First Trigonometric Parallax Measurements with the KVN and VERA Array (KaVA)
Abstract
To demonstrate the astrometric capability of the combined Korean VLBI (Very Long Baseline Interferometry) Network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA), we conducted six-epoch VLBI observations of 22-GHz H2O masers associated with the star-forming region W3(OH). Two atmospheric calibration methods, (1) GPS and (2) JMA (Japan Meteorological Agency) mesoscale analysis data, and two phase-reference sources were independently applied to the astrometric analysis. Trigonometric parallaxes of W3(OH) were successfully measured with all calibration strategies, including the first successful parallax measurement using JMA calibration. The combined-fit parallax is 0.497±0.024 mas, corresponding to a distance of 2.01+0.10−0.09 kpc. This value is consistent with the previous Very Long Baseline Array (VLBA) result of 0.489±0.017 mas. KaVA achieved a 55% higher signal-to-noise ratio in phase-referenced maps than VERA, in good agreement with theoretical expectations. These results suggest that KaVA will enable trigonometric parallax measurements of 22-GHz H2O masers that are difficult to observe with VERA alone because of low flux densities and/or limited uv coverage. A flux variation from 510\,±\,50 to 3900\,±\,400 Jy was detected in W3(OH) over a one-year observing campaign and is attributed to two nearby maser features separated by only ∼64 AU at 2.01 kpc. The brightest feature showed a decrease in linewidth with increasing peak flux density, consistent with unsaturated maser amplification, whereas no similar trend was found for the other feature, suggesting different responses to the same amplification conditions, possibly owing to differences in saturation state and internal velocity structure.
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BibTeX
@misc{sakai2026first,
title = {{First Trigonometric Parallax Measurements with the KVN and VERA Array (KaVA)}},
author = {Nobuyuki Sakai and Daisuke Sakai and Noriyuki Kawaguchi and Shuangjing Xu and Bo Zhang and Taehyun Jung and Chungsik Oh and Jeong-Sook Kim and Soon-Wook Kim and Hiroshi Imai and Yuanwei Wu and Maria Rioja and Niu Liu and Zehao Lin and Ibnu Nurul Huda and Shuaibo Bian and Leonid Petrov and Jingdong Zhang and Takaaki Jike and Yoshiaki Tamura and Jeong Ae Lee and Hao Ding and Koichiro Sugiyama and Kazuhiro Hada and Kiyoaki Wajima and Kazuya Hachisuka and Mareki Honma and Kee-Tae Kim and Se-Jin Oh},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.25300},
eprint = {2609.25300},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.25300},
}
RIS
TY - UNPB
TI - First Trigonometric Parallax Measurements with the KVN and VERA Array (KaVA)
AU - Nobuyuki Sakai
AU - Daisuke Sakai
AU - Noriyuki Kawaguchi
AU - Shuangjing Xu
AU - Bo Zhang
AU - Taehyun Jung
AU - Chungsik Oh
AU - Jeong-Sook Kim
AU - Soon-Wook Kim
AU - Hiroshi Imai
AU - Yuanwei Wu
AU - Maria Rioja
AU - Niu Liu
AU - Zehao Lin
AU - Ibnu Nurul Huda
AU - Shuaibo Bian
AU - Leonid Petrov
AU - Jingdong Zhang
AU - Takaaki Jike
AU - Yoshiaki Tamura
AU - Jeong Ae Lee
AU - Hao Ding
AU - Koichiro Sugiyama
AU - Kazuhiro Hada
AU - Kiyoaki Wajima
AU - Kazuya Hachisuka
AU - Mareki Honma
AU - Kee-Tae Kim
AU - Se-Jin Oh
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.25300
UR - https://arxiv.org/abs/2609.25300
AB - To demonstrate the astrometric capability of the combined Korean VLBI (Very Long Baseline Interferometry) Network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA), we conducted six-epoch VLBI observations of 22-GHz H_2O masers associated with the star-forming region W3(OH). Two atmospheric calibration methods, (1) GPS and (2) JMA (Japan Meteorological Agency) mesoscale analysis data, and two phase-reference sources were independently applied to the astrometric analysis. Trigonometric parallaxes of W3(OH) were successfully measured with all calibration strategies, including the first successful parallax measurement using JMA calibration. The combined-fit parallax is 0.497±0.024 mas, corresponding to a distance of 2.01^+0.10_−0.09 kpc. This value is consistent with the previous Very Long Baseline Array (VLBA) result of 0.489±0.017 mas. KaVA achieved a 55% higher signal-to-noise ratio in phase-referenced maps than VERA, in good agreement with theoretical expectations. These results suggest that KaVA will enable trigonometric parallax measurements of 22-GHz H_2O masers that are difficult to observe with VERA alone because of low flux densities and/or limited uv coverage. A flux variation from 510\,±\,50 to 3900\,±\,400 Jy was detected in W3(OH) over a one-year observing campaign and is attributed to two nearby maser features separated by only ∼64 AU at 2.01 kpc. The brightest feature showed a decrease in linewidth with increasing peak flux density, consistent with unsaturated maser amplification, whereas no similar trend was found for the other feature, suggesting different responses to the same amplification conditions, possibly owing to differences in saturation state and internal velocity structure.
ER -