110 research outputs found
The 2016 Reactivations of Main-Belt Comets 238P/Read and 288P/(300163) 2006 VW139
We report observations of the reactivations of main-belt comets 238P/Read and
288P/(300163) 2006 VW139, that also track the evolution of each object's
activity over several months in 2016 and 2017. We additionally identify and
analyze archival SDSS data showing 288P to be active in 2000, meaning that both
238P and 288P have now each been confirmed to be active near perihelion on
three separate occasions. From data obtained of 288P from 2012-2015 when it
appeared inactive, we find best-fit R-band H,G phase function parameters of
H_R=16.80+/-0.12 mag and G_R=0.18+/-0.11, corresponding to effective component
radii of r_c=0.80+/-0.04 km, assuming a binary system with equally-sized
components. Fitting linear functions to ejected dust masses inferred for 238P
and 288P soon after their observed reactivations in 2016, we find an initial
average net dust production rate of 0.7+/-0.3 kg/s and a best-fit start date of
2016 March 11 (when the object was at a true anomaly of -63 deg) for 238P, and
an initial average net dust production rate of 5.6+/-0.7 kg/s and a best-fit
start date of 2016 August 5 (when the object was at a true anomaly of -27 deg)
for 288P. Applying similar analyses to archival data, we find similar start
points for previous active episodes for both objects, suggesting that minimal
mantle growth or ice recession occurred between the active episodes in
question. Some changes in dust production rates between active episodes are
detected, however. More detailed dust modeling is suggested to further clarify
the process of activity evolution in main-belt comets.Comment: 21 pages, 9 figures, accepted by A
"TNOs are Cool": A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations
The classical Kuiper belt contains objects both from a low-inclination,
presumably primordial, distribution and from a high-inclination dynamically
excited population. Based on a sample of classical TNOs with observations at
thermal wavelengths we determine radiometric sizes, geometric albedos and
thermal beaming factors as well as study sample properties of dynamically hot
and cold classicals. Observations near the thermal peak of TNOs using infra-red
space telescopes are combined with optical magnitudes using the radiometric
technique with near-Earth asteroid thermal model (NEATM). We have determined
three-band flux densities from Herschel/PACS observations at 70.0, 100.0 and
160.0 m and Spitzer/MIPS at 23.68 and 71.42 m when available. We have
analysed 18 classical TNOs with previously unpublished data and re-analysed
previously published targets with updated data reduction to determine their
sizes and geometric albedos as well as beaming factors when data quality
allows. We have combined these samples with classical TNOs with radiometric
results in the literature for the analysis of sample properties of a total of
44 objects. We find a median geometric albedo for cold classical TNOs of 0.14
and for dynamically hot classical TNOs, excluding the Haumea family and dwarf
planets, 0.085. We have determined the bulk densities of Borasisi-Pabu (2.1
g/cm^3), Varda-Ilmare (1.25 g/cm^3) and 2001 QC298 (1.14 g/cm^3) as well as
updated previous density estimates of four targets. We have determined the
slope parameter of the debiased cumulative size distribution of dynamically hot
classical TNOs as q=2.3 +- 0.1 in the diameter range 100<D<500 km. For
dynamically cold classical TNOs we determine q=5.1 +- 1.1 in the diameter range
160<D<280 km as the cold classical TNOs have a smaller maximum size.Comment: 22 pages, 7 figures Accepted to be published in Astronomy and
Astrophysic
"TNOs are Cool": A survey of the trans-Neptunian region VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects
Trans-Neptunian objects (TNO) represent the leftovers of the formation of the
Solar System. Their physical properties provide constraints to the models of
formation and evolution of the various dynamical classes of objects in the
outer Solar System. Based on a sample of 19 classical TNOs we determine
radiometric sizes, geometric albedos and beaming parameters. Our sample is
composed of both dynamically hot and cold classicals. We study the correlations
of diameter and albedo of these two subsamples with each other and with orbital
parameters, spectral slopes and colors. We have done three-band photometric
observations with Herschel/PACS and we use a consistent method for data
reduction and aperture photometry of this sample to obtain monochromatic flux
densities at 70.0, 100.0 and 160.0 \mu m. Additionally, we use Spitzer/MIPS
flux densities at 23.68 and 71.42 \mu m when available, and we present new
Spitzer flux densities of eight targets. We derive diameters and albedos with
the near-Earth asteroid thermal model (NEATM). As auxiliary data we use
reexamined absolute visual magnitudes from the literature and data bases, part
of which have been obtained by ground based programs in support of our Herschel
key program. We have determined for the first time radiometric sizes and
albedos of eight classical TNOs, and refined previous size and albedo estimates
or limits of 11 other classicals. The new size estimates of 2002 MS4 and 120347
Salacia indicate that they are among the 10 largest TNOs known. Our new results
confirm the recent findings that there are very diverse albedos among the
classical TNOs and that cold classicals possess a high average albedo (0.17 +/-
0.04). Diameters of classical TNOs strongly correlate with orbital inclination
in our sample. We also determine the bulk densities of six binary TNOs.Comment: 21 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
A 2km-size asteroid challenging the rubble-pile spin barrier – A case for cohesion
The rubble pile spin barrier is an upper limit on the rotation rate of asteroids larger than ~200-300. m. Among thousands of asteroids with diameters larger than ~300. m, only a handful of asteroids are known to rotate faster than 2.0. h, all are in the sub-km range (≤0.6. km). Here we present photometric measurements suggesting that (60716) 2000 GD65, an S-complex, inner-main belt asteroid with a relatively large diameter of 2.3-0.7+0.6km, completes one rotation in 1.9529. ±. 0.0002. h. Its unique diameter and rotation period allow us to examine scenarios about asteroid internal structure and evolution: a rubble pile bound only by gravity; a rubble-pile with strong cohesion; a monolithic structure; an asteroid experiencing mass shedding; an asteroid experiencing YORP spin-up/down; and an asteroid with a unique octahedron shape results with a four-peak lightcurve and a 3.9. h period. We find that the most likely scenario includes a lunar-like cohesion that can prevent (60716) 2000 GD65 from disrupting without requiring a monolithic structure or a unique shape. Due to the uniqueness of (60716) 2000 GD65, we suggest that most asteroids typically have smaller cohesion than that of lunar regolith. Keywords: Asteroids; Asteroids, rotation; Rotational dynamics; PhotometryUnited States. National Aeronautics and Space Administration (Grant NNX12AL26G
The UT 7/8 February 2013 Sila-Nunam Mutual Event and Future Predictions
A superior mutual event of the Kuiper Belt binary system (79360) Sila-Nunam was observed over 15.47 h on UT 7/8 February 2013 by a coordinated effort at four different telescope facilities; it started approximately 1.5 h earlier than anticipated, the duration was approximately 9.5 h (about 10% longer than predicted), and was slightly less deep than predicted. It is the first full event observed for a comparably sized binary Kuiper Belt object. We provide predictions for future events refined by this and other partial mutual event observations obtained since the mutual event season began
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&
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