Astrometry of OH/IR stars using 1612 MHz hydroxyl masers. I. annual parallaxes of WX Psc and OH138.0+7.2

G. Orosz, H. Imai, R. Dodson, Maria J. Rioja , S. Frey, R. A. Burns, S. Etoka, A. Nakagawa, H. Nakanishi, Y. Asaki, S. R. Goldman, D. Tafoya

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Abstract

We report on the measurement of the trigonometric parallaxes of 1612 MHz hydroxyl masers around two asymptotic giant branch stars, WX Psc and OH 138.0+7.2, using the NRAO Very Long Baseline Array with in-beam phase referencing calibration. We obtain a 3σ upper limit of ≤5.3 mas on the parallax of WX Psc, corresponding to a lower limit distance estimate of ≳190 pc. The obtained parallax of OH 138.0+7.2 is 0.52 ±0.09 mas (±18%), corresponding to a distance of 1.9-0.3 +0.4, making this the first hydroxyl maser parallax below one milliarcsecond. We also introduce a new method of error analysis for detecting systematic errors in the astrometry. Finally, we compare our trigonometric distances to published phase-lag distances toward these stars and find a good agreement between the two methods.

Original languageEnglish
Article number119
Number of pages13
JournalAstronomical Journal
Volume153
Issue number3
DOIs
Publication statusPublished - 1 Mar 2017

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