| 其他摘要 | VLBI (Very Long Baseline Interferometry) is widely used in the field of astrometry, and its high-resolution characteristics enable it to play an important role in various precise astrometry. The celestial reference frame established based on high-precision astrometric measurements plays a crucial role in various fields such as astrophysics, geodesy, and deep space exploration. It serves as a fundamental basis for astronomical research and is of great importance. The International Celestial Reference Frame (ICRF) is established based on the radio positions of extragalactic radio sources obtained through VLBI observations, defining a quasi-inertial reference frame with the origin at the center of the Sun. The reference frame based on the Gaia optical satellite (Gaia Celestial Reference Frame, GCRF) and the ICRF based on VLBI observations are inevitably slightly different due to various reasons. The radio reference frame (ICRF) and Gaia Optical Reference Frame (GCRF) must be able to have the same concept under the International Celestial Spherical Reference System (ICRS). To link these two reference frames, celestial objects that emit radiation in both the optical and radio bands are typically utilized. Quasars are employed for faint sources, while radio stars are used for brighter sources. Quasars exhibit lower positional accuracy in the optical band and significant positional deviations that vary over time. These deviations are usually caused by various factors, such as contamination from background galaxies, binary systems, and the jet structures within quasars themselves. Since these deviations are difficult to eliminate through other means, therefore, in the bright regime, radio stars become the best candidates for verifying the consistency of GCRF and establishing the link between the optical and radio reference frames. In order to use radio stars to link the two reference frames, this work first selected the American Very Long Baseline Array (VLBA) in the phase-referencing mode to observe two strong radio stars HD199178 and AR Lacertae (hereinafter referred to as AR Lac); 6 epochs of observations carried out in one year, each epoch is 10 hours, including a geodesic block to reduce tropospheric errors; in order to reduce systematic errors caused by calibrators, each radio star has two calibrators; after data processing, this work obtained the offsets of the two radio stars relative to the reference position, and fitted their proper motions and parallaxes. The measured parallax of HD 199178 is 8.949 ± 0.059 mas and the proper motion is 𝜇 𝛼 cos 𝛿 = 26.393 ± 0.093 and 𝜇 𝛿 = −0.950 ± 0.083 mas yr −1 , while the parallax of AR Lac is 23.459 ± 0.094 mas and the proper motion is 𝜇 𝛼 cos 𝛿 = −51.906 ± 0.138 and 𝜇 𝛿 = 46.732 ± 0.131 mas yr −1 . The VLBI measured astrometric parameters of this work have accuracies about 4-5 times better than the corresponding historic VLBI measurements and comparable accuracies with those from Gaia; this work also gives The fluxes of each epoch of the two radio stars; for the close eclipse binary star AR Lac, this work also suspected to have detected its orbital motion. Then, the piggy-back phase-referencing observation mode which carried by the geodetic observation in the IVS (International VLBI Service for Geodesy and Astrometry) and Australia’s LBA (Long Baseline Array), and also the snapshot mode of the LBA, are used to analyze the 27 radio stars located in the southern celestial sphere. 11 of them were detected, and the images and rough fluxes estimation of the 11 radio stars were carried out, and their single-epoch coordinates and errors were given as well. Finally, this study attempted to link the radio and optical reference frames using the astrometric five-parameter data of HD199178 and AR Lac, along with single-epoch data from 11 other radio stars. The results showed that the use of multi-epoch highprecision astrometric measurements of HD199178 and AR Lac significantly improved the linking effect in terms of both orientation and spin parameters, with an approximate 25% increase in accuracy along the Y-axis. However, the single-epoch data of the 11 radio stars provide limited improvement in the accuracy of the linking results. This work explores the use of VLBI phase-referencing mode to observe radio stars, obtains the precise astrometric data of 2 radio stars, and obtains the rough coordinates and flux information of 11 radio stars, and gives the approximate lower limit of the flux of radio stars observed by LBA, which lays a certain foundation for the subsequent enrichment of the radio star sample and the follow-up observations of multiple epochs. |
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