72 research outputs found
Complicated variations of early optical afterglow of GRB 090726
We report on a detection of an early rising phase of optical afterglow (OA)
of a long GRB 090726. We resolve a complicated profile of the optical light
curve. We also investigate the relation of the optical and X-ray emission of
this event. We make use of the optical photometry of this OA obtained by the
0.5 m telescope of AI AS CR, supplemented by the data obtained by other
observers, and the X-ray Swift/XRT data.
The optical emission peaked at ~ 17.5 mag (R) at t-T0 ~ 500 s. We find a
complex profile of the light curve during the early phase of this OA: an
approximately power-law rise, a rapid transition to a plateau, a weak flare
superimposed on the center of this plateau, and a slowly steepening early
decline followed by a power-law decay. We discuss several possibilities to
explain the short flare on the flat top of the optical light curve at t-T0 ~
500 s; activity of the central engine is favored although reverse shock cannot
be ruled out. We show that power-law outflow with Theta_obs/Theta_c > 2.5 is
the best case for OA of GRB 090726. The initial Lorentz factor is Gamma_0 ~
230-530 in case of propagation of the blast wave in a homogeneous medium, while
propagation of this wave in a wind environment gives Gamma_0 ~ 80-300. The
value of Gamma_0 in GRB 090726 thus falls into the lower half of the range
observed in GRBs and it may even lie on the lower end. We also show that both
the optical and X-ray emission decayed simultaneously and that the spectral
profile from X-ray to the optical band did not vary. This OA belongs to the
least luminous ones in the phase of its power-law decay corresponding to that
observed for the ensemble of OAs of long GRBs.Comment: 5 pages, 5 figures, accepted to A&
Properties and nature of Be stars: 29. Orbital and long-term spectral variations of \gamma\ Cassiopei\ae
A detailed analysis of more than 800 electronic high-resolution spectra of
gamma Cas, which were obtained during a time interval of over 6000 days (16.84
yrs) at several observatories, documents the smooth variations in the density
and/or extend of its circumstellar envelope. We found a clear anticorrelation
between the peak intensity and FWHM of the H alpha emission, which seems to
agree with recent models of such emission lines. The main result of this study
is a confirmation of the binary nature of the object, determination of a
reliable linear ephemeris T_{min.RV} = HJD (2452081.90.6) +
(203.520.08)*E, and a rather definitive set of orbital elements. We
clearly demonstrated that the orbit is circular within the limits of accuracy
of our measurements and has a semi-amplitude of radial-velocity curve of
4.300.09 (km/s). No trace of the low-mass secondary was found. The time
distribution of our spectra does not allow a reliable investigation of rapid
spectral variations, which are undoubtedly present in the spectra. We postpone
this investigation for a future study, based on series of dedicated whole-night
spectral observations
Astrometric Control of the Inertiality of the Hipparcos Catalog
Based on the most complete list of the results of an individual comparison of
the proper motions for stars of various programs common to the Hipparcos
catalog, each of which is an independent realization of the inertial reference
frame with regard to stellar proper motions, we redetermined the vector
of residual rotation of the ICRS system relative to the extragalactic
reference frame. The equatorial components of this vector were found to be the
following: mas yr,
mas yr, and mas yr.Comment: 8 pages, 1 figur
Accession Site Does Not Influence the Risk of Stroke after Diagnostic Coronary Angiography or Intervention: Results from a Large Prospective Registry
INTRODUCTION: Periprocedural stroke represents a rare but serious complication of cardiac catheterization. Pooled data from randomized trials evaluating the risk of stroke following cardiac catheterization via transradial versus transfemoral access showed no difference. On the other hand, a significant difference in stroke rates favoring transradial access was found in a recent meta-analysis of observational studies. Our aim was to determine if there is a difference in stroke risk after transradial versus transfemoral catheterization within a contemporary real-world registry. METHODS: Data from 14,139 patients included in a single-center prospective registry between 2009 and 2016 were used to determine the odds of periprocedural transient ischemic attack (TIA) and stroke for radial versus femoral catheterization via multivariate logistic regression with Firth's correction. RESULTS: A total of 10,931 patients underwent transradial and 3,208 underwent transfemoral catheterization. Periprocedural TIA/stroke occurred in 41 (0.29%) patients. Age was the only significant predictor of TIA/stroke in multivariate analysis, with each additional year representing an odds ratio (OR) = 1.09 (CI 1.05-1.13, p < 0.000). The choice of accession site had no impact on the risk of periprocedural TIA/stroke (OR = 0.81; CI 0.38-1.72, p = 0.577). CONCLUSION: Observational data from a large prospective registry indicate that accession site has no influence on the risk of periprocedural TIA/stroke after cardiac catheterization
A Calanais myth and an alignment of the east stone-row with both the rising of the Pleiades and crossovers of Venus at sunrise on the summer solstices
Acknowledgements My thanks to Stefan Sagrott of Historic Environment Scotland for his help in obtaining Patrick Ashmore’s data and to David Forrest, School of Geographical and Earth Sciences, University of Glasgow, for providing a copy of David Tait’s map of Calanais.Peer reviewedPublisher PD
De l'intonation de la finale du nominatif pluriel des thèmes en -o-
Vondrák V. De l'intonation de la finale du nominatif pluriel des thèmes en -o-. In: Revue des études slaves, tome 4, fascicule 1-2, 1924. pp. 16-23
Solution of Earth orientation parameters in 20th century based on optical astrometry and new catalog EOC-3
The Earth Orientation Catalog 4
Context. The astrometric ground-based observations of latitude/universal time variations, covering the interval 1899.7–2003.0, were used in combination with Hipparcos/Tycho positions and some older ground-based catalogs to construct a family of catalogs, tailored to long-term Earth-rotation studies. These catalogs, called Earth Orientation Catalogs (EOC-1 through EOC-3) yielded
more accurate proper motions than the original Hipparcos
Catalogue, and its latest version, EOC-3, even periodic motions for a large portion of the stars.
Aims. It appeared that more stars than are contained in EOC-3 are double or multiple and that a better procedure can be used to improve the periodic terms, reflecting the orbital motions of the stars observed in the programs of monitoring Earth orientation.
Methods. We used about 4.5 million observations of latitude/universal
time variations at 33 observatories all over the world, and combined them with the catalogs ARIHIP, TYCHO-2, etc. to obtain the Earth Orientation Catalog (EOC-4). These observations are identical to those used to construct the previous version, EOC-3. Spectral analysis of
ground-based data and comparison with the USNO Sixth Catalog of Orbits of Visual Binary Stars was used to discover which of the observed objects display periodic motions. The corresponding amplitudes and phases were then estimated in one-step least-squares solution, together with positions and proper motions. Unlike in EOC-3, where annual averages were used, we use here the individual nightly observations.
Results. The fourth version of the catalog, EOC-4, contains 4418
different objects (i.e., stars, components of double stars,
photocenters), out of which 599 have significant orbital motions. The catalog will eventually be used for new determination of the Earth orientation parameters during the twentieth century
- …