3,431 research outputs found
Eclipses of the inner satellites of Jupiter observed in 2015
During the 2014-2015 campaign of mutual events, we recorded ground-based
photometric observations of eclipses of Amalthea (JV) and, for the first time,
Thebe (JXIV) by the Galilean moons. We focused on estimating whether the
positioning accuracy of the inner satellites determined with photometry is
sufficient for dynamical studies. We observed two eclipses of Amalthea and one
of Thebe with the 1 m telescope at Pic du Midi Observatory using an IR filter
and a mask placed over the planetary image to avoid blooming features. A third
observation of Amalthea was taken at Saint-Sulpice Observatory with a 60 cm
telescope using a methane filter (890 nm) and a deep absorption band to
decrease the contrast between the planet and the satellites. After background
removal, we computed a differential aperture photometry to obtain the light
flux, and followed with an astrometric reduction. We provide astrometric
results with an external precision of 53 mas for the eclipse of Thebe, and 20
mas for that of Amalthea. These observation accuracies largely override
standard astrometric measurements. The (O-C)s for the eclipse of Thebe are 75
mas on the X-axis and 120 mas on the Y-axis. The (O-C)s for the total eclipses
of Amalthea are 95 mas and 22 mas, along the orbit, for two of the three
events. Taking into account the ratio of (O-C) to precision of the astrometric
results, we show a significant discrepancy with the theory established by
Avdyushev and Ban'shikova in 2008, and the JPL JUP 310 ephemeris.Comment: 7 pages, 10 figures, 4 table
GRB 110205A: Anatomy of a long gamma-ray burst
The Swift burst GRB 110205A was a very bright burst visible in the Northern
hemisphere. GRB 110205A was intrinsically long and very energetic and it
occurred in a low-density interstellar medium environment, leading to delayed
afterglow emission and a clear temporal separation of the main emitting
components: prompt emission, reverse shock, and forward shock. Our observations
show several remarkable features of GRB 110205A : the detection of prompt
optical emission strongly correlated with the BAT light curve, with no temporal
lag between the two ; the absence of correlation of the X-ray emission compared
to the optical and high energy gamma-ray ones during the prompt phase ; and a
large optical re-brightening after the end of the prompt phase, that we
interpret as a signature of the reverse shock. Beyond the pedagogical value
offered by the excellent multi-wavelength coverage of a GRB with temporally
separated radiating components, we discuss several questions raised by our
observations: the nature of the prompt optical emission and the spectral
evolution of the prompt emission at high-energies (from 0.5 keV to 150 keV) ;
the origin of an X-ray flare at the beginning of the forward shock; and the
modeling of the afterglow, including the reverse shock, in the framework of the
classical fireball model.Comment: 21 pages, 5 figure (all in colors), accepted for publication in Ap
Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations
The prediction of stellar occultations by Transneptunian objects and Centaurs
is a difficult challenge that requires accuracy both in the occulted star
position as for the object ephemeris. Until now, the most used method of
prediction involving tens of TNOs/Centaurs was to consider a constant offset
for the right ascension and for the declination with respect to a reference
ephemeris. This offset is determined as the difference between the most recent
observations of the TNO and the reference ephemeris. This method can be
successfully applied when the offset remains constant with time. This paper
presents an alternative method of prediction based on a new accurate orbit
determination procedure, which uses all the available positions of the TNO from
the Minor Planet Center database plus sets of new astrometric positions from
unpublished observations. The orbit determination is performed through a
numerical integration procedure (NIMA), in which we develop a specific
weighting scheme. The NIMA method was applied for 51 selected TNOs/Centaurs.
For this purpose, we have performed about 2900 new observations during
2007-2014. Using NIMA, we succeed in predicting the stellar occultations of 10
TNOs and 3 Centaurs between 2013 and 2015. By comparing the NIMA and JPL
ephemerides, we highlighted the variation of the offset between them with time.
Giving examples, we show that the constant offset method could not accurately
predict 6 out of the 13 observed positive occultations successfully predicted
by NIMA. The results indicate that NIMA is capable of efficiently refine the
orbits of these bodies. Finally, we show that the astrometric positions given
by positive occultations can help to further refine the orbit of the TNO and
consequently the future predictions. We also provide the unpublished
observations of the 51 selected TNOs and their ephemeris in a usable format by
the SPICE library.Comment: 12 pages, 9 figures, accepted in A&
Dark matter directional detection with MIMAC
MiMac is a project of micro-TPC matrix of gaseous (He3, CF4) chambers for
direct detection of non-baryonic dark matter. Measurement of both track and
ionization energy will allow the electron-recoil discrimination, while access
to the directionnality of the tracks will open a unique way to distinguish a
geniune WIMP signal from any background. First reconstructed tracks of 5.9 keV
electrons are presented as a proof of concept.Comment: 4 pages, proc. of the 44th Rencontres De Moriond: Electroweak
Interactions And Unified Theories, 7-14 Mar 2009, La Thuile, Ital
Ultra low energy results and their impact to dark matter and low energy neutrino physics
We present ultra low energy results taken with the novel Spherical
Proportional Counter. The energy threshold has been pushed down to about 25 eV
and single electrons are clearly collected and detected. To reach such
performance low energy calibration systems have been successfully developed: -
A pulsed UV lamp extracting photoelectrons from the inner surface of the
detector - Various radioactive sources allowing low energy peaks through
fluorescence processes. The bench mark result is the observation of a well
resolved peak at 270 eV due to carbon fluorescence which is unique performance
for such large-massive detector. It opens a new window in dark matter and low
energy neutrino search and may allow detection of neutrinos from a nuclear
reactor or from supernova via neutrino-nucleus elastic scatteringComment: 14 pages,16 figure
Chemical and dynamical processes in the mesospheric emissive layer. First results of stereoscopic observations
[1] The mesospheric emissive layer is an efficient tracer of the dynamical processes propagating in the atmosphere at that level. CCD images in the near infrared taken from the ground at slant angles often reveal the existence of wavy fields. A series of such images has been transformed, using matrix operations, producing a downward satellite-type view that covers a circular area of radius âŒ1000 km at the altitude of the layer. The Fourier characteristics of the wave system are measured using a Morlet-type wavelet generator function with horizontal wavelengths of mostly âŒ20â40 km and 100â150 km and temporal periods of âŒ15â30 min. An oxygen-hydrogen model is used to evaluate the response of the emissive layer to a progressive density wave. The altitude of the layer is modulated with an amplitude of âŒ0.8â1.8 km when a density wave propagates vertically. The layer thickness is slightly modulated and is equal to âŒ7 km. Stereoscopic pairs of photographs taken simultaneously on 8â9 September 2000 at the ChĂąteau-Renard and Pic du Midi observatories are used to obtain surface maps of the emission layer barycenter altitude. A stereocorrelation method suitable for low contrast objects without discrete contours is employed. Preliminary results for areas âŒ50 Ă 50 km2 are presented. The surface maps of the layer barycenter altitude depict the existence of waves. They show the same wavy structure and compare favorably with the maps showing the emission intensity
Precise determination of stellar parameters of the ZZ Ceti and DAZ white dwarf GD 133 through asteroseismology
An increasing number of white dwarf stars show atmospheric chemical
composition polluted by heavy elements accreted from debris disk material. The
existence of such debris disks strongly suggests the presence of one or more
planet(s) whose gravitational interaction with rocky planetesimals is
responsible for their disruption by tidal effect. The ZZ Ceti pulsator and
polluted DAZ white dwarf GD 133 is a good candidate for searching for such a
potential planet. We started in 2011 a photometric follow-up of its pulsations.
As a result of this work in progress, we used the data gathered from 2011 to
2015 to make an asteroseismological analysis of GD 133, providing the star
parameters from a best fit model with / = 0.630 0.002,
= 12400 K 70 K, log() = -2.00 0.02,
log() = -4.50 0.02 and determining a rotation period of
7 days.Comment: 10 pages, 13 figures, accepted by MNRA
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