23 research outputs found
Near-Earth asteroids spectroscopic survey at Isaac Newton Telescope
The population of near-Earth asteroids (NEAs) shows a large variety of
objects in terms of physical and dynamical properties. They are subject to
planetary encounters and to strong solar wind and radiation effects. Their
study is also motivated by practical reasons regarding space exploration and
long-term probability of impact with the Earth. We aim to spectrally
characterize a significant sample of NEAs with sizes in the range of 0.25
- 5.5 km (categorized as large), and search for connections between their
spectral types and the orbital parameters. Optical spectra of NEAs were
obtained using the Isaac Newton Telescope (INT) equipped with the IDS
spectrograph. These observations are analyzed using taxonomic classification
and by comparison with laboratory spectra of meteorites. A total number of 76
NEAs were observed. We classified 44 of them as Q/S-complex, 16 as B/C-complex,
eight as V-types, and another eight belong to the remaining taxonomic classes.
Our sample contains 27 asteroids categorized as potentially hazardous and 31
possible targets for space missions including (459872) 2014 EK24, (436724) 2011
UW158, and (67367) 2000 LY27. The spectral data corresponding to (276049) 2002
CE26 and (385186) 1994 AW1 shows the 0.7 m feature which indicates the
presence of hydrated minerals on their surface. We report that Q-types have the
lowest perihelia (a median value and absolute deviation of AU)
and are systematically larger than the S-type asteroids observed in our sample.
We explain these observational evidences by thermal fatigue fragmentation as
the main process for the rejuvenation of NEA surfaces. In general terms, the
taxonomic distribution of our sample is similar to the previous studies and
matches the broad groups of the inner main belt asteroids. Nevertheless, we
found a wide diversity of spectra compared to the standard taxonomic types.Comment: Accepted in Astronomy & Astrophysics (A&A
A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS measured from stellar occultations
This work aims at constraining the size, shape, and geometric albedo of the
dwarf planet candidate 2002 MS4 through the analysis of nine stellar
occultation events. Using multichord detection, we also studied the object's
topography by analyzing the obtained limb and the residuals between observed
chords and the best-fitted ellipse. We predicted and organized the
observational campaigns of nine stellar occultations by 2002 MS4 between 2019
and 2022, resulting in two single-chord events, four double-chord detections,
and three events with three to up to sixty-one positive chords. Using 13
selected chords from the 8 August 2020 event, we determined the global
elliptical limb of 2002 MS4. The best-fitted ellipse, combined with the
object's rotational information from the literature, constrains the object's
size, shape, and albedo. Additionally, we developed a new method to
characterize topography features on the object's limb. The global limb has a
semi-major axis of 412 10 km, a semi-minor axis of 385 17 km, and
the position angle of the minor axis is 121 16. From
this instantaneous limb, we obtained 2002 MS4's geometric albedo and the
projected area-equivalent diameter. Significant deviations from the fitted
ellipse in the northernmost limb are detected from multiple sites highlighting
three distinct topographic features: one 11 km depth depression followed by a
25 km height elevation next to a crater-like depression with an
extension of 322 39 km and 45.1 1.5 km deep. Our results present an
object that is 138 km smaller in diameter than derived from thermal
data, possibly indicating the presence of a so-far unknown satellite. However,
within the error bars, the geometric albedo in the V-band agrees with the
results published in the literature, even with the radiometric-derived albedo
Two-compartment radial diffusive exchange analysis of the NMR lineshape of129Xe dissolved in a perfluorooctyl bromide emulsion
The Ponor-Plopa Cave System: Description, Sediments, and Genesis
The Ponor-Plopa cave system is located in the central part
of the Aninei Mountains, southwest of Steierdorf, a small
neighborhood of Anina, at elevations ranging between
575 m (the Ponor) and 545 m (the Plopa resurgence) for
the main river cave and ~600 m for the dry caves on the
Plopa Plateau. The system includes a total of six caves of
which two, Ponor and Plopa, were connected by cave diving.
The remaining four caves are relatively small, inactive
cavities that were connected to the system at various
stages during its evolution.
The karst area is entirely formed within the massive
reef Plopa limestones (Barremian), and its surface does
not exceed 0.5 km 2
(Figure 5.1). To the north, it is bordered
by a secondary ridge of the Culmea Frumoas ă ; to the west
the limit is very well marked by the rocky cliff formed
along the contact between the Barremian limestones and
the Hauterivian mudstones, while to the south and east
it is limited by the Mini ş River. The overall topography
of the karst plateau shows decreasing elevations toward
the southwest, and the distribution and topography of the
sinkholes suggest sinkhole alignments going from NNE
to SSW, with a bend toward the east, right above the current
Plopa resurgence. Such sinkhole alignments are usually
considered to indicate either the broad directions of
subterranean drainages or a succession of former ponors.info:eu-repo/semantics/publishedVersio
Exploration and Documentation of the Peştera cu Oase
Romania is a country dominated by one of the more
important mountain chains in Europe, the Carpathian
Mountains. They begin in the northwest, in southern
Poland, Slovakia, northern Hungary, and southwestern
Ukraine, continue southeastward toward the delta of the
Danube, then arc strongly around Bra ş ov and extend
westward parallel to the Danube, fading out north of the
Iron Gates and on to the plains of Banat. The southern
portion is sometimes referred to as the Transylvanian
Alps, because it helps to enclose Transylvania within the
arc of the Carpathians and separate it from the Danube
river valley. These mountains form a continuous and
important topographic feature of southeastern Europe,
and in fact of Europe as a whole.info:eu-repo/semantics/publishedVersio