VLBA determination of the distance to nearby star-forming regions VI. The distance to the young stellar object HW 9 in Cepheus A

TL;DR

This study uses VLBA radio observations to precisely measure the distance to the Cepheus A star-forming region, confirming the reliability of VLBA parallax measurements and refining the distance estimate to about 700 parsecs.

Contribution

The paper presents a new VLBA parallax measurement of HW 9 and confirms its consistency with previous measurements, improving the accuracy of the Cepheus A distance estimate.

Findings

Parallax of HW 9 is 1.43 ± 0.07 mas.

Distance to Cepheus A is 700_{-28}^{+31} pc.

VLBA measurements are reliable for star-forming region distances.

Abstract

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%.