Simultaneous radio and optical observations of UV Ceti-type flare stars

The UV Ceti-type stars, YZ Canis Minoris, AD Leonis, and Wolf 424 AB, were monitored for 57.8 hours from January 15 to February 22, 1974, using the 1000-foot (305-m) radio telescope at Arecibo, Puerto Rico, and the 91-cm or 76-cm reflector at McDonald Observatory. Radio observations were made at frequencies of 430, 318, and 196 MHz, and optical monitoring was done in the Johnson U or B band, the Stromgren u band, or white light. During the period of simultaneous observations, 62 optical flares were detected. A total of 13 RF flares were independently identified, of which 10 reached maximum flux within 10 min of the peak time of an optical flare. Using times of optical-flare events as reference data, an additional 15 cases of radio enhancements associated with optical flares are identified. The most probable delay interval between the optical-flare maximum and 318-MHz radio peak was found to be 0 to 5 min, with the optical flare occurring first. Aside from this statistical delay of peak occurrence and a general tendency for radio and optical flares to be associated, no systematic correlations of optical and radio amplitudes or morphology were found. The possible consequences of the radio emission's being due to a coherent process are discussed.