We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool ...dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M sub(5.8) versus 5.8-8.0, the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one-parameter family in T sub(eff). Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of 5 (670M sub(J) to 615M sub(J)), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 km fluxes to be lower than expected, from which we infer a stronger CO fundamental band at 64.67 km. This suggests that equilibrium CH sub(4)/CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of K sub(s), IRAC 3.6 km, and 4.5 km bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the M super(K.) versus K sub(s)-4.5 relation, which shows a smooth progression over spectral type, and splits the M, L, and T types cleanly.
► We develop quantitative search algorithms for faint tails and comae. ► Using these code, we find no main-belt comet (MBC) candidates in the TALCS data. ► We present evidence for very low-level tail ...activity in about 5% of our sample. ► We determine that the MBC:MBA ratio is <1:400 for
H
<
21.0. ► We statistically argue that the contemporary snow line is beyond 2.5
AU.
The first of a new class of objects now known as main belt comets (MBCs) or “activated asteroids” was identified in 1996. The seven known members of this class have orbital characteristics of main belt asteroids yet exhibit dust ejection like comets. In order to constrain their physical and orbital properties we searched the Thousand Asteroid Light Curve Survey (TALCS; Masiero, J.R., Jedicke, R., Durech, J., Gwyn, S., Denneau, L., Larsen, J. 2009. Icarus 204, 145–171) for additional candidates using two diagnostics: tail and coma detection. This was the most sensitive MBC survey effort to date, extending the search from MBCs with
H
∼
18 (
D
∼
1
km) to MBCs as small as
H
∼
21 (
D
∼
150
m).
We fit each of the 924 objects detected by TALCS to a PSF model incorporating both a coma and nuclear component to measure the fractional contribution of the coma to the total surface brightness. We determined the significance of the coma detection using the same algorithm on a sample of null detections of comparable magnitude and rate of motion. We did not identify any MBC candidates with this technique to a sensitivity limit on the order of cometary mass loss rate of about 0.1
kg/s.
Our tail detection algorithm relied on identifying statistically significant flux in a segmented annulus around the candidate object. We show that the technique can detect tail activity throughout the asteroid belt to the level of the currently known MBCs. Although we did not identify any MBC candidates with this technique, we find a statistically significant detection of faint activity in the entire ensemble of TALCS asteroids. This suggests that many main belt asteroids are active at very low levels.
Our null detection of MBCs allows us to set 90% upper confidence limits on the number distribution of MBCs as a function of absolute magnitude, semi-major axis, eccentricity, and inclination. There are ≲400,000 MBCs in the main belt brighter than
H
V
=
21 (∼150-m in diameter) and the MBC:MBA ratio is ≲1:400.
We further comment on the ability of observations to meaningfully constrain the snow line’s location. Under some reasonable and simple assumptions we claim 85% confidence that the contemporary snow line lies beyond 2.5
AU.
We present a database of spectral lags and internal luminosity function (ILF) measurements for gamma-ray bursts (GRBs) in the BATSE catalog. Measurements were made using 64 ms count rate data and are ...defined for various combinations of the four broadband BATSE energy channels. We discuss the processes used for measuring lags and ILF characteristics. We discuss the statistical and systematic uncertainties in measuring these attributes, as well as the role of temporal resolution in measuring lags and/or ILFs--these are particularly noticeable for GRBs belonging to the Short class. Correlative and clustering properties of the lag and ILF are examined, including the ability of these attributes to predict GRB time history morphologies. We conclude that the ILF and lag have great potential for studying GRB physics when used with other burst attributes.
ABSTRACT The Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) mission continues to detect, track, and characterize minor planets. We present diameters and albedos calculated from ...observations taken during the second year since the spacecraft was reactivated in late 2013. These include 207 near-Earth asteroids (NEAs) and 8885 other asteroids. Of the NEAs, 84% NEAs did not have previously measured diameters and albedos by the NEOWISE mission. Comparison of sizes and albedos calculated from NEOWISE measurements with those measured by occultations, spacecraft, and radar-derived shapes shows accuracy consistent with previous NEOWISE publications. Diameters and albedos fall within ∼20% and ∼40%, 1-sigma, respectively, of those measured by these alternate techniques. NEOWISE continues to preferentially discover near-Earth objects which are large (>100 m), and have low albedos.
ABSTRACT The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO2 production. ...We present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 m band excess. We find a possible relation between dust and CO + CO2 production, as well as possible differences in the sizes of long and short period comet nuclei.
Abstract
We present a new model for Haumea’s formation and evolution that relies on geophysical and geochemical data informed from observations of Haumea and meteorites to explain the characteristics ...of Haumea and its dynamical family. We hypothesize that after the impact of two partially differentiated Kuiper Belt objects, Haumea’s rocky core grew, decreasing its moment of inertia (MOI), spinning it up to the point that icy material was ejected from its surface. This ice, carrying about 3% of Haumea’s mass and 14% of its initial angular momentum, comprises the Haumean dynamical family and the ring system and moons observed today. Later, melted ice hydrated Haumea’s core and it grew, increasing Haumea’s MOI and spinning it down to the modern value. We use the geophysical code
kyushu
to demonstrate that solutions exist for a Haumea in hydrostatic equilibrium at each of these hypothesized stages. Geochemical modeling using the
IcyDwarf
code constrains the formation of Haumea’s core and the creation of the collision family to have occurred after roughly 150–160 Myr of solar system evolution (4.41 ± 0.01 Gyr ago). Hydration of the core was complete by about 0.20 Gyr, but a substantial subsurface ocean with half the mass of Earth’s oceans persisted until it froze at about 0.45 Gyr, making Haumea the solar system’s most distant potential relict ocean world.
MAIN-BELT COMET P/2012 T1 (PANSTARRS) Hsieh, Henry H; KALUNA, HEATHER M; Novakovic, Bojan ...
Astrophysical journal. Letters,
07/2013, Letnik:
771, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present initial results from observations and numerical analyses aimed at characterizing the main-belt comet P/2012 T1 (PANSTARRS). Optical monitoring observations were made between 2012 October ...and 2013 February using the University of Hawaii 2.2 m telescope, the Keck I telescope, the Baade and Clay Magellan telescopes, Faulkes Telescope South, the Perkins Telescope at Lowell Observatory, and the Southern Astrophysical Research Telescope. The object's intrinsic brightness approximately doubles from the time of its discovery in early October until mid-November and then decreases by ~60% between late December and early February, similar to photometric behavior exhibited by several other main-belt comets and unlike that exhibited by disrupted asteroid (596) Scheila. We also used Keck to conduct spectroscopic searches for CN emission as well as absorption at 0.7 mu m that could indicate the presence of hydrated minerals, finding an upper limit CN production rate of Q sub(CN) < 1.5 x 10 super(23) mol s super(-1) from which we infer a water production rate of Q sub(H2O) < 5 x 10 super(25) mol s super(-1), and no evidence of the presence of hydrated minerals. Numerical simulations indicate that P/2012 T1 is largely dynamically stable for >100 Myr and is unlikely to be a recently implanted interloper from the outer solar system, while a search for potential asteroid family associations reveals that it is dynamically linked to the ~155 Myr old Lixiaohua asteroid family.
The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO{sub 2} production. We ...present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 μm band excess. We find a possible relation between dust and CO + CO{sub 2} production, as well as possible differences in the sizes of long and short period comet nuclei.
Trans-Neptunian Objects (TNOs) are small bodies with orbits beyond Neptune (3050 AU). TNOs are cold and small enough to have remained relatively well-preserved, therefore providing our best ...observable proxy to the early solar system. Roughly 1/3 of TNOs possess neutral colors indicative of fresh surfaces. Three different mechanisms may explain the neutral colors: (i) collisional resurfacing, which only re-coats a fraction of the surface, producing heterogeneous colors; (ii) compositional differences, producing homogeneous colors; and (iii) cometary outgassing, through which either jets produce a heterogeneous object or a global outgassing event produces a homogeneous object. We conducted two surveys to search for homogeneity on the surfaces of neutral TNOs in order to help discern between these resurfacing theories a brightness variation survey (BVS) in which we sparsely sampled lightcurves of 38 neutral TNOs to select follow-up targets, and a color variation survey (CVS) of the 9 follow-up targets to densely sample their rotational lightcurves. Through the BVS, we found that the amplitude distributions of red and neutral TNOs are similar, suggesting a similar collisional histories and refuting the collisional resurfacing mechanism. We detected no close/contact binaries but placed upper limits to the binary fraction of ~ 12 – 20% at angular component separations of 0.02+0.03n–0.02, which supports the existence of a turnover in the binary fraction as a function of component separation. From our CVS results, updated spin distributions also reveal similarity between red and neutral TNOs, supporting the BVS findings. We constrained the spin periods of seven objects, one of which (collisional family member 2003 OP32) was found to have the fastest measured rotation period of any outer solar system object at ~ 2.4 or 2.6 hours. We found evidence for companions to four of our CVS targets, giving a binary fraction of > 24% for separations 0.04 ±0.02n. Combined with the BVS and other surveys, these limits suggest that two binary formation mechanisms not involving collisions were simultaneously at work in the Trans-Neptunian belt, one of which was likely the Goldreich et al. (2002) model of dynamical friction.
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