4,284 research outputs found
FUV variability of HD 189733. Is the star accreting material from its hot Jupiter?
Hot Jupiters are subject to strong irradiation from the host stars and, as a
consequence, they do evaporate. They can also interact with the parent stars by
means of tides and magnetic fields. Both phenomena have strong implications for
the evolution of these systems. Here we present time resolved spectroscopy of
HD~189733 observed with the Cosmic Origin Spectrograph (COS) on board to HST.
The star has been observed during five consecutive HST orbits, starting at a
secondary transit of the planet ( ~0.50-0.63). Two main episodes of
variability of ion lines of Si, C, N and O are detected, with an increase of
line fluxes. Si IV lines show the highest degree of variability. The FUV
variability is a signature of enhanced activity in phase with the planet
motion, occurring after the planet egress, as already observed three times in
X-rays. With the support of MHD simulations, we propose the following
interpretation: a stream of gas evaporating from the planet is actively and
almost steadily accreting onto the stellar surface, impacting at
ahead of the sub-planetary point.Comment: 35 pages, 19 Figures. Accepted for publication to Ap
Local quasiparticle density of states of superconducting SmFeAsOF single crystals: Evidence for spin-mediated pairing
We probe the local quasiparticles density-of-states in micron-sized
SmFeAsOF single-crystals by means of Scanning Tunnelling
Spectroscopy. Spectral features resemble those of cuprates, particularly a
dip-hump-like structure developed at energies larger than the gap that can be
ascribed to the coupling of quasiparticles to a collective mode, quite likely a
resonant spin mode. The energy of the collective mode revealed in our study
decreases when the pairing strength increases. Our findings support
spin-fluctuation-mediated pairing in pnictides.Comment: 11 pages, 4 figure
Fifteen years in the high-energy life of the solar-type star HD 81809. XMM-Newton observations of a stellar activity cycle
Aims. The data set of the long-term XMM-Newton monitoring program of HD 81809
is analyzed to study its X-ray cycle, to investigate if the latter is related
to the chromospheric one, to infer the structure of the corona of HD 81809, and
to explore if the coronal activity of HD 81809 can be ascribed to phenomena
similar to the solar ones and, therefore, considered an extension of the solar
case. Methods. We analyze the observations of HD 81809 performed with
XMM-Newton with a regular cadence of 6 months from 2001 to 2016 and
representing one of the longest available observational baseline (~yr)
for a solar-like star with a well-studied chromospheric cycle (with a period of
~yr). We investigate the modulation of coronal luminosity and
temperature and its relation with the chromospheric cycle. We interpret the
data in terms of a mixture of solar-like coronal regions, adopting a
methodology originally proposed to study the Sun as an X-ray star. Results. The
observations show a well-defined regular cyclic modulation of the X-ray
luminosity that reflects the activity level of HD 81809. The data covers
approximately two cycles of coronal activity; the modulation has an amplitude
of a factor of (excluding evident flares, as in the June 2002
observation) and a period of ~yr, consistent with that of the
chromospheric cycle. We demonstrate that the corona of HD 81809 can be
interpreted as an extension of the solar case and it can be modeled with a
mixture of solar-like coronal regions along the whole cycle. The activity level
is mainly determined by a varying coverage of very bright active regions,
similar to cores of active regions observed in the Sun. Evidence of unresolved
significant flaring activity is present especially in proximity of cycle
maxima.Comment: 11 pages, 5 Figures, A&A accepte
3D MODELING FOR UNDERWATER ARCHAEOLOGICAL DOCUMENTATION: METRIC VERIFICATIONS
The survey in underwater environment has always presented considerable difficulties both operative and technical and this has sometimes made it difficult to use the techniques of survey commonly used for the documentation of Cultural Heritage in dry environment. The work of study concerns the evaluation in terms of capability and accuracy of the Autodesk123DCatch software for the reconstruction of a three-dimensional model of an object in underwater context. The subjects of the study are models generated from sets of photographs and sets of frames extracted from video sequence. The study is based on comparative method, using a reference model, obtained with laser scanner technique
Polaronic signature in the metallic phase of La0.7Ca0.3MnO3 films detected by scanning tunneling spectroscopy
In this work we map tunnel conductance curves with nanometric spatial
resolution, tracking polaronic quasiparticle excitations when cooling across
the insulator-to-metal transition in La0.7Ca0.3MnO3 films. In the insulating
phase the spectral signature of polarons, a depletion of conductance at low
bias flanked by peaks, is detected all over the scanned surface. These features
are still observed at the transition and persist on cooling into the metallic
phase. Polaron-binding energy maps reveal that polarons are not confined to
regions embedded in a highly-conducting matrix but are present over the whole
field of view both above and below the transition temperature.Comment: 10 pages, 4 figure
Sesquiterpenoids in subtribe Centaureinae (Cass.) Dumort (tribe Cardueae, Asteraceae): distribution, 13C-NMR spectral data and biological properties
Asteraceae Bercht. & J. Presl is one of the biggest and most economically important plant families. The taxonomy and phylogeny of Asteraceae is rather complex and according to the latest and most reliable taxonomic classification of Panero & Funk, based on the analysis of nine chloroplast regions, the family is divided into 12 subfamilies and 35 tribes. One of the largest tribes of Asteraceae is Cardueae Cass. with four subtribes (Carlininae, Echinopinae, Carduinae and Centaureinae) and more than 2500 species. Susanna & Garcia-Jacas have organized the genera of Centaureinae (about 800 species) into seven informal groups, which recent molecular studies have confirmed: 1. Basal genera; 2. Volutaria group; 3. Rhaponticum group; 4. Serratula group; 5. Carthamus group; 6. Crocodylium group; 7. Centaurea group. This review summarizes reports on sesquiterpenoids from the Centaureinae subtribe of the Asteraceae family, as well as the 13C NMR spectral data described in the literature. It further reviews studies concerning the biological activities of these metabolites. For this work, literature data on sesquiterpenes from the Centaureinae subtribe were retrieved with the help of the SciFinder database and other similar data banks. All entries from 1958 until the end of 2011 were considered. This review is addressed to scientists working in the metabolomics field such as chemists, botanists, etc., the spectroscopic data reported make this work a good tool for structural elucidation, the biological section gives useful information to those who wish to study the structure activity relationships
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