Kozhevnikov V. Blue J. Martin E. Schneider J. Alvarez M. Gibson N. Glownia Z. Hall D. Kreiner J. Hebb L. Hellier C. Kipping D. Lanza A. Rosner R. Pringle J. Mayor M. Queloz D. Miller-Ricci E. Kocsis B. Rabus M. Alonso R. Belmonte J. Almenara J. Rafikov R. Saar S. Brandenburg A. Simon A. Soydugan F. Ulrich R.
Bertello L. Warner B. Watson C. Littlefair S. Collier Cameron A. Simpson E. Wolf S. Mantel K. Horne K. Barwig H. Schoembs R. Baerbantner O. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation.
Volume Article Contents Abstract. Orbital period variations of hot Jupiters caused by the Applegate effect. Watson , C. Oxford Academic. Google Scholar. Cite Cite C. Select Format Select format. Permissions Icon Permissions. Abstract Several authors have shown that precise measurements of transit time variations of exoplanets can be sensitive to other planetary bodies, such as exo-moons. Taking just one star to have a quadrupole moment Q in the equatorial plane and mass M then, as shown in equation 4 of Applegate , its companion orbits in a gravitational potential of the form,.
We can therefore re-express equation 4 as. In the model outlined in Applegate , variations in the quadrupole moment, Q , of the star are driven by the stellar activity cycle. Magnetic fields are supposed to drive the angular momentum transfer from within the star. For instance, if angular momentum is transported from the core of the star to its envelope, the star will become more oblate and its quadrupole moment will increase. Applegate computes the rate of change of the stellar quadrupole as a function of the angular momentum transport in his equation 26 ,.
As outlined in Section 2 , a change in the stellar quadrupole moment leads to a corresponding change in the orbital period given by equation 2 , where a is the orbital separation between, in this case, the star and the planet. Given that stellar activity cycles are rather variable, there is no well-defined amplitude or period of variation to be expected from Applegate's models.
The one constraint that we can invoke is a restriction on the energy budget allowed to drive the quadrupole moment. P rot d. P orb d. Open in new tab. Confusion with interior perturbing planets can be immediately rejected since the modulation of the orbital period will occur on far too short a time-scale, in order to cause TTVs modulated on decade time-scales requires an exterior planet on a relatively wide orbit. Furthermore, TTVs caused by an additional planet in a mean-motion resonance orbit generally drive significantly larger transit-time variations than those possible by the Applegate mechanism.
However, for exterior planets on eccentric orbits with much larger orbital periods and not in mean-motion resonance , Agol et al. Open in new tab Download slide.
The presence of a second planet in a long period may also cause TTVs through the variation of the light-travel time due to the reflex motion of the host star.
Indeed, Deeg et al. For an exterior planet of mass M p on an orbit with a semimajor axis a out , the amplitude of the timing deviation is.
Its main components are electron gun to produce the electron beam and a structure supporting the slow electromagnetic wave. Therefore the signal gets strengthened and amplified output is delivered at the other end of tube. TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc. In a klystron amplifier dc electron velocity is v 0 and dc electron charge density is r 0 the dc beam current is Options A.
Assertion A : A coaxial line is a non-radiating line. Reason R : In a coaxial line the electric and magnetic fields are confined to the region between the concentric conductors. A loss less line of characteristic impedance Z 0 is terminated in pure reactance of - j Z 0 value.
A line has a phase constant of At MHz the wavelength is Options A. Correct Answer: 0. The velocity factor of a transmission line depends on Options A. Correct Answer: relative permittivity of dielectric Explanation:? Assertion A : A backward wave oscillator has an internal positive feedback. Reason R : A positive feedback is necessary for sustained oscillations. The growing RF wave travels in opposite direction to the electron beam.
The frequency of wave can be changed by changing the voltage which controls the beam velocity. It features are: 1. Frequency range - 1 GHz to GHz. More Hide details. Collect to Blossary.
More Less. Member comments. You have to log in to post to discussions. Weekly Packet Language ; Online services ; Slang ; Internet Weekly Packet or "Paquete Semanal" as it is known in Cuba is a term used by Cubans to describe the information that is gathered from the internet outside of Cuba and saved onto hard drives to be transported into Cuba itself.
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