Poster presentations and abstracts

The Gaia mission will provide to the solar system scientific community with high quality observations of about 300,000 asteroids of all categories. Most will be from the main belt but small asteroids from the NEA group, Jupiter trojans, centaurs and transneptunians are also observed. Gaia Data Release 2 (DR2) was published in 2018 and consists of 22 months of observations of 14,099 known Solar System objects, mainly asteroids [2], based on more than 1.5 million observations (https://www.cosmos.esa.int/web/gaia/data-release-2). The scientific community must be prepared to analyze this large amount of data that will allow us to encompass a more detailed knowledge of asteroid populations, which are currently poorly characterized, since basic physical properties such as mass, density, rotation properties, shape and albedo are not yet known for most of them [1].

The purpose of this work is to obtain a catalogue of phase function parameters (H and G) for all asteroids that are observed by the Gaia mission and published in DR2.

To do this, we introduce an algorithm capable of building this catalogue from the magnitude and julian date data present in the Gaia mission DR2. For a first stage of testing, we started with those objects whose MPC number is less than 5000. Since Gaia will never observe asteroids at 0^o phase angle (corresponding to the opposition), but at phase angles greater than 10^o, we added data from ground-based observations (corresponding to small phase angles) and thus improved the determination of the H and G parameters of the phase function. As a next step in the search to improve this determination, we repeat the calculations for the phase function of three parameters H, G₁ and G₂ [4] . 

We obtained a catalogue with the estimation of the parameters two parameters of the phase functions (H and G) for 4208 asteroids (Figure 1). We compared our results with those in the Astorb database and noted that the level of agreement is satisfactory. In Figure 1 we can see the comparison of the obtained H versus the one published in the Astorb database. Furthermore, it is important to note the decrease of about 50% in the mean square error after combining the Gaia mission data with photometric data obtained from the ground (Figure 2). Data from the ground is obtained from the Asteroid Photometric Catalog V1.1 [3].

Figure 1: Comparison of the obtained H using Gaia data only versus the one published in the Astorb database. The colour scale indicates the number of GAIA observations, the darker the colour, the more observations the asteroid has.

Figure 2: Comparison of the obtained H using Gaia data and data obtained by ground-based telescopes versus the one published in the Astorb database. The colour scale indicates the number of GAIA observations as before.

We also obtained the G parameters for those 4208 asteroids (Figure 3). It is important to note that asteroids have G values in a wide range, as opposed to the fixed value G=0.15 that is assigned to most of them as established in MPC 17257 (December, 1990).

Figure 3: Histograms of the G-values obtained. The vertical green line marks G=0.15, which is the value adopted for the vast majority of asteroids.

We must be prepared with computer tools to analyze and take advantage of the large amount of data that the Gaia mission will provide to the scientific community in DR3. With our work we will not only be contributing with the catalogue of parameters of the phase function but also, we will be able to estimate the diameters of the thousands of observed asteroids using the obtained absolute magnitudes H combined with the information of the albedos of these objects. 
We highlight here the importance of been prepared to analyze all the data coming from the space and ground-based surveys. Special dedication to the preparation of dedicated pipelines to extract all the possible information in each survey. 

How to cite: Colazo, M. and Duffard, R.: H-G determination of 4000 asteroids from GAIA-DR2, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-406, https://doi.org/10.5194/epsc2020-406, 2020.

The Tomo-e Gozen project conducts optical wide-field survey programs with a wide-field CMOS camera, Tomo-e Gozen, attached on the 105-cm Schmidt telescope at the Kiso Observatory, the University of Tokyo, Japan. Tomo-e Gozen is the world's first wide-field CMOS camera which covers 20 square degrees with 84 chips of 35 mm full HD CMOS image sensors. A wide-field and high-cadence survey in the optical wavelengths began in 2018 with the Tomo-e Gozen (hereafter referred to as the Tomo-e Gozen transient survey). The main purpose of this survey is to detect young supernovae. However, the survey simultaneously detects a large number of moving objects in their images. As one of the by-products of the survey, here we show our preliminary result about production of phase curves (solar phase angles versus absolute magnitude) of more than 44,000 small solar system bodies including main-belt asteroids, near-Earth asteroids, Jupiter Trojans, Centaurs, and Transneptunian objects (this number is as of April 11, 2020). Combining the moving object catalogue derived from the survey and the output ephemeris that the Horizons/JPL system provides, we are now able to obtain phase curves of these objects almost automatically. As the Kiso moving object catalogue is updated and being expanded on a daily basis, the number of the objects (small bodies) that we deal with goes up as well. Our result, when completed, will make a fair complement as well as a significant keystone to what is already published such as from the Pan-STARRS systematic survey on the knowledge of the surface characteristics of the small solar system bodies.

How to cite: Yoshida, F., Ito, T., Urakawa, S., Terai, T., Tominaga, N., Morokuma, T., Sako, S., Ohsawa, R., Tanaka, M., and Hamasaki, R.: Phase curves of >40,000 small solar system bodies obtained by the Tomo-e Gozen transient survey, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-330, https://doi.org/10.5194/epsc2020-330, 2020.

According the H-G magnitude system ,this work using the known spectral-type asteroids (about three hundreds asteroids including MBAs and NEAs) found from literature, we derived the new G-value of two main taxonomic groups in both g and r filters (In g filter, C-type is 0.095±0.112, and S-type is 0.257±0.165. In r filter, C-type is 0.091±0.134, and S-type is 0.280±0.158). We then used these values to identify the unknown taxonomic near-Earth asteroids(NEAs) obtained by (ZTF) from June 2018 to May 2020. In total, more than one hundred NEAs had been classified into C- and S-complex. In addition, the investigation of size distribution in NEAs found that the C-complex asteroids are relatively larger than S-complex asteroids, probably due to observational bias (albedo).

How to cite: Lin, Z.-Y., Cheng, C.-C., Chang, C.-K., Tseng, W.-L., and Ip, W.-H.: Statistical analysis of asteroid taxonomic signatures from magnitude phase function , Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-994, https://doi.org/10.5194/epsc2020-994, 2020.

Asteroid Terrestrial-impact Last Alert System (ATLAS) is an all-sky survey consisting of two Schmidt telescopes located at on Haleakala and Mauna Loa in Hawaii. The telescopes have 65-cm primary mirror, f/2.0, and the field of view is 7.5 deg. They cover the whole visible sky during one night down to ~19 mag with 30 s exposures [1]. Apart from astrometric data, the system also produces photometric measurements that contain information about asteroid rotation. 

We used ATLAS photometry that was available for approximately 180,000 asteroids observed between 2015 and 2018 to derive asteroid rotation periods. Most of observations were done in orange (560-820 nm) and cyan (420-650 nm) filters. We fitted the data with an ellipsoidal shape model scanning rotation periods between 2 and 1000 hours. For each asteroid, we obtained the best-fit period and corresponding orientation of the spin axis and elongation of the ellipsoidal shape model. However, the best-fit period (corresponding to χ² minimum in the periodogram) was in most cases just random period that was not reliable because the number of data points was small or the lightcurve amplitude was lost in noise. 

To test how reliable the determined periods were and how sensitive they were to the actual data sets, we repeated the period scan with many bootstrapped samples of original data and each time derived a new best-fit period. Reliable period determinations had all these periods the same, while unreliable determinations had different periods for different bootstrapped samples. 

To check a typical rate of false positive solutions, we compared the periodogram results with periods reported in the Lightcurve Database (LCDB) [2] and with an independent analysis of ATLAS data [3]. From roughly 100,000 asteroids with more than hundred individual brightness measurement, we were able to uniquely and reliably determine rotation periods for thousands of them. For other thousands, their periods were likely correct but with less certainty.

We present the analysis of correlations between the number of data points and likelihood that the correct period was found. We estimate that by this approach, much larger number of periods can be determined when additional ATLAS or another survey data are available.

[1] Tonry, J. L., Denneau, L., Heinze, A. N. et al. (2018): ATLAS: A High-cadence All-sky Survey System, PASP 130(6), 064505.

[2] Warner, B. D., Harris, A. W., and Pravec, P. (2009): The asteroid lightcurve database, Icarus 202, 134.

[3] Erasmus, N., Navarro-Meza, S., McNeill, A. et al. (2020): Investigating taxonomic diversity within Asteroid Families through ATLAS dual-band photometry, ApJS 247, 13.

How to cite: Durech, J.: Rotation periods of asteroids determined from ATLAS photometry, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-101, https://doi.org/10.5194/epsc2020-101, 2020.

The main objective of the study is the verification of the V-type rotation distribution. Though numerical modelling, Nesvorny et al. (2008) showed that asteroids can migrate through Yarkovsky effect and resonaces outside the boundaries of the Vesta family. In particular they found that objects which end up in the scattered resonances region (so-called Cell I, defined by orbital elements 2.2 AU < a < 2.3 AU, 0.05 < e < 0.2, 0 < i deg < 10 deg) typically have retrograde rotation and thermal parameters that maximize the Yarkovsky drift. Consequently, most of the V-types in Cell I should be retrograde rotating. Similarly showed that asteroids migrating to the low inclination region (Cell II defined by 2.32 AU < a < 2.48 AU, 0.05 < e < 0.2, 2 deg < i < 6 deg) should be predominantly rotating prograde (60% of objects).

We perform photometric observations and determine spins and shapes of V-type objects in Cell I and II to verify the predicted statistics of sense of rotation. Finding significantly un-matching statistics for rotational properties may strengthen the idea that there may be fragments of other (than Vesta) differentiated planetesimals in the inner main belt. We show preliminary results for the first few asteroids in Cell I and II.

How to cite: Troianskyi, V. and the V-type asteroid team: Verification of the V-type asteroids rotation distribution outside Vesta family, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1128, https://doi.org/10.5194/epsc2020-1128, 2020.