arXiv subjects

Scott S. Sheppard

Publications and source records attributed to Scott S. Sheppard.

70 records · Page 4Linked to original sources

arXiv2011

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.

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arXiv2011

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.

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arXiv2010

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.

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arXiv2010

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.

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arXiv2010

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.

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arXiv2009

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.

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arXiv2008

An Infrared High Proper Motion Survey Using 2MASS and SDSS: Discovery of M, L and T Dwarfs

A search of the Two Micron All Sky Survey and Sloan Digital Sky Survey reveals 36 previously unknown high proper motion objects with J<17. Their red-optical colors indicate that 27 are M dwarfs, 8 are early-type L dwarfs, and 1 is a late-type T dwarf. The L dwarfs have J-Ks colors near the extrema of known L dwarfs indicating that previous surveys for L dwarfs using color as a selection criterion may be biased. Followup near-infrared spectroscopy of 6 dwarfs confirm they are all late-type with spectral types ranging from M8 to T4. Spectroscopy also shows that some of the L dwarf spectra exhibit peculiar features similar to other peculiar "blue" L dwarfs which may indicate that these dwarfs have a relatively condensate free atmosphere or may be metal poor. Photometric distance estimates indicate that 22 of the new M, L and T dwarfs lie within 100 pc of the Sun with the newly discovered T dwarf, 2MASS J10595185+3042059, located at about 25 pc. Based on the colors and proper motions of the newly identified objects, several appear to be good subdwarf candidates. The proper motions of known ultracool dwarfs detected in our survey were also measured, including, for the first time, SDSS J085834.42+325627.6 (T1), SDSS J125011.65+392553.9 (T4) and 2MASS J15261405+2043414 (L7).

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arXiv2007

Light Curves of Dwarf Plutonian Planets and other Large Kuiper Belt Objects: Their Rotations, Phase Functions and Absolute Magnitudes

(Abridged) I report new light curves and determine the rotations and phase functions of several large Kuiper Belt objects, including the dwarf planet Eris (2003 UB313). (120348) 2004 TY364 shows a light curve which if double-peaked has a period of 11.70+-0.01 hours and peak-to-peak amplitude of 0.22+-0.02 magnitudes. (84922) 2003 VS2 has a well defined double-peaked light curve of 7.41+-0.02 hours with a 0.21+-0.02 magnitude range. (126154) 2001 YH140 shows variability of 0.21+-0.04 magnitudes with a possible 13.25+-0.2 hour single-peaked period. The seven new KBOs in the sample which show no discernible variations within the uncertainties on short rotational time scales are 2001 UQ18, (55565) 2002 AW197, (119979) 2002 WC19, (120132) 2003 FY128, (136108) Eris 2003 UB313, (90482) Orcus 2004 DW, and (90568) 2004 GV9. The three medium to large sized Kuiper Belt objects 2004 TY364, Orcus and 2004 GV9 show fairly steep linear phase curves (~0.18 to 0.26 mags per degree) between phase angles of 0.1 and 1.5 degrees. The extremely large dwarf planet Eris (2003 UB313) shows a shallower phase curve (0.09+-0.03 mags per degree) which is more similar to the other known dwarf planet Pluto. It appears the surface properties of the largest dwarf planets in the Kuiper Belt maybe different than the smaller Kuiper Belt objects. This may have to do with the larger objects ability to hold more volatile ices as well as sustain atmospheres. The absolute magnitudes obtained using the measured phase slopes are a few tenths of magnitudes different from those given by the MPC.

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arXiv2006

Outer irregular satellites of the planets and their relationship with asteroids, comets and Kuiper Belt objects

Outer satellites of the planets have distant, eccentric orbits that can be highly inclined or even retrograde relative to the equatorial planes of their planets. These irregular orbits cannot have formed by circumplanetary accretion and are likely products of early capture from heliocentric orbit. The irregular satellites may be the only small bodies remaining which are still relatively near their formation locations within the giant planet region. The study of the irregular satellites provides a unique window on processes operating in the young solar system and allows us to probe possible planet formation mechanisms and the composition of the solar nebula between the rocky objects in the main asteroid belt and the very volatile rich objects in the Kuiper Belt. The gas and ice giant planets all appear to have very similar irregular satellite systems irrespective of their mass or formation timescales and mechanisms. Water ice has been detected on some of the outer satellites of Saturn and Neptune whereas none has been observed on Jupiter's outer satellites.

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arXiv2006

A Survey for "Normal" Irregular Satellites Around Neptune: Limits to Completeness

We surveyed 1.75 square degrees of sky near Neptune to an R-band 50% detection efficiency of 25.8 mags (corresponding to radii of about 17 km for an assumed albedo of 0.04). We discovered one new outer satellite, Psamathe (S/2003 N1), about 20 km in radius and having a distant retrograde orbit and moderate eccentricity. Until 2003 Neptune was only known to have two satellites which exhibited orbital signatures indicative of capture. Both of these, Triton and Nereid, are unusual when compared to the irregular satellites of other giant planets. With recent discoveries of four additional satellites by Holman et al. (2004) it is now apparent that Neptune has a distant ``normal'' irregular satellite system in which the satellites have radii and orbital properties similar to those of the satellites of other giant planets. We find that the satellite size distribution at Neptune is not well determined given the few objects known to date, being especially sensitive to the inclusion of Triton and Nereid in the sample. Finally, we note that Psamathe and S/2002 N4 have similar semi-major axes, inclinations and eccentricities. They may be fragments of a once larger satellite.

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arXiv2004

Ultra Deep Survey for Irregular Satellites of Uranus: Limits to Completeness

We present a deep optical survey of Uranus' Hill sphere for small satellites. The Subaru 8-m telescope was used to survey about 3.5 square degrees with a 50% detection efficiency at limiting red magnitude m = 26.1 mag. This magnitude corresponds to objects that are about 7 km in radius (assuming an albedo of 0.04). We detected (without prior knowledge of their positions) all previously known outer satellites and discovered two new irregular satellites (S/2001 U2 and S/2003 U3). The two inner satellites Titania and Oberon were also detected. One of the newly discovered satellites (S/2003 U3) is the first known irregular prograde of the planet. The population, size distribution and orbital parameters of Uranus' irregular satellites are remarkably similar to the irregular satellites of gas giant Jupiter. Both have shallow size distributions (power law indices q~2 for radii > 7 km) with no correlation between the sizes of the satellites and their orbital parameters. However, unlike those of Jupiter, Uranus' irregular satellites do not appear to occupy tight distinct dynamical groups in semi-major axis versus inclination phase space. Two groupings in semi-major axis versus eccentricity phase space appear to be statistically significant.

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arXiv2004

A Survey for Outer Satellites of Mars: Limits to Completeness

We surveyed the Hill sphere of Mars for irregular satellites. Our search covered nearly the entire Hill Sphere, but scattered light from Mars excluded the inner few arcminutes where the satellites Phobos and Deimos reside. No new satellites were found to an apparent limiting red magnitude of 23.5, which corresponds to radii of about 0.09 km using an albedo of 0.07.

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arXiv2004

Extreme Kuiper Belt Object 2001 QG298 and the Fraction of Contact Binaries

Extensive time-resolved observations of Kuiper Belt object 2001 QG298 show a lightcurve with a peak-to-peak variation of 1.14 +-0.04 magnitudes and single-peaked period of 6.8872 +- 0.0002 hr. The mean absolute magnitude is 6.85 magnitudes which corresponds to a mean effective radius of 122 (77) km if an albedo of 0.04 (0.10) is assumed. This is the first known Kuiper Belt object and only the third minor planet with a radius > 25 km to display a lightcurve with a range in excess of 1 magnitude. We find the colors to be typical for a Kuiper Belt object (B-V = 1.00 +- 0.04, V-R = 0.60 +- 0.02) with no variation in color between minimum and maximum light. The large light variation, relatively long double-peaked period and absence of rotational color change argue against explanations due to albedo markings or elongation due to high angular momentum. Instead, we suggest that 2001 QG298 may be a very close or contact binary similar in structure to what has been independently proposed for the Trojan asteroid 624 Hektor. If so, its rotational period would be twice the lightcurve period or 13.7744 +- 0.0004 hr. By correcting for the effects of projection, we estimate that the fraction of similar objects in the Kuiper Belt is at least 10% to 20% with the true fraction probably much higher. A high abundance of close and contact binaries is expected in some scenarios for the evolution of binary Kuiper Belt objects.

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arXiv2002

Time-Resolved Photometry of Kuiper Belt Objects: Rotations, Shapes and Phase Functions

We present a systematic investigation of the rotational lightcurves of trans-Neptunian objects based on extensive optical data from Mauna Kea. Four of 13 objects (corresponding to 31%) in our sample ((33128) 1998 BU48, 2000 GN171, (20000) Varuna and 1999 KR16) were found to exhibit lightcurves with peak-to-peak range > 0.15 magnitude. In a larger sample obtained by combining our data with reliably determined lightcurves from the literature, 7 of 22 objects (32%) display significant (> 0.15 magnitude range) lightcurves. About 23% of the sampled objects have lightcurve ranges > 0.4 magnitudes. Curiously, the objects are very large (> 250 km diameter, assuming an albedo of 0.04) and, in the absence of rotation, should be near spherical due to self compression. We propose that the large amplitude, short period objects are rotationally distorted, low density rubble piles. Statistically, the trans-Neptunian objects are less spherical than their main-belt asteroid counterparts, indicating a higher specific angular momentum perhaps resulting from the formation epoch. In addition to the rotational lightcurves, we measured phase darkening for 7 Kuiper Belt objects in the 0 to 2 degree phase angle range. Unlike Pluto, the measured values show steep slopes and moderate opposition surge indicating backscatter from low albedo porous surface materials.

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arXiv2002

Physical Properties of Trans-Neptunian Object (20000) Varuna

We present new time-resolved photometric observations of the bright trans-Neptunian object (20000) Varuna and use them to study the rotation period, shape, and color. In observations from 2001 February and April, we find a best-fit two-peaked lightcurve with period 6.3442 +-0.0002 hr. The peak-to-peak photometric range in the R-band is 0.42 +-0.02 mag. We find no rotational variation in colors over the 0.45 < lambda < 0.85 micron wavelength range. From the short double-peaked period and large amplitude we suggest that Varuna is an elongated, prolate body perhaps close in shape to one of the Jacobi ellipsoids. If so, the ratio of the axes projected into the plane of the sky is 1.5:1 and the density is near 1000 kg m^(-3). (20000) Varuna may be a rotationally distorted rubble pile, with a weak internal constitution due to fracturing by past impacts. The high specific angular momentum implied by our observations and recent detections of binary Trans-Neptunian Objects both point to an early, intense collisional epoch in which large Trans-Neptunian Objects were about 100 times more abundant than now. In order to maintain a cosmochemically plausible rock:ice mass ratio of about 0.5, Varuna must be internally porous.

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arXiv2001

The Evolution of Circumstellar Disks: Lessons from the VLT and ISO

There is strong evidence that the planets in the solar system evolved from a disk-shaped solar nebula ~4.56 Gyr ago. By studying young stars in various evolutionary stages, one aims at tracing back the early history of the solar system, in particular the timescales for disk dissipation and for the formation of planetary systems. We used the VLT & ISAAC, and ESA's Infrared Space Observatory & ISOCAM to study the circumstellar environment of young low-mass stars.

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