On the rapidly variable circular polarization of HR 1099 at radio frequencies

Abstract

view Abstract Citations (66) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the rapidly variable circular polarization of HR 1099 at radio frequencies. Brown, R. L. ; Crane, P. C. Abstract We studied the very rapid variations in total flux density and circular polarization of HR 1099 at 2695 and 8085 MHz during the outburst of February 1978. From these observations we find the following. (1) The flux density and the activity (percent variation) at 8085 MHz are greater than at 2695 MHz-the radio spectrum has a positive slope, S Va with a >0. (2) Often the radio emission is circularly polarized at both frequencies, although the polarity may be different at the two frequencies. (3) The degree of circular polarization is generally greater at 2695 MHz than it is at 8085 MHz; we find the degree of polarization at 2695 MHz to be as high as 40%. (4) During active periods of several hours duration we see changes factor of 2 in flux density at 2695 MHz that are wholly confined to one sense of circular polarization-the activity is altogether absent in the opposite polarity. (5) During two distinct epochs when the circular polarization at 2695 MHz was large, we find evidence for a characteristic sinusoidal modulation of the left circular flux density with a period of 4 min; this modulation appears to recur at intervals of 4.5-5.5 min. (6) Large degrees of circular polarization ( 10%) occur only when the phase of the HR 1099 binary system is near zero, that is, at conjunction with the more active component in front. These data support the conclusion that the radio emission is gyrosynchrotron radiation emitted by energetic electrons that are injected into an ordered magnetic field. The correlation of the degree of circular polarization with orbital phase when the source is active suggests that the magnetic field is a property of the binary system-it is shared by two stars. In contrast, the lack of correlation of radio flux density with orbital phase, together with the apparent correlation of radio activity with chromospheric events present in the more massive star in the HR 1099 system noted by Weiler et al. [Astrophys. J. (in press)], suggests that the energetic electrons are accelerated by the active star, not by a property of the binary system per se. The observed character of the radio emission from HR 1099 appears most analogous to that of solar microwave events in which the regions of opposite polarity are spatially distinct parts of the same magnetic structure. We suggest that a similar separation prevails in HR 1099 and is most pronounced when the binary is observed at conjunction. Publication: The Astronomical Journal Pub Date: December 1978 DOI: 10.1086/112352 Bibcode: 1978AJ.....83.1504B Keywords: Binary Stars; Circular Polarization; Radiant Flux Density; Radio Emission; Radio Stars; Stellar Radiation; Polarization Characteristics; Radio Bursts; Stellar Magnetic Fields; Astrophysics; Polarization:RS CVn Binaries; Radio Radiation:RS CVn Binaries; RS CVn Binaries:Synchrotron Radiation full text sources ADS | data products SIMBAD (1)