<p><strong>Slow rotators among asteroids</strong></p><p> Recently published results from Kepler and TESS space missions (Molnar 2018; Pal et al. 2020) revealed surprisingly large numbers<strong> </strong>of slow rotators (P>12 hours) among main belt asteroids. Previous, ground-based surveys usually disfavoured them, so they also lacked dense lightcurves from multiple apparitions, essential for the spin and shape reconstruction. Such targets are also poorly studied in the thermal infrared range, because thermophysical modelling (TPM) requires spin and shape model as input. However slow-rotators are particularly interesting on that matter, due to their expected larger skin depth able to probe their denser or more conductive layers underneath the upper regolith (Harris & Drube 2016, 2020)</p><p> Our ongoing survey (see e.g. Marciniak et al. 2015; and 2019) is targeted at slow rotators to decrease this bias, and complement our knowledge of various properties of these objects. We gather dense lightcurves using a rich network of small ground-based telescopes, supplementing the data with the results from TESS and Kepler spacecrafts, where available.</p><p><strong>Simultaneous optimisation</strong></p><p> For the modelling we are using a novel approach to simultaneously optimise model spin, shape, size and thermal inertia using both visible lightcurves mainly from our survey, and thermal data from the infrared satellites, primarily WISE (Wright et al. 2010), IRAS (Neugebauer 1984), and AKARI (Usui 2011). The method joining the two approaches is Convex Inversion Thermophysical Model (CITPM, Durech et al. 2017). As a result we get size-scaled shape models which fit both data types very well. This is often not the case when shape models from lightcurve inversion only are a posteriori used in the TPM. However their slight alteration, eg. via bootstrapping the lightcurves can improve the reduced χ<sup>2</sup> substantially (Hanus et al. 2015; 2018). With the CITPM method the thermal data are allowed to alter the shape models on the fly, instead of the two-step approach used in previous studies (see e.g. our benchmark studies within SBNAF project, Muller et al. 2018).</p><p> In cases where rich stellar occultation timings were available in the PDS (Herald et al. 2019), we also fit the obtained shape models to occultation chords, obtaining independent size determinations, consistent with the sizes from CITPM. This step also validates shape model topographic features, and in some cases allows to break the degeneracy between two mirror-pole solutions (see figure below). Sizes from CITPM and occultation fitting are in good agreement.  In the figure below two contours represent shape models for two mirror pole solutions, while black lines mark occultation shadow chords from occultation timings. Negative (no occultation) chords are marked with dotted lines. North is up and west is right. One of the pole solutions fits much better than its mirror counterpart.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.e29b54f962a062966521261/sdaolpUECMynit/1202CSPE&app=m&a=0&c=554d2a30ac6d7d8f6f3f7b322bf529f3&ct=x&pn=gnp.elif&d=1" alt="" width="401" height="333"></p><p><br><strong>Thermal inertia and sizes</strong></p><p> With this approach we recently obtained detailed models for 16 slow rotators (Marciniak et al., submitted). Figure below shows example thermal inertia vs reduced χ<sup>2</sup> curves (target: 667 Denise), where the range of solutions with low χ<sup>2</sup> values allows to define the range of possible thermal inertias. The solution also constraints the best size range, coded with colour scale, and gives some constraints on surface roughness coded with symbols  (f being the percentage of coverage with hemispherical craters, while their opening angle was also optimised in the process).</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.520db57a62a061286521261/sdaolpUECMynit/1202CSPE&app=m&a=0&c=822d989de5f048cec64b5e2d2cbc9ed1&ct=x&pn=gnp.elif&d=1" alt=""></p><p><strong> Results</strong></p><p> We substantially enlarged the sample of modelled and precisely scaled slow rotators with available thermal inertia, and validated the approach of simultaneous fitting two different types of data. Determined sizes are on average accurate at 5% precision level, with the diameters in the range from 25 to 145 km. Thermal inertia reaches wide range of values, from 2 to < 400 SI units, with inevitable degeneracy with surface roughness.</p><p> Overall, we found no common features or trends among our targets, in particular no trend with the rotation period. The reason might be still small size of the available sample, or the relatively small thermal skin depth (l<sub>s</sub>) of even the slowest rotators in our sample, where targets with periods up to 59 hours have l<sub>s</sub> in a few millimetre range.</p><p><br> References:</p><p> Durech, J., Delbo, M., Carry, B., Hanus, J., & Ali-Lagoa, V. 2017, A&A, 604, A27<br> Hanus, J., Delbo, M., Durech, J., & Ali-Lagoa, V. 2015, Icarus, 256, 101<br> Hanuš, J., Delbo, M., Durech, J., & Ali-Lagoa, V. 2018, Icarus, 309, 297<br> Harris, A. W. & Drube, L. 2016, ApJ, 832, 127<br> Harris, A. W. & Drube, L. 2020, ApJ, 901, 140<br> Herald, D., Frappa, E., Gault, D., et al. 2019, Asteroid Occultations V3.0, NASA Planetary Data System<br> Marciniak, A., Pilcher, F., Oszkiewicz, D., et al. 2015, Planet. Space Sci., 118, 256<br> Marciniak, A., Ali-Lagoa, V., Muller, T. G., et al. 2019, A&A, 625, A139<br> Molnar, L., Pal, A., Sarneczky, K., et al. 2018, ApJS, 234, 37<br> Muller, T. G., Marciniak, A., Kiss, C., et al. 2018, ASR, 62, 2326<br> Neugebauer, G., Habing, H. J., van Duinen, R., et al. 1984, ApJ, 278, L1<br> Pal, A., Szakats, R., Kiss, C., et al. 2020, ApJS, 247, 26<br> Usui, F., Kuroda, D., Muller, T. G., et al. 2011, PASJ, 63, 1117<br> Wright, E. L., Eisenhardt, P. R. M., Mainzer, A. K., et al. 2010, AJ, 140, 1868</p>

Context. Earlier work suggests that slowly rotating asteroids should have higher thermal inertias than faster rotators because the heat wave penetrates deeper into the sub-surface. However, thermal inertias have been determined mainly for fast rotators due to selection effects in the available photometry used to obtain shape models required for thermophysical modelling (TPM). Aims. Our aims are to mitigate these selection effects by producing shape models of slow rotators, to scale them and compute their thermal inertia with TPM, and to verify whether thermal inertia increases with the rotation period. Methods. To decrease the bias against slow rotators, we conducted a photometric observing campaign of main-belt asteroids with periods longer than 12 hours, from multiple stations worldwide, adding in some cases data from WISE and Kepler space telescopes. For spin and shape reconstruction we used the lightcurve inversion method, and to derive thermal inertias we applied a thermophysical model to fit available infrared data from IRAS, AKARI, and WISE. Results. We present new models of 11 slow rotators that provide a good fit to the thermal data. In two cases, the TPM analysis showed a clear preference for one of the two possible mirror solutions. We derived the diameters and albedos of our targets in addition to their thermal inertias, which ranged between 3 +33 −3 and 45 +60 −30 J m −2 s −1/2 K −1 . Conclusions. Together with our previous work, we have analysed 16 slow rotators from our dense survey with sizes between 30 and 150 km. The current sample thermal inertias vary widely, which does not confirm the earlier suggestion that slower rotators have higher thermal inertias.

Context. Recent results for asteroid rotation periods from the TESS mission showed how strongly previous studies have underestimated the number of slow rotators, revealing the importance of studying those targets. For most slowly rotating asteroids (those with P > 12 h), no spin and shape model is available because of observation selection effects. This hampers determination of their thermal parameters and accurate sizes. Also, it is still unclear whether signatures of different surface material properties can be seen in thermal inertia determined from mid-infrared thermal flux fitting. Aims. We continue our campaign in minimising selection effects among main belt asteroids. Our targets are slow rotators with low light-curve amplitudes. Our goal is to provide their scaled spin and shape models together with thermal inertia, albedo, and surface roughness to complete the statistics. Methods. Rich multi-apparition datasets of dense light curves are supplemented with data from Kepler and TESS spacecrafts. In addition to data in the visible range, we also use thermal data from infrared space observatories (mainly IRAS, Akari and WISE) in a combined optimisation process using the Convex Inversion Thermophysical Model. This novel method has so far been applied to only a few targets, and therefore in this work we further validate the method itself. Results. We present the models of 16 slow rotators, including two updated models. All provide good fits to both thermal and visible data.The obtained sizes are on average accurate at the 5% precision level, with diameters found to be in the range from 25 to 145 km. The rotation periods of our targets range from 11 to 59 h, and the thermal inertia covers a wide range of values, from 2 to <400 J m−2 s−1∕2 K−1, not showing any correlation with the period. Conclusions. With this work we increase the sample of slow rotators with reliable spin and shape models and known thermal inertia by 40%. The thermal inertia values of our sample do not display a previously suggested increasing trend with rotation period, which mightbe due to their small skin depth.

Photometric observations of the nearly equal-mass binary near-Earth asteroid 2017 YE5 were carried out at the Observatório Astronômico do Sertão de Itaparica (OASI, Brazil) and at the Blue Mountains Observatory (BMO, Australia) between July and August 2018, shortly after it made a close approach to Earth in June 2018. These observations allowed to determine an orbital period of the system in good agreement with the result of the radar observations. Our results also indicate that the 2017 YE5 system is not fully locked in a synchronous spin-orbit resonance, as there is a possible asynchronous component or tumbling rotator in the system. Additional data obtained at the Observatorio Astronómico Nacional de San Pedro Mártir (OAN-SPM, Mexico) in August 2018 allowed to derive the colour indices and the low resolution spectrum, which indicate that the object has a very reddish surface similar to the outer Solar system objetcs. This is consistent with a dark albedo of about 3 per cent, derived from an effective diameter of the combined components and an absolute magnitude of 19.2. Infrared data obtained at the NASA’s IRTF exhibit a thermal emission in the 2.5 μm range for which a low albedo of 2-4 per cent was adjusted by applying a thermal model. Regarding to the taxonomic classification, we found that the 2017 YE5 is a D-type in the Bus-DeMeo taxonomy. Therefore, according to our results and considering that the 2017 YE5 system has a typical comet orbit (TJ = 2.87), we suggest that it is a dormant Jupiter-family binary comet.

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The observation of NEOs allows us to study the physical properties of the smallest size bodies of our Solar System and help impose constraints on their origin and evolution. The solar phase curve is a very important tool to derive diverse physical properties of a small body so that we set up an observational campaign to derive the phase curve parameters (H, G1, G2) for a large number of NEOs. We present here the obtained phase curves for 12 NEOs, along with the rotation period for 2 of them and the V-R color for 4. The data was acquired mainly at the Astronomical Observatory of Sertão de Itaparica (Brazil), with some NEOs also observed at the Osservatorio di Campo Imperatore (Italy). Considering all the objects observed throughout our campaign we analyzed a homogeneous dataset of 30 NEOs along with data acquired by ATLAS (Asteroid Terrestrial-impact Last Alert System telescopes survey) for MB asteroids. The behavior in the phase space G1-G2 of 21,865 MBA and 103 NEOs was analyzed, separating the objects in intervals of albedos and sizes. From the large MB data set we found evidence that the distribution in the G1-G2 phase space has strong dependence not only on the albedo but also on the object’s size. This is particularly true for the smaller objects. The main result being that, on the contrary to what occurs with the MB larger objects, we are unable to estimate the albedo of a NEO from its phase curve parameters.