On the Wind from the Small Magellanic Cloud B1 V Companion to PSR J0045-7319

We report on multifrequency radio timing observations of the unique binary pulsar PSR J0045 - 7319, the only known radio pulsar in the Small Magellanic Cloud. Observations made at epochs near periastron and apastron, when the pulsar was at distances of 4 and 34 stellar radii from its B 1 V star companion, respectively, reveal no significant frequency dependence of the observed pulse-arrival times, implying a 3 a upper limit to variations of the integrated electron density along the line of sight of ADM <0.9 pc cm -3. Using simple geometric arguments we infer a 3 a upper limit to the ionized component of the B-star mass outflow of A < 3.4 x 10 ¹¹(V /Vesc) M_{0 }yr 1 This is the first constraint on a main-sequence B-star wind in the SMC and provides evidence in favor of the predicted metallicity dependence of models of radiation-driven winds in luminous stars....