QPO
In the analysis of GK Per, a strange phenomenon can be observedXquasi-periodic oscillations (QPO). "QPOs are defined as low-coherence brightness oscillations thought to be associated with material within the inner accretion flows of CVs (Morales-Rueda, Still & Roche, hereafter MSR, 1999). Though the source can be considered periodic, its period has a certain variance. The state of the GK Per system affects the observed QPO period (PQPO) (Yi & Kenyon 1997). Various people have analyzed the optical periodicity, but their results vary greatly. For example, Patterson (1981) observed the source during quiescence in 1978, finding PQPO to be about 380 seconds. During the decline phase of GK Per in 1983, Mazeh et al. (1985) found PQPO ~360 sec, and also determined PQPO ~400 s during two nights of GK Per's outburst phase (Yi & Kenyon 1997). Watson, King & Osborne (1985) also observed a ~5000 s QPO through the analysis of X-ray data. No consensus has been reached as to a single model for the QPO phenomenon. Theoretical models suggest dense blobs in orbit within the inner disk (Bath 1973), pulsations on the surface of the white dwarf (Papaloizou & Pringle 1978), or oscillating acou
they fitted the two spectra. fÖ0 represents the superior conjunction of the white dwarf, f× corresponds to the systematic velocity of the binary, K is the companion star's radial velocity semiamplitude, and fÖ represents the orbital phase. Fitting their data with that of previous researchers, MSR calculated f× = 30 „b 1 km/s, K = 119 „b 2 km/s, and fÖ0 = 0.998 „b 0.003. The spectroscopy of GK Per obtained by MSR exhibit broad Balmer and HeI lines, as well as high excitation lines of HeII, NIII and CIII. Faint absorption lines of FeI, CaI, TiII and SrII also appear. Kraft (1964), Gallagher & Oinas (1974), Crampton, Cowley & Fisher (1994) and Reinsch (1994) all identify these as characteristics of a K-type secondary star. Through the multiplication of a monochromatic constant, they determined the spectrum of background radiation, and subtracted this from the full spectrum, resulting in a true spectrum for GK Per. The spectrum then underwent a fÓ2 test to compare it with the spectra of the other K-type stars in order to find the best fit. The lowest reduced fÓ2 obtained was 2.5, from the K1IV star HD197964. By subtracting this fit from the spectra, they correlated the absorption spectra with their templates. With the circular function: The emission spectra show double peaks. It is generally accepted that these peaks are an indicator of the presence of an accretion disk. In intermediate polars, however, the flow of the accretion column is extremely complex, so a number of factors could
Some common words found in the essay are:
Cowley Fisher, King Osbourne, Yi Kenyon, Papaloizou Pringle, Hellier Livio, King Osborne, Morales-Rueda Roche, Observatory October, La Palma, QPO QPOs, accretion disk, msr 1999, emission spectra, lomb-scargle algorithm power, double peaks, kenyon 1997, biased blue, algorithm power, lomb-scargle algorithm, observations msr, watson king, yi kenyon 1997,
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