RADIOFREQUENCY CONTINUUM EMISSION FROM EVOLVED STARS

The evolution of stars between the asymptotic giant branch (AGE) and p lanetary nebula phases was investigated by sensitive radio continuum o bservations of a sample of 21 evolved stars with high mass-loss rates and extended circumstellar envelopes, in a search for a newly formed c ompact planetary nebulae. Four were found: two (CRL 618 and IRAS 21282 +5050) are well-known young planetary nebulae while the other two (IRA S 17423-1755 and CRL 915, the ''Red Rectangle'') are new detections. T hese recent observations show that the radio frequency flux of CRL 618 continues to increase. The strength of the radio continuum emission f rom CRL 915 gives a type of B3 or earlier for the exciting star. Radio continuum emission was detected from four more stars in the sample at an intensity too weak to be due to compact planetary nebulae but too strong to be photospheric. These stars may have extended partially ion ized chromospheres.