Quaoar: A Rock in the Kuiper belt

Here we report WFPC2 observations of the Quaoar-Weywot Kuiper belt binary. From these observations we find that Weywot is on an elliptical orbit with eccentricity of 0.14 {\pm} 0.04, period of 12.438 {\pm} 0.005 days, and a semi-major axis of 1.45 {\pm} 0.08 {\times} 104 km. The orbit reveals a surpsingly high Quaoar-Weywot system mass of 1.6{\pm}0.3{\times}10^21 kg. Using the surface properties of the Uranian and Neptunian satellites as a proxy for Quaoar's surface, we reanalyze the size estimate from Brown and Trujillo (2004). We find, from a mean of available published size estimates, a diameter for Quaoar of 890 {\pm} 70 km. We find Quaoar's density to be \rho = 4.2 {\pm} 1.3 g cm^-3, possibly the highest density in the Kuiper belt.Comment: 11 pages, 2 figures, accepted for publication in ApJ letters

The Hubble Wide Field Camera 3 Test of Surfaces in the Outer Solar System: The Compositional Classes of the Kuiper Belt

We present the first results of the Hubble Wide Field Camera 3 Test of Surfaces in the Outer Solar System (H/WTSOSS). The purpose of this survey was to measure the surface properties of a large number of Kuiper belt objects and attempt to infer compositional and dynamical correlations. We find that the Centaurs and the low-perihelion scattered disk and resonant objects exhibit virtually identical bifurcated optical colour distributions and make up two well defined groups of object. Both groups have highly correlated optical and NIR colours which are well described by a pair of two component mixture models that have different red components, but share a common neutral component. The small, $H_{606}\gtrsim5.6$ high-perihelion excited objects are entirely consistent with being drawn from the two branches of the mixing model suggesting that the colour bifurcation of the Centaurs is apparent in all small excited objects. On the other hand, objects larger than $H_{606}\sim5.6$ are not consistent with the mixing model, suggesting some evolutionary process avoided by the smaller objects. The existence of a bifurcation amongst all excited populations argues that the two separate classes of object existed in the primordial disk before the excited Kuiper belt was populated. The cold classical objects exhibit a different type of surface which has colours that are consistent with being drawn from the red branch of the mixing model, but with much higher albedos.Comment: Accepted to the Astrophysical Journal. 49 Pages, 15 Figure

Retention of a Primordial Cold Classical Kuiper Belt in an Instability-Driven Model of Solar System Formation

The cold classical population of the Kuiper belt exhibits a wide variety of unique physical characteristics, which collectively suggest that its dynamical coherence has been maintained through out the solar system's lifetime. Simultaneously, the retention of the cold population's relatively unexcited orbital state has remained a mystery, especially in the context of a solar system formation model, that is driven by a transient period of instability, where Neptune is temporarily eccentric. Here, we show that the cold belt can survive the instability, and its dynamical structure can be reproduced. We develop a simple analytical model for secular excitation of cold KBOs and show that comparatively fast apsidal precession and nodal recession of Neptune, during the eccentric phase, are essential for preservation of an unexcited state in the cold classical region. Subsequently, we confirm our results with self-consistent N-body simulations. We further show that contamination of the hot classical and scattered populations by objects of similar nature to that of cold classicals has been instrumental in shaping the vast physical diversity inherent to the Kuiper belt.Comment: 9 pages, 11 figures, accepted for publication in Ap

NICMOS Photometry of the Unusual Dwarf Planet Haumea and its Satellites

We present here Hubble Space Telescope NICMOS F110W and F160W observations of Haumea, and its two satellites Hi'iaka and Namaka. From the measured (F110W-F160W) colors of –1.208 ± 0.004, –1.48 ± 0.06, and –1.4 ± 0.2 mag for each object, respectively, we infer that the 1.6 μm water-ice absorption feature depths on Hi'iaka and Namaka are at least as deep as that of Haumea. The light curve of Haumea is detected in both filters, and we find that the infrared color is bluer by ~2%-3% at the phase of the red spot. These observations suggest that the satellites of Haumea were formed from the collision that produced the Haumea collisional family

The surface composition of large Kuiper belt object 2007 OR10

We present photometry and spectra of the large Kuiper belt object 2007 OR10. The data show significant near-infrared absorption features due to water ice. While most objects in the Kuiper belt with water ice absorption this prominent have the optically neutral colors of water ice, 2007 OR10 is among the reddest Kuiper belt objects known. One other large Kuiper belt object -- Quaoar -- has similar red coloring and water ice absorption, and it is hypothesized that the red coloration of this object is due to irradiation of the small amounts of methane able to be retained on Quaoar. 2007 OR10, though warmer than Quaoar, is in a similar volatile retention because it is sufficiently larger that its stronger gravity can still retain methane. We propose, therefore, that the red coloration on 2007 OR10 is also caused by the retention of small amounts of methane. Positive detection will require spectra of methane on 2007 OR10 will require spectra with higher signal-to-noise. Models for volatile retention on Kuiper belt objects appear to continue to do an excellent job reproducing all of the available observations

The Rarity of Star Formation in Brightest Cluster Galaxies as Measured by WISE

We present the mid-infrared (IR) star formation rates of 245 X-ray selected, nearby (z<0.1) brightest cluster galaxies (BCGs). A homogeneous and volume limited sample of BCGs was created by X-ray selecting clusters with L_x > 1x10^44 erg/s. The Wide-Field Infrared Survey Explorer (WISE) AllWISE Data Release provides the first measurement of the 12 micron star formation indicator for all BCGs in the nearby Universe. Perseus A and Cygnus A are the only galaxies in our sample to have star formation rates of > 40 M_sol/yr, indicating that these two galaxies are highly unusual at current times. Stellar populations of 99 +/- 0.6 % of local BCGs are (approximately) passively evolving, with star formation rates of <10 M_sol/yr. We find that in general, star formation produces only modest BCG growth at the current epoch.Comment: 5 pages, 3 figures, accepted for publication in MNRA

The size, density, and formation of the Orcus-Vanth system in the Kuiper belt

The Kuiper belt object Orcus and its satellite Vanth form an unusual system in the Kuiper belt. Orcus is amongst the largest objects known in the Kuiper belt, but the relative size of Vanth is much larger than that of the tiny satellites of the other large objects. From Hubble Space Telescope observations we find that Orcus and Vanth have different visible colors and that Vanth does not share the water ice absorption feature seen in the infrared spectrum of Orcus. We also find that Vanth has a nearly face-on circular orbit with a period of 9.5393 +-0.0001 days and semimajor axis of 8980+-20 km, implying a system mass of 6.32+- 0.01 X 10^20 kg or 3.8% the mass of dwarf planet Eris. From Spitzer Space Telescope observations we find that the thermal emission is consistent with a single body with diameter 940+-70 km and a geometric albedo of 0.28+-0.04. Assuming equal densities and albedos, this measurements implies sizes of Orcus and Vanth of 900 and 280 km, respectively, and a mass ratio of 33. Assuming a factor of 2 lower albedo for the non-icy Vanth, however, implies sizes of 820 and 640 km and a mass ratio of 2. The measured density depends on the assumed albedo ratio of the two objects but is approximately 1.5+-0.3 g cm^-3$, midway between typical densities measured for larger and for smaller objects. The orbit and mass ratio is consistent with formation from a giant impact and subsequent outward tidal evolution and even consistent with the system having now achieved a double synchronous state. The system can equally well be explained, however, by initial eccentric capture, Kozai cycling which increases the eccentricity and decreases the pericenter of the orbit of Vanth, and subsequent tidal evolution inward.Comment: Submitted to A

Variation of tow force with velocity during offshore ploughing in granular materials

Pipeline plough behaviour has been investigated by means of reduced scale physical model testing. A testing programme was devised to investigate the influence of permeability, relative density, and plough depth on the associated tow force measured during ploughing over a range of velocities in saturated granular material. An increase in tow force with velocity was found during all of the tests and the results have been compared to previously developed analytical models. A new empirical equation has been developed to describe the change in tow force with velocity for a variety of model siliceous sand conditions. Application of this new approach to full-scale ploughing requires consideration of scaling effects and the use of appropriate input parameters determined to replicate field conditions. </jats:p

The Absolute Magnitude Distribution of Kuiper Belt Objects

Here we measure the absolute magnitude distributions (H-distribution) of the dynamically excited and quiescent (hot and cold) Kuiper Belt objects (KBOs), and test if they share the same H-distribution as the Jupiter Trojans. From a compilation of all useable ecliptic surveys, we find that the KBO H-distributions are well described by broken power-laws. The cold population has a bright-end slope, $\alpha_{\textrm{1}}=1.5_{-0.2}^{+0.4}$, and break magnitude, $H_{\textrm{B}}=6.9_{-0.2}^{+0.1}$ (r'-band). The hot population has a shallower bright-end slope of, $\alpha_{\textrm{1}}=0.87_{-0.2}^{+0.07}$, and break magnitude $H_{\textrm{B}}=7.7_{-0.5}^{+1.0}$. Both populations share similar faint end slopes of $\alpha_2\sim0.2$. We estimate the masses of the hot and cold populations are $\sim0.01$ and \sim3\times10^{-4} \mbox{ M_{\bigoplus}}. The broken power-law fit to the Trojan H-distribution has $\alpha_\textrm{1}=1.0\pm0.2$, $\alpha_\textrm{2}=0.36\pm0.01$, and $H_{\textrm{B}}=8.3$. The KS test reveals that the probability that the Trojans and cold KBOs share the same parent H-distribution is less than 1 in 1000. When the bimodal albedo distribution of the hot objects is accounted for, there is no evidence that the H-distributions of the Trojans and hot KBOs differ. Our findings are in agreement with the predictions of the Nice model in terms of both mass and H-distribution of the hot and Trojan populations. Wide field survey data suggest that the brightest few hot objects, with $H_{\textrm{r'}}\lesssim3$, do not fall on the steep power-law slope of fainter hot objects. Under the standard hierarchical model of planetesimal formation, it is difficult to account for the similar break diameters of the hot and cold populations given the low mass of the cold belt.Comment: Accepted to the Astrophysical Journa

The Luminosity Function of the Hot and Cold Kuiper belt Populations

Abridged. We have performed an ecliptic survey of the Kuiper belt, with an areal coverage of 8.9 square degrees to a 50% limiting magnitude of r'=24.7, and have detected 88 Kuiper belt objects, roughly half of which received follow-up one to two months after detection. Using this survey data alone, we have measured the luminosity function of the Kuiper belt, thus avoiding any biases that might come from the inclusion of other observations. We have found that the Cold population defined as having inclinations less than 5 degrees has a luminosity function slope alpha=0.82+-0.23, and is different from the Hot population, which has inclinations greater than 5 degrees and a luminosity function slope alpha=0.35+-0.21. As well, we have found that those objects closer than 38 AU have virtually the same luminosity function slope as the Hot population. This result, along with similar findings of past surveys demonstrates that the dynamically cold Kuiper belt objects likely have a steep size distribution, and are unique from all of the excited populations which have much shallower distributions. This suggests that the dynamically excited population underwent a different accretion history and achieved a more evolved state of accretion than the cold population. As well, we discuss the similarities of the Cold and Hot populations with the size distributions of other planetesimal populations. We find that while the Jupiter family comets and the scattered disk exhibit similar size distributions, a power-law extrapolation to small sizes for the scattered disk cannot account for the observed influx of comets. As well, we have found that the Jupiter Trojan and Hot populations cannot have originated from the same parent popuation, a result that is difficult to reconcile with scattering models similar to the NICE model.Comment: Accepted for publication in Icarus. 27 pages, 10 figures, 4 table