OH emission from early-type emission-line stars with large infrared excesses

Abstract

Results are presented for a search for ground-state OH emission from 23 early-type emission-line stars with large infrared excesses. The objects were searched at 1612, 1665 and 1667 MHz with the 300-m Arecibo telescope. One new object, Vy 2-2, was detected, and the results of Fix and Mutel (1977) for the peculiar OH source M 1-92 have been confirmed. The 1612-MHz profile for Vy 2-2 displays a single strong asymmetric feature about 10 km/s wide. Vy 2-2 is also an infrared source and a thermal radio continuum source, and has been classified as a planetary nebula of stellar appearance. If the latter classification is correct, it is the first planetary nebula detected in OH. The association of 1612-MHz OH emission and the infrared spectrum suggest that the pump mechanism for Vy 2-2 is far-infrared radiation. Vy 2-2 may represent a planetary nebula in the process of formation. The bipolar nebula M 1-92 has remained unchanged in intensity since 1973. Its evolutionary state is not known. The stars HK Ori and Lk H-alpha 208, suggested as possible weak OH emitters by Lepine and Nguyen-Quang-Rieu (1974), were not detected.