SIMBAD references

The Parkes radio telescope has been used to study maser emission from the 13441-MHz transition of highly excited OH. The targets were 56 catalogued sites of 6035-MHz maser emission. Eight 13441-MHz maser sites were detected, six of them new and two that had previously been reported. This more than doubles the number now known to 11.

At every 13441-MHz maser site, spectral features occur as right- and left-hand circularly polarized matched pairs, with small, but mostly significant, frequency separation. This is attributed to the Zeeman effect in magnetic fields of a few mG. Some of the 13441-MHz maser sites show features at several different velocities.

All of the 13441-MHz maser features have 6035-MHz counterparts that closely correspond in velocity. At three sites, features of 13441-MHz emission rival the intensities of their 6035-MHz counterparts; at the other sites, features are weaker than at 6035 MHz by factors of between 3 and 50. Upper limits at some sites searched can be set more than 2 orders of magnitude weaker than 6035-MHz emission. The detection statistics provide unique opportunities to test recent advances in maser modelling.

A search for the 13434-MHz transition towards the same 56 targets yielded no detections.