14,455 research outputs found
A spatially resolved limb flare on Algol B observed with XMM-Newton
We report XMM-Newton observations of the eclipsing binary Algol A (B8V) and B
(K2III). The XMM-Newton data cover the phase interval 0.35 - 0.58, i.e.,
specifically the time of optical secondary minimum, when the X-ray dark B-type
star occults a major fraction of the X-ray bright K-type star. During the
eclipse a flare was observed with complete light curve coverage. The decay part
of the flare can be well described with an exponential decay law allowing a
rectification of the light curve and a reconstruction of the flaring plasma
region. The flare occurred near the limb of Algol B at a height of about 0.1R
with plasma densities of a few times 10^11 cm^-3 consistent with spectroscopic
density estimates. No eclipse of the quiescent X-ray emission is observed
leading us to the conclusion that the overall coronal filling factor of Algol B
is small.Comment: 8 pages, 7 figures, accepted by A&
Spatially resolved X-ray emission of EQ Pegasi
We present an analysis of an XMM-Newton observation of the M dwarf binary EQ
Pegasi with a special focus on the the spatial structure of the X-ray emission
and the analysis of light curves. Making use of data obtained with EPIC
(European Photon Imaging Camera) we were for the first time able to spatially
resolve the two components in X-rays and to study the light curves of the
individual components of the EQ Peg system. During the observation a series of
moderate flares was detected, where it was possible to identify the respective
flaring component.Comment: 6 pages, 11 figures, accepted by A&
Precision Measurement of a Particle Mass at the Linear Collider
Precision measurement of the stop mass at the ILC is done in a method based
on cross-sections measurements at two different center-of-mass energies. This
allows to minimize both the statistical and systematic errors. In the framework
of the MSSM, a light stop, compatible with electro-weak baryogenesis, is
studied in its decay into a charm jet and neutralino, the Lightest
Supersymmetric Particle(LSP), as a candidate of dark matter. This takes place
for a small stop-neutralino mass difference.Comment: 6 pages, 4 figures, 3tables,
Conference(Workshop)-LCWS/ILC2007-June,2,200
A planetary eclipse map of CoRoT-2a. Comprehensive lightcurve modeling combining rotational-modulation and transits
We analyze the surface structure of the planet host star CoRoT-2a using a
consistent model for both the `global' (i.e., rotationally modulated)
lightcurve and the transit lightcurves, using data provided by the CoRoT
mission. Selecting a time interval covering two stellar rotations and six
transits of the planetary companion CoRoT-2b, we adopt a `strip' model of the
surface to reproduce the photometric modulation inside and outside the transits
simultaneously. Our reconstructions show that it is possible to achieve
appropriate fits for the entire sub-interval using a low-resolution surface
model with 36 strips. The surface reconstructions indicate that the brightness
on the eclipsed section of the stellar surface is (6 +/- 1) % lower than the
average brightness of the remaining surface. This result suggests a
concentration of stellar activity in a band around the stellar equator similar
to the behavior observed on the Sun.Comment: accepted by A&A on 12/09/200
Skyrme models and nuclear matter equation of state
We investigate the role of pressure in a class of generalised Skyrme models. We introduce pressure as the trace of the spatial part of the energy-momentum tensor and show that it obeys the usual thermodynamical relation. Then, we compute analytically the mean-field equation of state in the high and medium pressure regimes by applying topological bounds on compact domains. The equation of state is further investigated numerically for the charge one skyrmions. We identify which term in a generalised Skyrme model is responsible for which part in the equation of state. Further, we compare our findings with the corresponding results in the Walecka model
The center-to-limb variation across the Fraunhofer lines of HD 189733; Sampling the stellar spectrum using a transiting planet
The center-to-limb variation (CLV) describes the brightness of the stellar
disk as a function of the limb angle. Across strong absorption lines, the CLV
can vary quite significantly. We obtained a densely sampled time series of
high-resolution transit spectra of the active planet host star HD 189733 with
UVES. Using the passing planetary disk of the hot Jupiter HD 189733 b as a
probe, we study the CLV in the wings of the Ca II H and K and Na I D1 and D2
Fraunhofer lines, which are not strongly affected by activity-induced
variability. In agreement with model predictions, our analysis shows that the
wings of the studied Fraunhofer lines are limb brightened with respect to the
(quasi-)continuum. The strength of the CLV-induced effect can be on the same
order as signals found for hot Jupiter atmospheres. Therefore, a careful
treatment of the wavelength dependence of the stellar CLV in strong absorption
lines is highly relevant in the interpretation of planetary transit
spectroscopy.Comment: Accepted in A&
Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit
HD 189733 is an exoplanetary system consisting of a transiting hot Jupiter
and an active K2V-type main sequence star. We aim to use VLT/UVES high
resolution echelle spectra to study a stellar flare. We have performed
simultaneous analyses of the temporal evolution in several chromospheric
stellar lines, namely, the Ca II H and K lines, Halpha, Hbeta, Hgamma, Hdelta,
Hepsilon, the Ca II infrared triplet line, and He I D3. Observations were
carried out with a time resolution of approximately 1 min for a duration of
four hours, including a complete planetary transit. We determine the energy
released during the flare in all studied chromospheric lines combined to be
about 8.7e31 erg, which puts this event at the upper end of flare energies
observed on the Sun. Our analysis does not reveal any significant delay of the
flare peak observed in the Balmer and Ca II H and K lines, although we find a
clear difference in the temporal evolution of these lines. The He I D3 shows
additional absorption possibly related to the flare event. Based on the flux
released in Ca II H and K lines during the flare, we estimate the soft X-ray
flux emission to be 7e30 erg. The observed flare can be ranked as a moderate
flare on a K-type star and confirms a rather high activity level of HD 189733
host star. The cores of the studied chromospheric lines demonstrate the same
behavior and let us study the flare evolution. We demonstrate that the activity
of an exoplanet host star can play an important role in the detection of
exoplanet atmospheres, since these are frequently discovered as an additional
absorption in the line cores. A possible star-planet interaction responsible
for a flare occurrence during a transit can neither be confirmed nor ruled out.Comment: 12 pages, 9 figures, accepted for publication in A&
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