New photometric and spectroscopic observations of 53 Per

We present the analysis of the variability of the SPB-type star 53 Per based on space photometry from BRITE-Constellation nano-satellites and SMEI-Coriolis experiment. The two photometries allowed us to detect 17 independent sinusoidal terms in the range 0.2 - 1.4 d^{-1} plus one combination, and one harmonic. The independent terms can be attributed to g modes excited in this star. Only three of these modes have been known earlier. In addition, we gathered almost 3500 new mid- and high-resolution spectra of 53 Per, which were used to calculate radial velocities. The frequency spectrum of the time-series radial-velocity data revealed four independent terms and one combination, all consistent with the frequencies detected in BRITE and SMEI photometry. The high-resolution and high signal-to-noise averaged spectrum was used to obtain atmospheric parameters of 53 Per, T_eff = 15600 ± 400 K and log (g/(cm s^{-2}))= 3.85 ± 0.10

Apophis planetary defense campaign

We describe results of a planetary defense exercise conducted during the close approach to Earth by the near-Earth asteroid (99942) Apophis during 2020 December–2021 March. The planetary defense community has been conducting observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. These community-led global exercises were carried out with the support of NASA's Planetary Defense Coordination Office and the International Asteroid Warning Network. The Apophis campaign is the third in our series of planetary defense exercises. The goal of this campaign was to recover, track, and characterize Apophis as a potential impactor to exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication. Based on the campaign results, we present lessons learned about our ability to observe and model a potential impactor. Data products derived from astrometric observations were available for inclusion in our risk assessment model almost immediately, allowing real-time updates to the impact probability calculation and possible impact locations. An early NEOWISE diameter measurement provided a significant improvement in the uncertainty on the range of hypothetical impact outcomes. The availability of different characterization methods such as photometry, spectroscopy, and radar provided robustness to our ability to assess the potential impact risk

Physical properties of the cubewano 19521 Chaos from a multi-chord stellar occultation

Trans-Neptunian Objects (TNOs) have had an increasing interest since the discovery of (15760) Albion in 1992. These objects are considered remnants of the Solar System formation, and can thus provide clues about its origin and evolution. One of the best techniques to study TNOs from ground-based telescopes are stellar occultations which, if combined with photometric data, permit to obtain physical properties of the TNO such as its size, shape, and albedo. With this in mind, we predicted, observed, and analyzed the stellar occultation of the Gaia source 3444789965847631104 caused by the cubewano (19521) Chaos on the 20th of November 2020. The prediction was part of the searching program carried out by the Lucky Star project collaboration. We observed the object with the 1.23-m telescope at Calar Alto Observatory (Almería, Spain) two days before the event to update the prediction. The occultation observing campaign involved 19 observing stations, both professional and amateur, and resulted in three positive detections and 11 negative detections. Five teams could not observe due to bad weather. We fitted the positive chords' extremities to an ellipse to derive Chaos' projected size and shape and determine its geometric albedo. The preliminary area-equivalent diameter obtained is slightly smaller than the one derived with Herschel thermal data. However, we are still analyzing photometric data to complement and improve these results