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See detailTRAPPIST comet production rates: 6P/d'Arrest, 67P/C-G, 4P/Faye, 19P/Borrelly, 57P/D-N-D
Jehin, Emmanuel ULiege; Moulane, Youssef ULiege; Manfroid, Jean ULiege et al

in The Astronomer's Telegram (2021), 15117

E. Jehin, Y. Moulane, J. Manfroid, M. Vander Donckt, S. Hmiddouch, F. Pozuelos, M. Ferrais, and D. Hutsemekers (STAR Institute, University of Liege) report that they obtained from TRAPPIST-South (code=I40 ... [more ▼]

E. Jehin, Y. Moulane, J. Manfroid, M. Vander Donckt, S. Hmiddouch, F. Pozuelos, M. Ferrais, and D. Hutsemekers (STAR Institute, University of Liege) report that they obtained from TRAPPIST-South (code=I40, Chile) robotic telescopes (Jehin el al. 2011) observations using HB narrowband filters (Farnham et al. 2000) for the following comets and computed preliminary production rates at 10.000 km using a Haser Model (Vp=Vd=1km/s) (Haser 1957). [less ▲]

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See detailRotation period determination of NASA Lucy mission target (52246) Donaldjohanson
Ferrais, Marin ULiege; Jehin, Emmanuel ULiege; Manfroid, Jean ULiege et al

in Bulletin of the American Astronomical Society (2021, October 01), 53(7), 30619

(52246) Donaldjohanson is a small 4 km in diameter main-belt asteroid, and a C-type belonging to the Erigone collisional family [1]. The Lucy Mission is a NASA Discovery class mission that will launch a ... [more ▼]

(52246) Donaldjohanson is a small 4 km in diameter main-belt asteroid, and a C-type belonging to the Erigone collisional family [1]. The Lucy Mission is a NASA Discovery class mission that will launch a spacecraft in October 2021 to explore several Jupiter Trojan asteroids. On its way to Jupiter's orbit, Lucy will first encounter Donaldjohanson in 2025. However, few physical characteristics are known about this body at present time. <P />Here, we present new photometric observations of Donaldjohanson acquired from November 2020 to February 2021 with the two 60-cm TRAPPIST telescopes [3]. During this apparition, we obtained 91 individual series that revealed a very slow rotator featuring a large amplitude of the rotational lightcurve. We determined a rotation period of ~252 h and an amplitude of ~1 magnitude. <P />References: <P />[1] Nesvorný, D., Broz, M., Carruba, V., et al., 2015, In: Asteroids IV, pp. 297-321 <P />[2] Marchi, S., Levison, H., Olkin, C., et al., 2020, EPSC, 163 <P />[3] Jehin, E., Gillon, M., Queloz, D., et al., 2011, The Messenger, 145, 2 [less ▲]

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See detailPhysical characterization of the active asteroid (6478) Gault from a multi-apparition campaign (2018-2020)
Devogele, Maxime; Ferrais, Marin ULiege; Jehin, Emmanuel ULiege et al

in Bulletin of the American Astronomical Society (2021, October 01), 53(7), 30904

(6478) Gault is a main-belt asteroid that was found to display cometary activity in late 2018-early 2019 [1]. During its 2018-2019 apparition, Gault experienced several activity events leading to the ... [more ▼]

(6478) Gault is a main-belt asteroid that was found to display cometary activity in late 2018-early 2019 [1]. During its 2018-2019 apparition, Gault experienced several activity events leading to the development of up to three distinct tails [2,3,4]. Many hypotheses such as impacts with smaller objects, YORP induced spin-up [5], sublimation of volatiles [6], or even the presence of a satellite in a highly eccentric and chaotic orbit, were considered to explain these events. <P />In this talk we present new photometric and spectroscopic observations of Gault obtained during the 2018-2019 and 2020 apparitions. These observations were obtained both when Gault was active (during the 2018-2019 apparition) and when it was found to be inactive during the 2020 apparition. For the first time we determine an accurate rotation period with high confidence of P=2.4929 ± 0.0003 h with a low amplitude of only 0.06 mag. This rotation period associated with a low lightcurve amplitude is consistent with a bulk density no smaller than 1.85 g cm3 in order for its activity to be triggered by the YORP spin-up mechanism. Our spectral analysis is consistent with Gault being of ordinary chondrite-like composition. Several spectra and a large datasets of broad band spectro-photometric observations obtained over the two oppositions do not show any sign of spectral variation over time. <P />Finally, we did not find any statistically significant signal of non-gravitational accelerations due to its activity even after the addition of previously unidentified detections of Gault dating back to 1958, which increased its orbital arc by a factor of almost 2. <P />These results were published in [7]. <P />References: <P />[1]: Smith K. W., Denneau L., Vincent J. B., et al., 2019, CBET, 4594 <P />[2]: Jehin E., Ferrais M., Moulane Y., et al. 2019, CBET, 4606 <P />[3]: Ye Q., et al., 2019, The ApJ Letters, 874, L16 <P />[4]: Jewitt D., Kim Y., Luu J., et al. 2019, The ApJ Letters, 876, L19 <P />[5]: Kleyna J. T., et al., 2019, The ApJ Letters, 874, L20 <P />[6]: Ferrín I., Fornari C., Acosta A., 2019, MNRAS, 490, 219 <P />[7]: Devogèle M., Ferrais M, Jehin E, et al. 2021, MNRAS, 505, 245 [less ▲]

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See detailProperties of slowly rotating asteroids from the Convex Inversion Thermophysical Model
Marciniak, A.; Ďurech, J.; Alí-Lagoa, V. et al

in Astronomy and Astrophysics (2021), 654

Context. Recent results for asteroid rotation periods from the TESS mission showed how strongly previous studies have underestimated the number of slow rotators, revealing the importance of studying those ... [more ▼]

Context. Recent results for asteroid rotation periods from the TESS mission showed how strongly previous studies have underestimated the number of slow rotators, revealing the importance of studying those targets. For most slowly rotating asteroids (those with P > 12 h), no spin and shape model is available because of observation selection effects. This hampers determination of their thermal parameters and accurate sizes. Also, it is still unclear whether signatures of different surface material properties can be seen in thermal inertia determined from mid-infrared thermal flux fitting. Aims: We continue our campaign in minimising selection effects among main belt asteroids. Our targets are slow rotators with low light-curve amplitudes. Our goal is to provide their scaled spin and shape models together with thermal inertia, albedo, and surface roughness to complete the statistics. Methods: Rich multi-apparition datasets of dense light curves are supplemented with data from Kepler and TESS spacecrafts. In addition to data in the visible range, we also use thermal data from infrared space observatories (mainly IRAS, Akari and WISE) in a combined optimisation process using the Convex Inversion Thermophysical Model. This novel method has so far been applied to only a few targets, and therefore in this work we further validate the method itself. Results: We present the models of 16 slow rotators, including two updated models. All provide good fits to both thermal and visible data.The obtained sizes are on average accurate at the 5% precision level, with diameters found to be in the range from 25 to 145 km. The rotation periods of our targets range from 11 to 59 h, and the thermal inertia covers a wide range of values, from 2 to <400 J m^−2 s^−1∕2 K^−1, not showing any correlation with the period. Conclusions: With this work we increase the sample of slow rotators with reliable spin and shape models and known thermal inertia by 40%. The thermal inertia values of our sample do not display a previously suggested increasing trend with rotation period, which mightbe due to their small skin depth. [less ▲]

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See detailVLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis
Vernazza, P.; Ferrais, Marin ULiege; Jorda, L. et al

in Astronomy and Astrophysics (2021), 654

Context. Until recently, the 3D shape, and therefore density (when combining the volume estimate with available mass estimates), and surface topography of the vast majority of the largest (D ≥ 100 km ... [more ▼]

Context. Until recently, the 3D shape, and therefore density (when combining the volume estimate with available mass estimates), and surface topography of the vast majority of the largest (D ≥ 100 km) main-belt asteroids have remained poorly constrained. The improved capabilities of the SPHERE/ZIMPOL instrument have opened new doors into ground-based asteroid exploration. Aims: To constrain the formation and evolution of a representative sample of large asteroids, we conducted a high-angular-resolution imaging survey of 42 large main-belt asteroids with VLT/SPHERE/ZIMPOL. Our asteroid sample comprises 39 bodies with D ≥ 100 km and in particular most D ≥ 200 km main-belt asteroids (20/23). Furthermore, it nicely reflects the compositional diversity present in the main belt as the sampled bodies belong to the following taxonomic classes: A, B, C, Ch/Cgh, E/M/X, K, P/T, S, and V. Methods: The SPHERE/ZIMPOL images were first used to reconstruct the 3D shape of all targets with both the ADAM and MPCD reconstruction methods. We subsequently performed a detailed shape analysis and constrained the density of each target using available mass estimates including our own mass estimates in the case of multiple systems. Results: The analysis of the reconstructed shapes allowed us to identify two families of objects as a function of their diameters, namely "spherical" and "elongated" bodies. A difference in rotation period appears to be the main origin of this bimodality. In addition, all but one object (216 Kleopatra) are located along the Maclaurin sequence with large volatile-rich bodies being the closest to the latter. Our results further reveal that the primaries of most multiple systems possess a rotation period of shorter than 6 h and an elongated shape (c∕a ≤ 0.65). Densities in our sample range from ~1.3 g cm^−3 (87 Sylvia) to ~4.3 g cm^−3 (22 Kalliope). Furthermore, the density distribution appears to be strongly bimodal with volatile-poor (ρ ≥ 2.7 g cm^−3) and volatile-rich (ρ ≤ 2.2 g cm^−3) bodies. Finally, our survey along with previous observations provides evidence in support of the possibility that some C-complex bodies could be intrinsically related to IDP-like P- and D-type asteroids, representing different layers of a same body (C: core; P/D: outer shell). We therefore propose that P/ D-types and some C-types may have the same origin in the primordial trans-Neptunian disk. [less ▲]

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See detailA fast rotation period and large amplitude for PHA 2021 NY1
Ferrais, Marin ULiege; Jehin, Emmanuel ULiege

in The Astronomer's Telegram (2021), 14944

We report optical light curve observations of the near earth asteroid 2021 NY1. It was first observed with Pan-STARRS 1, Haleakala, on 2021, July 7 and has been classified by the Minor Planet Center as a ... [more ▼]

We report optical light curve observations of the near earth asteroid 2021 NY1. It was first observed with Pan-STARRS 1, Haleakala, on 2021, July 7 and has been classified by the Minor Planet Center as a potentially hazardous asteroid. [less ▲]

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See detail(216) Kleopatra, a low density critically rotating M-type asteroid
Marchis, F.; Jorda, L.; Vernazza, P. et al

in Astronomy and Astrophysics (2021), 653

Context. The recent estimates of the 3D shape of the M/Xe-type triple asteroid system (216) Kleopatra indicated a density of ~5 g cm^−3, which is by far the highest for a small Solar System body. Such a ... [more ▼]

Context. The recent estimates of the 3D shape of the M/Xe-type triple asteroid system (216) Kleopatra indicated a density of ~5 g cm^−3, which is by far the highest for a small Solar System body. Such a high density implies a high metal content as well as a low porosity which is not easy to reconcile with its peculiar "dumbbell" shape. Aims: Given the unprecedented angular resolution of the VLT/SPHERE/ZIMPOL camera, here, we aim to constrain the mass (via the characterization of the orbits of the moons) and the shape of (216) Kleopatra with high accuracy, hence its density. Methods: We combined our new VLT/SPHERE observations of (216) Kleopatra recorded during two apparitions in 2017 and 2018 with archival data from the W. M. Keck Observatory, as well as lightcurve, occultation, and delay-Doppler images, to derive a model of its 3D shape using two different algorithms (ADAM, MPCD). Furthermore, an N-body dynamical model allowed us to retrieve the orbital elements of the two moons as explained in the accompanying paper. Results: The shape of (216) Kleopatra is very close to an equilibrium dumbbell figure with two lobes and a thick neck. Its volume equivalent diameter (118.75 ± 1.40) km and mass (2.97 ± 0.32) × 10^18 kg (i.e., 56% lower than previously reported) imply a bulk density of (3.38 ± 0.50) g cm^−3. Such a low density for a supposedly metal-rich body indicates a substantial porosity within the primary. This porous structure along with its near equilibrium shape is compatible with a formation scenario including a giant impact followed by reaccumulation. (216) Kleopatra's current rotation period and dumbbell shape imply that it is in a critically rotating state. The low effective gravity along the equator of the body, together with the equatorial orbits of the moons and possibly rubble-pile structure, opens the possibility that the moons formed via mass shedding. Conclusions: (216) Kleopatra is a puzzling multiple system due to the unique characteristics of the primary. This system certainly deserves particular attention in the future, with the Extremely Large Telescopes and possibly a dedicated space mission, to decipher its entire formation history. [less ▲]

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See detailAn advanced multipole model for (216) Kleopatra triple system
Brož, M.; Marchis, F.; Jorda, L. et al

in Astronomy and Astrophysics (2021), 653

Aims: To interpret adaptive-optics observations of (216) Kleopatra, we need to describe an evolution of multiple moons orbiting an extremely irregular body and include their mutual interactions. Such ... [more ▼]

Aims: To interpret adaptive-optics observations of (216) Kleopatra, we need to describe an evolution of multiple moons orbiting an extremely irregular body and include their mutual interactions. Such orbits are generally non-Keplerian and orbital elements are not constants. Methods: Consequently, we used a modified N-body integrator, which was significantly extended to include the multipole expansion of the gravitational field up to the order ℓ = 10. Its convergence was verified against the `brute-force' algorithm. We computed the coefficients C_ℓm, S_ℓm for Kleopatra's shape, assuming a constant bulk density. For Solar System applications, it was also necessary to implement a variable distance and geometry of observations. Our χ^2 metric then accounts for the absolute astrometry, the relative astrometry (second moon with respect to the first), angular velocities, and silhouettes, constraining the pole orientation. This allowed us to derive the orbital elements of Kleopatra's two moons. Results: Using both archival astrometric data and new VLT/SPHERE observations (ESO LP 199.C-0074), we were able to identify the true periods of the moons, P1 = (1.822359 ± 0.004156) d, P2 = (2.745820 ± 0.004820) d. They orbit very close to the 3:2 mean-motion resonance, but their osculating eccentricities are too small compared to other perturbations (multipole, mutual), meaning that regular librations of the critical argument are not present. The resulting mass of Kleopatra, m1 = (1.49 ± 0.16) × 10^−12 M⊙ or 2.97 × 10^18 kg, is significantly lower than previously thought. An implication explained in the accompanying paper is that (216) Kleopatra is a critically rotating body. [less ▲]

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See detail(6478) Gault: physical characterization of an active main-belt asteroid
Devogèle, Maxime; Ferrais, Marin ULiege; Jehin, Emmanuel ULiege et al

in Monthly Notices of the Royal Astronomical Society (2021), 505

In 2018 December, the main-belt asteroid (6478) Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was ... [more ▼]

In 2018 December, the main-belt asteroid (6478) Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was any other member of the Phocaea family. In this work, we present the results of photometric and spectroscopic observations that commenced soon after the discovery of activity. We obtained observations over two apparitions to monitor its activity, rotation period, composition, and possible non-gravitational orbital evolution. We find that Gault has a rotation period of P = 2.4929 ± 0.0003 h with a light-curve amplitude of 0.06 magnitude. This short rotation period close to the spin barrier limit is consistent with Gault having a density no smaller than ρ = 1.85 g cm^-3 and its activity being triggered by the YORP (Yarkovsky-O'Keefe-Radzievskii-Paddack) spin-up mechanism. Analysis of the Gault phase curve over phase angles ranging from 0.4° to 23.6° provides an absolute magnitude of H = 14.81 ± 0.04, G1 = 0.25 ± 0.07, and G2 = 0.38 ± 0.04. Model fits to the phase curve find the surface regolith grain size constrained between 100 and 500 $\rm {\mu }$m. Using relations between the phase curve and albedo, we determine that the geometrical albedo of Gault is p[SUB]v[/SUB] = 0.26 ± 0.05 corresponding to an equivalent diameter of $D = 2.8^{+0.4}_{-0.2}$ km. Our spectroscopic observations are all consistent with an ordinary chondrite-like composition (S, or Q-type in the Bus-DeMeo taxonomic classification). A search through archival photographic plate surveys found previously unidentified detections of Gault dating back to 1957 and 1958. Only the latter had been digitized, which we measured to nearly double the observation arc of Gault. Finally, we did not find any signal of activity during the 2020 apparition or non-gravitational effects on its orbit. [less ▲]

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See detailEvidence for differentiation of the most primitive small bodies
Carry, B.; Vernazza, P.; Vachier, F. et al

in Astronomy and Astrophysics (2021), 650

Context. Dynamical models of Solar System evolution have suggested that the so-called P- and D-type volatile-rich asteroids formed in the outer Solar System beyond Neptune's orbit and may be genetically ... [more ▼]

Context. Dynamical models of Solar System evolution have suggested that the so-called P- and D-type volatile-rich asteroids formed in the outer Solar System beyond Neptune's orbit and may be genetically related to the Jupiter Trojans, comets, and small Kuiper belt objects (KBOs). Indeed, the spectral properties of P- and D-type asteroids resemble that of anhydrous cometary dust. Aims: We aim to gain insights into the above classes of bodies by characterizing the internal structure of a large P- and D-type asteroid. Methods: We report high-angular-resolution imaging observations of the P-type asteroid (87) Sylvia with the Very Large Telescope Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. These images were used to reconstruct the 3D shape of Sylvia. Our images together with those obtained in the past with large ground-based telescopes were used to study the dynamics of its two satellites. We also modeled Sylvia's thermal evolution. Results: The shape of Sylvia appears flattened and elongated (a/b ~1.45; a/c ~1.84). We derive a volume-equivalent diameter of 271 ± 5 km and a low density of 1378 ± 45 kg m^−3. The two satellites orbit Sylvia on circular, equatorial orbits. The oblateness of Sylvia should imply a detectable nodal precession which contrasts with the fully-Keplerian dynamics of its two satellites. This reveals an inhomogeneous internal structure, suggesting that Sylvia is differentiated. Conclusions: Sylvia's low density and differentiated interior can be explained by partial melting and mass redistribution through water percolation. The outer shell should be composed of material similar to interplanetary dust particles (IDPs) and the core should be similar to aqueously altered IDPs or carbonaceous chondrite meteorites such as the Tagish Lake meteorite. Numerical simulations of the thermal evolution of Sylvia show that for a body of such a size, partial melting was unavoidable due to the decay of long-lived radionuclides. In addition, we show that bodies as small as 130-150 km in diameter should have followed a similar thermal evolution, while smaller objects, such as comets and the KBO Arrokoth, must have remained pristine, which is in agreement with in situ observations of these bodies. NASA Lucy mission target (617) Patroclus (diameter ≈140 km) may, however, be differentiated. [less ▲]

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See detail(208) Lacrimosa: A case that missed the Slivan state?
Vokrouhlický, D.; Ďurech, J.; Hanuš, J. et al

in Astronomy and Astrophysics (2021), 649

Context. The largest asteroids in the Koronis family (sizes ≥25 km) have very peculiar rotation state properties, with the retrograde- and prograde-rotating objects being distinctly different. A recent re ... [more ▼]

Context. The largest asteroids in the Koronis family (sizes ≥25 km) have very peculiar rotation state properties, with the retrograde- and prograde-rotating objects being distinctly different. A recent re-analysis of observations suggests that one of the asteroids formerly thought to be retrograde-rotating, 208 Lacrimosa, in reality exhibits prograde rotation, yet other properties of this object are discrepant with other members this group. Aims: We seek to understand whether the new spin solution of Lacrimosa invalidates the previously proposed model of the Koronis large members or simply reveals more possibilities for the long-term evolutionary paths, including some that have not yet been explored. Methods: We obtained additional photometric observations of Lacrimosa, and included thermal and occultation data to verify its new spin solution. We also conducted a more detailed theoretical analysis of the long-term spin evolution to understand the discrepancy with respect to the other prograde-rotating large Koronis members. <BR /> Results: We confirm and substantiate the previously suggested prograde rotation of Lacrimosa. Its spin vector has an ecliptic longitude and latitude of (λ, β) = (15° ± 2°, 67° ± 2°) and a sidereal rotation period P = 14.085734 ± 0.000007 h. The thermal and occultation data allow us to calibrate a volume equivalent size of D = 44 ± 2 km of Lacrimosa. The observations also constrain the shape model relatively well. Assuming uniform density, the dynamical ellipticity is Δ = 0.35 ± 0.05. Unlike other large prograde-rotating Koronis members, Lacrimosa spin is not captured in the Slivan state. We propose that Lacrimosa differed from this group in that it had initially slightly larger obliquity and longer rotation period. With those parameters, it jumped over the Slivan state instead of being captured and slowly evolved into the present spin configuration. In the future, it is likely to be captured in the Slivan state corresponding to the proper (instead of forced) mode of the orbital plane precession in the inertial space. [less ▲]

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See detailLightcurve Based Determination of 10 Hygiea'S Rotational Period With Trappist-North and -South
Ferrais, Marin ULiege; Jehin, Emmanuel ULiege; Vernazza, Pierre et al

in Minor Planet Bulletin (2021), 48

A densely-sampled lightcurve of the large main-belt asteroid 10 Hygiea was obtained with the TRAPPISTSouth (TS) and TRAPPIST-North (TN) telescopes in 2018 September and October. We found its synodic ... [more ▼]

A densely-sampled lightcurve of the large main-belt asteroid 10 Hygiea was obtained with the TRAPPISTSouth (TS) and TRAPPIST-North (TN) telescopes in 2018 September and October. We found its synodic rotation period and amplitude to be 13.8224 ± 0.0005 h and 0.27 mag. The data have been submitted to the ALCDEF database. [less ▲]

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See detail398P/Boattini a new JFC carbon-chain poor comet
Jehin, Emmanuel ULiege; Moulane, Youssef ULiege; Manfroid, Jean ULiege et al

in The Astronomer's Telegram (2020), 14251

E. Jehin, Y. Moulane, J. Manfroid, F. Pozuelos, M. Ferrais, D. Hutsemekers (STAR Institute, University of Liege, Belgium) report that they obtained with TRAPPIST-North (code=Z53, at Oukaimeden Observatory ... [more ▼]

E. Jehin, Y. Moulane, J. Manfroid, F. Pozuelos, M. Ferrais, D. Hutsemekers (STAR Institute, University of Liege, Belgium) report that they obtained with TRAPPIST-North (code=Z53, at Oukaimeden Observatory, Morocco) 0.6-m robotic telescope, three sets of observations of the recently recovered comet 398P/Boattini (= 2009 Q4 = 2020 P2, CBET 4829) on November 10, 15 and 20 UT under photometric conditions using HB cometary narrowband filters (Farnham et al. 2000). [less ▲]

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See detailTRAPPIST comet production rates: 88/Howell, C/2020 M3 (ATLAS), C/2020 S3 (Erasmus), 156P/Russell-LINEAR
Jehin, Emmanuel ULiege; Moulane, Youssef ULiege; Manfroid, Jean ULiege et al

in The Astronomer's Telegram (2020), 14174

E. Jehin, Y. Moulane, J. Manfroid, F. Pozuelos, M. Ferrais, D. Hutsemekers (STAR Institute, University of Liege) report that they obtained from TRAPPIST-South (code=I40, Chile) and TRAPPIST-North (code ... [more ▼]

E. Jehin, Y. Moulane, J. Manfroid, F. Pozuelos, M. Ferrais, D. Hutsemekers (STAR Institute, University of Liege) report that they obtained from TRAPPIST-South (code=I40, Chile) and TRAPPIST-North (code=Z53, Morocco) 0.6-m robotic telescopes (Jehin el al. 2011) observations using HB narrowband filters (Farnham et al. 2000) for the following comets and computed preliminary production rates at 10.000 km using a Haser Model (Vp=Vd=1km/s) (Haser 1957). [less ▲]

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See detailShape Model, Pole Solution Implications, and Refined Rotational Period of (155140) 2005 UD
Kueny, J. K.; Chandler, C. O.; Devogèle, M. et al

in Bulletin of the American Astronomical Society (2020, October 01), 52

(155140) 2005 UD is a Near-Earth Asteroid in a companion orbit with (3200) Phaethon, an active asteroid in a highly-elliptical orbit thought to be responsible for the Geminid meteor shower. Evidence ... [more ▼]

(155140) 2005 UD is a Near-Earth Asteroid in a companion orbit with (3200) Phaethon, an active asteroid in a highly-elliptical orbit thought to be responsible for the Geminid meteor shower. Evidence points to a genetic relationship between these two objects (Devogèle et al. 2020), but we have yet to fully understand how 2005 UD and Phaethon could have separated into this associated pair. Notably, 2005 UD is the extended mission target for the Japanese Aerospace Exploration Agency DESTINY+ mission scheduled to launch in 2024. Presented herein are new observations of 2005 UD using the Lowell Discovery Telescope, Nordic Optical Telescope, and TRAPPIST-North motivated by access to a previously unseen viewing geometry in October-November 2019. Lightcurve inversion using our new data, archival lightcurve data from an advantageous apparition in late 2018, and data from an epoch in late 2005 were used to derive a shape model of 2005 UD. Results pertaining to 2005 UD's mass loss from additional analyses involving these new data will also be discussed. We also determined a retrograde spin state, largely consistent with a previous thermophysical analysis, and a refined sidereal rotational period of P[SUB]sid[/SUB] = 5.2338 ± 0.0040 hours. Although a precise shape model is at present infeasible due to remaining gaps in lightcurve data at critical viewing aspects, we were able to leverage our results to help limit the range of formation scenarios and the link to Phaethon in the context of non-gravitational forces and timescales associated with the physical evolution of the system. [less ▲]

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See detailHeterogeneous surface of 1998 OR2
Devogèle, M.; Virkki, A.; Marshall, S. E. et al

in Bulletin of the American Astronomical Society (2020, October 01), 52

We report observations of the H=15.8 mag potentially hazardous asteroid 52768 (1998 OR2) obtained during its 2020 apparition. On April 29th 2020, OR2 experienced its closest approach to Earth (16.4 Lunar ... [more ▼]

We report observations of the H=15.8 mag potentially hazardous asteroid 52768 (1998 OR2) obtained during its 2020 apparition. On April 29th 2020, OR2 experienced its closest approach to Earth (16.4 Lunar distance) until 2079. Observations were obtained in polarimetry with the Torino Polarimeter at the Calern observatory (France; MPC 010) in February and April 2020, in radar with the Arecibo Radio telescope (Puerto Rico; MPC 251) Planetary Radar system from April 13th to 23rd 2020, and in photometry with the TRAPPIST-North and the Las Cumbres observatory (LCOGT) network of telescopes. One epoch was obtained by the NEOWISE mission. <P />Using the polarimetric albedo-polarization relation [1] we derived a visual albedo p[SUB]V[/SUB] = 0.16 ± 0.02 corresponding to an equivalent diameter of D=2.3 km based on its measured H=15.8 absolute magnitude. The NEOWISE observation provides other determinations of D=2.5 ± 0.5 km and p[SUB]V[/SUB] = 0.13 ± 0.04 consistent with the polarimetric data. Radar delay-Doppler images, with a resolution of 7.5 m per pixel in delay and 0.037 Hz in frequency, provide another independent size measurement and display a maximum extent of 2.16 km ± 0.05 km. Both radar and optical lightcurve observations confirm the rotation period of p=4.112 h [2], with a low amplitude lightcurve varying from single to double peaked, based on the phase angle and aspect angle variation throughout the apparition. <P />The polarimetric observations were conducted over more than one rotation period during each night and we observe a consistent phase-locked variation of the polarization. Asteroid polarization is independent of shape and is at first order dependent on the surface albedo. The observed variation of the polarization thus suggests that the surface of OR2 is heterogeneous. Such variation has only previously been observed for 4 Vesta [3], 1943 Anteros [4], and 3200 Phaethon [5,6]. <P />The radar images of OR2 suggest the presence of a large concavity or crater near the radar sub-latitude (closest point of the object to the observer). Phasing the radar and polarimetric observations, we find that the maximum of polarization occurs when the radar concavity is directly facing the observer. Such correlation suggests that the polarimetric variations could be related to the presence of the concavity and that it possesses lower albedo or different scattering properties than the rest of the surface. <P />1: Cellino et al., 2015 MNRAS, 451, 3473 ; 2: Skiff et al, 2019, MPB, 46 ; 3: Cellino et al., 2016, MNRAS, 456, 248 ; 4: Masiero et al., 2010, Icarus, 207, 795 ; 5: Devogèle et al., 2018 MNRAS, 465, 4335 ; 6: Borisov et al., 2018 MNRAS, 480, L131 [less ▲]

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See detailVolume uncertainty of (7) Iris shape models from disk-resolved images.
Dudziński, G.; Podlewska-Gaca, E.; Bartczak, P. et al

in Monthly Notices of the Royal Astronomical Society (2020)

High angular resolution disk-resolved images of (7) Iris collected by VLT/SPHERE instrument allowed for the detailed shape modelling of this large asteroid revealing its surface features. If (7) Iris did ... [more ▼]

High angular resolution disk-resolved images of (7) Iris collected by VLT/SPHERE instrument allowed for the detailed shape modelling of this large asteroid revealing its surface features. If (7) Iris did not suffer any events catastrophic enough to disrupt the body (which is very likely) by studying its topography we might get insights into the early Solar System's collisional history. When it comes to internal structure and composition, thoroughly assessing the volume and density uncertainties is necessary. In this work we propose a method of uncertainty calculation of asteroid shape models based on lightcurve and Adaptive Optics images. We apply this method on four models of (7) Iris produced from independent SAGE and ADAM inversion techniques and photoclinometry (MPCD). Obtained diameter uncertainties stem from both the observations from which the models were scaled and the models themselves. We show that despite the availability of high resolution AO images, the volume and density of (7) Iris have substantial error bars that were underestimated in the previous studies. [less ▲]

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See detailBinary asteroid (31) Euphrosyne: ice-rich and nearly spherical★
Yang, Bin ULiege; Hanuš, J.; Carry, B. et al

in Astronomy and Astrophysics (2020), 641

<BR /> Aims: Asteroid (31) Euphrosyne is one of the biggest objects in the asteroid main belt and it is also the largest member of its namesake family. The Euphrosyne family occupies a highly inclined ... [more ▼]

<BR /> Aims: Asteroid (31) Euphrosyne is one of the biggest objects in the asteroid main belt and it is also the largest member of its namesake family. The Euphrosyne family occupies a highly inclined region in the outer main belt and contains a remarkably large number of members, which is interpreted as an outcome of a disruptive cratering event. <BR /> Methods: The goals of this adaptive-optics imaging study are threefold: to characterize the shape of Euphrosyne, to constrain its density, and to search for the large craters that may be associated with the family formation event. <BR /> Results: We obtained disk-resolved images of Euphrosyne using SPHERE/ZIMPOL at the ESO 8.2 m VLT as part of our large program (ID: 199.C-0074, PI: Vernazza). We reconstructed its 3D shape via the ADAM shape modeling algorithm based on the SPHERE images and the available light curves of this asteroid. We analyzed the dynamics of the satellite with the Genoid meta-heuristic algorithm. Finally, we studied the shape of Euphrosyne using hydrostatic equilibrium models. <BR /> Conclusions: Our SPHERE observations show that Euphrosyne has a nearly spherical shape with the sphericity index of 0.9888 and its surface lacks large impact craters. Euphrosyne's diameter is 268 ± 6 km, making it one of the top ten largest main belt asteroids. We detected a satellite of Euphrosyne - S/2019 (31) 1 - that is about 4 km across, on a circular orbit. The mass determined from the orbit of the satellite together with the volume computed from the shape model imply a density of 1665 ± 242 kg m[SUP]-3[/SUP], suggesting that Euphrosyne probably contains a large fraction of water ice in its interior. We find that the spherical shape of Euphrosyne is a result of the reaccumulation process following the impact, as in the case of (10) Hygiea. However, our shape analysis reveals that, contrary to Hygiea, the axis ratios of Euphrosyne significantly differ from those suggested by fluid hydrostatic equilibrium following reaccumulation. <P />The reduced images are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/641/A80">http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/641/A80</A> <P />Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program 199.C-0074 (PI Vernazza). [less ▲]

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See detailAsteroid (16) Psyche's primordial shape: A possible Jacobi ellipsoid
Ferrais, Marin ULiege; Vernazza, P.; Jorda, L. et al

in Astronomy and Astrophysics (2020), 638

Context. Asteroid (16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Psyche mission. It is also the only asteroid of this size (D > 200 km) known to be metal rich ... [more ▼]

Context. Asteroid (16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Psyche mission. It is also the only asteroid of this size (D > 200 km) known to be metal rich. Although various hypotheses have been proposed to explain the rather unique physical properties of this asteroid, a perfect understanding of its formation and bulk composition is still missing. <BR /> Aims: We aim to refine the shape and bulk density of (16) Psyche and to perform a thorough analysis of its shape to better constrain possible formation scenarios and the structure of its interior. <BR /> Methods: We obtained disk-resolved VLT/SPHERE/ZIMPOL images acquired within our ESO large program (ID 199.C-0074), which complement similar data obtained in 2018. Both data sets offer a complete coverage of Psyche's surface. These images were used to reconstruct the three-dimensional (3D) shape of Psyche with two independent shape modeling algorithms (MPCD and ADAM). A shape analysis was subsequently performed, including a comparison with equilibrium figures and the identification of mass deficit regions. <BR /> Results: Our 3D shape along with existing mass estimates imply a density of 4.20 ± 0.60 g cm[SUP]-3[/SUP], which is so far the highest for a solar system object following the four telluric planets. Furthermore, the shape of Psyche presents small deviations from an ellipsoid, that is, prominently three large depressions along its equator. The flatness and density of Psyche are compatible with a formation at hydrostatic equilibrium as a Jacobi ellipsoid with a shorter rotation period of ∼3h. Later impacts may have slowed down Psyche's rotation, which is currently ∼4.2 h, while also creating the imaged depressions. <BR /> Conclusions: Our results open the possibility that Psyche acquired its primordial shape either after a giant impact while its interior was already frozen or while its interior was still molten owing to the decay of the short-lived radionuclide [SUP]26[/SUP]Al. <P />The reduced images are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/638/L15">http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/638/L15</A> <P />Based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 199.C-0074 (PI: P. Vernazza). [less ▲]

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See detailPhysical parameters of selected Gaia mass asteroids
Podlewska-Gaca, E.; Marciniak, A.; Alí-Lagoa, V. et al

in Astronomy and Astrophysics (2020), 638

Context. Thanks to the Gaia mission, it will be possible to determine the masses of approximately hundreds of large main belt asteroids with very good precision. We currently have diameter estimates for ... [more ▼]

Context. Thanks to the Gaia mission, it will be possible to determine the masses of approximately hundreds of large main belt asteroids with very good precision. We currently have diameter estimates for all of them that can be used to compute their volume and hence their density. However, some of those diameters are still based on simple thermal models, which can occasionally lead to volume uncertainties as high as 20-30%. <BR /> Aims: The aim of this paper is to determine the 3D shape models and compute the volumes for 13 main belt asteroids that were selected from those targets for which Gaia will provide the mass with an accuracy of better than 10%. <BR /> Methods: We used the genetic Shaping Asteroids with Genetic Evolution (SAGE) algorithm to fit disk- integrated, dense photometric lightcurves and obtain detailed asteroid shape models. These models were scaled by fitting them to available stellar occultation and/or thermal infrared observations. <BR /> Results: We determine the spin and shape models for 13 main belt asteroids using the SAGE algorithm. Occultation fitting enables us to confirm main shape features and the spin state, while thermophysical modeling leads to more precise diameters as well as estimates of thermal inertia values. <BR /> Conclusions: We calculated the volume of our sample of main-belt asteroids for which the Gaia satellite will provide precise mass determinations. From our volumes, it will then be possible to more accurately compute the bulk density, which is a fundamental physical property needed to understand the formation and evolution processes of small Solar System bodies. [less ▲]

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