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ABSTRACT: We present three near-infrared spectra of Pluto taken with the IRTF and SpeX,
an optical spectrum of Triton taken with the MMT and the Red Channel
Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We
combine these observations with a two-phase Hapke model, and gain insight into
the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the
methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf
planets. In addition, we present a laboratory experiment that demonstrates it
is essential to model methane bands in spectra of icy dwarf planets with two
methane phases - one highly-diluted by nitrogen and the other rich in methane.
For Pluto, we find bulk, hemisphere-averaged, methane abundances of 9.1 \pm
0.5%, 7.1 \pm 0.4%, and 8.2 \pm 0.3% for sub-Earth longitudes of 10\degree,
125\degree, and 257\degree. Application of the Wilcoxon rank sum test to our
measurements finds these small differences are statistically significant. For
Triton, we find bulk, hemisphere-averaged, methane abundances of 5.0 \pm 0.1%
and 5.3 \pm 0.4% for sub-Earth longitudes of 138\degree and 314\degree.
Application of the Wilcoxon rank sum test to our measurements finds the
differences are not statistically significant. For Eris, we find a bulk,
hemisphere-averaged, methane abundance of 10 \pm 2%. Pluto, Triton, and Eris do
not exhibit a trend in methane-nitrogen mixing ratio with depth into their
surfaces over the few cm range probed by these observations. This result is
contrary to the expectation (Grundy & Stansberry 2000) that since visible light
penetrates deeper into a nitrogen-rich surface than the depths from which
thermal emission emerges, net radiative heating at depth would drive
preferential sublimation of nitrogen leading to an increase in the methane
abundance with depth.
03/2012;
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S. C. Tegler,
D. M. Cornelison,
W. M. Grundy, W. Romanishin,
M. R. Abernathy,
M. J. Bovyn,
J. A. Burt,
D. E. Evans,
C. K. Maleszewski,
Z. Thompson,
and F. Vilas
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ABSTRACT: We present spectra of Eris from the MMT 6.5 m Telescope and Red Channel Spectrograph (5700-9800 Å, 5 Å pixel–1) on Mt. Hopkins, AZ, and of Pluto from the Steward Observatory 2.3 m Telescope and Boller and Chivens Spectrograph (7100-9400 Å, 2 Å pixel–1) on Kitt Peak, AZ. In addition, we present laboratory transmission spectra of methane-nitrogen and methane-argon ice mixtures. By anchoring our analysis in methane and nitrogen solubilities in one another as expressed in the phase diagram of Prokhvatilov & Yantsevich, and comparing methane bands in our Eris and Pluto spectra and methane bands in our laboratory spectra of methane and nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are ~10% and ~90% and Pluto's bulk methane and nitrogen abundances are ~3% and ~97%. Such abundances for Pluto are consistent with values reported in the literature. It appears that the bulk volatile composition of Eris is similar to the bulk volatile composition of Pluto. Both objects appear to be dominated by nitrogen ice. Our analysis also suggests, unlike previous work reported in the literature, that the methane and nitrogen stoichiometry is constant with depth into the surface of Eris. Finally, we point out that our Eris spectrum is also consistent with a laboratory ice mixture consisting of 40% methane and 60% argon. Although we cannot rule out an argon-rich surface, it seems more likely that nitrogen is the dominant species on Eris because the nitrogen ice 2.15 μm band is seen in spectra of Pluto and Triton.
The Astrophysical Journal 11/2010; 725(1):1296. · 6.02 Impact Factor
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ABSTRACT: We present new optical broadband colors, obtained with the Keck 1 and Vatican Advanced Technology telescopes, for six objects in the inner classical Kuiper Belt. Objects in the inner classical Kuiper Belt are of interest as they may represent the surviving members of the primordial Kuiper Belt that formed interior to the current position of the 3:2 resonance with Neptune, the current position of the plutinos, or, alternatively, they may be objects formed at a different heliocentric distance that were then moved to their present locations. The six new colors, combined with four previously published, show that the 10 inner belt objects with known colors form a neutral clump and a reddish clump in B-R color. Nonparametric statistical tests show no significant difference between the B-R color distribution of the inner disk objects compared to the color distributions of Centaurs, plutinos, or scattered disk objects. However, the B-R color distribution of the inner classical Kuiper belt objects does differ significantly from the distribution of colors in the cold (low inclination) main classical Kuiper belt. The cold main classical objects are predominately red, while the inner classical belt objects are a mixture of neutral and red. The color difference may reveal the existence of a gradient in the composition and /or surface processing history in the primordial Kuiper Belt, or indicate that the inner disk objects are not dynamically analogous to the cold main classical belt objects. Comment: Accepted for publication in AJ
04/2010;
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K. Z. Stanek,
P. M. Garnavich,
P. A. Nutzman,
J. D. Hartman,
A. Garg,
K. Adelberger,
P. Berlind,
A. Z. Bonanos,
M. L. Calkins,
P. Challis, [......],
M. J. Holman,
R. P. Kirshner,
B. A. McLeod,
D. Osip,
T. Pimenova,
T. H. Reiprich, W. Romanishin,
T. Spahr,
S. C. Tegler,
and X. Zhao
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ABSTRACT: We present deep optical photometry of the afterglow of gamma-ray burst (GRB) 041006 and its associated hypernova obtained over 65 days after detection (55 R-band epochs on 10 different nights). Our early data (t < 4 days) joined with published GCN data indicate a steepening decay, approaching Fν t-0.6 at early times (t 1 day) and Fν t-1.3 at late times. The break at tb = 0.16 ± 0.04 days is the earliest reported jet break among all GRB afterglows. During our first night, we obtained 39 exposures spanning 2.15 hr from 0.62 to 0.71 days after the burst that reveal a smooth afterglow, with an rms deviation of 0.024 mag from the local power-law fit, consistent with photometric errors. After t ~ 4 days, the decay slows considerably, and the light curve remains approximately flat at R ~ 24 mag for a month before decaying by another magnitude to reach R ~ 25 mag 2 months after the burst. This "bump" is well fit by a k-corrected light curve of supernova SN 1998bw, but only if stretched by a factor of 1.38 in time. In comparison with the other GRB-related SN bumps, GRB 041006 stakes out new parameter space for GRBs/SNe, with a very bright and significantly stretched late-time SN light curve. Within a small sample of fairly well observed GRB/SN bumps, we see a hint of a possible correlation between their peak luminosity and their "stretch factor," broadly similar to the well-studied Phillips relation for the Type Ia supernovae.
The Astrophysical Journal 12/2008; 626(1):L5. · 6.02 Impact Factor
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ABSTRACT: As a result of our continuing photometric survey, we report here optical colors for 36 Kuiper Belt objects, increasing our sample size to 91 objects. We find that certain dynamical classes of objects exhibit distinctive colors—21 out of 21 objects on small-inclination and small-eccentricity orbits with perihelion distances larger than 40 AU exhibit red surface colors (B-R > 1.5), while 17 out of 20 objects on large-inclination and large-eccentricity orbits with aphelion distances larger than 70 AU exhibit gray surface colors (B-R < 1.5). Our observations are consistent with a primordial origin for Kuiper Belt surface colors, if we assume that gray objects formed closer to the Sun than red objects, and as Neptune migrated outward it scattered gray objects onto dynamically hot orbits. By this model, the contrasting dynamically cold and red objects beyond 40 AU remained far enough away from Neptune that they were never perturbed by the planet.
The Astrophysical Journal 12/2008; 599(1):L49. · 6.02 Impact Factor
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ABSTRACT: We describe optical spectroscopic observations of the icy dwarf planet Eris with the 6.5 meter MMT telescope and the Red Channel Spectrograph. We report a correlation, that is at the edge of statistical significance, between blue shift and albedo at maximum absorption for five methane ice bands. We interpret the correlation as an increasing dilution of methane ice with another ice component, probably nitrogen, with increasing depth into the surface. We suggest a mechanism to explain the apparent increase in nitrogen with depth. Specifically, if we are seeing Eris 50 degrees from pole-on (Brown and Schaller, 2008), the pole we are seeing now at aphelion was in winter darkness at perihelion. Near perihelion, sublimation could have built up atmospheric pressure on the sunlit (summer) hemisphere sufficient to drive winds toward the dark (winter) hemisphere, where the winds would condense. Because nitrogen is more volatile and scarcer than methane, it sublimated from the sunlit hemisphere relatively early in the season, so the early summer atmosphere was nitrogen rich, and so was the ice deposited on the winter pole. Later in the season, much of the nitrogen was exhausted from the summer pole, but there was plenty of methane, which continued to sublimate. At this point, the atmosphere was more depleted in nitrogen, as was the ice freezing out on top of the earlier deposited nitrogen rich ice. Comment: This paper will appear in Icarus. It consists of 26 pages, 3 tables, and 5 figures
11/2008;
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02/2008;
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ABSTRACT: We present high signal precision optical reflectance spectra of 2005 FY9 taken with the Red Channel Spectrograph and the 6.5-m MMT telescope on 2006 March 4 UT (5000 - 9500 A; 6.33 A pixel-1) and 2007 February 12 UT (6600 - 8500 A; 1.93 A pixel-1). From cross correlation experiments between the 2006 March 4 spectrum and a pure CH4-ice Hapke model, we find the CH4-ice bands in the MMT spectrum are blueshifted by 3 +/- 4 A relative to bands in the pure CH4-ice Hapke spectrum. The higher resolution MMT spectrum of 2007 February 12 UT enabled us to measure shifts of individual CH4-ice bands. We find the 7296 A, 7862 A, and 7993 A CH4-ice bands are blueshifted by 4 +/- 2 A, 4 +/- 4 A, and 6 +/- 5 A. From four measurements we report here and one of our previously published measurements, we find the CH4-ice bands are shifted by 4 +/- 1 A. This small shift is important because it suggest the presence of another ice component on the surface of 2005 FY9. Laboratory experiments show that CH4-ice bands in spectra of CH4 mixed with other ices are blueshifted relative to bands in spectra of pure CH4-ice. A likely candidate for the other component is N2-ice because its weak 2.15 micron band and blueshifted CH4 bands are seen in spectra of Triton and Pluto. Assuming the shift is due to the presence of N2, spectra taken on two consecutive nights show no difference in CH4/N2. In addition, we find no measureable difference in CH4/N2 at different depths into the surface of 2005 FY9. Comment: The paper will appear in Icarus. It has 33 pages, 2 tables, and 7 figures. Replaced version fixed typo in abstract
01/2008;
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01/2008: pages 105-114;
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ABSTRACT: We present high signal precision optical reflectance spectra of the large Kuiper belt objects 2005 FY9 and 2003 EL61. The spectrum of 2005 FY9 exhibits strong CH4-ice bands. A comparison between the spectrum and a Hapke model indicates the CH4 bands are shifted 3.25 +/- 2.25A relative to pure CH4-ice, suggesting the presence of another ice component on the surface of 2005 FY9, possibly N2-ice, CO-ice, or Ar. The spectrum of 2003 EL61 is remarkably featureless. There is a hint of an O2-ice band at 5773A; however, this feature needs to be confirmed by future spectroscopic observations of 2003 EL61 with a higher continuum signal precision, sufficient to detect a second weaker O2-ice band at 6275A.
12/2006;
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ABSTRACT: We compare the shapes and spin states of well-characterized asteroids
with the stress/spin curves of Holsapple (2004). Applying these trends
to centaurs and KBOs we infer that most have densities
02/2006; 37:1222.
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ABSTRACT: From July 2001 to June 2002, an HST snapshot program obtained V, R and I photometry for 72 TNOs. The TNOs were sorted by dynamical class, and Spearman rank correlation statistics were calculated for each combination of color and orbital parameter. No strong correlations were found for the combined sample of TNOs, the resonant TNOs, or the non-resonant TNOs (classical). The results presented here suggest that if correlations reported by other authors are real, they are evident only at shorter wavelengths than observed in our survey.
Earth Moon and Planets 05/2003; 92(1):251-260. · 0.67 Impact Factor
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ABSTRACT: The recent discovery of an ancient reservoir of icy bodies at and beyond the orbit of Neptune-the Kuiper belt-has opened a new frontier in astronomy. Measurements of the physical and chemical nature of Kuiper belt objects (KBOs) can constrain our ideas of the processes of planet formation and evolution. Our 1.8-m Vatican Advanced Technology Telescope and charge-coupled device camera observations of the KBO 1998 SM(165) indicate its brightness periodically varies by 0.56 magnitudes over a 4-h interval. If we assume a uniform albedo of 0.04, which is typical of values found in the literature for a handful of KBOs, and an "equator-on" aspect, we find 1998 SM(165) has axes of length 600 x 360 km. If our assumptions are correct, such dimensions put 1998 SM(165) among the largest elongated objects known in our solar system. Perhaps long ago, two nearly spherical KBOs of comparable size coalesced to form a compound object, or perhaps 1998 SM(165) is the residual core of a catastrophic fragmentation of a larger precursor.
Proceedings of the National Academy of Sciences 11/2001; 98(21):11863-6. · 9.68 Impact Factor
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Nature 06/2001; 411(6836):423-4. · 36.28 Impact Factor
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ABSTRACT: Kuiper-belt objects (KBOs) are an ancient reservoir of comets beyond Neptune's orbit. Some of these objects were recently found to have the reddest optical colours in the Solar System, but the number of objects for which accurate colours were available was too small for any correlation to be discerned between colour and physical or dynamical properties, which might shed light on the origin of these objects. Here we report that all nine of the KBOs in our survey on near-circular (low-eccentricity) orbits with perihelion distances larger than 40 AU have extremely red surfaces, thereby connecting an observable property with a dynamical class. Of the objects with orbital eccentricities greater than 0.1, about half are also very red, while the rest have colours similar to the Sun, meaning that reflected sunlight is not strongly modified by the objects' surface properties. In addition, of the 13 'classical' KBOs (those with semimajor axis a approximately 45 AU and eccentricity e < 0.15), the ten that are very red are in orbits with small angles of inclination to the ecliptic, whereas the three with solar colours are all in high-inclination orbits. We suggest that these three 'grey' classical KBOs may be part of a dynamical group that is separate from the 'red' classical KBOs.
Nature 11/2000; 407(6807):979-81. · 36.28 Impact Factor
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ABSTRACT: The outer Solar System object 1999 TD10 is unusual in that it has a
perihelion distance similar to Centaurs, 12 AU, but a semi-major axis
similar to scattered disk objects, 190 AU. We obtained CCD images of
1999 TD10 using the University of Arizona 2.3-m telescope on Kitt Peak,
Arizona on 1999 November 8 and 9 UT and the Vatican Observatory VATT
1.8-m telescope on Mt. Graham, Arizona on 1999 November 11 and 12 UT.
All images were obtained through B, V, and R glass filters on
photometric nights. We find 1999 TD10 exhibits large variations in
brightness. It has a lightcurve with an average V magnitude of 20.20, an
amplitude of 0.68 magnitudes, which can be fit with a period of 5.8 hr.
We find an absolute magnitude, H, of 9.07. If we assume an albedo of
0.04, then 1999 TD10 has a mean diameter of 100 km. If the variation in
brightness is due to the rotation of an object with an irregular shape,
then the ratio of a/b is 1.88, giving the object dimensions of 130 x 70
km. Such an irregular shape for such a large object would be unusual for
a main belt asteroid; however, the largest Trojan, 624 Hektor, may be
larger and even more irregular in shape, and the largest irregular moon
(Hyperion) has a similar a/b with much larger dimensions (410 x 260 x
220 km). We find a B-V color of 0.77 +/- 0.02 and a V-R color of 0.47
+/- 0.01. Such colors place 1999 TD10 in the "gray" population of
centaurs and KBOs, comparable to the Trojans.
09/2000; 32:1032.
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08/1999; 31:1110.
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ABSTRACT: We report on our 1999 May 15 to 19 UT observations of the irregular
Uranian satellite Sycorax (S/1997 U2) and the short period comet nucleus
P/Neujmin 1 with the 1.8-m Vatican Observatory telescope on Mt. Graham,
Arizona, a high quantum efficiency CCD camera, and B, V, and R filters.
We present V magnitudes, B-V and V-R colors, and lightcurves for Sycorax
and P/Neujmin 1. Our measurements allow us to constrain the diameters,
surface compositions, and shapes of these two objects. We compare the
physical properties of Sycorax and P/Neujmin 1 to their possible
progenitors, Kuiper belt objects.
08/1999; 31.
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Nature 03/1999; 398(6723):129-132. · 36.28 Impact Factor
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11/1998; 30:1454.
