-This paper proposes a new nonparametric approach to the estimation of the mean Doppler velocity (first spectral moment) and the spectral width (square root of the second spectral centered moment) of a zero-mean stationary complex Gaussian process immersed in independent additive white Gaussian noise. By assuming that the power spectral density of the underlying process is bandlimited, the exac...

The statistical model of scattered by flowing Brownian particles coherent radiation is suggested. The model includes the random Doppler shifts caused by particle Brownian motion and the speckle fluctuations caused primarily by the flow motion of particles. Analytical expressions are obtained for the correlation function, power spectrum, and spectral width of scattered radiation in the imaging g...

We propose a four-level model where sub-Doppler resolution as well as enhanced absorption of a weak probe field are realized by using two coherently driving fields. We show that spectral resolution can be improved by modifying the coherent fields intensity and frequencies. Multi-photon transitions are embedded in a variety of optical effects based on correlated absorption and emission of two or...

We review the main observational characteristics of AM Herculis stars (polars) at X-ray, EUV, UV, IR and optical wavelengths. Particular emphasis is given to multi-epoch, multi-wavelength observations of the eclipsing polar HU Aqr (RXJ2107.9-0518). In AM Herculis stars the broad-band spectral energy distribution from X-rays to the IR is governed by only very small structures: the hot accretion ...

Visualization of the results a loop spectral fits onto time-averaged XMM-Newton / RGS spectrum Ultraluminous X-ray source NGC 247 ULX-1. The parameter space explored by covers range wind velocities (as constrained Doppler shift absorption lines) and photoionization parameters