1,938 research outputs found
Doppler imaging an X-ray flare on the ultrafast rotator BO Mic - A contemporaneous multiwavelength study using XMM-Newton and VLT
We present an analysis of contemporaneous photospheric, chromospheric and
coronal structures on the highly active K-dwarf star BO Mic (Speedy Mic). We
localize a moderate flare in the stellar atmosphere and study its energetics,
size and thermal behaviour. The analysis is based on strictly simultaneous
X-ray, UV- and optical observations carried out by XMM-Newton and the VLT. We
use Doppler imaging and related methods for the localization of features. Based
on X-ray spectroscopy we study the the coronal plasma in and outside the flare.
The flare emits in X-rays and UV, but is not detected in white light; it is
located at intermediate latitude between an extended spot group and the weakly
spotted pole. We estimate its height below 0.4 stellar radii making it clearly
distinct in longitude and height from the prominences found about two stellar
radii above the surface. While BO Mic's photospheric brightness is modulated
due to extended starspots, neither the chromospheric nor the X-ray emission
show a pronounced rotational modulation.Comment: Accepted by A&
The Remarkable Be Star HD110432
HD110432 has gained considerable attention because it is a hard, variable
X-ray source similar to gamma Cas. From time-serial echelle data obtained over
two weeks during 2005 January and February, we find several remarkable
characteristics in the star's optical spectrum. The line profiles show rapid
variations on some nights which can be most likely be attributed to irregularly
occurring and short-lived migrating subfeatures. Such features have only been
observed to date in gamma Cas and AB Dor, two stars for which it is believed
magnetic fields force circumstellar clouds to corotate over the stellar
surface. The star's optical spectrum also exhibits a number of mainly FeII and
HeI emission features with profiles typical of an optically thin disk viewed
edge-on. Using spectral synthesis techniques, we find that its temperature is
9800K +/-300K, that its projected area is a remarkably large 100 stellar areas,
and its emitting volume resides at a distance of 1 AU from the star. We also
find that the star's absorption profiles extend to +/-1000 km/s, a fact which
we cannot explain. Otherwise, HD110432 and gamma Cas share similarly peculiar
X-ray and optical characteristics such as high X-ray temperature, erratic X-ray
variability on timescales of a few hours, optical emission lines, and
submigrating features in optical line profiles. Because of these similarities,
we suggest that this star is a new member of a select class of "gamma Cas
analogs."Comment: 31 pages, 9 figures, accepted by ApJ (3/20/06
The first Doppler imaging of the active binary prototype RS Canum Venaticorum
We present the first Doppler images of the prototypical active binary star RS Canum Venaticorum, derived from high-resolution spectra observed in 2004, 2016 and 2017, using three different telescopes and observing sites. We apply the least-squares deconvolution technique to all observed spectra to obtain high signal-to-noise line profiles, which are used to derive the surface images of the active K-type component. Our images show a complex spot pattern on the K star, distributed widely in longitude. All star-spots revealed by our Doppler images are located below a latitude of about 70°. In accordance with previous light-curve modelling studies, we find no indication of a polar spot on the K star. Using Doppler images derived from two consecutive rotational cycles, we estimate a surface differential rotation rate of ΔΩ = −0.039 ± 0.003 rad d−1 and α = ΔΩ/Ωeq = −0.030 ± 0.002 for the K star. Given the limited phase coverage during those two rotations, the uncertainty of our differential rotation estimate is presumably higher
Phonon effects in molecular transistors: Quantum and classical treatment
We present a comprehensive theoretical treatment of the effect of
electron-phonon interactions in molecular transistors, including both quantal
and classical limits and we study both equilibrated and out of equilibrium
phonons. We present detailed results for conductance, noise and phonon
distribution in two regimes. One involves temperatures large as compared to the
rate of electronic transitions on and off the dot; in this limit our approach
yields classical rate equations, which are solved numerically for a wide range
of parameters. The other regime is that of low temperatures and weak
electron-phonon coupling where a perturbative approximation in the Keldysh
formulation can be applied. The interplay between the phonon-induced
renormalization of the density of states on the quantum dot and the
phonon-induced renormalization of the dot-lead coupling is found to be
important. Whether or not the phonons are able to equilibrate in a time rapid
compared to the transit time of an electron through the dot is found to affect
the conductance. Observable signatures of phonon equilibration are presented.
We also discuss the nature of the low-T to high-T crossover.Comment: 20 pages, 19 figures. Minor changes, version accepted for publication
in Phys. Rev.
High-precision photometry by telescope defocussing. III. The transiting planetary system WASP-2
We present high-precision photometry of three transits of the extrasolar
planetary system WASP-2, obtained by defocussing the telescope, and achieving
point-to-point scatters of between 0.42 and 0.73 mmag. These data are modelled
using the JKTEBOP code, and taking into account the light from the
recently-discovered faint star close to the system. The physical properties of
the WASP-2 system are derived using tabulated predictions from five different
sets of stellar evolutionary models, allowing both statistical and systematic
errorbars to be specified. We find the mass and radius of the planet to be M_b
= 0.847 +/- 0.038 +/- 0.024 Mjup and R_b = 1.044 +/- 0.029 +/- 0.015 Rjup. It
has a low equilibrium temperature of 1280 +/- 21 K, in agreement with a recent
finding that it does not have an atmospheric temperature inversion. The first
of our transit datasets has a scatter of only 0.42 mmag with respect to the
best-fitting light curve model, which to our knowledge is a record for
ground-based observations of a transiting extrasolar planet.Comment: Accepted for publication in MNRAS. 9 pages, 3 figures, 10 table
The ethical challenge of Touraine's 'living together'
In Can We Live Together? Alain Touraine combines a consummate analysis of crucial social tensions in contemporary societies with a strong normative appeal for a new emancipatory 'Subject' capable of overcoming the twin threats of atomisation or authoritarianism. He calls for a move from 'politics to ethics' and then from ethics back to politics to enable the new Subject to make a reality out of the goals of democracy and solidarity. However, he has little to say about the nature of such an ethics. This article argues that this lacuna could usefully be filled by adopting a form of radical humanism found in the work of Erich Fromm. It defies convention in the social sciences by operating from an explicit view of the 'is' and the 'ought' of common human nature, specifying reason, love and productive work as the qualities to be realised if we are to move closer to human solidarity. Although there remain significant philosophical and political differences between the two positions, particularly on the role to be played by 'the nation', their juxtaposition opens new lines of inquiry in the field of cosmopolitan ethics
Double-slit interference pattern from single-slit screen and its gravitational analogues
The double slit experiment (DSE) is known as an important cornerstone in the
foundations of physical theories such as Quantum Mechanics and Special
Relativity. A large number of different variants of it were designed and
performed over the years. We perform and discuss here a new verion with the
somewhat unexpected results of obtaining interference pattern from single-slit
screen. This outcome, which shows that the routes of the photons through the
array were changed, leads one to discuss it, using the equivalence principle,
in terms of geodesics mechanics. We show using either the Brill's version of
the canonical formulation of general relativity or the linearized version of it
that one may find corresponding and analogous situations in the framework of
general relativity.Comment: 51 pages, 12 Figures five of them contain two subfigures and thus the
number of figures is 17, 1 Table. Some minor changes introduced, especially,
in the reference
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