Against the biases in spins and shapes of asteroids

Abstract

Physical studies of asteroids depend on an availability of lightcurve data. Targets that are easy to observe and analyse naturally have more data available, so their synodic periods are confirmed from multiple sources. Also, thanks to availability of data from a number of apparitions, their spin and shape models can often be obtained. Almost half of bright (H<=11 mag) main-belt asteroid population with known lightcurve parameters have rotation periods considered long (P>12 hours) and are rarely chosen for photometric observations. There is a similar selection effect against asteroids with low lightcurve amplitudes (a_max<=0.25 mag). As a result such targets, though numerous in this brightness range, are underrepresented in the sample of spin and shape modelled asteroids. In the range of fainter targets such effects are stronger. These selection effects can influence what is now known about asteroid spin vs. size distribution, on asteroid internal structure and densities and on spatial orientation of asteroid spin axes. To reduce both biases at the same time, we started a photometric survey of a substantial sample of those bright main-belt asteroids that displayed both features: periods longer than 12 hours, and amplitudes that did not exceed 0.25 magnitude. First we aim at finding synodic periods of rotation, and after a few observed apparitions, obtaining spin and shape models. As an initial result of our survey we found that a quarter of the studied sample (8 out of 34 targets) have rotation periods different from those widely accepted. We publish here these newly found period values with the lightcurves. The size/frequency plot might in reality look different in the long-period range. Further studies of asteroid spins, shapes, and structure should take into account serious biases that are present in the parameters available today.

Published in Planetary and Space Science. 13 pages, 20 figures

References in corpus (2)

• Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution
• Testing the inversion of asteroids' Gaia photometry combined with ground-based observations

Cited by in corpus (16)

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• Reconstruction of asteroid spin states from Gaia DR3 photometry
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• Distribution of spin-axes longitudes and shape elongations of main-belt asteroids
• Thermal properties of slowly rotating asteroids: Results from a targeted survey
• (704) Interamnia: A transitional object between a dwarf planet and a typical irregular-shaped minor body
• $V$-band photometry of asteroids from ASAS-SN: Finding asteroids with slow spin
• Properties of slowly rotating asteroids from the Convex Inversion Thermophysical Model
• Volume uncertainty assessment method of asteroid models from disk-integrated visual photometry
• Asteroid phase curves using sparse Gaia DR2 data and differential dense light curves
• Scaling slowly rotating asteroids by stellar occultations
• Light curves of transneptunian objects from the K2 mission of the Kepler Space Telescope
• Development of the SPECULOOS exoplanet search project
• Statistical analysis of the ambiguities in the asteroid period determinations
• Asteroid sizes determined with thermophysical model and stellar occultations