1,904 research outputs found
Polarimetry and photometry of the peculiar main-belt object 7968 = 133P/Elst-Pizarro
133P/Elst-Pizarro is an object that has been described as either an active
asteroid or a cometary object in the main asteroid belt. Here we present a
photometric and polarimetric study of this object in an attempt to infer
additional information about its origin.
With the FORS1 instrument of the ESO VLT, we have performed during the 2007
apparition of 133P/Elst-Pizarro quasi-simultaneous photometry and polarimetry
of its nucleus at nine epochs in the phase angle range 0 - 20 deg. For each
observing epoch, we also combined all available frames to obtain a deep image
of the object, to seek signatures of weak cometary activity. Polarimetric data
were analysed by means of a novel physical interference modelling.
The object brightness was found to be highly variable over timescales <1h, a
result fully consistent with previous studies. Using the albedo-polarization
relationships for asteroids and our photometric results, we found for our
target an albedo of about 0.06-0.07 and a mean radius of about 1.6 km.
Throughout the observing epochs, our deep imaging of the comet detects a tail
and an anti-tail. Their temporal variations are consistent with an activity
profile starting around mid May 2007 of minimum duration of four months. Our
images show marginal evidence of a coma around the nucleus. The overall light
scattering behaviour (photometry and polarimetry) resembles most closely that
of F-type asteroids.Comment: Accepted by Astronomy and Astrophysic
The nucleus of 103P/Hartley 2, target of the EPOXI mission
103P/Hartley 2 was selected as the target comet for the Deep Impact extended
mission, EPOXI, in October 2007. There have been no direct optical observations
of the nucleus of this comet, as it has always been highly active when
previously observed. We aimed to recover the comet near to aphelion, to a)
confirm that it had not broken up and was in the predicted position, b) to
provide astrometry and brightness information for mission planning, and c) to
continue the characterisation of the nucleus. We observed the comet at
heliocentric distances between 5.7 and 5.5 AU, using FORS2 at the VLT, at 4
epochs between May and July 2008. We performed VRI photometry on deep stacked
images to look for activity and measure the absolute magnitude and therefore
estimate the size of the nucleus. We recovered the comet near the expected
position, with a magnitude of m_R = 23.74 \pm 0.06 at the first epoch. The
comet had no visible coma, although comparison of the profile with a stellar
one showed that there was faint activity, or possibly a contribution to the
flux from the dust trail from previous activity. This activity appears to fade
at further epochs, implying that this is a continuation of activity past
aphelion from the previous apparition rather than an early start to activity
before the next perihelion. Our data imply a nucleus radius of \le 1 km for an
assumed 4% albedo; we estimate a ~6% albedo. We measure a colour of (V-R) = 0.
26 \pm 0.09.Comment: 5 pages, 4 figures, accepted for publication in A&
Photometric observations of distant active comets
We present CCD VR_C observations of 6 distant comets located at heliocentric
distances of 3.4--7.2 AU. Time-series data were obtained on three nights in
July, 2000 covering 16 hours. Each comet was observed after the perihelion,
when a lower activity was expected. Contrary to expectation, we found
well-defined circular comae and extended tails visible out to a few (3-5)
arcminutes. We detected a quasi-cyclic light variation of C/1999 J2, while
C/1999 N4 showed some hints of a more complex variation. C/2000 K1 was constant
to +/-0.04 mag during the observing run. The standard V and R_C data were used
to estimate nuclear diameters, while the colour indices implied a slighly
reddish (V-R=0.68, C/2000 K1), a neutral (V-R=0.47, C/1999 N4) and a slightly
bluish (V-R=0.25, C/1999 J2) coma. Simple fits of the surface brightness
distributions are also presented enabling order of magnitude estimates of
nuclear radii. Beside the time-series observations, further single-shot
observations of three faint comets are briefly described.Comment: 8 pages, 5 figures, accepted for publication in A&
Commentary to "Denosumab for bone health in prostate and breast cancer patients receiving endocrine therapy? A systematic review and a meta-analysis of randomized trials" (Galvano et al. J Bone Oncol 2019; 18:100252).
Spectrophotometry and structural analysis of 5 comets
We discuss the morphology and spectrophotometry of 5 comets visible in
August, 2001. We decompose comae into coma profiles and azimuthally
renormalized images, in which general and local features are quantitatively
comparable. Comet 19P/Borrelly showed a strong gas fan toward the solar
direction, but no detectable gas in the tail. Dust in its inner coma was
collimated toward the antisolar direction and the tail, with no dust in the
outer coma. The contribution of spatial variations structure was moderate,
about 35%. Comet 29P Schwassmann-Wachmann 1 was observed in outburst: we
detected ``spinning'' jet structures. A high level of dust production resulted
in an unusually high Af\rho=16600 cm. The spatial variations reached -77%, at
the minimum, due in part to a jet and a ring-like structure in 1 arcminute
distance from the nucleus. In comet C/2001 A2, we detected a strong
post-perihelion increase of dust and gas activity, in which the C_2 profile
became one magnitude brighter over a 3-day period. For comets C/2000 SV74 and
C/2000 WM1, we present detailed pre-perihelion spectrophotometry and
morphological information. Comet C/2000 SV74 showed high dust production
(Af\rho=1479 cm). Its coma suggests a steady-state outflow of material, while
the low contribution of spatial variations support high level activity. The
coma of C/2000 WM1 is dominated by solar effects, and CO+ forms the bulk of its
gas activity. Despite its large heliocentric distance, we observed a nice tail.Comment: 10 pages, 4 figures, accepted for publication in A&
'I-V Characteristic and Crystal Structural Of a-As/c-Si Heterojunctions
In this research the a-As flims have been prepared by thermal evaporation with thickness 250 nm and rata of deposition r_d(1.04nm/sec) as function to annealing temperature (373 and 473K), from XRD analysis we can see that the degree of crystalline increase with T_a, and I-V characteristic for dark and illumination shows that forward bias current varieties approximately exponentially with voltage bias. Also we found that the quality factor and saturation current dependence on annealing temperatures
Charge state breeding with an ECRIS for ISAC at TRIUMF
For the acceleration of radioactive ions the usable mass range is limited by the A/q acceptance of the first accelerator stage. Since an efficient primary ion source normally produces singly charged ions, charge state breeding is necessary if higher masses are to be accelerated. At TRIUMF an ECR source has been chosen as a breeder due to its potential high efficiency in producing intermediate A/q values. To minimize the necessity for further stripping an A/q around 6 is desirable. A 14 GHz "PHOENIX" booster from Pantechnik has been set up on a test bench. The singly charged ions are produced from different ion sources, wihich can be mounted in a standard ISAC target-ion-source set-up. For the first tests an ECR source to produce noble gas beams has been chosen. The aim of the measurements at the test bench is to find the optimum operation conditions of the charge state booster and the injection and extraction ion optics. Working with radioactive ions always means that the system should aim for high efficiency, as the production of such species is limited. Therefore, special emphasis has to be put on the highest yield for the production of the desired charge state. A second point is the analysis of the extracted beam quality in order to optimize mass separation and transport efficiency. The paper shows the status of the set-up and reports on first results of the charge breeding of Ar, Ne and Xe. With Xe a total efficiency of 22.5% has been achieved
Properties of Saturn Kilometric Radiation measured within its source region
On 17 October 2008, the Cassini spacecraft crossed the southern sources of
Saturn kilometric radiation (SKR), while flying along high-latitude nightside
magnetic field lines. In situ measurements allowed us to characterize for the
first time the source region of an extra-terrestrial auroral radio emission.
Using radio, magnetic field and particle observations, we show that SKR sources
are surrounded by a hot tenuous plasma, in a region of upward field-aligned
currents. Magnetic field lines supporting radio sources map a continuous,
high-latitude and spiral-shaped auroral oval observed on the dawnside,
consistent with enhanced auroral activity. Investigating the Cyclotron Maser
Instability (CMI) as a mechanism responsible for SKR generation, we find that
observed cutoff frequencies are consistent with radio waves amplified
perpendicular to the magnetic field by hot (6 to 9 keV) resonant electrons,
measured locally
Spitzer observations of the asteroid-comet transition object and potential spacecraft target 107P (4015) Wilson-Harrington
Context. Near-Earth asteroid-comet transition object 107P/ (4015)
Wilson-Harrington is a possible target of the joint European Space Agency (ESA)
and Japanese Aerospace Exploration Agency (JAXA) Marco Polo sample return
mission. Physical studies of this object are relevant to this mission, and also
to understanding its asteroidal or cometary nature. Aims. Our aim is to obtain
significant new constraints on the surface thermal properties of this object.
Methods. We present mid-infrared photometry in two filters (16 and 22 microns)
obtained with NASA's Spitzer Space Telescope on February 12, 2007, and results
from the application of the Near Earth Asteroid Thermal Model (NEATM).We
obtained high S/N in two mid-IR bands allowing accurate measurements of its
thermal emission. Results. We obtain a well constrained beaming parameter (eta
= 1.39 +/- 0.26) and obtain a diameter and geometric albedo of D = 3.46 +/-
0.32 km, and pV = 0.059 +/- 0.011. We also obtain similar results when we apply
this best-fitting thermal model to single-band mid-IR photometry reported by
Campins et al. (1995), Kraemer et al. (2005) and Reach et al. (2007).
Conclusions. The albedo of 4015 Wilson-Harrington is low, consistent with those
of comet nuclei and primitive C-, P-, D-type asteorids. We establish a rough
lower limit for the thermal inertia of W-H of 60 Jm^-2s^(-0.5)K^-1 when it is
at r=1AU, which is slightly over the limit of 30 Jm^-2s^(-0.5)K-1 derived by
Groussin et al. (2009) for the thermal inertia of the nucleus of comet
22P/Kopff.Comment: 4 pages, 1 figure and 3 tables. Paper accepted for publicatio
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