T. Kwiatkowski's research while affiliated with Adam Mickiewicz University and other places

The aim of this paper is to find a set of photometric passbands that will give optimal results for spectrophotometric classification of asteroids into taxonomic types and classes. For this purpose various machine-learning methods are used, namely multinomial logistic regression, naive Bayes, support vector machines, gradient boosting, and multilayer perceptrons. Sequential feature selection is performed to assess the contribution of each reflectance difference. We find that to determine the taxonomic complexes with a balanced accuracy of 85%, a set of five spectrophotometric bands is required. For taxonomy type determination with the balanced accuracy of 80% a set of eight bands is necessary. Furthermore, only a three-band system is enough for distinguishing the C-complex asteroids with 92% balanced accuracy. These results can be used for designing future asteroid multifilter sky surveys.

We present a database of the absolute magnitudes of asteroids named the Kharkiv Asteroid Absolute Magnitude Database (KhAAMD). The database includes a homogeneous set of the absolute magnitudes for about 400 asteroids in the new $HG_{1}G_{2}$ magnitude system. We performed a comparative analysis of the asteroid absolute magnitudes between the Kharkiv database and other main magnitude databases (MPC, Pan-STARRS, ATLAS, PTF, and Gaia). We show that the Pan-STARRS absolute magnitude dataset has no systematic deviations and is the most suitable for the determination of diameters and albedos of asteroids. For the MPC dataset, there is a linear trend of overestimating the absolute magnitudes of bright objects and underestimating the magnitudes of faint asteroids. The ATLAS dataset has both a systematic overestimation of asteroid magnitudes and a linear trend. We propose equations that can be used to correct for systematic errors in the MPC and the ATLAS magnitude datasets. There are possible systematic deviations of about 0.1 mag for the Gaia and PTF databases but there are insufficient data overlapping with our data for a definitive analysis.

The amount of sparse asteroid photometry being gathered by both space- and ground-based surveys is growing exponentially. This large volume of data poses a computational challenge owing to both the large amount of information to be processed and the new methods needed to combine data from different sources (e.g. obtained by different techniques, in different bands, and having different random and systematic errors). The main goal of this work is to develop an algorithm capable of merging sparse and dense data sets, both relative and differential, in preparation for asteroid observations originating from, for example, Gaia, TESS, ATLAS, LSST, K2, VISTA, and many other sources. We present a novel method to obtain asteroid phase curves by combining sparse photometry and differential ground-based photometry. In the traditional approach, the latter cannot be used for phase curves. Merging those two data types allows for the extraction of phase-curve information for a growing number of objects. Our method is validated for 26 sample asteroids observed by the Gaia mission.

Aims. Very small asteroids (VSAs, objects with diameters smaller than about 150 m) can be spun up by the YORP effect to rotation periods as short as tens of seconds. This effect has been observed for many of them. It is also hypothesised, that in the same process their spin axes are asymptotically drawn to the position perpendicular to the orbital plane. So far this effect has been observed only for one VSA and needs further verification. For that, spin axes of several other VSAs should be determined by observing their brightness variations at many different positions on the sky. Methods. On 4 March 2021 at 9 UTC a 30-m in diameter near-Earth asteroid 2021 DW 1 passed the Earth at a distance of 570 000 km, reaching the maximum brightness of V = 14.6 mag. We observed it photometrically from 2 March, when it was visible at V = 16.5 mag, until 7 March ( V = 18.2 mag). During that time 2021 DW 1 swept a 170° long arc in the northern sky, spanning solar phase angles in the range from 36° to 86°. This made it an excellent target for physical characterisation, including spin axis and shape derivation. Results. Convex inversion of the asteroid lightcurves gives a sidereal period of rotation P sid = 0.013760 ± 0.000001 h, and two solutions for the spin axis ecliptic coordinates: (A) λ 1 = 57° ± 10°, β 1 = 29° ± 10° and (B) λ 2 = 67° ± 10°, β 2 = −40° ± 10°. The magnitude-phase curve can be fitted with a standard H , G function with H = 24.8 ± 0.5 mag and an assumed G = 0.24. The asteroid colour indices are g − i = 0.79 ± 0.01 mag, and i − z = 0.01 ± 0.02 mag which indicates an S taxonomic class, with an average geometric albedo p V = 0.23 ± 0.02. The asteroid effective diameter, derived from H and p V , is D eff = 30 ± 10 m. Conclusions. It was found that the inclination of the spin axis of 2021 DW 1 is not perpendicular to the orbital plane (obliquity ϵ = 54° ± 10° or ϵ = 123° ± 10°). More spin axes of VSAs should be determined to check, if 2021 DW 1 is an exception or a typical case.

On 4 March 2021 at 9 UTC a 30-m in diameter near-Earth asteroid 2021 DW1 passed the Earth at a distance of 570000 km, reaching the maximum brightness of V=14.6 mag. We observed it photometrically from 2 March, when it was visible at V=16.5 mag, until 7 March (V=18.2 mag). During that time 2021 DW1 swept a 170 degrees long arc in the northern sky, spanning solar phase angles in the range from 36 to 86 degrees. This made it an excellent target for physical characterisation, including spin axis and shape derivation. Convex inversion of the asteroid lightcurves gives a sidereal period of rotation P=0.013760 +/- 0.000001 h, and two solutions for the spin axis ecliptic coordinates: (A) lambda_1=57 +/- 10, beta_1=29 +/- 10, and (B) lambda_2=67 +/- 10, beta_2=-40 +/- 10. The magnitude-phase curve can be fitted with a standard H, G function with H=24.8 +/- 0.5 mag and an assumed G=0.24. The asteroid colour indices are g-i=0.79 +/- 0.01 mag, and i-z=0.01 +/- 0.02 mag which indicates an S taxonomic class, with an average geometric albedo p_V=0.23 +/- 0.02. The asteroid effective diameter, derived from H and p_V, is D=30 +/- 10 m. It was found that the inclination of the spin axis of 2021 DW1 is not perpendicular to the orbital plane (obliquity epsilon=54 +/- 10 or epsilon=123 +/- 10). More spin axes of VSAs should be determined to check, if 2021 DW1 is an exception or a typical case.

We present new photometric observations for twelve asteroids ((122) Gerda, (152) Atala, (260) Huberta, (665) Sabine, (692) Hippodamia, (723) Hammonia, (745) Mauritia, (768) Struveana, (863) Benkoela, (1113) Katja, (1175) Margo, (2057) Rosemary) from the outer part of the main belt aimed to obtain the magnitude-phase curves and to verify geometric albedo and taxonomic class based on their magnitude-phase behaviors. The measured magnitude-phase relations confirm previously determined composition types of (260) Huberta (C-type), (692) Hippodamia (S-type) and (1175) Margo (S-type). Asteroids (665) Sabine and (768) Struveana previously classified as X-type show phase-curve behavior typical for moderate-albedo asteroids and may belong to the M-type. The phase-curve of (723) Hammonia is typical for the S-type which contradicts the previously determined C-type. We confirmed the moderate-albedo of asteroids (122) Gerda and (152) Atala, but their phase-curves are different from typical for the S-type and may indicate more rare compositional types. Based on magnitude-phase behaviors and V-R colors, (2057) Rosemary most probably belongs to M-type, while asteroids (745) Mauritia and (1113) Katja belong to S-complex. The phase curve of the A-type asteroid (863) Benkoela does not cover the opposition effect range and further observations are needed to understand typical features of the phase-curves of A-type asteroids in comparison with other types. We have also determined lightcurve amplitudes of the observed asteroids and obtained new or improved values of the rotation periods for most of them.

We present new photometric observations for twelve asteroids ((122) Gerda, (152) Atala, (260) Huberta, (665) Sabine, (692) Hippodamia, (723) Hammonia, (745) Mauritia, (768) Struveana, (863) Benkoela, (1113) Katja, (1175) Margo, (2057) Rosemary) from the outer part of the main belt aimed to obtain the magnitude-phase curves and to verify geometric albedo and taxonomic class based on their magnitude-phase behaviors. The measured magnitude-phase relations confirm previously determined composition types of (260) Huberta (C-type), (692) Hippodamia (S-type) and (1175) Margo (S-type). Asteroids (665) Sabine and (768) Struveana previously classified as X-type show phase-curve behavior typical for moderate-albedo asteroids and may belong to the M-type. The phase-curve of (723) Hammonia is typical for the S-type which contradicts the previously determined C-type. We confirmed the moderate-albedo of asteroids (122) Gerda and (152) Atala, but their phase-curves are different from typical for the S-type and may indicate more rare compositional types. Based on magnitude-phase behaviors and V-R colors, (2057) Rosemary most probably belongs to M-type, while asteroids (745) Mauritia and (1113) Katja belong to S-complex. The phase curve of the A-type asteroid (863) Benkoela does not cover the opposition effect range and further observations are needed to understand typical features of the phase-curves of A-type asteroids in comparison with other types. We have also determined lightcurve amplitudes of the observed asteroids and obtained new or improved values of the rotation periods for most of them.

Context. Basaltic V-type asteroids play a crucial role in studies of Solar System evolution and planetesimal formation. Comprehensive studies of their physical, dynamical, and statistical properties provide insight into these processes. Thanks to wide surveys, currently there are numerous known V-type and putative V-type asteroids, allowing a detailed statistical analysis. Aims. Our main goal is to analyze I corrected for US language conventions in this paper the currently available large sample of V-type spin rates, to find signatures of the non-gravitational Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect among the different V-type populations, and to estimate the spin barrier and critical density for V-type asteroids. Our intention is to increase the pool of information about the intriguing V-types. Methods. We collected rotational periods from the literature for spectrally confirmed V-types, putative V-types, and Vesta family members. Through spectroscopic observations we confirmed their taxonomic type and verified the high confirmation rates of the putative V-types. We combined the collected periods with periods estimated in this manuscript and produced rotational frequency distributions. We determined the spin barrier in the frequency–light curve amplitude space for V-type asteroids. Results. We analyzed rotational periods of 536 asteroids in our sample. As expected, due to the small size of the objects analyzed, the frequency distributions for the Vesta family and the V-types outside the family are inconsistent with a Maxwellian shape. The Vesta family shows an excess of slow-rotators. V-types outside the family show an excess of both slow and fast rotators. Interestingly, we found that the population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. The estimated critical density for V-type asteroids exceeds ρ c = 2.0 g cm ⁻³ , which surpasses the previous estimates. Conclusions. We demonstrated that V-type asteroids have been influenced by the thermal radiation YORP effect and that their critical spin rate is higher than for C-type asteroids. The population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. We hypothesize that the objects that evolved from the Vesta family though the Yarkovsky drift are also more susceptible to the YORP effect. Objects for which YORP has not yet had enough time to act and those that are more YORP resistant will be left in the family, which explains the relatively small proportion of fast rotators being left. The YORP timescale must thus be similar to the migration timescale for those objects.

The V-type asteroids are of major scientific interest as they may sample multiple differentiated planetesimals. Determination of their physical properties is crucial for understanding the diversity and multiplicity of planetesimals. Previous studies have suggested distinct polarimetric behaviours for the V-type asteroids. Similarly to phase-polarization curves, asteroid phase-magnitude curves (hereinafter called “phase curves”) are also diagnostic of surface and regolith properties, and can be used to unveil a variety of distinct behaviours. We present well determined phase curves for ~20 V-type asteroids for the first time. Their phase curve parameters are consistent with those for moderate and high albedo asteroids. The computed median G12 parameter for the V-type asteroids is G12∗ = 0.14. We do not find substantial evidence for any clustering into distinct phase curve parameters groups. Only one asteroid (2763) Jeans shows exceptionally high G2 value. The derived median G12 may be used in single parameters fitting of V-type asteroids.