- ID:
- ivo://CDS.VizieR/J/A+A/619/A123
- Title:
- Lightcurves of Near-Earth Asteroid 3200 Phaethon
- Short Name:
- J/A+A/619/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The near-Earth asteroid 3200 Phaethon (1983 TB) is an attractive object not only from a scientific viewpoint but also because of JAXA's DESTINY+ target. The rotational lightcurve and spin properties were investigated based on the data obtained in the ground-based observation campaign of Phaethon. We aim to refine the lightcurves and shape model of Phaethon using all available lightcurve datasets obtained via optical observation, as well as our time-series observation data from the 2017 apparition. Using eight 1-2-m telescopes and an optical imager, we acquired the optical lightcurves and derived the spin parameters of Phaethon. We applied the lightcurve inversion method and SAGE (Shaping Asteroids with Genetic Evolution) algorithm to deduce the convex and non-convex shape model and pole orientations.
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- ID:
- ivo://CDS.VizieR/J/A+A/511/A49
- Title:
- Lightcurves of 12 NEAs
- Short Name:
- J/A+A/511/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Very small asteroids (VSAs) are thought to be the building blocks of larger asteroids and, as such, are interesting to study. Many of these monolithic or deeply fractured objects display rapid rotations with periods as short as several minutes. Observations of such asteroids can reveal their spin limits, which can be related to the tensile strength of their interiors. The evolution of the spins of these objects is primarily shaped by the YORP effect, the theory of which needs comparison with observations. With the 10m SALT telescope, we observed VSAs belonging to near-Earth asteroids. The obtained lightcurves were used to derive synodical periods of rotation, amplitudes, and elongations of these bodies. Results for 14 rapidly rotating asteroids were reported in the first paper in this series. Here we show lightcurves of 2 fast rotators, 9 objects with periods >=1h, and a possible non-principal axis rotator. We also list negative detections that most probably indicate asteroids with long periods and/or low amplitudes. Combining our results with the data from the literature, we obtain a set of 79 near-Earth VSAs with a median period of 0.25h (15min). By adjusting the spin limits predicted by theory to those observations, we find tentative evidence that the tensile strengths of VSAs, after scaling them to the same size, are of the same order as the minimum tensile strengths of stony meteoroids that undergo fragmentation under the atmospheric load.
- ID:
- ivo://CDS.VizieR/J/A+A/509/A94
- Title:
- Lightcurves of 14 NEAs
- Short Name:
- J/A+A/509/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report first results from our extensive survey of the very small (H>21.5mag) near-Earth asteroids. Our aim was to obtain photometric lightcurves for these faint, fast moving objects and to measure their rotation periods and amplitudes of light variations. These parameters can be used to make statistical analysis of the still little known population of the smallest asteroids, test present theories of the YORP effect as well as to study their spin limits, which are connected with their internal structure. Due to the faintness of the targets and the expected short periods of rotation, observations were performed with the large, 10-m SALT telescope in SAAO (South Africa). For most asteroids, V filter images with exposure times of 5-60 seconds were obtained with the instrument's SALTICAM's CCD camera. Even though the non-sidereal tracking was not available, the SALTICAM's relatively large field-of-view of 8'x8' helped to perform the relative photometry of the fast-moving targets. The presented asteroids have synodic periods ranging from 77s to 44min, effective diameters from 21 to 94m, and significantly elongated shapes.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A80
- Title:
- 122 long-period comets non-gravitational param.
- Short Name:
- J/A+A/633/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The original 1/a-distribution is the only observational basis for the origin of long-period comets (LPCs) and the dynamical properties of the Oort Cloud. Although they are very subtle in the motion of these comets, non-gravitational effects can cause major changes in the original semimajor axis, 1/a_ori_ We obtained reliable non-gravitational orbits for as many LPCs with small perihelion distances of q<3.1au as possible, and determined the corresponding shape of the Oort spike. We determined the osculating orbits of each comet using several data-processing methods, and selected the preferred orbit using a few specific criteria. The distribution of 1/a_ori_ for the whole comet sample was constructed using the individual Gaussian distribution we obtained for the preferred solution of each comet. The derived distribution of 1/a_ori_ for almost all known small-perihelion Oort spike comets was based on 64% of the non-gravitational orbits. This was compared with the distribution based on purely gravitational orbits, as well as with 1/a_ori_ constructed earlier for LPCs with q>3.1 au. We present a statistical analysis of the magnitudes of the non-gravitational acceleration for about 100~LPCs. The 1/a_ori_-distribution, which is based mainly on the non-gravitational orbits of small-perihelion Oort spike comets, is shifted by about 10x10^-6^au^-1^ to higher values of 1/a_ori_ compared with the distribution that is obtained when the non-gravitational effects on comet motion are ignored. We show the differences in the 1/a_ori_-distributions between LPCs with q<3.1au and those with q>3.1au. These findings indicate the important role of non-gravitational~acceleration in the motion and origin of LPCs and in the formation of the Oort Cloud.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A57
- Title:
- Lowell Photometric Database asteroid models. II.
- Short Name:
- J/A+A/617/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Information about the spin state of asteroids is important for our understanding of the dynamical processes affecting them. However, spin properties of asteroids are known for only a small fraction of the whole population. To enlarge the sample of asteroids with a known rotation state and basic shape properties, we combined sparse-in-time photometry from the Lowell Observatory Database with flux measurements from NASA's WISE satellite. We applied the light curve inversion method to the combined data. The thermal infrared data from WISE were treated as reflected light because the shapes of thermal and visual light curves are similar enough for our purposes. While sparse data cover a wide range of geometries over many years, WISE data typically cover an interval of tens of hours, which is comparable to the typical rotation period of asteroids. The search for best-fitting models was done in the framework of the Asteroids@home distributed computing project. By processing the data for almost 75000 asteroids, we derived unique shape models for about 900 of them. Some of them were already available in the DAMIT database and served us as a consistency check of our approach. In total, we derived new models for 662 asteroids, which significantly increased the total number of asteroids for which their rotation state and shape are known. For another 789 asteroids, we were able to determine their sidereal rotation period and estimate the ecliptic latitude of the spin axis direction. We studied the distribution of spins in the asteroid population. Apart from updating the statistics for the dependence of the distribution on asteroid size, we revealed a significant discrepancy between the number of prograde and retrograde rotators for asteroids smaller than about 10km. Combining optical photometry with thermal infrared light curves is an efficient approach to obtaining new physical models of asteroids. The amount of asteroid photometry is continuously growing and joint inversion of data from different surveys could lead to thousands of new models in the near future.
- ID:
- ivo://CDS.VizieR/J/A+A/471/1069
- Title:
- Lunar ephemeris long-term development
- Short Name:
- J/A+A/471/1069
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this study is to develop new analytical series representing lunar coordinates to accuracy compatible with the accuracy of the modern numerical ephemeris of the Moon.
- ID:
- ivo://CDS.VizieR/J/AJ/156/139
- Title:
- Main belt asteroid shape distrib. from Gaia DR2
- Short Name:
- J/AJ/156/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gaia Data Release 2 (Cat. I/345) includes observational data for 14099 pre-selected asteroids. From the sparsely sampled G-band photometry, we derive lower-limit light curve amplitudes for 11665 main belt asteroids (MBA) in order to provide constraints on the distribution of shapes in the asteroid main belt. Assuming a triaxial shape model for each asteroid, defined through the axial aspect ratios a>b and b=c, we find an average b/a=0.80+/-0.04 for the ensemble, which is in agreement with previous results. By combining the Gaia data with asteroid properties from the literature, we investigate possible correlations of the aspect ratio with size, semimajor axis, geometric albedo, and intrinsic color. Based on our model simulations, we find that MBAs greater than 50 km in diameter on average have higher b/a aspect ratios (are rounder) than smaller asteroids. We furthermore find significant differences in the shape distribution of MBAs as a function of the other properties that do not affect the average aspect ratios. We conclude that a more detailed investigation of shape distribution correlations requires a larger data sample than is provided in Gaia Data Release 2.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A15
- Title:
- Mars Express astrometric obs. of Martian moons
- Short Name:
- J/A+A/614/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Both Martian moons, Phobos and Deimos, have been observed during several imaging campaigns by the SRC on Mars Express. Several tens of images are obtained during mutual event observations - when the Martian moons are both observed or together with another solar system body. These observations provide new opportunities to determine the bodies' positions in their orbits. A method was sought to automate the observation of the positions of the imaged bodies. Within one image sequence a similarly accurate localization of the objects in all images should be possible. Shape models of Phobos and Deimos are applied to simulate the appearance of the bodies in the images. Matching the illuminated simulation against the observation provides a reliable determination of the bodies' location within the image. To enhance the matching confidence several corrections need to be applied to the simulation to closely reconstruct the observation. In total 884 relative positions between the different objects are provided.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A64
- Title:
- Mars moon ephemerides for 14yrs Mars Express data
- Short Name:
- J/A+A/650/A64
- Date:
- 17 Mar 2022 14:12:25
- Publisher:
- CDS
- Description:
- The Mars Express (MEX) mission has been successfully operated around Mars since 2004. Among many results, MEX has provided some of the most accurate astrometric data of the two Mars moons, Phobos and Deimos. We present new ephemerides of the Mars moons benefitting from all previously published astrometric data to the most recent MEX SRC data. Observations from 1877 until 2018 and including spacecraft measurements from Mariner 9 to MEX were included. Assuming a homogeneous interior, we fitted the forced libration amplitude of Phobos simultaneously with the Martian tidal k2/Q ratio and the initial state of the moons. Our solution of the physical libration 1.09+/-0.01 degrees deviates notably from the homogeneous solution. Considering the very low error bar, however, this may essentially suggest the necessity to consider higher order harmonics with an improved rotation model in the future. While most data could be successfully fitted, we found a disagreement between the Mars Reconnaissance Orbiter and the Mars Express astrometric data at the kilometer level, probably associated with a biased phase correction. The current solution precision is expected at the level of a few hundred meters for Phobos and several hundred meters for Deimos for the coming years. The real accuracy of our new ephemerides will have to be confirmed by comparison with independent observational means.
- ID:
- ivo://CDS.VizieR/J/AJ/154/76
- Title:
- Masses of 30 large subject asteroids
- Short Name:
- J/AJ/154/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The conventional least-squares asteroid mass determination algorithm allows us to solve for the mass of a large subject asteroid that is perturbing the trajectory of a smaller test asteroid. However, this algorithm is necessarily a first approximation, ignoring the possibility that the subject asteroid may itself be perturbed by the test asteroid, or that the encounter's precise geometry may be entangled with encounters involving other asteroids. After reviewing the conventional algorithm, we use it to calculate the masses of 30 main-belt asteroids. Compared to our previous results, we find new mass estimates for eight asteroids (11 Parthenope, 27 Euterpe, 51 Neimausa, 76 Freia, 121 Hermione, 324 Bamberga, 476 Hedwig, and 532 Herculina) and significantly more precise estimates for six others (2 Pallas, 3 Juno, 4 Vesta, 9 Metis, 16 Psyche, and 88 Thisbe). However, we also find that the conventional algorithm yields questionable results in several gravitationally coupled cases. To address such cases, we describe a new algorithm that allows the epoch state vectors of the subject asteroids to be included as solve-for parameters, allowing for the simultaneous solution of the masses and epoch state vectors of multiple subject and test asteroids. We then apply this algorithm to the same 30 main-belt asteroids and conclude that mass determinations resulting from current and future high-precision astrometric sources (such as Gaia) should conduct a thorough search for possible gravitational couplings and account for their effects.
