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)

Direct measurement of the size of 2003 UB313 from the Hubble Space Telescope

We have used the Hubble Space Telescope to directly measure the angular size of the large Kuiper belt object 2003 UB313. By carefully calibrating the point spread function of a nearby field star, we measure the size of 2003 UB313 to be 34.3$\pm$1.4 milliarcseconds, corresponding to a diameter of 2400$\pm$100 km or a size $\sim5$% larger than Pluto. The V band geometric albedo of 2003 UB313 is $86\pm7$%. The extremely high albedo is consistent with the frosty methane spectrum, the lack of red coloring, and the lack of observed photometric variation on the surface of 2003 UB313. Methane photolysis should quickly darken the surface of 2003 UB313, but continuous evaporation and redeposition of surface ices appears capable of maintaining the extreme alebdo of this body

Water Ice on the Satellite of Kuiper Belt Object 2003 EL61

We have obtained a near infrared spectrum of the brightest satellite of the large Kuiper Belt Object, 2003 EL61. The spectrum has absorption features at 1.5 and 2.0 microns, indicating that water ice is present on the surface. We find that the satellite's absorption lines are much deeper than water ice features typically found on Kuiper Belt Objects. We argue that the unusual spectrum indicates that the satellite was likely formed by impact and not by capture

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

Methane, ammonia, and their irradiation products at the surface of an intermediate-size KBO? A portrait of Plutino (90482) Orcus

Orcus is an intermediate-size 1000km-scale Kuiper Belt Object in 3:2 mean-motion resonance with Neptune, in an orbit very similar to that of Pluto. We present visible and near-infrared photometry and spectroscopy obtained with the Keck 10m-telescope and the Gemini 8m-telescope . We confirm the unambiguous detection of crystalline water ice as well as absorption in the 2.2\mu m region. Both in the visible and near-infrared Orcus' spectral properties appear to be homogeneous over time (and probably rotation) at the resolution available. From Hapke radiative transfer models involving intimate mixtures of various ices we find for the first time that ammonium (NH+4) and traces of ethane (C2 H6), which are most probably solar irradiation products of ammonia and methane, and a mixture of methane and ammonia (diluted or not) are the best candidates to improve the description of the data with respect to a simple water ice mixture (Haumea type surface). The possible more subtle structure of the 2.2\mu m band(s) should be investigated thoroughly in the future for Orcus and other intermediate size Plutinos to better understand the methane and ammonia chemistry at work, if any. We investigated the thermal history of Orcus with a new 3D thermal evolution model. Simulations over 4.5 x109 yrs with an input 10% porosity, bulk composition of 23% amorphous water ice and 77% dust, and cold accretion show that even with the action of long-lived radiogenic elements only, Orcus should have a melted core and most probably suffered a cryovolcanic event in its history which brought large amounts of crystalline ice to the surface. The presence of ammonia in the interior would strengthen the melting process. The crystalline water ice possibly brought to the surface by a past cryovolcanic event sbe detectable after several billion years despite the irradiation eects, as demonstrated by recent laboratory experiments.Comment: 15 pages, 9 figure

Silica in Protoplanetary Disks

Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope show prominent narrow emission features indicating silica (crystalline silicon dioxide). Silica is not a major constituent of the interstellar medium; therefore, any silica present in the circumstellar protoplanetary disks of TTS must be largely the result of processing of primitive dust material in the disks surrouding these stars. We model the silica emission features in our spectra using the opacities of various polymorphs of silica and their amorphous versions computed from earth-based laboratory measurements. This modeling indicates that the two polymorphs of silica, tridymite and cristobalite, which form at successively higher temperatures and low pressures, are the dominant forms of silica in the TTS of our sample. These high temperature, low pressure polymorphs of silica present in protoplanetary disks are consistent with a grain composed mostly of tridymite named Ada found in the cometary dust samples collected from the STARDUST mission to Comet 81P/Wild 2. The silica in these protoplanetary disks may arise from incongruent melting of enstatite or from incongruent melting of amorphous pyroxene, the latter being analogous to the former. The high temperatures of 1200K-1300K and rapid cooling required to crystallize tridymite or cristobalite set constraints on the mechanisms that could have formed the silica in these protoplanetary disks, suggestive of processing of these grains during the transient heating events hypothesized to create chondrules.Comment: 47 pages, 9 figures, to appear in the 1 January, 2009 issue of the Astrophysical Journa

TNOs are Cool: A survey of the trans-Neptunian region V. Physical characterization of 18 Plutinos using Herschel PACS observations

We present Herschel PACS photometry of 18 Plutinos and determine sizes and albedos for these objects using thermal modeling. We analyze our results for correlations, draw conclusions on the Plutino size distribution, and compare to earlier results. Flux densities are derived from PACS mini scan-maps using specialized data reduction and photometry methods. In order to improve the quality of our results, we combine our PACS data with existing Spitzer MIPS data where possible, and refine existing absolute magnitudes for the targets. The physical characterization of our sample is done using a thermal model. Uncertainties of the physical parameters are derived using customized Monte Carlo methods. The correlation analysis is performed using a bootstrap Spearman rank analysis. We find the sizes of our Plutinos to range from 150 to 730 km and geometric albedos to vary between 0.04 and 0.28. The average albedo of the sample is 0.08 \pm 0.03, which is comparable to the mean albedo of Centaurs, Jupiter Family comets and other Trans-Neptunian Objects. We were able to calibrate the Plutino size scale for the first time and find the cumulative Plutino size distribution to be best fit using a cumulative power law with q = 2 at sizes ranging from 120-400 km and q = 3 at larger sizes. We revise the bulk density of 1999 TC36 and find a density of 0.64 (+0.15/-0.11) g cm-3. On the basis of a modified Spearman rank analysis technique our Plutino sample appears to be biased with respect to object size but unbiased with respect to albedo. Furthermore, we find biases based on geometrical aspects and color in our sample. There is qualitative evidence that icy Plutinos have higher albedos than the average of the sample.Comment: 18 pages, 8 figures, 8 tables, accepted for publication in A&

Minimum Wage Channels of Adjustment

Industrial Relations, forthcoming Abstract: The effects of minimum wage increases in 2007-2009 are analyzed using a sample of restaurants from Georgia/Alabama. Store-level payroll records provide precise measures of compliance costs. Examined are multiple adjustment channels. Exploiting variation in compliance costs across restaurants, we find employment and hours responses to be variable and in most cases statistically insignificant. Channels of adjustment to wage increases and to changes in non-labor costs include prices, profits, wage compression, turnover, and performance standards

Efficacies of plant phenolic compounds on sodium butyrate induced anti-tumour activity

861-864The ability of the differentiation inducing agent sodium butyrate (NaB) alone or combined with plant -derived phenolic compounds to produce growth inhibition in human erythroleukemic cells was investigated. As a single agent,curcumin produced a marked inhibition of proliferation indicated by its low concentration used. The effect of phenolics on the cell cycle could probably contribute to the augmented antiproliferative activity of NaB. The present data show that quercetin produced synergistic effect in terms of cell killing in association with NaB. Both curcumin and ferulic acid potentiated NaB induced reduction of cell number. When NaB was added before exposure to graded doses of quercetin it did induce a greater inhibitory effect. The combination of NaB and quercetin seems less effective on S180 ascites tumour cells. As a single agent quercetin was found to be the most efficacious on S180 tumour model