Accretion, Outflows, and Winds of Magnetized Stars

Many types of stars have strong magnetic fields that can dynamically influence the flow of circumstellar matter. In stars with accretion disks, the stellar magnetic field can truncate the inner disk and determine the paths that matter can take to flow onto the star. These paths are different in stars with different magnetospheres and periods of rotation. External field lines of the magnetosphere may inflate and produce favorable conditions for outflows from the disk-magnetosphere boundary. Outflows can be particularly strong in the propeller regime, wherein a star rotates more rapidly than the inner disk. Outflows may also form at the disk-magnetosphere boundary of slowly rotating stars, if the magnetosphere is compressed by the accreting matter. In isolated, strongly magnetized stars, the magnetic field can influence formation and/or propagation of stellar wind outflows. Winds from low-mass, solar-type stars may be either thermally or magnetically driven, while winds from massive, luminous O and B type stars are radiatively driven. In all of these cases, the magnetic field influences matter flow from the stars and determines many observational properties. In this chapter we review recent studies of accretion, outflows, and winds of magnetized stars with a focus on three main topics: (1) accretion onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and (3) winds from isolated massive magnetized stars. We show results obtained from global magnetohydrodynamic simulations and, in a number of cases compare global simulations with observations.Comment: 60 pages, 44 figure

Modulation of cochlear tuning by low-frequency sound

An intense, low-frequency tone (about 30 Hz) modulates the sensitivity of the inner ear to high-frequency stimulation. This modulation is correlated with the displacement of the basilar membrane. The findings suggest that the modulation may also affect cochlear tuning. We have investigated modulation of cochlear tuning by low-frequency sound in the guinea pig. Applying indirect methods of measurement (narrow-band analysis of compound action potentials and compound-action-potential tuning curves), the results suggest a shift of the excitation pattern along the basilar membrane towards higher-frequency areas. The shift occurred for both scala tympani and scala vestibuli displacement of the cochlear partition. Tuning curves, obtained from single units in the cochlear nerve, show sensitivity loss and a tip shift towards lower frequencies. This was also found for both scala tympani displacement and scala vestibuli displacement. The shift of the tip of the tuning curve towards lower frequencies corresponds to the inferred high-frequency shift of the excitation pattern. The relationship of these phenomena with the pathophysiology of Ménière's disease and with possible active mechanisms in cochlear transduction is discussed

High-speed Keck II and RXTE spectroscopy of Cygnus X-2 - I. Three X-ray components revealed by correlated variability

We have performed simultaneous X-ray and optical spectroscopic observations of the Low Mass X-ray Binary Cygnus X-2. We have used a new data system attached to the Low Resolution Imaging Spectrograph instrument on Keck II to obtain spectra with a mean time resolution of 72.075 milliseconds, simultaneous with pointed X-ray observations using the PCA onboard XTE. In this paper, we have analysed the variability in both wavebands on timescales of 16 seconds. During our observations Cygnus X-2 covered all three branches of the Z-curve, allowing us to study how the changes in X-ray spectral state affect the optical emission. As the optical flux rises the X-ray intensity first rises on the Horizontal Branch (0<S_z<1) but then falls on the Normal Branch (1<S_z<2) and Flaring Branch (2<S_z<3), where S_z is a rank number characterising the position on the Z-curve. This linear increase in the optical flux with S_z indicates the optical flux is a good predictor of the accretion rate (possibly normalized by its own long-term average) inferred from the Z-state S_z. We have used this correlation to decompose the total X-ray count-rate into three distinct spectral components.Comment: 10 pages, 7 figures, accepted for publication in MNRAS, corrected problem with references in previous versio