The time dependent radio sources in cepheus A

Extract

The radio object Cepheus A is a known region of star formation, in a region of very heavy optical obscuration. It has been observed at the VLA since 1980, and is known to consist of 2 lines of about 13 objects. In particular, the central region has been monitored since 1988, at L, C, and U-band, with resolutions of 1″.0, 0″.3 and 0″.1, corresponding to linear resolutions of 700, 200 and 70 au. The presence of a highly variable Source 8 had been known since 1980, and was known to appear and disappear in a period of less than 1 year. However, a new and much more intense Source 9 was seen 1988 November 2. Over the period 1990 March 13 – 1990 May 8, it showed increases in flux density at C-band by a factor of nearly six times over a period of 50 days. Spectra have been obtained, and show that the flux density peaks at about 5 × 10⁹ Hz, and an increase in flux density is accompanied by an increase in the frequency of the peak. The variable sources are not resolved at 0.″1 at U-Band. This strongly suggests gyrosynchrotron emission from a region of size ~ 1 au, magnetic field ~ 100 G, temperature ~ 10⁸ K and density ~ 10⁶ cm^–3. The variations in flux density are then due to increases in magnetic field, as might occur if the source were a protostar, or pre-main sequence star, which is rotating and shedding its magnetic field, by converting magnetic flux energy into particle energy. This would provide also a mechanism for molecular outflows. The observations and model will be described.