Abstract
We performed photometric observations of the binary near-Earth asteroid (65803) Didymos in support of the Double Asteroid Redirection Test (DART) mission that will test the Kinetic Impactor ...technology for diverting dangerous asteroids. It will hit the Didymos secondary, called Dimorphos, on 2022 September 26. We observed Didymos with 11 telescopes with diameters from 3.5 to 10.4 m during four apparitions in 2015–2021, obtaining data with rms residuals from 0.006 to 0.030 mag. We analyzed the light-curve data and decomposed them into the primary rotational and secondary orbital light curves. We detected 37 mutual eclipse/occultation events between the binary system components. The data presented here, in combination with 18 mutual events detected in 2003, provide the basis for modeling the Dimorphos orbit around the Didymos primary. The orbit modeling is discussed in detail by Scheirich & Pravec and Naidu et al. The primary light curves were complex, showing multiple extrema on some epochs. They suggest a presence of complex topography on the primary’s surface that is apparent in specific viewing/illumination geometries; the primary shape model by Naidu et al. (Icarus 348, 113777, 2020) needs to be refined. The secondary rotational light-curve data were limited and did not provide a clear solution for the rotation period and equatorial elongation of Dimorphos. We define the requirements for observations of the secondary light curve to provide the needed information on Dimorphos’s rotation and elongation when Didymos is bright in 2022 July–September before the DART impact.
We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord ...occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R sub(equiv) = 555+ or -2.5 km and geometric visual albedo p sub(v) = 0.109+ or -0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of member of = 0.087 super(+0.0268) sub(-0.0175), an equatorial radius of 569 super(+24) sub(-17)km, and a density of 1.99 + or - 0.46 g cm super(-3). The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere.
We analyze two multi-chord stellar occultations by Pluto that were observed on 2012 July 18th and 2013 May 4th, and respectively monitored from five and six sites. They provide a total of fifteen ...light curves, 12 of which were used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no haze) and pure N2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that satisfactorily fits (i.e., within the noise level) all of the 12 light curves, providing atmospheric constraints between ~1190 km (pressure ~11 mu bar) and ~1450 km (pressure -0.1 mu bar) from Pluto's center. Alternative explanations like zonal winds or vertical compositional variations of the atmosphere are unable to explain the observed mesospheric negative thermal gradient.
Context. Time series observations of the dwarf planet Haumea and the Plutinos 2003 VS2 and 2003 AZ(84) with Herschel/PACS are presented in this work. Thermal emission of these trans‐Neptunian objects ...(TNOs) were acquired as part of the ``TNOs are Cool'' Herschel Space Observatory key programme. Aims. We search for the thermal light curves at 100 and 160 mu m of Haumea and 2003 AZ(84), and at 70 and 160 mu m for 2003 VS2 by means of photometric analysis of the PACS data. The goal of this work is to use these thermal light curves to obtain physical and thermophysical properties of these icy Solar System bodies. Methods. When a thermal light curve is detected, it is possible to derive or constrain the object thermal inertia, phase integral and/or surface roughness with thermophysical modeling. Results. Haumea's thermal light curve is clearly detected at 100 and 160 mu m. The effect of the reported dark spot is apparent at 100 mu m. Different thermophysical models were applied to these light curves, varying the thermophysical properties of the surface within and outside the spot. Although no model gives a perfect fit to the thermal observations, results imply an extremely low thermal inertia (<0.5 J m(‐2) s(‐1/2) K‐1, hereafter MKS) and a high phase integral (>0.73) for Haumea's surface. We note that the dark spot region appears to be only weakly different from the rest of the object, with modest changes in thermal inertia and/or phase integral. The thermal light curve of 2003 VS2 is not firmly detected at 70 mu m and at 160 mu m but a thermal inertia of (2 +/‐ 0.5) MKS can be derived from these data. The thermal light curve of 2003 AZ(84) is not firmly detected at 100 mu m. We apply a thermophysical model to the mean thermal fluxes and to all the Herschel/PACS and Spitzer/MIPS thermal data of 2003 AZ(84), obtaining a close to pole‐on orientation as the most likely for this TNO. Conclusions. For the three TNOs, the thermal inertias derived from light curve analyses or from the thermophysical analysis of the mean thermal fluxes confirm the generally small or very small surface thermal inertias of the TNO population, which is consistent with a statistical mean value Gamma(mean) = 2.5 +/‐ 0.5 MKS.
Context. A group of trans-Neptunian objects (TNOs) are dynamically related to the dwarf planet 136108 Haumea. Ten of them show strong indications of water ice on their surfaces, are assumed to have ...resulted from a collision, and are accepted as the only known TNO collisional family. Nineteen other dynamically similar objects lack water ice absorptions and are hypothesized to be dynamical interlopers. Aims. We have made observations to determine sizes and geometric albedos of six of the accepted Haumea family members and one dynamical interloper. Ten other dynamical interlopers have been measured by previous works. We compare the individual and statistical properties of the family members and interlopers, examining the size and albedo distributions of both groups. We also examine implications for the total mass of the family and their ejection velocities. Methods. We use far-infrared space-based telescopes to observe the target TNOs near their thermal peak and combine these data with optical magnitudes to derive sizes and albedos using radiometric techniques. Using measured and inferred sizes together with ejection velocities, we determine the power-law slope of ejection velocity as a function of effective diameter. Results. The detected Haumea family members have a diversity of geometric albedos ~0.3–0.8, which are higher than geometric albedos of dynamically similar objects without water ice. The median geometric albedo for accepted family members is pV = 0.48−0.18+0.28 $0.48_{-0.18}^{+0.28}$ 0.48 −0.18 +0.28 , compared to 0.08 −0.05+0.07 $_{-0.05}^{+0.07}$ −0.05 +0.07 for the dynamical interlopers. In the size range D = 175−300 km, the slope of the cumulative size distribution is q = 3.2 −0.4+0.7 $_{-0.4}^{+0.7}$ −0.4 +0.7 for accepted family members, steeper than the q = 2.0 ± 0.6 slope for the dynamical interlopers with D < 500 km. The total mass of Haumea’s moons and family members is 2.4% of Haumea’s mass. The ejection velocities required to emplace them on their current orbits show a dependence on diameter, with a power-law slope of 0.21–0.50.
Aims. We studied the rotational properties of the dwarf planet Makemake. Methods. The photometric observations were carried out at different telescopes between 2006 and 2017. Most of the measurements ...were acquired in BVRI broad-band filters of a standard Johnson-Cousins photometric system. Results. We found that Makemake rotates more slowly than was previously reported. A possible lightcurve asymmetry suggests a double-peaked period of P = 22.8266 ± 0.0001 h. A small peak-to-peak lightcurve amplitude in R-filter A = 0.032 ± 0.005 mag implies an almost spherical shape or near pole-on orientation. We also measured BVRI colours and the R-filter phase-angle slope and revised the absolute magnitudes. The absolute magnitude of Makemake has remained unchanged since its discovery in 2005. No direct evidence of a newly discovered satellite was found in our photometric data; however, we discuss the possible existence of another larger satellite.
The young Datura asteroid family Vokrouhlický, D.; Pravec, P.; Ďurech, J. ...
Astronomy and astrophysics (Berlin),
02/2017, Letnik:
598
Journal Article
Recenzirano
Odprti dostop
Context. Asteroid families are the outcomes of disruption or cratering events on a size and energy scales that are not reproducible in laboratory experiments. Overall structure, as well as properties ...of individual members, in the old families could have been changed since their formation. Therefore young families preserve best the characteristics of the initial event. Aims. We study the most suitable known asteroid family with an age of less than 1 Myr, the Datura family. We aim (i) to obtain information about rotation state and shape of the largest members in the family; and (ii) to constrain its debiased population down to couple of hundreds of meters in size. Methods. We have analyzed the up-to-date catalog of orbital elements of main belt asteroids. We evaluated the detection efficiency of Catalina Sky Survey (CSS) in regard to detections of members in the Datura family, and we have used our photometric observations and lightcurve inversion methods to determine the rotation states and shapes of the largest members of the family. Results. We determined rotation periods of the seven largest members of the Datura family, and we also derived accurate mean absolute magnitudes for six of them. Except for the largest fragment (1270) Datura, the asteroids tend to have long rotation periods and large amplitude of the lightcurve, witnessing an elongated shape. For the four largest asteroids, our observations allow us to resolve rotation pole and a rough shape. All of them are prograde-rotating and have the latitude of the rotation pole >50°. Our search in orbital catalogs resulted in the discovery of many small, sub-kilometer members of the Datura family. Using the CSS detection efficiency, we inverted this information into the debiased population of Datura family members. We show that the mass and angular momentum content in small fragments is negligible compared to the largest fragment (1270) Datura. These findings may help to constrain the formation mechanism of the family.
We present estimates of the basic physical properties including size and albedo of the extreme Centaur 2013 AZ sub(60). These properties have been derived from optical and thermal infrared ...measurements. Our optical measurements revealed a probable full period of approximate9.4 h with a shallow amplitude of 4.5%. By combining optical brightness information and thermal emission data, we are able to derive a diameter of 62.3 + or - 5.3 km and a geometric albedo of 2.9%, which corresponds to an extremely dark surface. Additionally, our finding of > ~50 Jm super(-2) K super(-1) s super(-1/2) for the thermal inertia is also remarkable for objects in such a distance. The results of dynamical simulations yield an unstable orbit, with a 50% probability that the target will be ejected from the solar system within 700 000 yr. The current orbit of this object and its instability could imply a pristine cometary surface. This possibility agrees with the observed low geometric albedo and red photometric colour indices for the object, which match the surface of a dormant comet well, as would be expected for a long-period cometary body approaching perihelion. Although it was approaching ever closer to the Sun, however, the object exhibited star-like profiles in each of our observations, lacking any sign of cometary activity. According to the albedo, 2013 AZ sub(60) is a candidate for the darkest body among the known trans-Neptunian objects.
PDF
