A SEARCH FOR THE OPTICAL COUNTERPART OF THE TRIPLE PULSAR SYSTEM PSR B1620-26 IN M4

摘要

We have performed photometry in B and V of the field of the triple system PSR B1620—26 in the globular cluster M4. Our images were taken with two two-dimensional imaging photon-counting detectors, which permitted deep exposures to be made without saturation. Photometry of the proposed optical counterpart of the second companion of PSR B1620—26 was obtained, yielding a magnitude V = 21.30 ± 0.08 and a color B — V = 1.32 ± 0.20. The color index has not been successfully determined previously. These values locate the counterpart on the main sequence of the cluster color-magnitude diagram and lead to a mass determination that is consistent with a 0.48 solar mass cluster main-sequence star.