2015 Seminar List:
We present results of the Very Long Baseline Array (VLBA) observations of 22 GHz H2O and 43 GHz SiO masers toward the protoplanetary nebula OH 231.8+4.2. Our observations were carried out at 4 epochs over 1 year in order to measure an accurate distance and proper motions of OH 231.8+4.2. Based on astrometric monitoring for 1 year, we detected an annual parallax of OH 231.8+4.2 to be 0.65 \pm 0.01 mas, corresponding to a distance of 1.54 (+0.02/-0.01) kpc.
The measured proper motion of OH 231.8+4.2 is mu_x = -4.35 \pm 0.02 mas/yr eastward and mu_y = 0.71 \pm 0.59 mas/yr northward.
The spatial distribution of the H 2 O masers is consistent with that found in previous studies.
After removing the average proper motion of 1.4 mas/yr, corresponding to 10 km/s, the internal motions of the H2O maser spots indicate a bipolar outflow.