Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConvex Shape and Rotation Model of Lucy Target (11351) Leucus from Lightcurves and Occultations
81
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report new photometric lightcurve observations of the Lucy Mission target (11351) Leucus acquired during the 2017, 2018 and 2019 apparitions. We use these data in combination with stellar occultations captured during five epochs (Buie et al. 2020) to determine the sidereal rotation period, the spin axis orientation, a convex shape model, the absolute scale of the object, its geometric albedo, and a model of the photometric properties of the target. We find that Leucus is a prograde rotator with a spin axis located within a sky-projected radius of 3{deg} (1$sigma$) from J2000 Ecliptic coordinates ($lambda=208deg$, $beta=+77deg$) or J2000 Equatorial Coordinates (RA=248$deg$, Dec=+58$deg$). The sidereal period is refined to $P_{sid}=445.683pm0.007$ h. The convex shape model is irregular, with maximum dimensions of (60.8, 39.1, 27.8) km. The convex model accounts for global features of the occultation silhouettes, although minor deviations suggest that local and global concavities are present. We determine a geometric albedo $p_V=0.043pm0.002$. The derived phase curve supports a D-type classification for Leucus.
rate research
Read More
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by SOFIA with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 Aug 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 $pm$ 0.0005 hours. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.
We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklos size and shape, and the ring reflectivity. We consider four possible models for Chariklo (sphere, Maclaurin spheroid, tri-axial ellipsoid and Jacobi ellipsoid) and we use a Bayesian approach to estimate the corresponding parameters. The spherical model has a radius $R=129pm3$ km. The Maclaurin model has equatorial and polar radii $a=b=143^{+3}_{-6}$ km and $c=96^{+14}_{-4}$ km, respectively, with density $970^{+300}_{-180}$ kg m$^{-3}$. The ellipsoidal model has semiaxes $a=148^{+6}_{-4}$ km, $b=132^{+6}_{-5}$ km and $c=102^{+10}_{-8}$ km. Finally, the Jacobi model has semiaxes $a$=157$pm$4 km, $b$=139$pm$ 4 km and $c$=86$pm$1 km, and density $796^{+2}_{-4}$ kg m$^{-3}$ . Depending on the model, we obtain topographic features of 6-11 km, typical of Saturn icy satellites with similar size and density. We constrain Chariklos geometric albedo between 3.1% (sphere) and 4.9% (ellipsoid), while the ring $I/F$ reflectivity is less constrained between 0.6% (Jacobi) and 8.9% (sphere). The ellipsoid model explains both the optical light curve and the long-term photometry variation of the system, giving a plausible value for the geometric albedo of the ring particles of $10-15%$. The derived Chariklos mass of 6-8$times10^{18}$ kg places the rings close to the 3:1 resonance between the ring mean motion and Chariklos rotation period.
In the absence of dense photometry for a large population of Near Earth Objects (NEOs), the best method of obtaining a shape distribution comes from sparse photometry and partial lightcurves. We have used 867 partial lightcurves obtained by Spitzer to determine a shape distribution for sub-kilometre NEOs. From this data we find a best fit average elongation $frac{b}{a}=0.72 pm 0.08$. We compare this result with a shape distribution obtained from 1869 NEOs in the same size range observed by Pan-STARRS 1 and find the Spitzer-obtained elongation to be in excellent agreement with this PS1 value of $frac{b}{a}=0.70 pm 0.10$. These values are also in agreement with literature values for $1<D<10$ km objects in the main asteroid belt, however, there is a size discrepancy between the two datasets. Using a smaller sample of NEOs in the size range $1<D<5$ km from PS1 data, we obtain an average axis ratio $b/a = 0.70 pm 0.12$. This is more elongated than the shape distribution for main belt objects in the same size regime, although the current uncertainties are sizeable and this should be verified using a larger data set. As future large surveys come online it will be possible to observe smaller main belt asteroids to allow for better comparisons of different sub-kilometre populations.
We present results derived from four stellar occultations by the plutino object (208996) 2003~AZ$_{84}$, detected at January 8, 2011 (single-chord event), February 3, 2012 (multi-chord), December 2, 2013 (single-chord) and November 15, 2014 (multi-chord). Our observations rule out an oblate spheroid solution for 2003~AZ$_{84}$s shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial solution with semi axes $(470 pm 20) times (383 pm 10) times (245 pm 8)$~km % axis ratios $b/a= 0.82 pm 0.05$ and $c/a= 0.52 pm 0.02$, can better account for all our occultation observations. Combining these dimensions with the rotation period of the body (6.75~h) and the amplitude of its rotation light curve, we derive a density $rho=0.87 pm 0.01$~g~cm$^{-3}$ a geometric albedo $p_V= 0.097 pm 0.009$. A grazing chord observed during the 2014 occultation reveals a topographic feature along 2003~AZ$_{84}$s limb, that can be interpreted as an abrupt chasm of width $sim 23$~km and depth $> 8$~km or a smooth depression of width $sim 80$~km and depth $sim 13$~km (or an intermediate feature between those two extremes).
Most asteroids are somewhat elongated and have non-zero lightcurve amplitudes. Such asteroids can be detected in large-scale sky surveys even if their mean magnitudes are fainter than the stated sensitivity limits. We explore the detection of elongated asteroids under a set of idealized but useful approximations. We find that objects up to 1 magnitude fainter than a surveys sensitivity limit are likely to be detected, and that the effect is most pronounced for asteroids with lightcurve amplitudes 0.1-0.4 mag.This imposes a bias on the derived size and shape distributions of the population that must be properly accounted for.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
