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Astron. Astrophys. 335, 991-994 (1998)

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5. Conclusions

On the basis of luminosity, colour and timing we conclude that neither of the proposed optical counterparts are the pulsar PSR B1951+32.

We note that the slight blue extension to candidate 1 shows the expected characteristics of a hot object. We would not expect to be sensitive to thermal radiation from the neutron star surface itself, as we estimate that a pulsar with T [FORMULA] K at the distance of CTB 80 would have a magnitude in the range [FORMULA]=30-31. We may, however, be able to see emission from any hot circumstellar material.

From phenomenological models of pulsar optical emission (Pacini & Salvati 1983, 1987) we can derive estimated magnitudes for the emission. For PSR 1951+32 this leads to values in the range 24-26. However recent observations of other middle-aged pulsars, 0656+14 and Geminga (Caraveo et al. 1994, Shearer et al. 1998), have indicated a magnitude considerably in excess of that predicted by the Pacini and Salvati model. It is clearly very important to establish a positive optical identification for PSR B1951+32 in order to compare emission from pulsars of similar ages but with a range of other parameters such as [FORMULA] and magnetic field. These observations will be crucial if we are to distinguish between the various models for high-energy emission. In particular, the pulse shape and fraction can be used to differentiate the polar cap and outer gap models.

We suggest observations with the VLT, Keck or the HST in order to definitively identify the optical counterpart of PSR B1951+32.

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© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998