A reassessment of the kinematics of PV Cephei based on accurate proper motion measurements

Abstract

We present two Very Large Array observations of the pre-main-sequence star PV Cephei, taken with a separation of 10.5 years. These data show that the proper motions of this star are $\mu_\alpha \cos \delta = +10.9 \pm 3.0$ mas yr$^{-1}$; $\mu_\delta = +0.2 \pm 1.8$ mas yr$^{-1}$, very similar to those -previously known- of HD 200775, the B2Ve star that dominates the illumination of the nearby reflection nebula NGC 7023. This result suggests that PV Cephei is not a rapidly moving run-away star as suggested by previous studies. The large velocity of PV Cephei had been inferred from the systematic eastward displacement of the bisectors of successive pairs of Herbig Haro knots along its flow. These systematic shifts might instead result from an intrinsic dissymmetry in the ejection mechanisms, or from an asymmetric distribution of the circumstellar material.