnitudes of these asteroids.
Chromatic Afterglow of GRB 200829A Pankov, N. S.; Pozanenko, A. S.; Minaev, P. Yu ...
Astronomy letters,
03/2023, Letnik:
49, Številka:
3
Journal Article
Recenzirano
We present the results of our analysis of multiwavelength observations for the long gamma-ray burst GRB 200829A. The burst redshift
has been determined photometrically at the afterglow phase. In ...gamma rays the event is one of the brightest (in isotropic equivalent),
erg. The multicolor light curve of the GRB 200829A afterglow is characterized by chromatic behavior and the presence of a plateau gradually transitioning into a power-law decay that can also be interpreted as a quasi-synchronous inhomogeneity (flare). We assume that the presence of a chromatic inhomogeneity in the early afterglow is consistent with the model of a structured jet.
Aims. Asteroid (1862) Apollo is one of two asteroids in which the YORP effect was detected. We carried out new photometric observations of Apollo in April 2007 to enlarge the time line and to derive ...a more precise shape and spin state model. We also observed another YORP-candidate, asteroid (25143) Itokawa, in December 2006 and January 2007 to obtain a longer time line. An estimation of the YORP strength on Itokawa based on its precise shape model from the Hayabusa mission predicted the deceleration to be already observable during the 2007 apparition. Methods. We used the lightcurve inversion method to model the shape and spin state of Apollo. For Itokawa, the shape and pole direction are known to a high degree of accuracy from the Hayabusa mission, so we used a modified version of lightcurve inversion with only two free parameters – the rotation period and its linear change in time. Results. The new model of Apollo confirms earlier results. The observed acceleration of Apollo's rotation rate is $(5.5 \pm 1.2) \times 10^{-8}\,\mathrm{rad\,d}^{-2}$, which is in agreement with the theoretically predicted value. For Itokawa, the theoretical YORP value is sensitive to the resolution of the shape model and lies in the range from -2 to $-3\times 10^{-7}\,\mathrm{rad\,d}^{-2}$. This is inconsistent with results of lightcurve inversion that place an upper limit to the change of Itokawa's rotation rate ∼$1.5 \times 10^{-7}\,\mathrm{rad}\,\mathrm{d}^{-2}$.
Asteroid pairs: A complex picture Pravec, P.; Fatka, P.; Vokrouhlický, D. ...
Icarus (New York, N.Y. 1962),
11/2019, Letnik:
333
Journal Article
Recenzirano
We studied a sample of 93 asteroid pairs, i.e., pairs of genetically related asteroids that are on highly similar heliocentric orbits. We estimated times elapsed since separation of pair members ...(i.e., pair age) that are between 7 × 103 yr and a few 106 yr. With photometric observations, we derived the rotation periods P1 for all the primaries (i.e., the larger members of asteroid pairs) and a sample of secondaries (the smaller pair members). We derived the absolute magnitude differences of the studied asteroid pairs that provide their mass ratios q. For a part of the studied pairs, we refined their WISE geometric albedos and collected or estimated their taxonomic classifications. For 17 asteroid pairs, we also determined their pole positions. In two pairs where we obtained the spin poles for both pair components, we saw the same sense of rotation for both components and constrained the angles between their original spin vectors at the time of their separation. We found that the primaries of 13 asteroid pairs in our sample are actually binary or triple systems, i.e., they have one or two bound, orbiting secondaries (satellites). As a by-product, we found also 3 new young asteroid clusters (each of them consisting of three known asteroids on highly similar heliocentric orbits). We compared the obtained asteroid pair data with theoretical predictions and discussed their implications. We found that 86 of the 93 studied asteroid pairs follow the trend of primary rotation period vs mass ratio that was found by Pravec et al. (2010). Of the 7 outliers, 3 appear insignificant (may be due to our uncertain or incomplete knowledge of the three pairs), but 4 are high mass ratio pairs that were unpredicted by the theory of asteroid pair formation by rotational fission. We discuss a (remotely) possible way that they could be created by rotational fission of flattened parent bodies followed by re-shaping of the formed components. The 13 asteroid pairs with binary primaries are particularly interesting systems that place important constraints on formation and evolution of asteroid pairs. We present two hypotheses for their formation: The asteroid pairs having both bound and unbound secondaries could be “failed asteroid clusters”, or they could be formed by a cascade primary spin fission process. Further studies are needed to reveal which of these two hypotheses for formation of the paired binary systems is real.
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