The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration

Abstract

We report astrometric results of VLBI phase-referencing observations of 22 GHz \hho\ masers emission toward the red hypergiant \vxsgr, one of most massive and luminous red hypergiant stars in our Galaxy, using the Very Long Baseline Array. A background source, \Jtwoze, projected 4\d4 from the target \vxsgr, was used as the phase reference. For the low declinations of these sources, such a large separation normally would seriously degrade the relative astrometry. We use a two-step method of tropospheric delay calibration, which combines the VLBI geodetic-block (or GPS) calibration with an image-optimization calibration, to obtain a trigonometric parallax of $0.64\pm 0.04$ mas, corresponding to a distance of 1.56${}_{-0.10}^{+0.11}$ kpc. The measured proper motion of \vxsgr\ is $0.36\pm 0.76$ and $-2.92\pm 0.78$ \masy\ in the eastward and northward directions. The parallax and proper motion confirms that \vxsgr\ belong to the Sgr OB1 association. Rescaling bolometric luminosities in the literature to our parallax distance, we find the luminosity of \vxsgr~is $(1.95\pm 0.62)\times 10^5$ \Lsun, where the uncertainty is dominated by differing photometry measurements.

arXiv comment16 pages, 10 figures, accepted by ApJ

References in corpus (16)

• Validation of the new Hipparcos reduction
• The SIMBAD astronomical database
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• DiFX: A software correlator for very long baseline interferometry using multi-processor computing environments
• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles - II. CO line survey of evolved stars: derivation of mass-loss rate formulae
• The mass-loss rates of red supergiants and the de Jager prescription
• The Proper Motion of SgrA*: I. First VLBA Results
• Trigonometric Parallaxes of Massive Star Forming Regions: I. S 252 & G232.6+1.0
• Trigonometric Parallax of W51 Main/South
• Micro-Arcsecond Radio Astrometry
• Astrometric accuracy of phase-referenced observations with the VLBA and EVN
• Distance to VY Canis Majoris with VERA
• VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphere
• Distance and Proper Motion Measurement of the Red Supergiant, S Persei, with VLBI H2O Maser Astrometry
• The Distance and Size of the Red Hypergiant NML Cyg from VLBA and VLA Astrometry
• Techniques for Accurate Parallax Measurements for 6.7-GHz Methanol Masers

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