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 ± 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.
Disentangling techniques are often needed to obtain the spectra of the individual components of binary or multiple systems. A thorough analysis of the shift‐and‐add algorithm of Marchenko et al, PASP, 1999;110:1416 reveals that, in many cases, the line fluxes are poorly reproduced, and spurious wings appear. The causes of these discrepancies are discussed, and a new disentangling package, QER20, is presented, which significantly reduces these errors and vastly increases the performance. When applied to the massive binary 9 Sgr, our new code yields line fluxes that are notably different from those previously published and lead us to revise the spectral classification to slightly earlier subtypes: O 3 V ((f +)) for the primary and O 5 V ((f)) for the secondary. We show that, with the MME98 algorithm, the classification of massive stars in binaries can be off by several subtypes, while there are no such errors when the QER20 package is used.
During the night of the discovery of an asteroid, a large number of images spaced in time, that represent an arc too short to propagate an orbit, are obtained. Initially, it is necessary to recover the body in the celestial vault to have more observations to determine its orbit. The first step in this process is to establish the admissible region, defined as the region in space where the object can be found. In this paper we present the calculation of the Admissible Regions from data from a single night observation, considering the geocentric and topocentric versions and restrictions such as belonging to the Solar System, the object does not belong to the Earth-Moon gravitational system, and the body is at a minimum distance from Earth. This procedure was applied in the calculation of the admissible regions of 2003 BH84, 3122 Florence, 3200 Phaethon, 555 Norma, 1738 Oosterhoff and 2006 SO375. The respective admissible regions were generated in their geocentric and topocentric variant, and the respective metric changes were made to visualize their geometric characteristics. It was found that the topocentric version generates a simpler geometry than the geocentric version, decreasing the re-observation area. It was identified that the logarithmic metric is appropriate for the study of regions near the Earth (NEO’s).
This paper presents a methodology for Initial Orbit Determination (IOD) based on a modification of the Laplace’s geocentric method. The orbital elements for Near-Earth asteroids (1864) Daedalus, 2003 GW, 2019 JA8, a Hungaria-type asteroid (4690) Strasbourg, and the asteroids of the Main Belt (1738) Oosterhoff, (2717) Tellervo, (1568) Aisleen and (2235) Vittore were calculated. Input data observations from the Minor Planet Center MPC database and Astronomical Observatory of the Technological University of Pereira (OAUTP; MPC code W63) were used. These observations cover observation arcs of less than 22 days. The orbital errors, in terms of shape and orientation for the estimated orbits of the asteroids, were calculated. The shape error was less than 53 × 10–3 AU, except for the asteroid 2019 JA8. On the other hand, errors in orientation were less than 0.1 rad, except for (4690) Strasbourg. Additionally, we estimated ephemerides for all bodies for up to two months. When compared with actual ephemerides, the errors found allowed us to conclude that these bodies can be recovered in a field of vision of 95’ × 72’ (OAUTP field). This shows that Laplace’s method, though simple, may still be useful in the IOD study, especially for observatories that initiate programs of minor bodies observation.
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