312 research outputs found
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
On the chromospheric activity of stars with planets
Context. Signatures of chromospheric activity enhancement have been found for
a dozen stars, pointing to a possible star-planet interaction. Nevertheless in
the coronal activity regime, there is no conclusive observational evidence for
such an interaction. Does star-planet interaction manifest itself only for a
few particular cases, without having a major effect on stars with planets in
general? Aims. We aim to add additional observational constraints to support or
reject the major effects of star-planet interactions in stellar activity, based
on CaII chromospheric emission flux. Methods. We performed a statistical
analysis of CaII emission flux of stars with planets, as well as a comparison
between CaII and X-ray emission fluxes, searching for dependencies on planetary
parameters. Results. In the present sample of stars with planets, there are no
significant correlations between chromospheric activity indicator log(R'HK) and
planetary parameters. Further, the distribution of the chromospheric activity
indicator for stars without planets is not distinguishable from the one with
planets.Comment: 6 pages, 5 figures, submitted to A&
Photospheric activity, rotation, and star-planet interaction of the planet-hosting star CoRoT-6
The CoRoT satellite has recently discovered a hot Jupiter that transits
across the disc of a F9V star called CoRoT-6 with a period of 8.886 days. We
model the photospheric activity of the star and use the maps of the active
regions to study stellar differential rotation and the star-planet interaction.
We apply a maximum entropy spot model to fit the optical modulation as observed
by CoRoT during a uninterrupted interval of about 140 days. Photospheric active
regions are assumed to consist of spots and faculae in a fixed proportion with
solar-like contrasts. Individual active regions have lifetimes up to 30-40
days. Most of them form and decay within five active longitudes whose different
migration rates are attributed to the stellar differential rotation for which a
lower limit of \Delta \Omega / \Omega = 0.12 \pm 0.02 is obtained. Several
active regions show a maximum of activity at a longitude lagging the
subplanetary point by about 200 degrees with the probability of a chance
occurrence being smaller than 1 percent. Our spot modelling indicates that the
photospheric activity of CoRoT-6 could be partially modulated by some kind of
star-planet magnetic interaction, while an interaction related to tides is
highly unlikely because of the weakness of the tidal force.Comment: 9 pages, 7 figures, accepted to Astronomy & Astrophysic
Low-Mass Eclipsing Binaries in the Initial Kepler Data Release
We identify 231 objects in the newly released Cycle 0 dataset from the Kepler
Mission as double-eclipse, detached eclipsing binary systems with Teff < 5500 K
and orbital periods shorter than ~32 days. We model each light curve using the
JKTEBOP code with a genetic algorithm to obtain precise values for each system.
We identify 95 new systems with both components below 1.0 M_sun and eclipses of
at least 0.1 magnitudes, suitable for ground-based follow-up. Of these, 14 have
periods less than 1.0 day, 52 have periods between 1.0 and 10.0 days, and 29
have periods greater than 10.0 days. This new sample of main-sequence,
low-mass, double-eclipse, detached eclipsing binary candidates more than
doubles the number of previously known systems, and extends the sample into the
completely heretofore unexplored P > 10.0 day period regime. We find
preliminary evidence from these systems that the radii of low-mass stars in
binary systems decrease with period. This supports the theory that binary
spin-up is the primary cause of inflated radii in low-mass binary systems,
although a full analysis of each system with radial-velocity and multi-color
light curves is needed to fully explore this hypothesis. As well, we present 7
new transiting planet candidates that do not appear among the recently released
list of 706 candidates by the Kepler team, nor in the Kepler False Positive
Catalog, along with several other new and interesting systems. We also present
novel techniques for the identification, period analysis, and modeling of
eclipsing binaries.Comment: 22 pages in emulateapj format. 9 figures, 4 tables, 2 appendices.
Accepted to AJ. Includes a significant addition of new material since last
arXiv submission and an updated method for estimating masses and radi
A coordinated optical and X-ray spectroscopic campaign on HD179949: searching for planet-induced chromospheric and coronal activity
HD179949 is an F8V star, orbited by a close-in giant planet with a period of
~3 days. Previous studies suggested that the planet enhances the magnetic
activity of the parent star, producing a chromospheric hot spot which rotates
in phase with the planet orbit. However, this phenomenon is intermittent since
it was observed in several but not all seasons. A long-term monitoring of the
magnetic activity of HD179949 is required to study the amplitude and time
scales of star-planet interactions. In 2009 we performed a simultaneous optical
and X-ray spectroscopic campaign to monitor the magnetic activity of HD179949
during ~5 orbital periods and ~2 stellar rotations. We analyzed the CaII H&K
lines as a proxy for chromospheric activity, and we studied the X-ray emission
in search of flux modulations and to determine basic properties of the coronal
plasma. A detailed analysis of the flux in the cores of the CaII H&K lines and
a similar study of the X-ray photometry shows evidence of source variability,
including one flare. The analysis of the the time series of chromospheric data
indicates a modulation with a ~11 days period, compatible with the stellar
rotation period at high latitudes. Instead, the X-ray light curve suggests a
signal with a period of ~4 days, consistent with the presence of two active
regions on opposite hemispheres. The observed variability can be explained,
most likely, as due to rotational modulation and to intrinsic evolution of
chromospheric and coronal activity. There is no clear signature related to the
orbital motion of the planet, but the possibility that just a fraction of the
chromospheric and coronal variability is modulated with the orbital period of
the planet, or the stellar-planet beat period, cannot be excluded. We conclude
that any effect due to the presence of the planet is difficult to disentangle
Signatures of Star-planet interactions
Planets interact with their host stars through gravity, radiation and
magnetic fields, and for those giant planets that orbit their stars within
10 stellar radii (0.1 AU for a sun-like star), star-planet
interactions (SPI) are observable with a wide variety of photometric,
spectroscopic and spectropolarimetric studies. At such close distances, the
planet orbits within the sub-alfv\'enic radius of the star in which the
transfer of energy and angular momentum between the two bodies is particularly
efficient. The magnetic interactions appear as enhanced stellar activity
modulated by the planet as it orbits the star rather than only by stellar
rotation. These SPI effects are informative for the study of the internal
dynamics and atmospheric evolution of exoplanets. The nature of magnetic SPI is
modeled to be strongly affected by both the stellar and planetary magnetic
fields, possibly influencing the magnetic activity of both, as well as
affecting the irradiation and even the migration of the planet and rotational
evolution of the star. As phase-resolved observational techniques are applied
to a large statistical sample of hot Jupiter systems, extensions to other
tightly orbiting stellar systems, such as smaller planets close to M dwarfs
become possible. In these systems, star-planet separations of tens of stellar
radii begin to coincide with the radiative habitable zone where planetary
magnetic fields are likely a necessary condition for surface habitability.Comment: Accepted for publication in the handbook of exoplanet
Observation of Spin Relaxation Anisotropy in Semiconductor Quantum Wells
Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs
quantum wells are measured by means of Hanle effect. Three different spin
relaxation times for spins oriented along [110], [1-10] and [001]
crystallographic directions are extracted demonstrating anisotropy of
D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba
and Dresselhaus terms describing the spin-orbit coupling in semiconductor
quantum well structures. It is shown that the Rashba spin-orbit splitting is
about four times stronger than the Dresselhaus splitting in the studied
structure.Comment: 4 pages, 3 figure
Показатели окислительного метаболизма и антиоксидантной защиты у больных хроническим обструктивным бронхитом, осложненным хроническим легочным сердцем, и их изменения в процессе лечения
Nowadays there is no a unique approach for evaluation of a role of lipid peroxidation (LP) and its regulation in chronic obstructive bronchitis (COB) complicated by the chronic cor pulmonale (CCP).The aim of our trial was to investigate the LP, the antioxidant defence system (AODS) and the proteases — antiproteases system in patients with COB complicated by the CCP and also to determine opportunities for a pharmacological correction of their disorders.Forty-eight patients aged 28 to 52 years (the average age was 43±1.7 years) suffering from COB complicated by the CCP were examined. Among them 36 persons received the antioxidant drug cytochrome С and 12 ones formed the comparative group. The controls were 14 healthy persons with the average age of 44±1.0 years. We studied initial parameters of LP-AODS in erythrocytes and blood plasma, hemodymanics parameters and their changes under the treatment.The patients with COB complicated by the CCP were found to increase LP products level and lysosomal and proteolytic enzymes activity. The activity of antioxidant enzymes and proteases’ inhibitors were noted to reduce simultaneously. The vigour of these shifts depended on a respiratory failure severity and respiratory system's structural disorders. A combination of cytochrome С and enalapril in patients with COB complicated by the CCP decreased pulmonary hypertension, improved the central and peripheral haemodynamics, blood gas content and acid-and-alkaline blood condition more effective than a traditional therapy. Such the dynamics facilitates shortening the inpatient period and improves the course of the disease.До настоящего времени отсутствует единая концепция в оценке значимости реакция перекисного окисления липидов (ПОЛ) и систем их регуляции при хроническом обструктивном бронхите (ХОБ), осложненном хроническим легочным сердцем (ХЛС).Цель нашего исследования — изучить показатели ПОЛ, антиоксидантной защиты (АОС), систему протеаз — ингибиторы протеаз у больных ХОБ, осложненным ХЛС, и определить возможность фармакологической регуляции этих нарушений.Обследовано 48 пациентов в возрасте от 28 до 52 лет (в среднем 43±1,7 года) с ХОБ, осложненным ХЛС, из них 36 человек получали антиоксидант цитохром С, 12 человек составили группу сравнения. Группу контроля составили 14 практически здоровых лиц, средний возраст 44±1 года. Изучали исходные показатели ПОЛ-АОС в эритроцитах и плазме крови и показатели гемодинамики, а также их динамику на фоне лечения.Установлено, что у больных ХОБ, осложненным ХЛС, повышены содержание продуктов ПОЛ, активность лизосомальных и протеолитических ферментов. Параллельно отмечалось снижение активности антиоксидантных ферментов и ингибиторов протеаз. Выраженность этих изменений зависела от степени дыхательной недостаточности и структурных изменений бронхолегочной системы. Использование цитохрома С в сочетании с эналаприлом в комплексном лечении больных ХОБ, осложненном ХЛС, позволяет достичь большего, чем при традиционном лечении, снижения легочной гипертензии, улучшить показатели центральной и периферической гемодинамики, газового и кислотнощелочного состояния крови, что способствует сокращению сроков стационарного лечения и улучшает течение заболевания
Searching for star-planet magnetic interaction in CoRoT observations
Close-in massive planets interact with their host stars through tidal and
magnetic mechanisms. In this paper, we review circumstantial evidence for
star-planet interaction as revealed by the photospheric magnetic activity in
some of the CoRoT planet-hosting stars, notably CoRoT-2, CoRoT-4, and CoRoT-6.
The phenomena are discussed in the general framework of activity-induced
features in stars accompanied by hot Jupiters. The theoretical mechanisms
proposed to explain the activity enhancements possibly related with hot Jupiter
are also briefly reviewed with an emphasis on the possible effects at
photospheric level. The unique advantages of CoRoT and Kepler observations to
test these models are pointed out.Comment: Invited review paper accepted by Astrophysics and Space Science, 13
pages, 5 figure
Magnetospheric Emission from Extrasolar Planets
The magnetospheric emissions from extrasolar planets represent a science
frontier for the next decade. All of the solar system giant planets and the
Earth produce radio emissions as a result of interactions between their
magnetic fields and the solar wind. In the case of the Earth, its magnetic
field may contribute to its habitability by protecting its atmosphere from
solar wind erosion and by preventing energetic particles from reaching its
surface. Indirect evidence for at least some extrasolar giant planets also
having magnetic fields includes the modulation of emission lines of their host
stars phased with the planetary orbits, likely due to interactions between the
stellar and planetary magnetic fields. If magnetic fields are a generic
property of giant planets, then extrasolar giant planets should emit at radio
wavelengths allowing for their direct detection. Existing observations place
limits comparable to the flux densities expected from the strongest emissions.
Additional sensitivity at low radio frequencies coupled with algorithmic
improvements likely will enable a new means of detection and characterization
of extrasolar planets within the next decade.Comment: Science white paper for Astro2010; submitted to PSF pane
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