arXiv subjects

A. A. Sickafoose

Publications and source records attributed to A. A. Sickafoose.

10 recordsLinked to original sources

arXiv2025

The Near-Centaur Environment: Satellites, Rings, and Debris

The unexpected finding of a ring system around the Centaur (10199) Chariklo opened a new window for dynamical studies and posed many questions about the formation and evolutionary mechanisms of Centaurs as well as the relationship to satellites and outbursting activity. As minor planets that cross the orbits of the giant planets, Centaurs have short dynamical lifetimes: Centaurs are supplied from the trans-Neptunian region and some fraction migrates inward to become Jupiter-family comets. Given these dynamical pathways, a comparison of attributes across these classifications provides information to understand the source population(s) and the processes that have affected these minor planets throughout their lifetimes. In this chapter we review the current knowledge of satellites, rings, and debris around Centaur-like bodies, discuss the observational techniques involved, place the information into context with the trans-Neptunian Objects, and consider what the results tell us about the outer solar system. We also examine open questions and future prospects.

astro-ph.EP↗

arXiv2020

Investigating Taxonomic Diversity within Asteroid Families through ATLAS Dual-Band Photometry

We present here the c-o colors for identified Flora, Vesta, Nysa-Polana, Themis, and Koronis family members within the historic data set (2015-2018) of the Asteroid Terrestrial-impact Last Alert System (ATLAS). The Themis and Koronis families are known to be relatively pure C- and S-type Bus-DeMeo taxonomic families, respectively, and the extracted color data from the ATLAS broadband c- and o-filters of these two families is used to demonstrate that the ATLAS c-o color is a sufficient parameter to distinguish between the C- and S-type taxonomies. The Vesta and Nysa-Polana families are known to display a mixture of taxonomies possibly due to Vesta's differentiated parent body origin and Nysa-Polana actually consisting of two nested families with differing taxonomies. Our data show that the Flora family also displays a large degree of taxonomic mixing and the data reveal a substantial H-magnitude dependence on color. We propose and exclude several interpretations for the observed taxonomic mix. Additionally, we extract rotation periods of all of the targets reported here and find good agreement with targets that have previously reported periods.

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arXiv2019

Characterization of material around the centaur (2060) Chiron from a visible and near-infrared stellar occultation in 2011

The centaur (2060) Chiron has exhibited outgassing behaviour and possibly hosts a ring system. On 2011 November 29, Chiron occulted a fairly bright star (R approximately 15 mag) as observed from the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea and the 2-m Faulkes Telescope North (FTN) at Haleakala. Data were taken as visible wavelength images and simultaneous, low-resolution, near-infrared (NIR) spectra. Here, we present a detailed examination of the light-curve features in the optical data and an analysis of the near-infrared spectra. We place a lower limit on the diameter of Chiron's nucleus of 160.2+/-1.3 km. Sharp, narrow dips were observed between 280-360 km from the centre (depending on event geometry). For a central chord and assumed ring plane, the separated features are 298.5 to 302 and 308 to 310.5 km from the nucleus, with normal optical depth approximately 0.5-0.9, and a gap of 9.1+/-1.3 km. These features are similar in equivalent depth to Chariklo's inner ring. The absence of absorbing or scattering material near the nucleus suggests that these sharp dips are more likely to be planar rings than a shell of material. The region of relatively-increased transmission is within the 1:2 spin-orbit resonance, which is consistent with the proposed clearing pattern for a non-axisymmetric nucleus. Characteristics of additional, azimuthally incomplete features are presented, which are likely to be transient, as well as detection of an extended shell or diffuse ring from approximately 900-1500 km. There are no significant features in the NIR light curves, nor any correlation between optical features and NIR spectral slope.

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arXiv2019

A Taxonomic Study of Asteroid Families from KMTNet-SAAO Multi-band Photometry

We present here multi-band photometry for over 2000 Main-belt asteroids. For each target we report the probabilistic taxonomy using the measured V-R and V-I colors in combination with a machine-learning generated decision surface in color-color space. Through this method we classify >85% of our targets as one the four main Bus-DeMeo complexes: S-, C-, X-, or D-type. Roughly one third of our targets have a known associated dynamic family with 69 families represented in our data. Within uncertainty our results show no discernible difference in taxonomic distribution between family members and non-family members. Nine of the 69 families represented in our observed sample had 20 or more members present and therefore we investigate the taxonomy of these families in more detail and find excellent agreement with literature. Out of these 9 well-sampled families, our data show that the Themis, Koronis, Hygiea, Massalia, and Eunomia families display a high degree of taxonomic homogeneity and that the Vesta, Flora, Nysa-Polana, and Eos families show a significant level of mixture in taxonomies. Using the taxonomic purity and the degree of dispersion in observed colors for each of the 9 well-sampled collisional families we also speculate which of these families potentially originated from a differentiated parent body and/or is a family with a possible undetermined nested family. Additionally, we obtained sufficient photometric data for 433 of our targets to extract reliable rotation periods and observe no obvious correlation between rotation properties and family membership.

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arXiv2018

A stellar occultation by Vanth, a satellite of (90482) Orcus

A stellar occultation by the large trans-Neptunian object (90482) Orcus was predicted to occur on 2017 March 07. Observations were made at five sites in North and South America. High-speed, visible-wavelength images were taken at all sites, in addition to simultaneous K-band images at one location. Solid-body occultations were observed from two sites. Post-event reconstruction suggested an occultation of two different stars observed from two different sites. Follow-up, speckle imaging at Gemini Observatory revealed a second star, which verified that the occulting body in both cases was Orcus` satellite, Vanth. The two single-chord detections, with an anomalously large timing delay in one chord, have lengths of 291+/-125 km and 434.4+/-2.4 km. The observations, combined with a non-detection at a nearby site, allow a tight constraint of 443+/-10 km to be placed on Vanth`s size (assuming it is spherical). A 3-σ upper limit of 1-4 μbar (depending on constituent) is found for a global Vanth atmosphere. The immersion and emersion profiles are slightly different, with atmospheric constraints 40 percent higher on immersion than on emersion. No rings or other material were detected within ten thousand kms of Vanth, and beyond 8010 km from Orcus, to the tightest optical depth limit of approximately 0.1 at 5 km scale. The occultation probed as close as 5040 km from Orcus, placing an optical depth limit of approximately 0.3 at 5 km scale on any encircling material at that distance.

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arXiv2018

Solar system science with the Wide-Field InfraRed Survey Telescope (WFIRST)

We present a community-led assessment of the solar system investigations achievable with NASA's next-generation space telescope, the Wide Field InfraRed Survey Telescope (WFIRST). WFIRST will provide imaging, spectroscopic, and coronagraphic capabilities from 0.43-2.0 $μ$m and will be a potential contemporary and eventual successor to JWST. Surveys of irregular satellites and minor bodies are where WFIRST will excel with its 0.28 deg$^2$ field of view Wide Field Instrument (WFI). Potential ground-breaking discoveries from WFIRST could include detection of the first minor bodies orbiting in the Inner Oort Cloud, identification of additional Earth Trojan asteroids, and the discovery and characterization of asteroid binary systems similar to Ida/Dactyl. Additional investigations into asteroids, giant planet satellites, Trojan asteroids, Centaurs, Kuiper Belt Objects, and comets are presented. Previous use of astrophysics assets for solar system science and synergies between WFIRST, LSST, JWST, and the proposed NEOCam mission are discussed. We also present the case for implementation of moving target tracking, a feature that will benefit from the heritage of JWST and enable a broader range of solar system observations.

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arXiv2018

Taxonomy and Light-Curve Data of 1000 Serendipitously Observed Main-Belt Asteroids

We present VRI spectrophotometry of 1003 Main-Belt Asteroids (MBAs) observed with the Sutherland, South Africa, node of the Korea Microlensing Telescope Network (KMTNet). All of the observed MBAs were serendipitously captured in KMTNet's large 2deg $\times$ 2deg field of view during a separate targeted near-Earth Asteroid study (Erasmus et al. 2017). Our broadband spectrophotometry is reliable enough to distinguish among four asteroid taxonomies and we confidently categorize 836 of the 1003 observed targets as either a S-, C-, X-, or D-type asteroid by means of a Machine Learning (ML) algorithm approach. Our data show that the ratio between S-type MBAs and (C+X+D)-type MBAs, with H magnitudes between 12 and 18 (12 km $\gtrsim$ diameter $\gtrsim$ 0.75 km), is almost exactly 1:1. Additionally, we report 0.5- to 3-hour (median: 1.3-hour) light-curve data for each MBA and we resolve the complete rotation periods and amplitudes for 59 targets. Two out of the 59 targets have rotation periods potentially below the theoretical zero cohesion boundary limit of 2.2 hours. We report lower limits for the rotation periods and amplitudes for the remaining targets. Using the resolved and unresolved light curves we determine the shape distribution for this population using a Monte Carlo simulation. Our model suggests a population with an average elongation $b/a = 0.74\pm0.07$ and also shows that this is independent of asteroid size and taxonomy.

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arXiv2017

The structure of Chariklo's rings from stellar occultations

Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklo's system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the $\pm 3.3$ km formal uncertainty for the ring radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal significant width variations from $\sim 5$ to 7.5 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2R's edges is available. A 1$σ$ upper limit of $\sim 20$ m is derived for the equivalent width of narrow (physical width <4 km) rings up to distances of 12,000 km, counted in the ring plane.

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arXiv2017

Characterization of Near-Earth Asteroids using KMTNet-SAAO

We present here VRI spectrophotometry of 39 near-Earth asteroids (NEAs) observed with the Sutherland, South Africa, node of the Korea Microlensing Telescope Network (KMTNet). Of the 39 NEAs, 19 were targeted, but because of KMTNet's large 2 deg by 2 deg field of view, 20 serendipitous NEAs were also captured in the observing fields. Targeted observations were performed within 44 days (median: 16 days, min: 4 days) of each NEA's discovery date. Our broadband spectrophotometry is reliable enough to distinguish among four asteroid taxonomies and we were able to confidently categorize 31 of the 39 observed targets as either a S-, C-, X- or D-type asteroid by means of a Machine Learning (ML) algorithm approach. Our data suggest that the ratio between "stony" S-type NEAs and "not-stony" (C+X+D)-type NEAs, with H magnitudes between 15 and 25, is roughly 1:1. Additionally, we report ~1-hour light curve data for each NEA and of the 39 targets we were able to resolve the complete rotation period and amplitude for six targets and report lower limits for the remaining targets.

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arXiv2016

The OmegaWhite survey for Short-Period Variable Stars III: Follow-up Photometric and Spectroscopic Observations

We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey: a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0-m and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 also with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find many of these variables have spectra which are consistent with being delta Scuti type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the `Bump Cepheid' phenomena in a delta Scuti star, with OW J175848.21-271653.7 showing a pronounced 22% amplitude dip lasting 3 minutes during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.

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