We have used deep high-resolution multiband images taken at the ESO Very Large Telescope to identify the optical binary companion to the millisecond pulsar (PSR J1911 - 5958A) located in the halo of the Galactic globular cluster NGC 6752. The object turns out to be a blue star whose position in the color-magnitude diagram is consistent with the cooling sequence of a low-mass (M similar to 0.17-0.20 M-.), low-metallicity helium white dwarf (He WD) at the cluster distance. This is the second He WD, with this mass, that has been found to orbit a millisecond pulsar in Galactic globular clusters. The anomalous position of PSR J1911 - 5958A with respect to the globular cluster center (similar to6') suggested that this system has recently (less than or similar to1 Gyr) been ejected from the cluster core as the result of a strong dynamical interaction. The data presented here allow us to constrain the cooling age of the companion within a fairly narrow range (similar to1.2 - 2.8 Gyr), therefore suggesting that such a dynamical encounter must have acted on an already recycled millisecond pulsar.
The helium white dwarf orbiting the millisecond pulsar in the halo of the globular cluster NGC 6752
D'AMICO, NICOLO'
2003-01-01
Abstract
We have used deep high-resolution multiband images taken at the ESO Very Large Telescope to identify the optical binary companion to the millisecond pulsar (PSR J1911 - 5958A) located in the halo of the Galactic globular cluster NGC 6752. The object turns out to be a blue star whose position in the color-magnitude diagram is consistent with the cooling sequence of a low-mass (M similar to 0.17-0.20 M-.), low-metallicity helium white dwarf (He WD) at the cluster distance. This is the second He WD, with this mass, that has been found to orbit a millisecond pulsar in Galactic globular clusters. The anomalous position of PSR J1911 - 5958A with respect to the globular cluster center (similar to6') suggested that this system has recently (less than or similar to1 Gyr) been ejected from the cluster core as the result of a strong dynamical interaction. The data presented here allow us to constrain the cooling age of the companion within a fairly narrow range (similar to1.2 - 2.8 Gyr), therefore suggesting that such a dynamical encounter must have acted on an already recycled millisecond pulsar.
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