203 research outputs found
Fahrzeugfuhrung durch ein Fahrermodell
Modelling a driver strictly separated into calculation of reference values and feedback
follow-up control of the car, a driver model closely connected to predictive control has been
developed. Since the reference calculation is represented by a sequence of locally defined
optimal control problems, only local, e. g. measured data is used. Especially advantageous,
the driver may be adapted to various characteristics. Yet, the presented approach is by no
means limited to driver models
First Observation of Planet-Induced X-ray Emission: The System HD 179949
We present the first observation of planet-induced stellar X-ray activity,
identified for the HD 179949 system, using Chandra / ACIS-S. The HD 179949
system consists of a close-in giant planet orbiting an F9V star. Previous
ground-based observations already showed enhancements in Ca II K in phase with
the planetary orbit. We find an ~30% increase in the X-ray flux over quiescent
levels coincident with the phase of the Ca II enhancements. There is also a
trend for the emission to be hotter at increased fluxes, confirmed by modeling,
showing the enhancement at ~1 keV compared to ~0.4 keV for the background star.Comment: 3 pages, 1 figure; Exoplanets: Detection, Formation and Dynamics, IAU
Symposium 249, eds. Y.-S. Sun, S. Ferraz-Mello, and J.-L. Zhou (Cambridge:
Cambridge University Press
Searching for Star-Planet interactions within the magnetosphere of HD 189733
HD 189733 is a K2 dwarf, orbited by a giant planet at 8.8 stellar radii. In
order to study magnetospheric interactions between the star and the planet, we
explore the large-scale magnetic field and activity of the host star.
We collected spectra using the ESPaDOnS and the NARVAL spectropolarimeters,
installed at the 3.6-m Canada-France-Hawaii telescope and the 2-m Telescope
Bernard Lyot at Pic du Midi, during two monitoring campaigns (June 2007 and
July 2008).
HD 189733 has a mainly toroidal surface magnetic field, having a strength
that reaches up to 40 G. The star is differentially rotating, with latitudinal
angular velocity shear of domega = 0.146 +- 0.049 rad/d, corresponding to
equatorial and polar periods of 11.94 +- 0.16 d and 16.53 +- 2.43 d
respectively. The study of the stellar activity shows that it is modulated
mainly by the stellar rotation (rather than by the orbital period or the beat
period between the stellar rotation and the orbital periods). We report no
clear evidence of magnetospheric interactions between the star and the planet.
We also extrapolated the field in the stellar corona and calculated the
planetary radio emission expected for HD 189733b given the reconstructed field
topology. The radio flux we predict in the framework of this model is time
variable and potentially detectable with LOFAR
Magnetic cycles of the planet-hosting star Tau Bootis: II. a second magnetic polarity reversal
In this paper, we present new spectropolarimetric observations of the
planet-hosting star Tau Bootis, using ESPaDOnS and Narval spectropolarimeters
at Canada-France-Hawaii Telescope (CFHT) and Telescope Bernard Lyot (TBL),
respectively. We detected the magnetic field of the star at three epochs in
2008. It is a weak magnetic field of only a few Gauss, oscillating between a
predominant toroidal component in January and a dominant poloidal component in
June and July. A magnetic polarity reversal was observed relative to the
magnetic topology in June 2007. This is the second such reversal observed in
two years on this star, suggesting that Tau Boo has a magnetic cycle of about 2
years. This is the first detection of a magnetic cycle for a star other than
the Sun. The role of the close-in massive planet in the short activity cycle of
the star is questioned.
Tau Boo has strong differential rotation, a common trend for stars with
shallow convective envelope. At latitude 40 deg., the surface layer of the star
rotates in 3.31 d, equal to the orbital period. Synchronization suggests that
the tidal effects induced by the planet may be strong enough to force at least
the thin convective envelope into corotation. Tau Boo shows variability in the
Ca H & K and Halpha throughout the night and on a night to night time scale. We
do not detect enhancement in the activity of the star that may be related to
the conjunction of the planet. Further data is needed to conclude about the
activity enhancement due to the planet.Comment: 9 pages, 5 figures, 3 tables Accepted to MNRA
Magnetic field, differential rotation and activity of the hot-Jupiter hosting star HD 179949
HD 179949 is an F8V star, orbited by a giant planet at ~8 R* every 3.092514
days. The system was reported to undergo episodes of stellar activity
enhancement modulated by the orbital period, interpreted as caused by
Star-Planet Interactions (SPIs). One possible cause of SPIs is the large-scale
magnetic field of the host star in which the close-in giant planet orbits.
In this paper we present spectropolarimetric observations of HD 179949 during
two observing campaigns (2009 September and 2007 June). We detect a weak
large-scale magnetic field of a few Gauss at the surface of the star. The field
configuration is mainly poloidal at both observing epochs. The star is found to
rotate differentially, with a surface rotation shear of dOmega=0.216\pm0.061
rad/d, corresponding to equatorial and polar rotation periods of 7.62\pm0.07
and 10.3\pm0.8 d respectively. The coronal field estimated by extrapolating the
surface maps resembles a dipole tilted at ~70 degrees. We also find that the
chromospheric activity of HD 179949 is mainly modulated by the rotation of the
star, with two clear maxima per rotation period as expected from a highly
tilted magnetosphere. In September 2009, we find that the activity of HD 179949
shows hints of low amplitude fluctuations with a period close to the beat
period of the system.Comment: Accepted for publication in Monthly Notices of The Royal Astronomical
Societ
3-D tomographic observations of Rossby wave breaking over the North Atlantic during the WISE aircraft campaign in 2017
This paper presents measurements of ozone, water vapour and nitric acid (HNO3) in the upper troposphere/lower stratosphere (UTLS) over North Atlantic and Europe. The measurements were acquired with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) during the Wave Driven Isentropic Exchange (WISE) campaign in October 2017. GLORIA is an airborne limb imager capable of acquiring both 2-D data sets (curtains along the flight path) and, when the carrier aircraft is flying around the observed air mass, spatially highly resolved 3-D tomographic data. Here, we present a case study of a Rossby wave (RW) breaking event observed during two subsequent flights 2 d apart. RW breaking is known to steepen tracer gradients and facilitate stratosphere–troposphere exchange (STE). Our measurements reveal complex spatial structures in stratospheric tracers (ozone and nitric acid) with multiple vertically stacked filaments. Backward-trajectory analysis is used to demonstrate that these features are related to several previous Rossby wave breaking events and that the small-scale structure of the UTLS in the Rossby wave breaking region, which is otherwise very hard to observe, can be understood as stirring and mixing of air masses of tropospheric and stratospheric origin. It is also shown that a strong nitric acid enhancement observed just above the tropopause is likely a result of NOx production by lightning activity. The measurements showed signatures of enhanced mixing between stratospheric and tropospheric air near the polar jet with some transport of water vapour into the stratosphere. Some of the air masses seen in 3-D data were encountered again 2 d later, stretched to very thin filament (horizontal thickness down to 30 km at some altitudes) rich in stratospheric tracers. This repeated measurement allowed us to directly observe and analyse the progress of mixing processes in a thin filament over 2 d. Our results provide direct insight into small-scale dynamics of the UTLS in the Rossby wave breaking region, which is of great importance to understanding STE and poleward transport in the UTLS
Models of Star-Planet Magnetic Interaction
Magnetic interactions between a planet and its environment are known to lead
to phenomena such as aurorae and shocks in the solar system. The large number
of close-in exoplanets that were discovered triggered a renewed interest in
magnetic interactions in star-planet systems. Multiple other magnetic effects
were then unveiled, such as planet inflation or heating, planet migration,
planetary material escape, and even modification of the host star properties.
We review here the recent efforts in modelling and understanding magnetic
interactions between stars and planets in the context of compact systems. We
first provide simple estimates of the effects of magnetic interactions and then
detail analytical and numerical models for different representative scenarii.
We finally lay out a series of future developments that are needed today to
better understand and constrain these fascinating interactions.Comment: 23 pages, 10 figures, accepted as a chapter in the Handbook of
Exoplanet
Deep RNA sequencing of muscle tissue reveals absence of viral signatures in dermatomyositis
Objective: To explore a possible connection between active viral infections and manifestation of Dermatomyositis (DM).
Methods: Skeletal muscle biopsies were analyzed from patients diagnosed with juvenile (n=10) and adult (n=12) DM. Adult DM patients harbored autoantibodies against either TIF-1Îł (n=7) or MDA5 (n=5). Additionally, we investigated skeletal muscle biopsies from non-diseased controls (NDC, n=5). We used an unbiased high-throughput sequencing (HTS) approach to detect viral sequences. To further increase sequencing depth, a host depletion approach was applied.
Results: In this observational study, no relevant viral sequences were detected either by native sequencing or after host depletion. The absence of detectable viral sequences makes an active viral infection of the muscle tissue unlikely to be the cause of DM in our cohorts.
Discussion: Type I interferons (IFN) play a major role in the pathogenesis of both juvenile and adult dermatomyositis (DM). The IFN response is remarkably conserved between DM subtypes classified by specific autoantibodies. Certain acute viral infections are accompanied by a prominent type I IFN response involving similar downstream mechanisms as in DM. Aiming to elucidate the pathogenesis of DM in skeletal muscle tissue, we used an untargeted high-throughput sequencing and a host depletion approach to detect possible causative viruses
Modeling magnetospheric fields in the Jupiter system
The various processes which generate magnetic fields within the Jupiter
system are exemplary for a large class of similar processes occurring at other
planets in the solar system, but also around extrasolar planets. Jupiter's
large internal dynamo magnetic field generates a gigantic magnetosphere, which
is strongly rotational driven and possesses large plasma sources located deeply
within the magnetosphere. The combination of the latter two effects is the
primary reason for Jupiter's main auroral ovals. Jupiter's moon Ganymede is the
only known moon with an intrinsic dynamo magnetic field, which generates a
mini-magnetosphere located within Jupiter's larger magnetosphere including two
auroral ovals. Ganymede's magnetosphere is qualitatively different compared to
the one from Jupiter. It possesses no bow shock but develops Alfv\'en wings
similar to most of the extrasolar planets which orbit their host stars within
0.1 AU. New numerical models of Jupiter's and Ganymede's magnetospheres
presented here provide quantitative insight into the processes that maintain
these magnetospheres. Jupiter's magnetospheric field is approximately
time-periodic at the locations of Jupiter's moons and induces secondary
magnetic fields in electrically conductive layers such as subsurface oceans. In
the case of Ganymede, these secondary magnetic fields influence the oscillation
of the location of its auroral ovals. Based on dedicated Hubble Space Telescope
observations, an analysis of the amplitudes of the auroral oscillations
provides evidence that Ganymede harbors a subsurface ocean. Callisto in
contrast does not possess a mini-magnetosphere, but still shows a perturbed
magnetic field environment. Callisto's ionosphere and atmospheric UV emission
is different compared to the other Galilean satellites as it is primarily been
generated by solar photons compared to magnetospheric electrons.Comment: Chapter for Book: Planetary Magnetis
- …