481 research outputs found
Grandes espectáculos celestes
Los mayores espectáculos que pueden observarse en los cielos de nuestro planeta son los eclipses totales de Sol y de Luna, las Auroras Polares y las Tormentas de Estrellas. Estos espectáculos celestes son el objetivo principal de las expediciones científicas que organiza la asociación Shelios, nacida a mediados de 1998, y que desde su creación ha organizado diversas expediciones a los lugares más remotos de la Tierra, como por ejemplo Turquía, Groenlandia, Teide, Zimbabwe, desierto de Australia, Sudáfrica, Antártida, desierto de Líbia o China.The greatest shows that can be seen in the skies of our planet are a total eclipse of the sun and moon, Polar Aurora and Stara storms. These celestial events are the main target of the scientific expeditions organized Shelios association, born in 1998, and since its creation has organized several expeditions to the remotest parts of Earth, such as Turkey, Greenland, Teide, Zimbabwe, desert of Australia, South Africa, Antarctic, desert of Libya or China
Digital Image Compression Using Artificial Neural Networks
The problem of storing, transmitting, and manipulating digital images is considered. Because of the file sizes involved, large amounts of digitized image information are becoming common in modern projects. Our goal is to described an image compression transform coder based on artificial neural networks techniques (NNCTC). A comparison of the compression results obtained from digital astronomical images by the NNCTC and the method used in the compression of the digitized sky survey from the Space Telescope Science Institute based on the H-transform is performed in order to assess the reliability of the NNCTC
Short-timescale Fluctuations in the Difference Light Curves of QSO 0957+561A,B: Microlensing or Noise?
From optical R band data of the double quasar QSO 0957+561A,B, we made two
new difference light curves (about 330 days of overlap between the time-shifted
light curve for the A image and the magnitude-shifted light curve for the B
image). We observed noisy behaviours around the zero line and no
short-timescale events (with a duration of months), where the term event refers
to a prominent feature that may be due to microlensing or another source of
variability. Only one event lasting two weeks and rising - 33 mmag was found.
Measured constraints on the possible microlensing variability can be used to
obtain information on the granularity of the dark matter in the main lensing
galaxy and the size of the source. In addition, one can also test the ability
of the observational noise to cause the rms averages and the local features of
the difference signals. We focused on this last issue. The combined
photometries were related to a process consisting of an intrinsic signal plus a
Gaussian observational noise. The intrinsic signal has been assumed to be
either a smooth function (polynomial) or a smooth function plus a stationary
noise process or a correlated stationary process. Using these three pictures
without microlensing, we derived some models totally consistent with the
observations. We finally discussed the sensitivity of our telescope (at Teide
Observatory) to several classes of microlensing variability.Comment: MNRAS, in press (LaTeX, 14 pages, 22 eps figures
Spectroscopic and dynamical properties of comet C/2018 F4, likely a true average former member of the Oort cloud
The population of comets hosted by the Oort cloud is heterogeneous. Most
studies in this area focused on highly active objects, those with small
perihelion distances or examples of objects with peculiar physical properties
and/or unusual chemical compositions. This may have produced a biased sample of
Oort cloud comets in which the most common objects may be rare, particularly
those with perihelia well beyond the orbit of the Earth. Within this context,
the known Oort cloud comets may not be representative of the full sample. Here,
we study the spectral properties in the visible region and the cometary
activity of Comet C/2018 F4 (PANSTARRS). We also explore its orbital evolution
with the aim of understanding its origin within the context of known minor
bodies moving along nearly parabolic or hyperbolic paths. We present
observations obtained with the 10.4 m Gran Telescopio Canarias (GTC), derive
the spectral class and visible slope of C/2018 F4 and characterise its level of
cometary activity. Direct N-body simulations are carried out to explore its
orbital evolution. The absolute magnitude of C/2018 F4 is Hr=13.62+/-0.04.
Assuming a pV=0.04 its diameter is D<10.4 km. The object presents a conspicuous
coma, with a level of activity comparable to those of other comets observed at
similar heliocentric distances. Comet C/2018 F4 has a visible spectrum
consistent with that of an X-type asteroid, and has a spectral slope
S'=4.0+/-1.0 %/1000\AA and no evidence of hydration. The spectrum matches those
of well-studied primitive asteroids and comets. The analysis of its dynamical
evolution prior to discovery suggests that C/2018 F4 is not of extrasolar
origin. Although the present-day heliocentric orbit of C/2018 F4 is slightly
hyperbolic, its observational properties and past orbital evolution are
consistent with those of a dynamically old comet with an origin in the Oort
cloud.Comment: 6 pages, 5 figures. In pres
ATLAS-TEIDE: The next generations of ATLAS units for the Teide Observatory
In this work we present the design of the ATLAS unit (Asteroid
Terrestrial-impact Last Alert System) that will be installed at Teide
Observatory in Tenerife island (Spain). ATLAS-Teide will be built by the
Instituto de Astrofisica de Canarias (IAC) and will be operated as part of the
ATLAS network in the framework of an operation and science exploitation
agreement between the IAC and the ATLAS team at University of Hawaii.
ATLAS-Teide will be the first ATLAS unit based on commercial on the shelf
(COTS) components. Its design is modular, each module (building block) consist
of four Celestron RASA 11 telescopes that point to the same sky field, equipped
with QHY600PRO CMOS cameras on an equatorial Direct Drive mount. Each module is
equivalent to a 56cm effective diameter telescope and provides a 7.3 deg^2
field of view and a 1.26 arcsec/pix plate scale. ATLAS-Teide will consist of
four ATLAS modules in a roll-off roof building. This configuration allows to
cover the same sky area of the actual ATLAS telescopes.
The first ATLAS module was installed in November 2022 in an existing
clamshell at the TO. This module (ATLAS-P) is being used as a prototype to test
the system capabilities, develop the needed software (control, image
processing, etc.) and complete the fully integration of ATLAS-Teide in the
ATLAS network. The preliminary results of the tests are presented here, and the
benefits of the new ATLAS design are discussed.Comment: 5 pages, 8 figures, Conference pape
Spectroscopy of the Lens Galaxy of Q0957+561A,B. Implications of a possible central massive dark object
We present new long-slit William Herschel Telescope spectroscopic
observations of the lens galaxy G1 associated with the double-imaged QSO
0957+561A,B. The obtained central stellar velocity dispersion, sigma_l = 310
+/- 20 km/s, is in reasonable agreement with other measurements of this
dynamical parameter. Using all updated measurements of the stellar velocity
dispersion in the internal region of the galaxy (at angular separations < 1".5)
and a simple isotropic model, we discuss the mass of a possible central massive
dark object. It is found that the data of Falco et al. (1997) suggest the
existence of an extremely massive object of (0.5-2.1) x 10E10/h M_\odot (80%
confidence level), whereas the inclusion of very recent data (Tonry & Franx
1998, and this paper) substantially changes the results: the compact central
mass must be 6 x10E9/h M_\odot at the 90% confidence level. We note that,
taking into account all the available dynamical data, a compact nucleus with a
mass of 10E9/h M_\odot (best fit) cannot be ruled out.Comment: 20 pages, 10 figures ApJ, in pres
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