[Previous] | [Session 45] | [Next]
B. M. Lewis (Arecibo Observatory)
Many color-selected IRAS sources have 1612\,MHz masers. That in 19566+3423 was a little unusual, in having the appearance of emanating from a double shell, each with a more or less normal aspect. It was first detected by Galt et al. (AJ 98, 2182), who monitored it for two years as a variable source of circularly polarised emission, though the general morphology of the spectrum was stable. It has mainline masers, and a strong water maser, but no detected SiO or CO. However, new Arecibo 1612, 1665 and 1667\,MHz spectra taken in April and September 1999 are dramatically different.
The 1612 MHz intensity is about a factor of three larger now. Moreover this is dwarfed by a factor of {~}30 increase in its 1665\,MHz intensity. But the unprecedented changes are in the velocity range of its emission, which has expanded from 16 to 42\,km/s in the 1612\,MHz line, and from 28 to 80\,km/s in the 1667\,MHz. Much of the extra OH emission is reminiscent of the gently rounded morphology seen in the 1667\,MHz spectrum of the proto planetary nebula, 18095+2704 (ApJ, 362, 634). But the original range of the 1612\,MHz emission is still characterized by 6-10 discrete features, only two of which coincide in velocity with ones from the discovery epoch. These spectra can be found at ftp://www.naic.edu/pub/publications/bml/19566.ps.Z
The 1667\,MHz velocity range rivals that from the hypergiant, IRC+10420, which has, however, always exhibited the same velocity range throughout the 24 years since it was discovered. 19566+3423 is probably a hypergiant or supergiant too, which may well have lost its present circumstellar shell in a sudden mass ejection event, rather than in a wind.