Lunar occultation observations of PKS 1514-24 (= AP Lib)

Abstract

The radio source PKS 1514-24 was found by Biraud and Bond to be associated with the optical object AP Lib which was discovered by Ashbrook3 as an irregular variable star. It has, however, been classified as an N-type galaxy by Westerlund and Wall, a classification supported by its appearance and UBV colours. In its rapid and erratic variability and in its optical spectrum, which shows no emission lines, it resembles the peculiar variable object BL Lac (= VRO 42.22.01). Further, Frye et al. have now detected a discrete source of high energy î³-rays, possibly identified with AP Lib. The radio-optical association of the object has recently been placed on a firm footing by Hunstead8 on the basis of an accurate determination of the radio position at 408 MHz with the Molonglo cross radio telescope and an accurate measurement of the optical position from the Palomar Sky Survey. Hunstead's observations indicated that the radio and optical positions did not actually coincide; the observed difference of about 4.9 arc s in right ascension was significantly larger than the combined radio and optical position errors. Lunar occultation observations of PKS 1514-24 made with the Ooty radio telescope on February 18, 1971, however, indicate a radio position which does not agree with that determined by Hunstead. We find that most of the radio emission arises in a region coincident with the optical position measured by Hunstead. From the occultation we have also been able to study its radio structure with a resolution of 1 arc s.