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1998ApJ...507..371M - Astrophys. J., 507, 371-383 (1998/November-1)
Radio emission from algol. I. Coronal geometry and emission mechanisms determined from VLBA and Green Bank interferometer observations.
MUTEL R.L., MOLNAR L.A., WALTMAN E.B. and GHIGO F.D.
Abstract (from CDS):
We also analyze Green Bank Interferometer (GBI) synoptic observations of right- and left-circularly polarized (RCP and LCP) flux densities of Algol at 2.3 and 8.3 GHz several times a day from early 1995 to mid-1997. The resulting data set, which consists of more than 2500 observations over 2 years, is by far the most comprehensive available for any stellar system. In addition, we analyzed GBI observations of the very similar (but noneclipsing) binary system HR 1099 over the same time period in order to compare the two systems. We summarize the GBI observations using several statistical descriptions. We find no phase dependence of either the radio luminosity or circular polarization for either system. The luminosity histograms for the two systems are remarkably similar. The distribution functions are not well represented by exponentials as previously suggested, but can be represented by power laws truncated at low luminosity. The cutoff occurs at 20-30 mJy and may represent emission from a slowly varying basal level that is always detected. We confirm several previous results, including the strong dependence of spectral index on luminosity, the decrease of fractional circular polarization with luminosity, and the dependence of fractional circular polarization on orbital inclination angle.
We suggest that the radio emission at 8.3 GHz is x-mode gyrosynchrotron emission from optically thin emission regions containing mildly relativistic electrons in a dipolar magnetic field. There is no evidence for highly circularly polarized coherent flares at 8.3 GHz, although it is possible that such flares occasionally occur at 2.25 GHz. The lack of orbital phase dependence in the GBI light curves, combined with the significant inclination of the VLBA structure with respect to the orbital plane, is inconsistent with previous models in which the radio lobes are located in the equatorial plane. The individual lobes seen in the VLBI maps may be associated with the polar regions, with the strong circular polarization resulting from the opposed mean magnetic field vector component along the observer's line of sight in opposite hemispheres.
Astrometric results from the VLBA observations are discussed in a companion paper.
Abstract Copyright: ∼
Journal keyword(s): Stars: Binaries: Eclipsing - Radiation Mechanisms: Nonthermal - Radio Continuum: Stars - Stars: Coronae - Stars: Imaging - Stars: Individual: Constellation Name: β Aurigae
CDS comments: Calibrator source 0309+410 not in SIMBAD
Simbad objects: 6
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