Search

We report a measurement of the trigonometric parallax of 22 GHz water masers in the massive star-forming region G034.43+0.24 as part of the Bar and Spiral Structure Legacy Survey using the Very Long Baseline Array. The parallax is 0.330 ± 0.018 mas, corresponding to a distance of 3.03 − 0.16 + 0.17 kpc. This locates G034.43+0.24 near the inner edge of the Sagittarius spiral arm and at one end of a linear distribution of massive young stars that cross nearly the full width of the arm. The measured three-dimensional motion of G034.43+0.24 indicates a near-circular Galactic orbit. The water masers display arc-like distributions, possibly bow shocks, associated with winds from one or more massive young stars. [ABSTRACT FROM AUTHOR]

We report Very Long Baseline Array observations of 22 GHz H2O and 43 GHz SiO masers toward the Mira variable RR Aql. By fitting the SiO maser emission to a circular ring, we estimate the absolute stellar position of RR Aql and find agreement with Gaia astrometry to within the joint uncertainty of ≈1 mas. Using the maser astrometry we measure a stellar parallax of 2.44 ± 0.07 mas, corresponding to a distance of 410 âˆ' 11 + 12 pc. The maser parallax deviates significantly from the Gaia EDR3 parallax of 1.95 ± 0.11 mas, indicating a 3.8 σ tension between radio and optical measurements. This tension is most likely caused by optical photocenter variations limiting the Gaia astrometric accuracy for this Mira variable. Combining infrared magnitudes with parallaxes for RR Aql and other Miras, we fit a periodâ€"luminosity relation using a Bayesian approach with Markov Chain Monte Carlo sampling and a strong prior for the slope of âˆ'3.60 ± 0.30 from the Large Magellanic Cloud. We find a K -band zero-point (defined at logP(days) = 2.30) of âˆ'6.79 ± 0.15 mag using very long baseline interferometry (VLBI) parallaxes and âˆ'7.08 ± 0.29 mag using Gaia parallaxes. The Gaia zero-point is statistically consistent with the more accurate VLBI value. [ABSTRACT FROM AUTHOR]