696 research outputs found
Near-Infrared Photometry of Irregular Satellites of Jupiter and Saturn
We present JHKs photometry of 10 Jovian and 4 Saturnian irregular satellites,
taken with the Near-InfraRed Imager (NIRI) at the 8-m Gemini North Observatory
on Mauna Kea, Hawaii. The observed objects have near-infrared colors consistent
with C, P and D-type asteroids, although J XII Ananke and S IX Phoebe show weak
indications of possible water features in the H filter. The four members of the
Himalia-family have similar near-infrared colors, as do the two members of the
Gallic family, S XX Paaliaq and S XXIX Siarnaq. From low resolution normalized
reflectance spectra based on the broadband colors and covering 0.4 to 2.2
microns, the irregular satellites are identified as C-type (J VII Pasiphae, J
VI Himalia and S IX Phoebe), P-type (J XII Ananke and J XVIII Themisto) and
D-type (J IX Carme and J X Sinope), showing a diversity of origins of these
objects.Comment: Accepted by ApJ Letters (emulateapj, 8pages, including 4 figures);
Typos corrected, references adde
Light curves and colours of the faint Uranian irregular satellites Sycorax, Prospero, Stephano, Setebos and Trinculo
After the work of Gladman et al. (1998), it is now assessed that many
irregular satellites are orbiting around Uranus. Despite many studies have been
performed in past years, very few is know for the light-curves of these objects
and inconsistencies are present between colours derived by different authors.
This situation motivated our effort to improve both the knowledge of colours
and light curves. We present and discuss time series observations of Sycorax,
Prospero, Stephano, Setebos and Trinculo, five faint irregular satellites of
Uranus, carried out at VLT, ESO Paranal (Chile) in the nights between 29 and 30
July, 2005 and 25 and 30 November, 2005. We derive light curves for Sycorax and
Prospero and colours for all of these these bodies. For Sycorax we obtain
colours B-V =0.839 +/- 0.014, V-R = 0.531 +/- 0.005 and a light curve which is
suggestive of a periodical variation with period about 3.6 hours and amplitude
about 0.067 +/- 0.004 mag. The periods and colours we derive for Sycorax are in
agreement with our previous determination in 1999 using NTT. We derive also a
light-curve for Prospero which suggests an amplitude of about 0.2 mag and a
periodicity of about 4 hours. However, the sparseness of our data, prevents a
more precise characterization of the light-curves, and we can not determine
wether they are one-peaked or two-peaked. Hence, these periods and amplitudes
have to be considered preliminary estimates. As for Setebos, Stephano and
Trinculo the present data do not allow to derive any unambiguous periodicity,
despite Setebos displays a significant variability with amplitude about as
large as that of Prospero. Colours for Prospero, Setebos, Stephano and Trinculo
are in marginal agreement with the literature.Comment: Submitted to A&A 13 Dec 2006, Accepted 17 Apr 2007. 18 pages, 8
colours figures BW printable, 6 tables. LaTeX 2.09, with packages: natbib,
graphicx, longtable, aa4babbage included in the submission file (tar gzipped
of 349 KBytes
A new perspective on the irregular satellites of Saturn - II Dynamical and physical origin
The origin of the irregular satellites of the giant planets has been long
debated since their discovery. Their dynamical features argue against an
in-situ formation suggesting they are captured bodies, yet there is no global
consensus on the physical process at the basis of their capture. In this paper
we explore the collisional capture scenario, where the actual satellites
originated from impacts occurred within Saturn's influence sphere. By modeling
the inverse capture problem, we estimated the families of orbits of the
possible parent bodies and the specific impulse needed for their capture. The
orbits of these putative parent bodies are compared to those of the minor
bodies of the outer Solar System to outline their possible region of formation.
Finally, we tested the collisional capture hypothesis on Phoebe by taking
advantage of the data supplied by Cassini on its major crater, Jason. Our
results presented a realistic range of solutions matching the observational and
dynamical data.Comment: 26 Pages, 21 Figure
The Albedo Distribution of Near Earth Asteroids
The cryogenic WISE mission in 2010 was extremely sensitive to asteroids and
not biased against detecting dark objects. The albedos of 428 Near Earth
Asteroids (NEAs) observed by WISE during its fully cryogenic mission can be fit
quite well by a 3 parameter function that is the sum of two Rayleigh
distributions. The Rayleigh distribution is zero for negative values, and
follows for positive x. The peak
value is at x=\sigma, so the position and width are tied together. The three
parameters are the fraction of the objects in the dark population, the position
of the dark peak, and the position of the brighter peak. We find that 25.3% of
the NEAs observed by WISE are in a very dark population peaking at , while the other 74.7% of the NEAs seen by WISE are in a moderately dark
population peaking at . A consequence of this bimodal distribution
is that the Congressional mandate to find 90% of all NEAs larger than 140 m
diameter cannot be satisfied by surveying to H=22 mag, since a 140 m diameter
asteroid at the very dark peak has H=23.7 mag, and more than 10% of NEAs are
darker than p_V = 0.03.Comment: 7 pages LaTex, 4 figures, accepted for publication in the
Astronomical Journa
The Complex History of Trojan Asteroids
The Trojan asteroids provide a unique perspective on the history of Solar
System. As a large population of small bodies, they record important
gravitational interactions and dynamical evolution of the Solar System. In the
past decade, significant advances have been made in understanding physical
properties, and there has been a revolution in thinking about the origin of
Trojans. The ice and organics generally presumed to be a significant part of
Trojan compositions have yet to be detected directly, though low density of the
binary system Patroclus (and possibly low density of the binary/moonlet system
Hektor) is consistent with an interior ice component. By contrast, fine-grained
silicates that appear to be similar to cometary silicates in composition have
been detected, and a color bimodality may indicate distinct compositional
groups among the Trojans. Whereas Trojans had traditionally been thought to
have formed near 5 AU, a new paradigm has developed in which the Trojans formed
in the proto-Kuiper Belt, and they were scattered inward and captured in the
Trojan swarms as a result of resonant interactions of the giant planets.
Whereas the orbital and population distributions of current Trojans are
consistent with this origin scenario, there are significant differences between
current physical properties of Trojans and those of Kuiper Belt objects. These
differences may be indicative of surface modification due to the inward
migration of objects that became the Trojans, but understanding of appropriate
modification mechanisms is poor and would benefit from additional laboratory
studies. Many open questions remain, and the future promises significant
strides in our understanding of Trojans. The time is ripe for a spacecraft
mission to the Trojans, to turn these objects into geologic worlds that can be
studied in detail to unravel their complex history.Comment: Chapter for Asteroids IV book (UA Press), accepted for publication,
33 pages, 10 figure
Biologics 4.0: Emergence of the CHO Biofoundry
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AC Breakdown Voltage of 50-Year-Old Service Aged Hydro Power Generator Stator Bars
Randomly selected generator bars from a 50-year-old Norwegian hydro power generator were examined in this work. Typical non-destructive tests, as partial discharge and dissipation factor measurements were initially performed at both 50 Hz and 0.1 Hz. Then, the AC breakdown strength of the epoxy/mica/glass fibre reinforced bar insulation was measured by gradually increasing the voltage in steps of 5 kV with duration of 1 min until breakdown occurred. The field graded terminations were soaked in transformer oil during breakdown testing to prevent external surface flashovers. The AC breakdown voltage ranged between 60 kV and 75 kV, which corresponds to 8-10-fold the service voltage of 7.4 kV. No significant difference in breakdown voltage was observed between bars being located close to the high voltage or neutral terminal during service. This indicates minor degradation caused by the AC service stress, even after 50 years in service. No correlations were found between the measured breakdown voltage and the diagnostic partial discharge activity and dissipation factor measurements.AC Breakdown Voltage of 50-Year-Old Service Aged Hydro Power Generator Stator BarspublishedVersio
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