Possible Disintegration of Main-belt Asteroid 2008 BJ22

We are searching for new active asteroids using data from the Subaru Hyper Suprime-Cam (HSC) Public Data Release 3 (PDR3). The active asteroids are a poorly understood class of asteroids, which have orbits similar to other asteroids but exhibit tails or comae like comets. Of the over 1.4 million catalogued minor planets, most of which are main belt asteroids, fewer than 100 of the asteroids have exhibited activity, and roughly half of those are thought to be driven by water ice. The true fraction and solar system distribution of active asteroids is poorly known as most have been discovered serendipitously by a variety of methods. In this work, we search for activity among the known asteroids using one of the deepest wide-area public datasets available, the HSC PDR3. The goal of this work is to discover new active asteroid candidates and recurring activity in known active asteroids in archival data, collect contemporary images of those asteroids using ground based telescopes, and assess the true rate of active asteroid activity in a consistent manner using a large dataset. This will lead to insights into the present day distribution of water ice in our solar system.The HSC PDR3 has been collected using one of the largest ground-based optical telescopes, the 8.2 m Subaru telescope atop Maunakea in Hawaii which regularly achieves image quality better than 0.7 arcseconds yielding single-image depths of 25 to 25.5 magnitudes in the typical exposure times used for the PDR3. In addition, HSC itself has an extremely wide field of view, about 1.8 square degrees, for such a large telescope. Over 13,000 fields were imaged in good conditions with HSC as part of the PDR3, representing over 23,000 square degrees. The PDR3 dataset was collected for scientific purposes unrelated to the asteroids but many fields contain serendipitous images of asteroids. We have cross-correlated the PDR3 fields and the Minor Planet Database using the SkyBoT project and find that over 230,000 minor planets (over 15% of all minor planets and the vast majority asteroids) were serendipitously imaged in the dataset for a total of over 1.6 million minor planet images. We have begun the process of constructing thumbnail images of these minor planets from the full HSC PDR3 data release and expect to finish this year.Initially, we are examining images by eye ourselves to determine activity candidates. However, we will launch a Citizen Science campaign akin to activeasteroids.net, which has to date only used data from the DECam public archive. This will allow us to mobilize volunteers to examine more images than we can reliably categorize ourselves. We present first results from this work including an assessment of activity levels for thousands of asteroids most likely to exhibit activity including: previously known active asteroids, distant C-type main belt asteroids, and Centaurs on unstable orbits that could have recently moved inward from the trans-Neptunian region.Figure 1: One of 4 images from the HSC PDR3 archive of known active outer main belt asteroid 331P/Gibbs, exhibiting a faint linear tail.Figure 2: One of 17 images from the HSC PDR3 archive of known Jupiter family comet 242P/Spahr, exhibiting a tail. While not a primary target of this work, many comets are present in the HSC PDR3.

We present archival observations of main-belt asteroid (248370) 2005 QN173 (also designated 433P) that demonstrate this recently discovered active asteroid (a body with a dynamically asteroidal orbit displaying a tail or coma) has had at least one additional apparition of activity near perihelion during a prior orbit. We discovered evidence of this second activity epoch in an image captured 2016 July 22 with the DECam on the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile. As of this writing, (248370) 2005 QN173 is just the eighth active asteroid demonstrated to undergo recurrent activity near perihelion. Our analyses demonstrate (248370) 2005 QN173 is likely a member of the active asteroid subset known as main-belt comets, a group of objects that orbit in the main asteroid belt that exhibit activity that is specifically driven by sublimation. We implement an activity detection technique, wedge photometry, that has the potential to detect tails in images of solar system objects and quantify their agreement with computed antisolar and antimotion vectors normally associated with observed tail directions. We present a catalog and an image gallery of archival observations. The object will soon become unobservable as it passes behind the Sun as seen from Earth, and when it again becomes visible (late 2022) it will be farther than 3 au from the Sun. Our findings suggest (248370) 2005 QN173 is most active interior to 2.7 au (0.3 au from perihelion), so we encourage the community to observe and study this special object before 2021 December.

This paper presents a new optical imaging survey of four deep drilling fields (DDFs), two Galactic and two extragalactic, with the Dark Energy Camera (DECam) on the 4-m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO). During the first year of observations in 2021, >4000 images covering 21 deg2 (seven DECam pointings), with ∼40 epochs (nights) per field and 5 to 6 images per night per filter in g, r, i, and/or z have become publicly available (the proprietary period for this program is waived). We describe the real-time difference-image pipeline and how alerts are distributed to brokers via the same distribution system as the Zwicky Transient Facility (ZTF). In this paper, we focus on the two extragalactic deep fields (COSMOS and ELAIS-S1) characterizing the detected sources, and demonstrating that the survey design is effective for probing the discovery space of faint and fast variable and transient sources. We describe and make publicly available 4413 calibrated light curves based on difference-image detection photometry of transients and variables in the extragalactic fields. We also present preliminary scientific analysis regarding the Solar system small bodies, stellar flares and variables, Galactic anomaly detection, fast-rising transients and variables, supernovae, and active Galactic nuclei.

A study of photometric observations of (3200) phaethon from Lulin Observatory

Properties and evolution of NEO families created by tidal disruption at Earth

Fifteen Anomalous Cepheid (ACeph) candidates were recently identified in the dwarf galaxy Crater II via an extended survey done with the Dark Energy Camera at the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory (CTIO). Using various Period–Luminosity relationships found in the literature, we anchor these candidates to the nearby RR-Lyrae stars’ distances to confirm 14 of the candidates as not only being ACephs, but as confidently belonging to Crater II rather than the field within the line-of-sight.

We present the most extensive set to date of high-quality RR Lyrae light curve templates in the ɡriz bands, based on time-series observations of the Dark Energy Camera Plane Survey (DECaPS) East field, located in the Galactic bulge at coordinates (RA, Dec)(J2000) = (18:03:34, −29:32:02), obtained with the Dark Energy Camera (DECam) on the 4-m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO). Our templates, which cover both fundamental-mode (RRab) and first-overtone (RRc) pulsators, can be especially useful when there is insufficient data for accurately calculating the average magnitudes and colors, hence distances, as well as to inform multiband light curve classifiers, as will be required in the case of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). In this paper, we describe in detail the procedures that were adopted in producing these templates, including a novel approach to account for the presence of outliers in photometry. Our final sample comprises 136 RRab and 144 RRc templates, all of which are publicly available. Lastly, in this paper we study the inferred Fourier parameters and other light curve descriptors, including rise time, skewness, and kurtosis, as well as their correlations with the pulsation mode, period, and effective wavelength.

On 2019 August 14 at 21:10:39 UTC, the LIGO/Virgo Collaboration (LVC) detected a possible neutron star–black hole merger (NSBH), the first ever identified. An extensive search for an optical counterpart of this event, designated GW190814, was undertaken using the Dark Energy Camera on the 4 m Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory. Target of Opportunity interrupts were issued on eight separate nights to observe 11 candidates using the 4.1 m Southern Astrophysical Research (SOAR) telescope’s Goodman High Throughput Spectrograph in order to assess whether any of these transients was likely to be an optical counterpart of the possible NSBH merger. Here, we describe the process of observing with SOAR, the analysis of our spectra, our spectroscopic typing methodology, and our resultant conclusion that none of the candidates corresponded to the gravitational wave merger event but were all instead other transients. Finally, we describe the lessons learned from this effort. Application of these lessons will be critical for a successful community spectroscopic follow-up program for LVC observing run 4 (O4) and beyond.

We report the discovery of cometary activity in the form of a pronounced tail emanating from Near-Earth Object (523822) 2012 DG61, identified in UT 2024 April 18 Dark Energy Camera images by our AI assistant TailNet. TailNet is an AI designed to filter out images unlikely to show activity for volunteers of our NASA Partner “Active Asteroids” Citizen Science campaign, from which our AI is trained. Subsequently, our archival investigation revealed 2012 DG61 is recurrently active after we found it displaying a pronounced tail in a UT 2018 April 16 Steward Observatory Bart Bok 2.3 m telescope image and UT 2018 May 14 observations by G. Borisov with the 0.3 m telescope at MARGO Observatory. Our dynamical integrations reveal that 2012 DG61, an Apollo dynamical class member, is likely in 2:1 mean-motion resonance with Jupiter. We encourage additional observations to help characterize the activity morphology of this near-Earth comet.

Main-belt comets are small Solar System bodies located in the asteroid belt that repeatedly exhibit comet-like activity (that is, dust comae or tails) during their perihelion passages, strongly indicating ice sublimation1,2. Although the existence of main-belt comets implies the presence of extant water ice in the asteroid belt, no gas has been detected around these objects despite intense scrutiny with the world's largest telescopes3. Here we present James Webb Space Telescope observations that clearly show that main-belt comet 238P/Read has a coma of water vapour, but lacks a significant CO2 gas coma. Our findings demonstrate that the activity of comet Read is driven by water-ice sublimation, and implies that main-belt comets are fundamentally different from the general cometary population. Whether or not comet Read experienced different formation circumstances or evolutionary history, it is unlikely to be a recent asteroid belt interloper from the outer Solar System. On the basis of these results, main-belt comets appear to represent a sample of volatile material that is currently unrepresented in observations of classical comets and the meteoritic record, making them important for understanding the early Solar System's volatile inventory and its subsequent evolution.

As a new class of comet, main belt comets (MBCs) have attracted more and more attention in recent years. To study activity and physical properties of three MBCs 176P/LINEAR, 238P/Read and 288P/(300163) 2006 VW139, we carried out broadband CCD photometry of three MBCs on UT 2016 November 18–19 with the 1-m optical telescope at Lulin Observatory in Taiwan. By comparing cometary surface brightness profiles to stellar surface brightness profiles, and by comparing cometary absolute magnitude to the expected magnitude of inactive nucleus, we found that 176P/LINEAR was inactive, while 238P/Read and 288P/(300163) 2006 VW139 were active. By photometric studies, we obtained the Afρ values and the dust production rates. Finally, the activity of three MBCs were discussed. Our photometric results show that the total dust mass of 238P/Read and 288P/(300163) 2006 VW139 obtained in this work are of the same magnitude as the majority of known MBCs.

Investigation of dynamical and physical properties of the main-belt and near-Earth asteroids is a priority research area, which has reached a new level in recent years. This progress has been facilitated by space missions to asteroids as well as modern all-sky surveys aimed to discover new objects which also provide highly accurate astrometric and photometric data. However, the role of ground-based programs remains valuable. The long-term monitoring program is crucial for retrieving asteroid physical properties and its evolution. The primary aim of our Project is obtaining new observational data of asteroids by carrying out their spectrophotometric (Shevchenko et al. 2022) and polarimetric (Belskaya, Krugly 2024) observations which allow us to determine absolute magnitudes, rotation periods, surfaces properties, albedo, sizes and shapes of these objects. Our observations are based on cooperation with colleagues from different observatories in several countries (Bulgaria, Georgia, Kazakhstan, Slovakia, Uzbekistan, Chili, USA) with using the 0.6 - 2 m telescopes which are equipped with modern CCD cameras. Our priority targets include newly discovered and potentially hazardous near-Earth asteroids, binary asteroids, especially those observed by Gaia, objects studied through radar observations, and targets of ongoing and future space missions (Hayabusa2#, Hera etc). During January-April 2025, new photometric observations of over 40 NEAs (4 newly discovered, 17 PHAs, for 18 the rotation periods were determined for the first time) and 8 known main-belt binary asteroids were carried out, as well as polarimetric observations of 2 NEAs were obtained at high phase angles. Preliminary results of our new and long-term observations will be presented. AcknowledgmentsThe Kharkiv team is thankful to Ukrainian soldiers who defend our lives and freedom against russian aggression. YK thanks the French PAUSE program for its support of scientists at risk. ReferencesShevchenko, V. G., I. N. Belskaya, I. G. Slyusarev, O. I. Mikhalchenko, Yu. N. Krugly et al. 2022. Kharkiv database of asteroid absolute magnitudes: Comparative analysis with other datasets. 2022A&A...666A.190S Belskaya I., Y. Krugly. 2024. Study of near-Earth asteroids by polarimetric technique. Report on “EU-ESA Workshop on Size Determination of Potentially Hazardous Near-Earth Objects”, 11–13 Nov 2024, Darmstadt, Germany.

The near-Earth asteroid population from two decades of observations

Wide Field Survey Telescope (WFST), with a powerful sky survey capability in the northern hemisphere, will play an important role in asteroid searching and monitoring. However, WFST is not a telescope dedicated to near-Earth asteroids (NEOs) searching. In order to improve the efficiency of finding NEOs on the premise of meeting the needs of other scientific research, we ran mock observations for WFST to study its search capability for NEOs. The NEO population model, the WFST detection model and site conditions are taken into account in our simulations. Based on the original scheduling scheme, we present two new schemes. Compared to the original scheme, the optimized scheme can improve the search capability of known and unknown NEOs by 100% and 50%. We also emphasized the importance of trailing loss and proposed an improved effective field of view model. In addition, it is predicted that adopting the clear-day ratio of 0.7 and the optimized scheme, during one year of regular survey, for NEOs with absolute magnitude from 17 to 25, WFST can provide tracklets for about 1800 NEOs if their orbits are known, and in the case of blind search, more than 600 NEOs can be found by WFST. The new schemes provide valuable reference and suggestions for the WFST’s regular survey strategy.

Comets and asteroids have traditionally been separated categories, but main belt comets skew this view, portraying a possible intermediate stage between these two endmembers. Investigating the relationship between these bodies can improve our understanding of the formation and evolution of the Solar System and help to identify potentially interesting parent bodies from within our solar system, for future sample return missions. Furthermore, elucidating the ice-organic-silicate ratios of potential meteorite parent bodies can help to explain the observed isotopic ratios and petrography of meteorite samples. While the ice-organic-silicate ratios of particular bodies have been estimated, there has been no study undertaken which compares different types of bodies in terms of their ice-organic-silicate ratios. Therefore, this study presents a geophysical-chemical mass balance model, to estimate the ice-organic-silicate ratios of comets, main belt comets and asteroids. The results drawn from the model form a diagonal trend upon an ice-organic-silicate ternary diagram, in which comets and main belt comets plot together at generally higher ice contents, with asteroids typically plotting at lower ice contents. However, an overlap between all three body types is observed and supports the scenario in which comets, main belt comets and asteroids are genetically linked.