Positions of Twenty-One Quasi-Stellar Objects

Abstract

Accurate positions have been determined for twenty-one quasi-stellar objects, which form the first set of objects for a proposed catalogue of optical positions. A tentative identification is given for OA 33. A program of photographic observations of quasi-stellar objects (QSOs) has been undertaken at the Yale University Observatory. This program includes a photometric patrol of bright QSOs and astrometric positional measurements of faint QSOs. A pro- posed positional catalogue of QSOs with an average accuracy of ± O'~'5 or better will provide a homogeneous system for two reasons: First, QSOs can be used as an astrometric frame of reference for proper-motion study of high galactic objects, if their redshifts represent cosmological distances. Second, it is of great interest to compare radio and optical positions in order to reveal systematic positional differences between the two systems. - The plate-overlap method has been employed for some objects which have been used for calibration of radio observation (LU 1968), where the accuracy is about O'~O7, or for some QSO fields that do not have sufficient reference stars. Photographic photometry extends oniy to objects brighter than 17 mag; optical variations of several QSOs have been reported by LU and Hunter (1969). In order to identify OA 33, all stellar objects in the neighborhood of radio positions were measured. A stellar object with a magnitude of about 19.5 coincided with the radio position (see Fig. 1, P1. Li). The physical importance of the identification of this object has been emphasized by Hogg and Roberts (1968). The procedures of observation and reduction were discussed by Lu (1969). Results for twenty-one QSOs are listed in Table 1

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