The Mass of Dwarf Planet Eris

The discovery of dwarf planet Eris was followed shortly by the discovery of its satellite, Dysnomia, but the satellite orbit, and thus the system mass, was not known. New observations with the Keck Observatory and the Hubble Space Telescopes show that Dysnomia has a circular orbit with a radius of 37,350 ± 140 (1-σ) kilometers and a 15.774 ± 0.002 day orbital period around Eris. These orbital parameters agree with expectations for a satellite formed out of the orbiting debris left from a giant impact. The mass of Eris from these orbital parameters is 1.67 × 10^(22) ± 0.02 × 10^(22) kilograms, or 1.27 ± 0.02 that of Pluto

Detection of methane on Kuiper Belt Object (50000) Quaoar

The near-infrared spectrum of (50000) Quaoar obtained at the Keck Observatory shows distinct absorption features of crystalline water ice, solid methane and ethane, and possibly other higher order hydrocarbons. Quaoar is only the fifth Kuiper belt object on which volatile ices have been detected. The small amount of methane on an otherwise water ice dominated surface suggests that Quaoar is a transition object between the dominant volatile-poor small Kuiper belt objects (KBOs) and the few volatile-rich large KBOs such as Pluto and Eris.Comment: 8 pages, 2 figures, accepted for publication in ApJ

Stress and social support in normal weight and overweight/obese prepubertal children

Background: Overweight and obesity in children are public health problems. Understanding the risk factors is essential in order to develop effective interventions. Besides the more classical known risk factors, the impact of stress either caused by major life events or by repetitive daily hassles has been proposed to be a more novel important risk factor. Social support is often considered a protective factor concerning the negative effects of stress. Objectives: This cross-­‐sectional study aimed at comparing normal weight and overweight/obese children with regards to their stress exposure (number of stressful major life events and chronic daily hassles), their stress perception, and the level of social support Methods: For this part of the study, 50 normal weight and overweight/obese children aged 7 to 10 years old were recruited. Upon arrival, anthropometric measures of children were taken while parents filled out questionnaires about family major life events (including recent life events and early separation), their perceived stress, chronic daily hassles (including socioeconomic status, migrant status, parental worries and parenting practices), and their social support. Results: There were no group differences with regards to serious life events, recent life events or early separation (all p=NS). In contrast, chronic daily hassles in the form of lower socioeconomic, migrant status and certain unfavourable parenting practices such as corporal punishment occurred more frequently in overweight/obese children than in normal weight children (all p ≤0.06) and parents of overweight/obese children had a tendency to be more worried (p=0.08). Finally, there was no difference in social support between the two groups. Conclusion: In this more clinical sample of children, we found no differences in major life events or social support between normal weight and overweight/obese children, but the latter experienced more chronic daily hassles. Our results highlight the importance and influence of a child's environment on his weight and thus show that actions should be undertaken to treat childhood obesity on different levels. Further research is needed to study the interplay of the determinants influencing childhood overweight in a more epidemiological setting

Near-infrared (NIR) spectra of Centaurs and Kuiper belt objects

We present here an extensive survey of near-infrared (NIR) spectra of Kuiper belt objects (KBOs) and Centaurs taken with the Keck I Telescope. We find that most spectra in our sample are well characterized by a combination of water ice and a featureless continuum. A comparative analysis reveals that the NIR spectral properties have little correlation to the visible colors or albedo, with the exception of the fragment KBOs produced from the giant impact on 2003 EL61. The results suggest that the surface composition of KBOs is heterogeneous, though the exposure of water ice may be controlled by geophysical processes. The Centaurs also display diverse spectral properties, but the source of the variability remains unclear. The results for both the KBOs and the Centaurs point to inherent heterogeneity in either the processes acting on these objects or materials from which they formed

Fermionic reaction coordinates and their application to an autonomous Maxwell demon in the strong coupling regime

We establish a theoretical method which goes beyond the weak coupling and Markovian approximations while remaining intuitive, using a quantum master equation in a larger Hilbert space. The method is applicable to all impurity Hamiltonians tunnel-coupled to one (or multiple) baths of free fermions. The accuracy of the method is in principle not limited by the system-bath coupling strength, but rather by the shape of the spectral density and it is especially suited to study situations far away from the wide-band limit. In analogy to the bosonic case, we call it the fermionic reaction coordinate mapping. As an application we consider a thermoelectric device made of two Coulomb-coupled quantum dots. We pay particular attention to the regime where this device operates as an autonomous Maxwell demon shoveling electrons against the voltage bias thanks to information. Contrary to previous studies we do not rely on a Markovian weak coupling description. Our numerical findings reveal that in the regime of strong coupling and non-Markovianity, the Maxwell demon is often doomed to disappear except in a narrow parameter regime of small power output.Comment: 18 pages incl. references, appendix and 10 figures; accepted versio

Water ice in the Kuiper belt

We examine a large collection of low-resolution near-infrared spectra of Kuiper Belt objects (KBOs) and centaurs in an attempt to understand the presence of water ice in the Kuiper Belt. We find that water ice on the surface of these objects occurs in three separate manners: (1) Haumea family members uniquely show surfaces of nearly pure water ice, presumably a consequence of the fragmentation of the icy mantle of a larger differentiated proto-Haumea; (2) large objects with absolute magnitudes of H < 3 (and a limited number to H = 4.5) have surface coverings of water ice—perhaps mixed with ammonia—that appears to be related to possibly ancient cryovolcanism on these large objects; and (3) smaller KBOs and centaurs which are neither Haumea family members nor cold-classical KBOs appear to divide into two families (which we refer to as "neutral" and "red"), each of which is a mixture of a common nearly neutral component and either a slightly red or very red component that also includes water ice. A model suggesting that the difference between neutral and red objects due to formation in an early compact solar system either inside or outside, respectively, of the ~20 AU methanol evaporation line is supported by the observation that methanol is only detected on the reddest objects, which are those which would be expected to have the most of the methanol containing mixture

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.Comment: 38 pages, 7 figure

The Surface of 2003 EL_(61) in the Near-Infrared

We report the detection of crystalline water ice on the surface of 2003 EL_(61). Reflectance spectra were collected from the Gemini North telescope in the 1.0 to 2.4 μm wavelength range and from the Keck telescope across the 1.4-2.4 μm wavelength range. The signature of crystalline water ice is obvious in all data collected. Like the surfaces of many outer solar system bodies, the surface of 2003 EL_(61) is rich in crystalline water ice, which is energetically less favored than amorphous water ice at low temperatures, suggesting that resurfacing processes may be taking place. The near-infrared color of the object is much bluer than a pure water ice model. Adding a near-infrared blue component such as hydrogen cyanide or phyllosilicate clays improves the fit considerably, with hydrogen cyanide providing the greatest improvement. The addition of hydrated tholins and bitumens also improves the fit, but is inconsistent with the neutral V - J reflectance of 2003 EL_(61). A small decrease in reflectance beyond 2.3 μm may be attributable to cyanide salts. Overall, the reflected light from 2003 EL_(61) is best fit by a model of 2/3-4/5 pure crystalline water ice and 1/3-1/5 near-infrared blue component such as hydrogen cyanide or kaolinite. The surface of 2003 EL_(61) is unlikely to be covered by significant amounts of dark material such as carbon black, as our pure ice models reproduce published albedo estimates derived from the spin state of 2003 EL_(61)