arXiv subjects

Tsutomu Hayamizu

Publications and source records attributed to Tsutomu Hayamizu.

5 recordsLinked to original sources

arXiv2026

The first detection of an atmosphere on a trans-Neptunian object beyond Pluto

Trans-Neptunian objects (TNOs) in the outer Solar System are predominantly small, icy worlds long presumed to be atmosphereless except for the largest bodies. Until now, Pluto has been unique among TNOs in exhibiting a substantial atmosphere (nitrogen with trace methane and carbon monoxide) at microbar pressure levels. All other known TNOs, including ~ 1000-km-sized bodies such as Eris, Haumea, Makemake, and Quaoar, have shown no detectable atmospheres in stellar occultation observations, with surface pressure upper limits of order 1-100 nanobars. Here we report the first detection of an atmosphere around a TNO besides Pluto. A stellar occultation by the ~ 250-km-radius plutino (612533) 2002 XV93 on 10 January 2024 revealed a refractive signature, indicating the presence of a thin atmosphere. The derived surface pressure is 100-200 nanobars, i.e. approximately a hundred times lower than Pluto's and yet significantly above previous limits for other larger bodies. This discovery provides the first evidence that even a sub-1000-km TNO can retain an atmosphere, challenging current paradigms of volatile retention. Our findings indicate that a fraction of distant icy minor planets can exhibit atmospheres possibly caused by ongoing cryovolcanic activity or a recent impact event of a small icy object.

astro-ph.EP↗

arXiv2024

Diffraction modelling of a 2023 March 5 stellar occultation by subkilometer-sized asteroid (98943) 2001 CC21

We present an analysis of a stellar occultation event caused by a near-Earth asteroid (98943) 2001 CC21, an upcoming flyby target in the Hayabusa2 extended mission, on March 5, 2023. To accurately determine the asteroid's shape from diffraction-affected light curves, we developed a novel data reduction technique named the Diffracted Occultation's United Simulator for Highly Informative Transient Explorations (DOUSHITE). Using DOUSHITE-generated synthetic models, we derived constraints on (98943) 2001 CC21's shadow shape from the single-chord occultation data. Our results suggest a significant elongation of the shadow with an axis ratio of $b/a = 0.37\pm0.09$. This shape can be crucial for planning Hayabusa2's high-speed flyby to optimise the limited imaging opportunities.

astro-ph.EP↗

arXiv2020

Precise astrometry and diameters of asteroids from occultations -- a data-set of observations and their interpretation

Occultations of stars by asteroids have been observed since 1961, increasing from a very small number to now over 500 annually. We have created and regularly maintain a growing data-set of more than 5,000 observed asteroidal occultations. The data-set includes: the raw observations; astrometry at the 1 mas level based on centre of mass or figure (not illumination); where possible the asteroid's diameter to 5 km or better, and fits to shape models; the separation and diameters of asteroidal satellites; and double star discoveries with typical separations being in the tens of mas or less. The data-set is published at NASA's Planetary Data System and is regularly updated. We provide here an overview of the data-set, discuss the issues associated with determining the astrometry and diameters, and give examples of what can be derived from the data-set. We also compare the occultation diameters of asteroids with the diameters measured by the satellites NEOWISE, AKARI AcuA, and IRAS, and show that the best satellite-determined diameter is a combination of the diameters from all three satellites.

astro-ph.EP↗

arXiv2017

Volumes and bulk densities of forty asteroids from ADAM shape modeling

Disk-integrated photometric data of asteroids do not contain accurate information on shape details or size scale. Additional data such as disk-resolved images or stellar occultation measurements further constrain asteroid shapes and allow size estimates. We aim to use all available disk-resolved images of about forty asteroids obtained by the Near-InfraRed Camera (Nirc2) mounted on the W.M. Keck II telescope together with the disk-integrated photometry and stellar occultation measurements to determine their volumes. We can then use the volume, in combination with the known mass, to derive the bulk density. We download and process all asteroid disk-resolved images obtained by the Nirc2 that are available in the Keck Observatory Archive (KOA). We combine optical disk-integrated data and stellar occultation profiles with the disk-resolved images and use the All-Data Asteroid Modeling (ADAM) algorithm for the shape and size modeling. Our approach provides constraints on the expected uncertainty in the volume and size as well. We present shape models and volume for 41 asteroids. For 35 asteroids, the knowledge of their mass estimates from the literature allowed us to derive their bulk densities. We clearly see a trend of lower bulk densities for primitive objects (C-complex) than for S-complex asteroids. The range of densities in the X-complex is large, suggesting various compositions. Moreover, we identified a few objects with rather peculiar bulk densities, which is likely a hint of their poor mass estimates. Asteroid masses determined from the Gaia astrometric observations should further refine most of the density estimates.

astro-ph.EP↗

arXiv2011

Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes

Asteroid sizes can be directly measured by observing occultations of stars by asteroids. When there are enough observations across the path of the shadow, the asteroid's projected silhouette can be reconstructed. Asteroid shape models derived from photometry by the lightcurve inversion method enable us to predict the orientation of an asteroid for the time of occultation. By scaling the shape model to fit the occultation chords, we can determine the asteroid size with a relative accuracy of typically ~ 10%. We combine shape and spin state models of 44 asteroids (14 of them are new or updated models) with the available occultation data to derive asteroid effective diameters. In many cases, occultations allow us to reject one of two possible pole solutions that were derived from photometry. We show that by combining results obtained from lightcurve inversion with occultation timings, we can obtain unique physical models of asteroids.

astro-ph.EP↗