157 research outputs found
Comet P/Tempel: Some highlights and conclusions from the 1988 apparition
From the brightness development and a sequence of imaging observations of the coma activity onset of comet P/Tempel 2 in 1988, it is concluded that there might have happened eruptive events of strong dust and gas outbursts during May and June 1988. A comparison of dust coma modeling calculations with CCD observations of the coma widely confirms Sekanina's nucleus model for the comet
The role of organic polymers in the structure of cometary dust
Several phenomena observed in P/Halley and other comets indicate additional fragmentation of dust particles or dust aggregates in cometary atmospheres. The disintegration of dust aggregates may be explained by sublimation of polymerized formaldehyde - POM - which play a role as binding material between submicron individual particles
Coma imaging of comet P/Brorsen-Metcalf at Calar Alto in late July to mid August 1989
Comet P/Brorsen-Metcalf was observed on 1989/07/28+30 and on 1989/08/04+12(+14) with the 3.5 m telescope and the 0.8 m Schmidt camera at Calar Alto/Spain. The images exhibit a narrow plasma tail pointing into anti-solar direction. On 1989/07/30 a triple tail was found which can be interpreted as tail ray event. The coma isophotes show prominent asymmetries with the nucleus located on the tailward side of the isophote foci and with a slightly higher brightness in the Northern Hemisphere of the coma. A strong curved jet feature was detected in the coma on 1989/07/30. The jet extended at least 30,000 km into the sunward coma hemisphere. The rotation period of about 1.3 days, estimated from the curvature of the coma jet, needs verification by other observations
Thermal Infrared and Optical Photometry of Asteroidal Comet C/2002 CE
C/2002 CE is an object in a retrograde elliptical orbit with Tisserand
parameter indicating a likely origin in the Oort Cloud. It appears to
be a rather inactive comet since no coma and only a very weak tail was detected
during the past perihelion passage. We present multi-color optical photometry,
lightcurve and thermal mid-IR observations of the asteroidal comet.
\textcolor{blue}{ With the photometric analysis in , the surface color is
found to be redder than asteroids, corresponding to cometary nuclei and
TNOs/Centaurs. The time-resolved differential photometry supports a rotation
period of 8.190.05 h. The effective diameter and the geometric albedo are
17.90.9 km and 0.030.01, respectively, indicating a very dark
reflectance of the surface. The dark and redder surface color of C/2002
CE may be attribute to devolatilized material by surface aging suffered
from the irradiation by cosmic rays or from impact by dust particles in the
Oort Cloud. Alternatively, C/2002 CE was formed of very dark refractory
material originally like a rocky planetesimal. In both cases, this object lacks
ices (on the surface at least). The dynamical and known physical
characteristics of C/2002 CE are best compatible with those of the
Damocloids population in the Solar System, that appear to be exhaust cometary
nucleus in Halley-type orbits. The study of physical properties of rocky Oort
cloud objects may give us a key for the formation of the Oort cloud and the
solar system.Comment: 9 pages, 4 figures accepted to Icaru
Spitzer Observations of Comet 67P/Churyumov-Gerasimenko at 5.5-4.3 AU From the Sun
We report Spitzer Space Telescope observations of comet
67P/Churyumov-Gerasimenko at 5.5 and 4.3 AU from the Sun, post-aphelion. Comet
67P is the primary target of the European Space Agency's Rosetta mission. The
Rosetta spacecraft will rendezvous with the nucleus at heliocentric distances
similar to our observations. Rotationally resolved observations at 8 and 24
microns (at a heliocentric distance, rh, of 4.8 AU) that sample the size and
color-temperature of the nucleus are combined with aphelion R-band light curves
observed at the Very Large Telescope (VLT) and yield a mean effective radius of
2.04 +/- 0.11 km, and an R-band geometric albedo of 0.054 +/- 0.006. The
amplitudes of the R-band and mid-infrared light curves agree, which suggests
that the variability is dominated by the shape of the nucleus. We also detect
the dust trail of the comet at 4.8 and 5.5 AU, constrain the grain sizes to be
less than or similar to 6 mm, and estimate the impact hazard to Rosetta. We
find no evidence for recently ejected dust in our images. If the activity of
67P is consistent from orbit to orbit, then we may expect the Rosetta
spacecraft will return images of an inactive or weakly active nucleus as it
rendezvous with the comet at rh = 4 AU in 2014.Comment: 19 pages, 2 tables, 10 figures. Accepted for publication in the
Astronomical Journa
Detecting and analysing geomorphological structures in images of comet 67P/Churyumov-Gerasimenko using Fourier transform
We present a method for automatised detection and analysis of quasi-periodic
lineament structures from images at pixel-precision. The method exploits
properties of the images' frequency domain found by using the Fourier
transform. We developed this method with the goal of detecting lineament
structures in an image of the Hathor cliff of comet 67P/Churyumov-Gerasimenko,
which are caused by layerings and furrows in the nucleus material. Using our
method, we determined the orientation and wavelength-range of these structures.
The detected layering edges have similar orientations, spatial separations of
9-20 m, and are ubiquitous throughout the image. We suggest that the layerings
are a global feature of the comet nucleus that provide information about
formation and evolution of comet 67P. The furrows are non-uniformly distributed
throughout the image. Their orientation is broadly parallel to the direction of
the local gravity vector at the Hathor cliff, with spacings similar to that of
the layering structures. The furrows are interpreted as signatures of local
down-slope movement of cliff material. We demonstrate that the developed method
is broadly applicable to the detection and analysis of various kinds of
quasi-periodic structures like geological layering, folding and faulting, and
texture analysis in general. In order to facilitate the application of our
method, this paper is accompanied by a demo program written in Matlab
Mt. Wendelstein imaging of comet 41P/Tuttle-Giacobini-Kresak during the 2017 perihelion arc
Comet 41P/Tuttle-Giacobini-Kresak (41P), a Jupiter family comet with three
discoveries over about 100 years, is in a short-periodic orbit around the Sun
with the perihelion close to the Earth distance. The 2017 apparition of 41P
offered a long-lasting visibility of the comet at a close distance to Earth.
The four month-long imaging campaign with the 2 m telescope at the Mount
Wendelstein Observatory was aimed at characterizing dust activity and nucleus
properties of the comet. Using a new analysis method of the inner coma flux, we
derived a small mean equivalent radius of about 600 m for the nucleus with an
unusual body axes ratio that is higher than two. The nucleus rotation axis was
determined from the geometric appearance of coma structures, which were
enhanced in the images. A long-lasting coma fan was produced by an extended
region at high latitudes on the slowly rotating nucleus, whereas isolated jets
originated from narrow, low latitude active regions on the nucleus. The dust
activity of 41P, despite being difficult to quantify exactly because of an
unknown phase function correction for the comet, indicates a steep radial
profile that falls off with an increasing distance from the Sun. Colors and
flux profiles provide evidence for dust fragmentation in the inner coma of the
comet. A singular outburst event created various dust structures in the coma.
The outburst came from an extended region on the nucleus and was due to either
a landslide on the nucleus or a sudden material release from a subsurface
pocket of volatile ice.Comment: Published on 29 May 2020 in A&A, 25 pages, 12 figures, 9 table
ESO Large Programme on Trans-Neptunian Objects and Centaurs: Spectroscopic Investigation of Centaur 2001 BL41 and TNOs (26181) 1996 GQ21 and (26375) 1999 DE9*
Observational results that are part of an ESO Large Programme dedicated to the characterization of the physical properties of trans-Neptunian objects and Centaurs are presented. We report observations related to the Centaur 2001 BL41 and two trans-Neptunian objects, (26181) 1996 GQ21 and (26375) 1999 DE9. We present results from broadband photometry (JHK filters) and low-dispersion infrared spectroscopy performed with ISAAC at the Very Large Telescope, in Chile. None of the spectra show evidence of absorption features—in particular, water ice features. We use a radiative transfer model to investigate the surface composition of these icy and primitive outer solar system bodies. We suggest models composed of geographical mixtures of organic compounds and minerals
Analysis of layering-related linear features on comet 67P/Churyumov-Gerasimenko
We analysed layering-related linear features on the surface of comet
67P/Churyumov-Gerasimenko (67P) to determine the internal configuration of the
layerings within the nucleus. We used high-resolution images from the OSIRIS
Narrow Angle Camera onboard the Rosetta spacecraft, projected onto the SHAP7
shape model of the nucleus, to map 171 layering-related linear features which
we believe to represent terrace margins and strata heads. From these curved
lineaments, extending laterally to up to 1925 m, we extrapolated the subsurface
layering planes and their normals. We furthermore fitted the lineaments with
concentric ellipsoidal shells, which we compared to the established shell model
based on planar terrace features. Our analysis confirms that the layerings on
the comet's two lobes are independent from each other. Our data is not
compatible with 67P's lobes representing fragments of a much larger layered
body. The geometry we determined for the layerings on both lobes supports a
concentrically layered, `onion-shell' inner structure of the nucleus. For the
big lobe, our results are in close agreement with the established model of a
largely undisturbed, regular, concentric inner structure following a generally
ellipsoidal configuration. For the small lobe, the parameters of our
ellipsoidal shells differ significantly from the established model, suggesting
that the internal structure of the small lobe cannot be unambiguously modelled
by regular, concentric ellipsoids and could have suffered deformational or
evolutional influences. A more complex model is required to represent the
actual geometry of the layerings in the small lobe
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