VLBA determination of the distance to nearby star-forming regions VI.
  The distance to the young stellar object HW 9 in Cepheus A
  Using the Very Long Baseline Array (VLBA), we have observed the radio
continuum emission from the young stellar object HW 9 in the Cepheus A
star-forming region at ten epochs between 2007 February and 2009 November. Due
to its strong radio variability, the source was detected at only four of the
ten epochs. From these observations, the trigonometric parallax of HW 9 was
determined to be $\pi$ = 1.43 $\pm$ 0.07 mas, in excellent agreement with a
recent independent VLBA determination of the trigonometric parallax of a
methanol maser associated with the nearby young stellar source HW 2 ($\pi$ =
1.43 $\pm$ 0.08 mas). This concordance in results, obtained in one case from
continuum and in the other from line observations, confirms the reliability of
Very Long Baseline Array trigonometric parallax measurements. By combining the
two results, we constrain the distance to Cepheus A to be 700$_{-28}^{+31}$ pc,
an uncertainty of 3.5%.
