1,444 research outputs found
The Dynamics of Stellar Coronae Harboring Hot-jupiters II. A Space Weather Event on A Hot-jupiter
We carry out a numerical simulation depicting the effects of a Coronal Mass
Ejection (CME) event on a close-in giant planet in an extrasolar system. We
drive the CME in a similar manner as in simulations of space weather events on
Earth. The simulation includes the planetary orbital motion, which leads to the
forming of a comet-like planetary magnetotail which is oriented almost
perpendicular to the direction of propagation of the CME. The combination of
this feature and the fact that the CME does not expand much by the time it
reaches the planet leads to a unique CME-magnetosphere interaction, where the
CME itself is highly affected by the presence of the planetary magnetosphere.
We find that the planet is well-shielded from CME penetration, even for a
relatively weak internal magnetic field. The planetary angular momentum loss
associated with such an event is negligible compared to the total planetary
angular momentum. We also find that the energy which is deposited in the
magnetosphere is much higher than in the case of the Earth, and our simulation
suggests there is a large-scale change in the orientation of the
magnetosphere-ionosphere current system during the CME event.Comment: 16 pages, 10 figures, accepted to Ap
The Impact of Split and Displacement Sudden Stratospheric Warmings on the Troposphere
Although sudden stratospheric warmings (SSWs) can improve subseasonal-to-seasonal forecasts, it is unclear whether the two types of SSW - displacements and splits - have different near-surface effects. To examine the longer-term (i.e., multi-week lead) tropospheric response to displacements and splits, we utilize an intermediate-complexity model and impose wave-1 and wave-2 stratospheric heating perturbations spun-off from a control run. At longer lags, the tropospheric response is found to be insensitive to both the wavenumber and location of the imposed heating, in agreement with freely evolving displacements and splits identified in the control run. At shorter lags, however, large differences are found between displacements and splits in both the control run and the different wavenumber-forced events. In particular, in the control run, the free-running splits have an immediate barotropic response throughout the stratosphere and troposphere whereas displacements take 1–2 weeks before a near-surface response becomes evident. Interestingly, this barotropic response found during CTRL splits is not captured by the barotropically forced wave-2 events, indicating that the zonal-mean tropospheric circulation is somehow coupled with the generation of the wave-2 splits. It is also found that in the control run, displacements yield stronger Polar-Cap temperature anomalies than splits, yet both still yield similar magnitude tropospheric responses. Hence, the strength of the stratospheric warming is not the only governing factor in the surface response. Overall, SSW classification based on vortex morphology may be useful for subseasonal but not seasonal tropospheric prediction
X-ray activity phased with planet motion in HD 189733?
We report on the follow-up XMM-Newton observation of the planet-hosting star
HD 189733 we obtained in April 2011. We observe a flare just after the
secondary transit of the hot Jupiter. This event shares the same phase and many
of the characteristics of the flare we observed in 2009. We suggest that a
systematic interaction between planet and stellar magnetic fields when the
planet passes close to active regions on the star can lead to periodic
variability phased with planetary motion. By mean of high resolution X-ray
spectroscopy with RGS we determine that the corona of this star is unusually
dense.Comment: accepted for publication on ApJ
Star-planet magnetic interaction and activity in late-type stars with close-in planets
Late-type stars interact with their close-in planets through their coronal
magnetic fields. We introduce a theory for the interaction between the stellar
and planetary fields focussing on the processes that release magnetic energy in
the stellar coronae. We consider the energy dissipated by the reconnection
between the stellar and planetary magnetic fields as well as that made
available by the modulation of the magnetic helicity of the coronal field
produced by the orbital motion of the planet. We estimate the powers released
by both processes in the case of axisymmetric and non-axisymmetric, linear and
non-linear force-free coronal fields finding that they scale as v_r (B_s)^(4/3)
(B_p)^(2/3) (R_p)^2, where v_r is the relative velocity between the stellar and
planetary fields, B_s the mean stellar surface field, B_p the planetary field
at the poles, and R_p the radius of the planet. A chromospheric hot spot or a
flaring activity phased to the orbital motion of the planet are found only when
the stellar field is axisymmetric. In the case of a non-axisymmetric field, the
time modulation of the energy release is multiperiodic and can be easily
confused with the intrinsic stellar variability. We apply our theory to the
systems with some reported evidence of star-planet magnetic interaction finding
a dissipated power at least one order of magnitude smaller than that emitted by
the chromospheric hot spots. The phase lags between the planets and the hot
spots are reproduced by our models in all the cases except for upsilon And. In
conclusion, the chromospheric hot spots rotating in phase with the planets
cannot be explained by the energy dissipation produced by the interaction
between stellar and planetary fields as considered by our models and require a
different mechanism.Comment: 16 pages, 3 figures, accepted by Astronomy and Astrophysic
Deglacial sea surface temperatures of the western tropical Pacific : a new look at old coral
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 19 (2004): PA4031, doi:10.1029/2004PA001084.Using Secondary Ion Mass Spectrometry (SIMS) ion microprobe techniques, we generated annual Sr/Ca cycles with subweekly resolution from chunks of Porites coral retrieved from a Tahiti barrier reef drill core (149°W, 17°S), representing the period 13,650 to 13,100 years B.P. The centers of pristine skeletal septa were selectively targeted with a 10 μm diameter ion beam spot, avoiding adjacent pore spaces occupied by secondary aragonite needles. Applying a Sr/Ca–sea surface temperature (SST) calibration equation derived from modern Tahiti Porites having the same low growth rate as the fossil specimens, we obtained SSTs ∼0.5°–1.5°C cooler during the Bølling-Allerod relative to the present day, with no significant change in seasonality. On the contrary, we estimate that analysis of bulk samples would yield excessively cool Sr/Ca-based SST estimates due to the occupation by secondary aragonite crystals of up to 50% of the skeletal pore space in the ancient samples. We find that growth rate effects on coral Sr/Ca further depress the apparent mean annual derived SSTs (by >3°C) and amplify the apparent seasonality by selectively enhancing wintertime cooling. Our microscale analysis of pristine skeleton and application of an appropriate growth-dependent calibration yield Sr/Ca-derived SSTs that are in good agreement with those derived from Mg/Ca ratios of calcitic foraminifera which indicate a continuous postglacial warming of the western tropical Pacific, in phase with the warming of the tropical Atlantic.Funds for this study were provided by NSF MG&G award number
OCE-0241075
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
Fine structure of the diamagnetic cavity boundary in comet Halley
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95105/1/jgra16786.pd
Protective Measurement-A New Quantum Measurement Paradigm: Detailed Description of the First Realization
We present a detailed description of the experiment realizing for the first time a protective measurement, a novel measurement protocol which combines weak interactions with a "protection mechanism" preserving the measured state coherence during the whole measurement process. Furthermore, protective measurement allows finding the expectation value of an observable, i.e., an inherently statistical quantity, by measuring a single particle, without the need for any statistics. This peculiar property, in sharp contrast to the framework of traditional (projective) quantum measurement, might constitute a groundbreaking advance for several quantum technology related fields
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