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Scott S. Sheppard

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Published work

27 published item(s)

preprint2026arXiv

You Only Stack Once (YOSO): A Motion-Filtered, Deep-Learning Framework for Detecting Faint Moving Sources

We present You Only Stack Once (YOSO), an automated pipeline designed to detect faint, slow-moving Solar System objects in wide-field astronomical surveys. The pipeline integrates a novel Gaussian Motion Filter (GMoF) that operates at the pixel level to enhance signal-to-noise for objects exhibiting a range of apparent rates of motion. Unlike conventional shift-and-stack methods, which rely on discrete velocity trials, GMoF amplifies trails while suppressing random noise and static background features. Applied to a subset of DEEP observations from the Dark Energy Camera, YOSO recovered 45 out of 73 previously detected objects, as well as 11 new TNOs. It also discovered 216 objects in the near Solar System. Although alternative shift-and-stack methods are sensitive to objects about 0.88 magnitudes fainter, YOSO's false positive rate is extremely low, since it detects only sources that exhibit a trail and are consistent with a point source when shifted at the right rate. We show how this method can be deployed on large surveys like LSST, and adapted for other domains that require motion-based signal enhancement, including exoplanet imaging through Angular Differential Imaging (ADI), and near-Earth object (NEO) detection for missions like NEO Surveyor. YOSO thus provides a versatile, scalable approach for extracting faint, motion-dependent signals in the era of data-intensive astronomy.

preprint2022arXiv

Lightcurves and Rotations of Trans-Neptunian Objects in the 2:1 Mean Motion Resonance with Neptune

We report the rotational lightcurves of 21 trans-Neptunian objects (TNOs) in Neptune's 2:1 mean motion resonance obtained with the 6.5 m Magellan-Baade telescope and the 4.3 m Lowell Discovery Telescope. The main survey's goal is to find objects displaying a large lightcurve amplitude which is indicative of contact binaries or highly elongated objects. In our sample, two 2:1 resonant TNOs showed a significant short-term lightcurve amplitude: 2002 VD$_{130}$ and (531074) 2012 DX$_{98}$. The full lightcurve of 2012 DX$_{98}$ infers a periodicity of 20.80$\pm$0.06h and amplitude of 0.56$\pm$0.03mag whereas 2002 VD$_{130}$ rotates in 9.85$\pm$0.07h with a 0.31$\pm$0.04mag lightcurve amplitude. Based on lightcurve morphology, we classify (531074) 2012 DX$_{98}$ as a likely contact binary, but 2002 VD$_{130}$ as a likely single elongated object. Based on our sample and the lightcurves reported in the literature, we estimate the lower percentage of nearly equal-sized contact binaries at only 7-14$\%$ in the 2:1 resonance, which is comparable to the low fraction reported for the dynamically Cold Classical trans-Neptunian objects. This low contact binary fraction in the 2:1 Neptune resonance is consistent with the lower estimate of the recent numerical modeling. We report the Sloan g', r', i' surface colors of 2002 VD$_{130}$ which is an ultra-red TNO whereas 2012 DX$_{98}$ is a very red object based on published surface colors.

preprint2021arXiv

The Reactivation of Main-Belt Comet 259P/Garradd (P/2008 R1)

We present observations of main-belt comet 259P/Garradd from four months prior to its 2017 perihelion passage to five months after perihelion using the Gemini North and South telescopes. The object was confirmed to be active during this period, placing it among seven MBCs confirmed to have recurrent activity. We find an average net pre-perihelion dust production rate for 259P in 2017 of dM/dt = 4.6+/-0.2 kg/s (assuming grain densities of rho = 2500 kg/m^3 and a mean effective particle size of a_d = 2 mm) and a best-fit start date of detectable activity of 2017 April 22+/-1, when the object was at a heliocentric distance of r_h = 1.96-/+0.03 au and a true anomaly of nu = 313.9+/-0.4 deg. We estimate the effective active fraction of 259P's surface area to be from f_act ~ 7x10^-3 to f_act ~ 6x10^-2 (corresponding to effective active areas of A_act ~ 8x10^3 m^2 to A_act ~ 7x10^4 m^2) at the start of its 2017 active period. A comparison of estimated total dust masses measured for 259P in 2008 and 2017 shows no evidence of changes in activity strength between the two active apparitions. The heliocentric distance of 259P's activity onset point is much smaller than those of other MBCs, suggesting that its ice reservoirs may be located at greater depths than on MBCs farther from the Sun, increasing the time needed for a solar irradiation-driven thermal wave to reach subsurface ice. We suggest that deeper ice on 259P could be a result of more rapid ice depletion caused by the object's closer proximity to the Sun compared to other MBCs.

preprint2020arXiv

A Deep Search for Stable Venus Co-Orbital Asteroids: Limits on The Population

A stable population of objects co-orbiting with Venus was recently hypothesized in order to explain the existence of Venus's co-orbital dust ring. We conducted a 5 day twilight survey for these objects with the Cerro-Tololo Inter-American Observatory (CTIO) 4 meter telescope covering about 35 unique square degrees to 21 mag in the $r$-band. Our survey provides the most stringent limit so far on the number of Venus co-orbital asteroids; it was capable of detecting $5\%$ of the entire population of those asteroids brighter than 21 magnitude. We estimate an upper limit on the number of co-orbital asteroids brighter than 21 magnitude (approximately 400-900 m in diameter depending on the asteroid albedo) to be $N=18^{+30}_{-14}$. Previous studies estimated the mass of the observed dust ring co-orbiting with Venus to be equivalent to an asteroid with a 2 km diameter ground to dust. Our survey estimates $<6$ asteroids larger than 2 km. This implies the following possibilities: that Venus co-orbitals are non-reflective at the observed phase angles, have a very low albedo ($<1\%$), or that the Venus co-orbital dust ring has a source other than asteroids co-orbiting Venus. We discuss this result, and as an aid to future searches, we provide predictions for the spatial, visual magnitude, and number density distributions of stable Venus co-orbitals based on the dynamics of the region and magnitude estimates for various asteroid types.

preprint2016arXiv

Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With Moderate Semi-major Axes and Eccentricities

We have been conducting a survey for distant solar system objects beyond the Kuiper Belt edge (~50 AU) with new wide-field cameras on the Subaru 8 meter and CTIO 4 meter telescopes. We are interested in the orbits of objects that are decoupled from the giant planet region in order to understand the structure of the outer solar system, including whether a massive planet exists beyond a few hundred AU as first reported by Trujillo and Sheppard (2014). In addition to discovering extreme trans-Neptunian objects detailed elsewhere, we have found several objects with high perihelia (q>40 AU) that differ from the extreme and inner Oort cloud objects due to their moderate semi-major axes (50<a<100 AU) and eccentricities (e<0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have the third and fourth highest perihelia known after Sedna and 2012 VP113, yet their orbits are not nearly as eccentric or distant. We found several of these high perihelion but moderate orbit objects and observe that they are mostly near Neptune mean motion resonances and have significant inclinations (i>20 degrees). These moderate objects likely obtained their unusual orbits through combined interactions with Neptune's mean motion resonances and the Kozai resonance, similar to the origin scenarios for 2004 XR190. We also find the distant 2008 ST291 has likely been modified by the MMR+KR mechanism through the 6:1 Neptune resonance. We discuss these moderately eccentric, distant objects along with some other interesting low inclination outer classical belt objects like 2012 FH84 discovered in our ongoing survey.

preprint2016arXiv

Maximizing Science in the Era of LSST: A Community-Based Study of Needed US Capabilities

The Large Synoptic Survey Telescope (LSST) will be a discovery machine for the astronomy and physics communities, revealing astrophysical phenomena from the Solar System to the outer reaches of the observable Universe. While many discoveries will be made using LSST data alone, taking full scientific advantage of LSST will require ground-based optical-infrared (OIR) supporting capabilities, e.g., observing time on telescopes, instrumentation, computing resources, and other infrastructure. This community-based study identifies, from a science-driven perspective, capabilities that are needed to maximize LSST science. Expanding on the initial steps taken in the 2015 OIR System Report, the study takes a detailed, quantitative look at the capabilities needed to accomplish six representative LSST-enabled science programs that connect closely with scientific priorities from the 2010 decadal surveys. The study prioritizes the resources needed to accomplish the science programs and highlights ways that existing, planned, and future resources could be positioned to accomplish the science goals.

preprint2016arXiv

New Extreme Trans-Neptunian Objects: Towards a Super-Earth in the Outer Solar System

We are conducting a survey for extreme solar system objects to understand Sedna and 2012 VP113 and determine if an unknown massive planet exists in the outer solar system. Two new objects, 2014 SR349 and 2013 FT28, are extreme detached trans-Neptunian objects, with a>150 AU and perihelia well beyond Neptune (q>40 AU). Both new objects have orbits with arguments of perihelia within the range of clustering of this angle for other extreme objects. One of these objects, 2014 SR349, has a longitude of perihelion similar to the other extreme objects, but 2013 FT28 is about 180 degrees away or anti-aligned in its longitude of perihelion. We also discovered the first outer Oort cloud object with a perihelion beyond Neptune, 2014 FE72. We discuss these and other interesting objects discovered in our ongoing survey. All the high semi-major axis (a>150 AU) and high perihelion (q>35 AU) bodies follow the previously identified argument of perihelion clustering as first reported and explained as being from an unknown massive planet by Trujillo and Sheppard (2014), which some have called Planet X or Planet 9. Finally, with the discovery of 2013 FT28, we find that the longitude of perihelion is significantly correlated with the argument of perihelion and orbit pole angle for all extreme objects. This previous unnoticed correlation is further evidence of an unknown massive planet on an eccentric inclined orbit, as extreme eccentric objects with perihelia on opposite sides of the sky (180 degree longitude of perihelion differences) would approach the inclined eccentric planet at opposite points in their orbits, thus making the extreme objects prefer to stay away from opposite ecliptic latitudes to avoid the planet (i.e. opposite argument of perihelia or pole angles).

preprint2016arXiv

Rotational properties of the Haumea family members and candidates: Short-term variability

Haumea is one of the most interesting and intriguing transneptunian objects (TNOs). It is a large, bright, fast rotator, and its spectrum indicates nearly pure water ice on the surface. It has at least two satellites and a dynamically related family of more than ten TNOs with very similar proper orbital parameters and similar surface properties. The Haumean family is the only one currently known in the transneptunian belt. Various models have been proposed but the formation of the family remains poorly understood. In this work, we have investigated the rotational properties of the family members and unconfirmed family candidates with short-term variability studies, and report the most complete review to date. We present results based on five years of observations and report the short-term variability of five family members, and seven candidates. The mean rotational periods, from Maxwellian fits to the frequency distributions, are 6.27+/-1.19 h for the confirmed family members, 6.44+/-1.16 h for the candidates, and 7.65+/-0.54 h for other TNOs (without relation to the family). According to our study, there is a suggestion that Haumea family members rotate faster than other TNOs, however, the sample of family member is still too limited for a secure conclusion. We also highlight the fast rotation of 2002 GH32. This object has a 0.36+/-0.02 mag amplitude lightcurve and a rotational period of about 3.98 h. Assuming 2002 GH32 is a triaxial object in hydrostatic equilibrium, we derive a lower limit to the density of 2.56 g cm^-3. This density is similar to Haumea's and much more dense than other small TNO densities.

preprint2016arXiv

The AllWISE Motion Survey, Part 2

We use the AllWISE Data Release to continue our search for WISE-detected motions. In this paper, we publish another 27,846 motion objects, bringing the total number to 48,000 when objects found during our original AllWISE motion survey are included. We use this list, along with the lists of confirmed WISE-based motion objects from the recent papers by Luhman and by Schneider et al. and candidate motion objects from the recent paper by Gagne et al. to search for widely separated, common-proper-motion systems. We identify 1,039 such candidate systems. All 48,000 objects are further analyzed using color-color and color-mag plots to provide possible characterizations prior to spectroscopic follow-up. We present spectra of 172 of these, supplemented with new spectra of 23 comparison objects from the literature, and provide classifications and physical interpretations of interesting sources. Highlights include: (1) the identification of three G/K dwarfs that can be used as standard candles to study clumpiness and grain size in nearby molecular clouds because these objects are currently moving behind the clouds, (2) the confirmation/discovery of several M, L, and T dwarfs and one white dwarf whose spectrophotometric distance estimates place them 5-20 pc from the Sun, (3) the suggestion that the Na 'D' line be used as a diagnostic tool for interpreting and classifying metal-poor late-M and L dwarfs, (4) the recognition of a triple system including a carbon dwarf and late-M subdwarf, for which model fits of the late-M subdwarf (giving [Fe/H] ~ -1.0) provide a measured metallicity for the carbon star, and (5) a possible 24-pc-distant K5 dwarf + peculiar red L5 system with an apparent physical separation of 0.1 pc.

preprint2016arXiv

Tracking Neptune's Migration History through High-Perihelion Resonant Trans-Neptunian Objects

Recently, Sheppard et al. (2016) presented the discovery of seven new trans-Neptunian objects with moderate eccentricities, perihelia beyond 40 AU, and semimajor axes beyond 50 AU. Like the few previously known objects on similar orbits, these objects' semimajor axes are just beyond the Kuiper belt edge and clustered around Neptunian mean motion resonances (MMRs). These objects likely obtained their observed orbits while trapped within MMRs, when the Kozai-Lidov mechanism raised their perihelia and weakened Neptune's dynamical influence. Using numerical simulations that model the production of this population, we find that high-perihelion objects near Neptunian MMRs can constrain the nature and timescale of Neptune's past orbital migration. In particular, the population near the 3:1 MMR (near 62 AU) is especially useful due to its large population and short dynamical evolution timescale. If Neptune finishes migrating within ~100 Myrs or less, we predict over 90% of high-perihelion objects near the 3:1 MMR will have semimajor axes within 1 AU of each other, very near the modern resonance's center. On the other hand, if Neptune's migration takes ~300 Myrs, we expect ~50% of this population to reside in dynamically fossilized orbits over ~1 AU closer to the Sun than the modern resonance. We highlight 2015 KH162 as a likely member of this fossilized 3:1 population. Under any plausible migration scenario, nearly all high-perihelion objects in resonances beyond the 4:1 MMR (near 76 AU) reach their orbits well after Neptune stops migrating and comprise a recently generated, dynamically active population.

preprint2015arXiv

Fast Rotation and Trailing Fragments of the Active Asteroid P/2012 F5 (Gibbs)

While having a comet-like appearance, P/2012 F5 (Gibbs) has an orbit native to the Main Asteroid Belt, and physically is a km-sized asteroid which recently (mid 2011) experienced an impulsive mass ejection event. Here we report new observations of this object obtained with the Keck II telescope on UT 2014 August 26. The data show previously undetected 200-m scale fragments of the main nucleus, and reveal a rapid nucleus spin with a rotation period of 3.24 $\pm$ 0.01 hr. The existence of large fragments and the fast nucleus spin are both consistent with rotational instability and partial disruption of the object. To date, many fast rotators have been identified among the minor bodies, which, however, do not eject detectable fragments at the present-day epoch, and also fragmentation events have been observed, but with no rotation period measured. P/2012 F5 is unique in that for the first time we detected fragments and quantified the rotation rate of one and the same object. The rapid spin rate of P/2012 F5 is very close to the spin rates of two other active asteroids in the Main Belt, 133P/Elst-Pizarro and (62412), confirming the existence of a population of fast rotators among these objects. But while P/2012 F5 shows impulsive ejection of dust and fragments, the mass loss from 133P is prolonged and recurrent. We believe that these two types of activity observed in the rapidly rotating active asteroids have a common origin in the rotational instability of the nucleus.

preprint2015arXiv

The Reactivation of Main-Belt Comet 324P/La Sagra (P/2010 R2)

We present observations using the Baade Magellan and Canada-France-Hawaii telescopes showing that main-belt comet 324P/La Sagra, formerly known as P/2010 R2, has become active again for the first time since originally observed to be active in 2010-2011. The object appears point-source-like in March and April 2015 as it approached perihelion (true anomaly of ~300 deg), but was ~1 mag brighter than expected if inactive, suggesting the presence of unresolved dust emission. Activity was confirmed by observations of a cometary dust tail in May and June 2015. We find an apparent net dust production rate of <0.1 kg/s during these observations. 324P is now the fourth main-belt comet confirmed to be recurrently active, a strong indication that its activity is driven by sublimation. It now has the largest confirmed active range of all likely main-belt comets, and also the most distant confirmed inbound activation point at R~2.8 AU. Further observations during the current active period will allow direct comparisons of activity strength with 324P's 2010 activity.

preprint2014arXiv

Characterization of High Proper Motion Objects from the Wide-field Infrared Survey Explorer

We present an analysis of high proper motion objects that we have found in a recent study and in this work with multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE). Using photometry and proper motions from 2MASS and WISE, we have identified the members of this sample that are likely to be late type, nearby, or metal poor. We have performed optical and near-infrared spectroscopy on 41 objects, from which we measure spectral types that range from M4-T2.5. This sample includes 11 blue L dwarfs and five subdwarfs; the latter were also classified as such in the recent study by Kirkpatrick and coworkers. Based on their spectral types and photometry, several of our spectroscopic targets may have distances of <20 pc with the closest at ~12 pc. The tangential velocities implied by the spectrophotometric distances and proper motions indicate that four of the five subdwarfs are probably members of the Galactic halo while several other objects, including the early-T dwarf WISE J210529.08-623558.7, may belong to the thick disk.

preprint2013arXiv

2011 HM102: Discovery of a High-Inclination L5 Neptune Trojan in the Search for a post-Pluto New Horizons Target

We present the discovery of a long-term stable L5 (trailing) Neptune Trojan in data acquired to search for candidate Trans-Neptunian objects for the New Horizons spacecraft to fly by during an extended post-Pluto mission. This Neptune Trojan, 2011 HM102, has the highest inclination (29.4 degrees) of any known member of this population. It is intrinsically brighter than any single L5 Jupiter Trojan at H~8.18. We have determined its gri colors (a first for any L5 Neptune Trojan), which we find to be similar to the moderately red colors of the L4 Neptune Trojans, suggesting similar surface properties for members of both Trojan clouds. We also present colors derived from archival data for two L4 Neptune Trojans (2006 RJ103 and 2007 VL305), better refining the overall color distribution of the population. In this document we describe the discovery circumstances, our physical characterization of 2011 HM102, and this object's implications for the Neptune Trojan population overall. Finally, we discuss the prospects for detecting 2011 HM102 from the New Horizons spacecraft during their close approach in mid- to late-2013.

preprint2013arXiv

A Study of the Diverse T Dwarf Population Revealed by WISE

We report the discovery of 87 new T dwarfs uncovered with the Wide-field Infrared Survey Explorer (WISE) and three brown dwarfs with extremely red near-infrared colors that exhibit characteristics of both L and T dwarfs. Two of the new T dwarfs are likely binaries with L7+/-1 primaries and mid-type T secondaries. In addition, our follow-up program has confirmed 10 previously identified T dwarfs and four photometrically-selected L and T dwarf candidates in the literature. This sample, along with the previous WISE discoveries, triples the number of known brown dwarfs with spectral types later than T5. Using the WISE All-Sky Source Catalog we present updated color-color and color-type diagrams for all the WISE-discovered T and Y dwarfs. Near-infrared spectra of the new discoveries are presented, along with spectral classifications. To accommodate later T dwarfs we have modified the integrated flux method of determining spectral indices to instead use the median flux. Furthermore, a newly defined J-narrow index differentiates the early-type Y dwarfs from late-type T dwarfs based on the J-band continuum slope. The K/J indices for this expanded sample show that 32% of late-type T dwarfs have suppressed K-band flux and are blue relative to the spectral standards, while only 11% are redder than the standards. Comparison of the Y/J and K/J index to models suggests diverse atmospheric conditions and supports the possible re-emergence of clouds after the L/T transition. We also discuss peculiar brown dwarfs and candidates that were found not to be substellar, including two Young Stellar Objects and two Active Galactic Nuclei. The coolest WISE-discovered brown dwarfs are the closest of their type and will remain the only sample of their kind for many years to come.

preprint2013arXiv

Discovery of the Young L Dwarf WISE J1741102.78-464225.5

We report the discovery of the L dwarf WISE J174102.78$-$464225.5, that was discovered as part of a search for nearby L dwarfs using the Wide-field Infrared Survey Explorer (WISE). The distinct triangular peak of the H-band portion of its near-infrared spectrum and its red near-infrared colors ($J-K_S$ = 2.35$\pm$0.08 mag) are indicative of a young age. Via comparison to spectral standards and other red L dwarfs, we estimate a near-infrared spectral type to be L7$\pm$2 (pec). From a comparison to spectral and low-mass evolutionary models, we determine self-consistent effective temperature, log $g$, age, and mass values of 1450$\pm$100 K, 4.0$\pm$0.25 (cm s$^{-2}$), 10-100 Myr, and 4-21 M$_{Jup}$, respectively. With an estimated distance of 10-30 pc, we explore the possibility that WISE J174102.78-464225.5 belongs to one of the young nearby moving groups via a kinematic analysis and we find potential membership in the $β$ Pictoris or AB Doradus associations. A trigonometric parallax measurement and a precise radial velocity can help to secure its membership in either of these groups.

preprint2013arXiv

Lightcurves of 32 Large Transneptunian Objects

We present observations of 32 primarily bright, newly discovered Transneptunian objects observable from the Southern Hemisphere during 39 nights of observation with the 2.5-m telescope at Las Campanas Observatory. Our dataset includes objects in all dynamical classes, but is weighted towards Scattered objects. We find 15 objects for which we can fit periods and amplitudes to the data, and place lightcurve amplitude upper limits on the other 17 objects. Combining our sample with the larger sample in the literature, we find a 3-sigma correlation between lightcurve amplitude and absolute magnitude with fainter objects having larger lightcurve amplitudes. We looked for correlations between lightcurve and individual orbital properties, but did not find any statistically significant results. However, if we consider lightcurve properties with respect to dynamical classification, we find statistically different distributions between the Classical-Scattered and Classical-Resonant populations, respectively, with the Classical objects having larger amplitude lightcurves. The properties of binary lightcurves are largely consistent with the greater population except in the case of tidally locked systems. All the Haumea family objects measured so far have measurable amplitudes and rotation periods le 10 hr suggesting that they are not significantly different from the larger TNO population. We expect multiple factors are influencing object rotations: object size dominates lightcurve properties except in the case of tidal, or proportionally large collisional interactions with other objects, the influence of the latter being different for each sub-population. We also present phase curves and colors for some objects; our values are not significantly different from those presented in the literature for other samples.

preprint2013arXiv

Main-Belt Comet P/2012 T1 (PANSTARRS)

We present initial results from observations and numerical analyses aimed at characterizing main-belt comet P/2012 T1 (PANSTARRS). Optical monitoring observations were made between October 2012 and February 2013 using the University of Hawaii 2.2 m telescope, the Keck I telescope, the Baade and Clay Magellan telescopes, Faulkes Telescope South, the Perkins Telescope at Lowell Observatory, and the Southern Astrophysical Research (SOAR) telescope. The object's intrinsic brightness approximately doubles from the time of its discovery in early October until mid-November and then decreases by ~60% between late December and early February, similar to photometric behavior exhibited by several other main-belt comets and unlike that exhibited by disrupted asteroid (596) Scheila. We also used Keck to conduct spectroscopic searches for CN emission as well as absorption at 0.7 microns that could indicate the presence of hydrated minerals, finding an upper limit CN production rate of QCN<1.5x10^23 mol/s, from which we infer a water production rate of QH2O<5x10^25 mol/s, and no evidence of the presence of hydrated minerals. Numerical simulations indicate that P/2012 T1 is largely dynamically stable for >100 Myr and is unlikely to be a recently implanted interloper from the outer solar system, while a search for potential asteroid family associations reveal that it is dynamically linked to the ~155 Myr-old Lixiaohua asteroid family.

preprint2013arXiv

Resolved Near-Infrared Spectroscopy of WISE J104915.57-531906.1AB: A Flux-Reversal Binary at the L dwarf/T dwarf Transition

We report resolved near-infrared spectroscopy and photometry of the recently identified brown dwarf binary WISE J104915.57-531906.1AB, located 2.02+/-0.15 pc from the Sun. Low-resolution spectral data from Magellan/FIRE and IRTF/SpeX reveal strong H2O and CO absorption features in the spectra of both components, with the secondary also exhibiting weak CH4 absorption at 1.6 micron and 2.2 micron. Spectral indices and comparison to low-resolution spectral standards indicate component types of L7.5 and T0.5, the former consistent with the optical classification of the primary. Relative photometry reveals a flux reversal between the J- and K-bands, with the T dwarf component being brighter in the 0.95--1.3 micron range. As with other L/T transition binaries, this reversal likely reflects significant depletion of condensate opacity across the transition, a behavior that may be enhanced in WISE J1049-5319AB if the unusual red color of its L dwarf component is indicative of thick clouds. On the other hand, differing cloud properties may have modified the evolutionary paths of these two components, and we propose a scenario in which the cooler secondary could be the more massive of the two components. Fortunately, the proximity, brightness and small separation (3.12+/-0.25 AU) of this system make it amenable to astrometric and radial velocity orbit measurement during its estimated 25 yr orbit, providing a rare opportunity for the direct determination of individual brown dwarf masses and a unique benchmark for studying cloud evolution across the L dwarf/T dwarf transition.

preprint2012arXiv

The Color Differences of Kuiper Belt Objects in Resonance with Neptune

(Abridged) New optical colors of 58 objects in mean motion resonances with Neptune show the various resonant populations have significantly different color distributions. The 5:3 and 7:4 resonances have semi-major axes near the middle of the main Kuiper Belt and both are dominated by ultra-red material. The 5:3 and 7:4 resonances have statistically the same color distribution as the low inclination "cold" classical belt. The inner 4:3 and distant 5:2 resonances have objects with mostly moderately red colors, similar to the scattered and detached disk populations. The 2:1 resonance, which is near the outer edge of the main Kuiper Belt, has a large range of colors with similar numbers of moderately red and ultra-red objects at all inclinations. The inner 3:2 resonance, like the outer 2:1, has a large range of objects from neutral to ultra-red. The Neptune Trojans (1:1 resonance) are only slightly red, similar to the Jupiter Trojans. The inner 5:4 resonance only has four objects with measured colors but shows equal numbers of ultra-red and moderately red objects. The 9:5, 12:5, 7:3, 3:1 and 11:3 resonances do not have reliable color distribution statistics, though it appears noteworthy that all three of the measured 3:1 objects have only moderately red colors, similar to the 4:3 and 5:2 resonances. The different color distributions are likely a result from the disruption of the primordial Kuiper Belt from the scattering and migration of the giant planets. The few low inclination objects known in the outer 2:1 and 5:2 resonances are mostly only moderately red. This suggests if the 2:1 and 5:2 have a cold low inclination component, the objects likely had a significantly different origin than the ultra-red dominated cold components of the cold classical belt and 5:3 and 7:4 resonances.

preprint2011arXiv

2007 TY430: A Cold Classical Kuiper Belt Type Binary in the Plutino Population

(Abridged) 2007 TY430 is the first wide, equal-sized, binary known in the 3:2 mean motion resonance with Neptune. The binary has a maximum separation of 1 arcsec with less than 0.1 mags difference between components with identical ultra-red colors (g-i=1.49+-0.01 mags). The orbit of the mutual components was found to have a period of 961.2+-4.6 days with a semi-major axis of 21000+-160 km and eccentricity of 0.1529+-0.0028. The inclination is 15.68+-0.22 degs and the mirror orbit rejected at high confidence. The total system mass is 7.90+-0.21 x 10^17 kg. Equal-sized, wide binaries and ultra-red colors are common in the low inclination "cold" classical part of the Kuiper Belt and likely formed through some sort of three body interactions within a much denser Kuiper Belt. To date 2007 TY430 is the only ultra-red, equal-sized binary known outside of the classical Kuiper belt. Numerical simulations suggest 2007 TY430 is moderately unstable in the outer part of the 3:2 resonance and thus 2007 TY430 is likely an escaped "cold" classical object that later got trapped in resonance. Similar to the known binaries in the cold classical population, 2007 TY430 requires a high albedo and very low density to obtain the total mass found. For a realistic minimum density of 0.5 g/cm^3 the albedo of 2007 TY430 would be greater than 0.17. The radii of either component should be less than 60 km and thus the relatively low eccentricity of the binary is interesting since no tides should be operating on the bodies. The low prograde inclination of the binary also makes it unlikely the Kozai mechanism has altered the orbit, making 2007 TY430 likely one of the few relatively unaltered primordial binary orbits known. Under some binary formation models, the low inclination prograde orbit of the 2007 TY430 binary indicates formation within a relatively high velocity regime in the Kuiper Belt.

preprint2011arXiv

A Photometric System for Detection of Water and Methane Ices on Kuiper Belt Objects

We present a new near-infrared photometric system for detection of water ice and methane ice in the solar system. The system consists of two medium-band filters in the K-band region of the near-infrared, which are sensitive to water ice and methane ice, plus continuum observations in the J-band and Y-band. The primary purpose of this system is to distinguish between three basic types of Kuiper Belt Objects (KBOs) --- those rich in water ice, those rich in methane ice, and those with little absorbance. In this work, we present proof-of-concept observations of 51 KBOs using our filter system, 21 of which have never been observed in the near-IR spectroscopically. We show that our custom photometric system is consistent with previous spectroscopic observations while reducing telescope observing time by a factor of 3. We use our filters to identify Haumea collisional family members, which are thought to be collisional remnants of a much larger body and are characterized by large fractions of water ice on their surfaces. We add 2009 YE7 to the Haumea collisional family based on our water ice band observations(J-H2O = -1.03 +/- 0.27) which indicate a high amount of water ice absorption, our calculated proper orbital elements, and the neutral optical colors we measured, V-R = 0.38 +/- 0.04, which are all consistent with the rest of the Haumea family. We identify several objects dynamically similar to Haumea as being distinct from the Haumea family as they do not have water ice on their surfaces. In addition, we find that only the largest KBOs have methane ice, and we find that Haumea itself has significantly less water ice absorption than the smaller Haumea family members. We find no evidence for other families in the Kuiper Belt.

preprint2011arXiv

Measuring the Sizes, Shapes, Surface Features and Rotations of Solar System Objects with Interferometry

We consider the application of interferometry to measuring the sizes and shapes of small bodies in the solar system that cannot be spatially resolved by today's single-dish telescopes. Assuming ellipsoidal shapes, our results indicate that interferometers can measure the size of an object to better than 15% uncertainty if the limb-darkening is unknown. Assuming a Minnaert scattering model, one can theoretically derive the limb-darkening parameters from simultaneous measurements of visibilities at several different projected baseline lengths to improve the size and shape determination to an accuracy of a few percent. With a 3-D shape model for the dwarf planet Haumea, we demonstrate that when photometric light curve, visibility light curve, and visibility phase center displacement are combined, the rotational period and sense of rotation can all be derived, and the rotational pole can be estimated. Because of its elongated shape and the dark red spot, the rotation of Haumea causes its optical photocenter to move in a loop on the sky, extending of ~80 \muas without the dark red spot, and ~200 \muas with it. Such movements are easily detectable by space-based astrometric interferometer designed e.g. for planet detection. As an example, we consider the possible contributions to the study of small bodies in the solar system by the Space Interferometry Mission. We show that such a mission could make substantial contributions in characterizing the fundamental physical properties of the brightest Kuiper Belt Objects and Centaurs as well as a large number of main belt asteroids. We compile a list of Kuiper Belt Objects and Centaurs that are potentially scientifically interesting and observable by such missions.

preprint2010arXiv

Spectroscopic Discovery of the Broad-Lined Type Ic Supernova 2010bh Associated with the Low-Redshift GRB 100316D

We present the spectroscopic discovery of a broad-lined Type Ic supernova (SN 2010bh) associated with the nearby long-duration gamma-ray burst (GRB) 100316D. At z = 0.0593, this is the third-nearest GRB-SN. Nightly optical spectra obtained with the Magellan telescopes during the first week after explosion reveal the gradual emergence of very broad spectral features superposed on a blue continuum. The supernova features are typical of broad-lined SNe Ic and are generally consistent with previous supernovae associated with low-redshift GRBs. However, the inferred velocities of SN 2010bh at 21 days after explosion are a factor of ~2 times larger than those of the prototypical SN 1998bw at similar epochs, with v ~ 26,000 km/s, indicating a larger explosion energy or a different ejecta structure. A near-infrared spectrum taken 13.8 days after explosion shows no strong evidence for He I at 1.083 microns, implying that the progenitor was largely stripped of its helium envelope. The host galaxy is of low luminosity (M_R ~ -18.5 mag) and low metallicity (Z < 0.4 Z_solar), similar to the hosts of other low-redshift GRB-SNe.

preprint2010arXiv

The Colors of Extreme Outer Solar System Objects

(Abridged) Thirty-three objects with possible origins beyond the Kuiper Belt edge, very high inclinations, very large semi-major axes or large perihelion distances were observed to determine their surface colors. All three objects that have been dynamically linked to the inner Oort cloud (Sedna, 2006 SQ372, and 2000 OO67) were found to have ultra-red surfaces (S~25). Ultra-red material is generally associated with rich organics and the low inclination "cold" classical Kuiper Belt objects. The observations detailed here show very red material may be a more general feature for objects kept far from the Sun. The recently discovered retrograde outer Solar System objects (2008 KV42 and 2008 YB3) and the high inclination object (127546) 2002 XU93 show only moderately red surfaces (S~9), very similar to known comets. The extended or detached disk objects, which have large perihelion distances and large eccentricities, are found to have mostly moderately red colors (10 < S < 18). The colors of the detached disk objects, including the dynamically unusual 2004 XR190 and 2000 CR105, are similar to the scattered disk and Plutino populations. Thus the detached and scattered disk likely have a similar mix of objects from the same source regions. Outer classical belt objects, including 1995 TL8, were found to have very red surfaces (18 < S < 30). The "cold" classical belt, outer classical belt and inner Oort cloud appear to be dominated by ultra-red objects (S > 25) and thus don't likely have a similar mix of objects as the scattered disk, detached disk and Trojan populations. A possible trend was found for the detached disk and outer classical belt in that objects with smaller eccentricities have redder surfaces irrespective of inclinations or perihelion distances. There is also a clear trend that objects more distant appear redder.

preprint2010arXiv

The Size Distribution of the Neptune Trojans and the Missing Intermediate Sized Planetesimals

We present an ultra-deep survey for Neptune Trojans using the Subaru 8.2-m and Magellan 6.5-m telescopes. The survey reached a 50% detection efficiency in the R-band at 25.7 magnitudes and covered 49 square degrees of sky. This depth corresponds to Neptune Trojans that are about 16 km in radius (assuming an albedo of 0.05). A paucity of smaller Neptune Trojans (radii < 45 km) compared to larger ones was found. The brightest Neptune Trojans appear to follow a steep power-law slope (q = 5+-1) similar to the brightest objects in the other known stable reservoirs such as the Kuiper Belt, Jupiter Trojans and main belt asteroids. We find a roll-over for the Neptune Trojans that occurs around a radii of r=45+-10 km (23.5+-0.3 mags), which is also very similar to the other stable reservoirs. All the observed stable regions in the the solar system show evidence for Missing Intermediate Sized Planetesimals (MISPs). This indicates a primordial and not collisional origin, which suggests planetesimal formation proceeded directly from small to large objects. The scarcity of intermediate and smaller sized Neptune Trojans may limit them as being a strong source for the short period comets.

preprint2009arXiv

A Survey for Satellites of Venus

We present a systematic survey for satellites of Venus using the Baade-Magellan 6.5 meter telescope and IMACS wide-field CCD imager at Las Campanas observatory in Chile. In the outer portions of the Hill sphere the search was sensitive to a limiting red magnitude of about 20.4, which corresponds to satellites with radii of a few hundred meters when assuming an albedo of 0.1. In the very inner portions of the Hill sphere scattered light from Venus limited the detection to satellites of about a kilometer or larger. Although several main belt asteroids were found, no satellites (moons) of Venus were detected.