The Lunar Orbital VLBI Experiment (LOVEX) is a scientific component of the Chinese Lunar Exploration Project (CLEP) Chang’E-7. The spaceborne component of LOVEX is implemented onboard the relay satellite QueQiao-2, which was launched on 20 March 2024, and later placed into an elliptical selenocentric orbit. The LOVEX-specific payload consists of an X-band cryogenic receiver, a hydrogen maser frequency standard, and VLBI data formatting and acquisition electronics. Several components of the QueQiao-2 nominal onboard instrumentation, such as the 4.2-m antenna, the data storage device, and the downlink communication system, contribute to the overall spaceborne VLBI instrumentation. This allows us to form a space radio telescope capable of co-observing with Earth-based radio telescopes in VLBI mode. In this space VLBI system, the length of the baseline extends up to approximately 380000 km. This paper presents the LOVEX scientific objectives, architecture, instrumentation, prelaunch tests, in-flight verification and calibration, and the first in-flight detections of interferometric response (“fringes”) achieved through observations of the quasar AO 0235+164 and the Chang’E-6 orbital module, positioned at the Sun-Earth Lagrange point L2. These initial results demonstrate the successful performance of LOVEX, verifying its capability for both astronomical and spacecraft tracking observations at ultra-long VLBI baselines.

High-mass stars, born in massive dense cores (MDCs), profoundly affect the cosmic ecosystem through feedback processes and metal enrichment, yet little is known about how MDCs assemble and transfer mass across scales to form high-mass young stellar objects (HMYSOs). Using multiscale [40 to 2500 astronomical units (au)] observations of an MDC hosting an HMYSO, we identify a coherent dynamical structure analogous to barred spiral galaxies: three ~20,000 au spiral arms feed a ~7500 au central bar, which channels gas to a ~2000 au pseudodisk. Further accretion proceeds through the inner structures, including a Keplerian disk and an inner disk (~100 au), which are thought to be driving a collimated bipolar outflow. These multiscale structures (spiral arms, bar, streamers, envelope, disk, and outflow) have been simultaneously observed as a physically coherent structure within an MDC. Our discovery suggests that well-organized hierarchical structures play a crucial role during the gas accretion and angular momentum buildup of a massive disk.

The positions of millisecond pulsars (MSPs) can be determined with sub-milliarcsecond (mas) accuracy using both Very Long Baseline Interferometry (VLBI) and timing, referenced to the International Celestial Reference Frame (ICRF) and planetary ephemerides frame, respectively, representing kinematic and dynamical reference frames. The two frames can be connected through observations of common celestial objects, MSPs observed with VLBI and timing. However, previous attempts to establish this connection were unreliable due to the limited number of MSPs observed by both techniques. Currently, 23 MSPs have been precisely measured using both multiple timing and VLBI networks. Among them, 17 MSPs are used to link the two reference frames, marking a significant three-fold increase in the number of common MSPs used for frame linking. Nevertheless, six MSPs located near the ecliptic plane are excluded from frame linkage due to positional differences exceeding 20 mas measured by VLBI and timing. This discrepancy is primarily attributed to errors introduced in fitting positions in timing methods. With astrometric parameters obtained via both VLBI and timing for these MSPs, the precision of linking DE436 and ICRF3 has surpassed 0.4 mas. Furthermore, thanks to the improved timing precision of MeerKAT, even with data from just 13 MSPs observed by both MeerKAT and VLBI, the precision of linking DE440 and ICRF3 can also exceed 0.4 mas. The reliability of this linkage depends on the precision of pulsar astrometric parameters, their spatial distribution, and discrepancies in pulsar positions obtained by the two techniques. Notably, proper motion differences identified by the two techniques are the most critical factors influencing the reference frame linking parameters. The core shift of the calibrators in VLBI pulsar observations is one of the factors causing proper motion discrepancies, and multi-wavelength observations are expected to solve it. With the improvement in timing accuracy and the application of new observation modes like multi-view and multi-band observations in VLBI, the linkage accuracy of the dynamical and kinematic reference frames is expected to reach 0.3 mas.

In the optical band, very few pulsars can be directly detected, but some of the pulsar binary companions can be observed. This study leverages high-precision astrometric data from Gaia Data Release 3 (DR3) to identify pulsar companions in binary systems. Cross-matching the Australia Telescope National Facility (ATNF) Pulsar Catalogue with Gaia DR3 yielded 58 astrometric pairs, including 9 newly confirmed companions—primarily in the southern hemisphere—expanding the known pulsar distribution there. Among newly confirmed companions, eight are redback pulsars, offering insights into millisecond pulsar evolution and companion composition. All 58 companions are classified as main-sequence stars, neutron stars, white dwarfs, or ultra-light companion stars, with ∼40% being spider pulsars. Gaia’s exceptional astrometric precision advances pulsar studies, enabling gravitational wave detection via Pulsar Timing Arrays (PTAs) and improved reference frame link. Future multi-wavelength research will benefit from Gaia DR4, International Pulsar Timing Array (IPTA) collaborations (including Five-hundred-meter Aperture Spherical radio Telescope (FAST)), and Very Long Baseline Interferometry (VLBI) networks like the Chinese VLBI Network (CVN).

The surface accuracy of a radio telescope is directly related to its operational efficiency and detection sensitivity.This is crucial under high-frequency observation conditions,where surface shape errors need to be controlled to within 1/16 of the working wavelength.In addition,the primary reflector of large radio telescopes is subject to dynamic deformation,caused by factors such as gravity and thermal effects.This paper presents a method for detecting the surface shape of radio telescopes using radio interferometry techniques combined with active reflector adjustment technology.This enables accurate assessment and correction of surface errors,ensuring the electrical performance of the radio telescope.This study investigates the practical applications of high-precision measurement techniques,such as microwave holography,out-of-focus holography,and wavefront distortion methods at the Tianma 65 m radio telescope(TMRT).Furthermore,the study presents the construction method of gravity models at different elevation angles and demonstrates the efficacy of the active reflector model.The results of the measurements indicate that the application of these methods to the TMRT has led to a notable enhancement of the accuracy of the primary reflector and a substantial improvement in efficiency in the Q-band.Through a process of iterative measurements and adjustments,the surface shape error is ultimately reduced to 0.28 mm root mean square(RMS).

Abstract The determination of reference points for telescopes is crucial for obtaining the local‐tie vector for a multi‐technology co‐located station. Traditional methods suffer from labor‐intensive fieldwork, long execution cycles, and systematic errors due to the incident angle of the total station's laser beam on the prism. In this paper, we propose an algorithm aligning the prism pointing vector with the prism‐to‐total station vector and introduce a pan‐tilt platform and the Tianma VGOS telescope for sub‐millimeter unmanned reference point monitoring. Our results show that the prototype system based on the pan‐tilt achieves a formal error of ±100 μm (1σ) in reference point positions with just 2.5 hr of automated monitoring. The consistency of reference point positions is comparable to the local control network accuracy. Single‐direction observations may introduce a deviation of ±1 mm in the reference point compared to multiple direction observations. Preliminary experiments on the Tianma VGOS telescope have also shown that this system can efficiently automate the monitoring of prism scatter points (one measurement every minute) and achieve sub‐millimeter horizontal precision in reference point positions within a single day.

Extending geodetic and astrometric Very Long Baseline Interferometry (VLBI) observations from traditional centimeter wavebands to millimeter wavebands offers numerous scientific potentials and benefits. However, it was considered quite challenging due to various factors, including the increased effects of atmospheric opacity and turbulence at millimeter wavelengths. Here, we present the results of the first geodetic-mode VLBI experiment, simultaneously observing 82 sources at 22/43/88/132 GHz (K/Q/W/D bands) using the Korean VLBI Network (KVN). We introduced the frequency phase transfer (FPT) method to geodetic VLBI analysis, an approach for calibrating atmospheric phase fluctuations at higher frequencies by transferring phase solutions from lower frequencies. With a 2 minute scan, FPT improved the signal-to-noise ratio of most fringes, some by over 100%, thereby enhancing the detection rate of weak sources at millimeter wavebands. Additionally, FPT reduced systematic errors in group delay and delay rate, with the weighted root mean squares (WRMS) of the postfitting residuals decreasing from 25.0 to 20.5 ps at the W band and from 39.3 to 27.6 ps at the D band. There were no notable differences observed in calibrating atmospheric phase fluctuations at the K band (WRMS = 12.4 ps) and Q band (WRMS = 11.8 ps). This experiment demonstrated that the millimeter waveband can be used for geodetic and astrometric applications with high precision.

High-mass stars, born in massive dense cores (MDCs), play a major role in the cosmic ecosystem. Yet, little is known about how MDCs assemble their mass beyond ∼0.1 pc and transport their mass into smaller and denser seeds of stellar embryos (∼100 au) and finally onto HighMass Young Stellar Objects (HMYSOs), which is the key to understand the high-mass star formation processes. Leveraging multi-scale observations at 40–2500 au resolutions toward an MDC with at least one HMYSO associated, we discovered a dynamical system analogous to the barred spiral structures in galaxies. It shows three prominent ∼20,000 au long spiral arms feeding a bar-like elongated structure (∼7,500 au, hereafter denoted as “bar”) at the center. The “bar” further transports gas to a disk through gas streamers. The pseudodisk (>2,000 au) revealed in methanol thermal emission, the Keplerian disk (∼500 au) traced by Class II methanol masers, and the inner disk (∼100 au) traced by long-baseline (0.03 ′′ ) 1.3 mm continuum emission are misaligned. A collimated bipolar outflow is detected launching from the HMYSO. These dynamical features highlight the multi-scale mass accretion through well-organized hierarchical structures during the formation of HMYSOs. Our discovery manifests that this “spirals-bar-disk-outflow” complex exists not only in galaxies as a whole but also in the galactic localized regions where high-mass stars form. The structures and dynamics of galaxies could provide stimulating insights into high-mass star formation, and vice versa.

Chang'e-5 is the most complicated mission of Chinese lunar project. Many separations of several detectors and unmanned rendezvous and docking in lunar orbit are accomplished. During the course of separating and approaching of two detectors, the same-beam very long baseline interferometry (VLBI) observations are carried on. We firstly present the real-time positioning for multi-detectors and differential positioning of CE-5 ascender and combination of orbiter-returner, which is the more direct and quick method to charge the orbit status. The CE-5 mission first achieved the orbital maneuver of CE-5 orbiter-returner combination from the lunar gravity back to the Earth at the distance of lunar orbit. We use the method of instantaneous states reduction to monitor the twice orbital transfer from the lunar to the Earth in real time, and precisely present the status of orbital maneuver, which provides the important reference for the positioning and orbit determination in the future deep-space exploration.

This paper describes the method of using the optical telescope to assist the Tianma 13 m radio telescope for pointing measurement and establishing the pointing error correction model. For small-aperture telescopes, there are few target sources for pointing and calibration, and it is difficult to establish a pointing model by radio method to cover the whole sky area. The Tianma 13 m radio telescope of Shanghai Astronomical Observatory is used to conduct optical-assisted pointing measurement research. A set of optical pointing system was installed on the back frame of Tianma 13 m antenna, which obtained a repeatable measurement accuracy better than 3”. In addition, through the analysis of the factors affecting the antenna pointing, a pointing error correction model containing 8 error terms, as well as the optical axis and electrical axis deviation models were established. The pointing model was brought into the antenna servo control system to cross-scan the calibration target radio source, and a pointing error of about 5” was obtained. This research can provide a reference method for high-precision pointing modeling.

We report a trigonometric parallax measurement of 22 GHz water masers in the massive star-forming region G034.43+0.24 as part of the Bar and Spiral Structure Legacy (BeSSeL) Survey using the Very Long Baseline Array. The parallax is 0.330$\pm$50.018 mas, corresponding to a distance of $3.03^{+0.17}_{-0.16}$ 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 which cross nearly the full width of the arm. The measured 3-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.

嫦娥五号(Change'E-5,CE-5)着上组合体与上升器先后成功着陆于月面.两探测器承担的任务不同,着陆方式不同,因此月面位置解算方法不同.联合统一 X波段(united X-band,UXB)深空测距站及甚长基线干涉测量技术(very long baseline interferometry,VLBI)的测量数据计算两者的月面位置.采用联合统计定位方法得到CE-5着上组合体的月面位置.讨论分别基于数传与侧音差分单向测距(differential one-way ranging,DOR)两种信号对月面位置的影响.观测资料的时间跨度在一定程度上影响定位结果.采用多项式拟合的运动学统计定轨方法归算了上升器受控落月轨迹及落月位置,并与单点定位结果符合在40m内.根据相关处理机最后输出时刻推算得到精确至ms的上升器的落月时刻.

对2021 年VLBI(Very Long Baseline Interferometry)全球观测系统(VLBI Global Observing System,VGOS)单基线开展的1 h世界时(Universal Time,UT1)加强观测数据进行分析,结果表明,VGOS单基线测得的UT1 与IERS(International Earth Rotation Service)C04序列提供的UT1 之差的RMS(Root Mean Square)为25.3 μs,优于传统S/X双频段UT1加强观测(Intensive observation,INT1)试验的28.2 μs,且UT1的平均形式精度提高1倍.因VGOS单基线1 h观测数目比INT1多1倍,其测得的UT1受极移误差的影响更加稳定,每100 μas的极移误差将对UT1引入2.8μs的偏移.此外分析了VGOS 30 min观测数据,除平均形式精度变差外,UT1测量结果与1 h结果相当,表明VGOS单基线30 min观测可用于UT1的超快速服务.同时分析和评估了2021年国内佘山与南山13 m VGOS基线的UT1加强观测能力,统计得到8次观测的RMS为46.2μs,平均形式误差为17.7μs,相比佘山25 m和南山25 m天线的S/X双频观测有显著提升.

We report the results of position ties for short baselines at eight geodetic sites based on phase delays that are extracted from global geodetic very‐long‐baseline interferometry (VLBI) observations rather than dedicated short‐baseline experiments. An analysis of phase delay observables at X band from two antennas at the Geodetic Observatory Wettzell, Germany, extracted from 107 global 24‐hr VLBI sessions since 2019 yields weighted root‐mean‐square scatters about the mean baseline vector of 0.3, 0.3, and 0.8 mm in the east, north, and up directions, respectively. Position ties are also obtained for other short baselines between legacy antennas and nearby, newly built antennas. They are critical for maintaining a consistent continuation of the realization of the terrestrial reference frame, especially when including the new VGOS network. The phase delays of the baseline WETTZ13N – WETTZELL enable an investigation of sources of error at the sub‐millimeter level. We found that a systematic variation of larger than 1 mm can be introduced to the Up estimates of this baseline vector when atmospheric delays were estimated. Although the sub‐millimeter repeatability has been achieved for the baseline vector WETTZ13N – WETTZELL , we conclude that long term monitoring should be conducted for more short baselines to assess the instrumental effects, in particular the systematic differences between phase delays and group delays, and to find common solutions for reducing them. This will be an important step toward the goal of global geodesy at the 1 mm level.

China is planning to launch a relay satellite in the coming years with a payload for the Earth–Moon very-long-baseline interferometer observation research and scientific applications, known as the lunar orbit very-long-baseline interferometry (VLBI) experiment (LOVEX) system. This system will perform the LOVEXs for in the world, and will improve the accuracy of planetary spacecraft orbit determination and the scientific observation capabilities of astrophysics and astrometry. Prior to launch, key technologies of the system must be verified, so we have established a LOVEX ground validation system with similar performance to the LOVEX system. The LOVEX ground validation system consists of a 4.5-m ring-focus antenna, $X$ -band receiver, frequency converter and digital backend, hydrogen maser, and monitoring and control software. Using this system, we have successfully conducted VLBI differential observation experiments with the Shanghai 65 m radio telescope and Beijing 50 m radio telescope. The experimental results show that, after calibration with NRAO150, the standard deviations (STDs) of delay error of Tianwen-1 are within 0.5 ns, consistent with the theoretical timing accuracy, verifying the feasibility of the LOVEX time-delay calibration.

This article mainly discusses the compatibility of satellite navigation and radio astronomy services as well as the simulation and measurement analysis based on the Tianma 65-m radio telescope's response to the interference signals from a navigation satellite. First, the frequency division of satellite navigation and radio astronomy services are introduced in the CN frequency band. Then, the sensitivity and interference thresholds of radio astronomy observation are estimated. This paper mainly describes the antenna pattern, interference simulation calculation method, and the performance advantages of the Tianma 65-m radio telescope. The solution methods are introduced in detail. Finally, the measurement results show that the noise temperature generated by the sidelobe response of the Tianma 65-m radio telescope to the interference signals from the navigation satellite is <1/10 of the antenna system noise temperature. Furthermore, the differences between the simulation and measurement are thoroughly examined.

射电望远镜的热膨胀是大地测量和天体测量VLBI(甚长基线干涉测量)数据分析中不可忽视的影响因素.为了研究天马13.2 m VGOS(VLBI全球观测系统)射电望远镜热膨胀,开发了一套监测系统,可自动和实时地监测天线结构的热形变.通过连续观测安装在天线方位轴上、距离参考点正下方1.5 m的靶标,监测系统可以确定棱镜的三维位置变化.通过从2020年11月10日至2021年8月31日的连续监测,发现10个月内棱镜高度最大变化为2.6 mm,一天之内最大变化为0.2 mm;10个月内棱镜在水平方向上的位移为0.1 mm.最后,利用天马VGOS的高度热形变验证了 IERS(国际地球自转服务)热膨胀模型,结果表明它们之间的残差小于1.5 mm,残差的RMS为0.43 mm.该结果可以满足当前常规的VLBI测量,但不能满足VGOS的精度要求.因此,对于VGOS天线,需要重新考虑IERS热膨胀模型.

The thermal expansion of radio telescopes has been recognized as a significant systematic error in Very Long Baseline Interferometry (VLBI) data analysis. Although the thermal expansion model recommended by International Earth Rotation Service (IERS) Conventions 2010 can achieve millimeter accuracy for the International VLBI Service for Geodesy and Astrometry (IVS) routine telescopes, both the International Terrestrial Reference Frame 2020 (ITRF2020) in preparation and the VLBI2010 project encourage the scientific community to reconsider its modeling. To this end, we developed a monitoring system for the Tianma 13.2 m VLBI Global Observing System (VGOS) telescope. Based on the observed data, we refined the IERS expansion model, with results showing that the accuracy of our modified model was improved by 1.9 times. It suggested that the IERS thermal expansion model can achieve the declared millimeter accuracy, and refining its modeling can meet the requirement of 0.3 mm rms stability of the VGOS antenna reference point for the VLBI2010 project.

ΔDOR测量是一种应用于深空探测中的差分VLBI技术,通过对探测器和射电源的测量结果进行差分处理,从而减弱或消除传播介质、台站设备、时钟等引起的测量误差.目前我国ΔDOR测量的相关后处理中,有以首颗射电源作为参考源和邻近射电源作为参考源的两种不同时延修正方法.利用对嫦娥四号实时任务期间VLBI测量数据对这两种方法进行研究分析,得到两者的时延结果相差在2ns以内,且存在随时间变化的趋势;通过对基线时延闭合差以及定轨残差进行分析发现,相较于首颗射电源修正的方法,邻近源修正存在一定优势.

The absolute position of Sgr A*, the compact radio source at the center of the Milky Way, had been uncertain by several tens of milliarcseconds. Here we report improved astrometric measurements of the absolute position and proper motion of Sgr A*. Three epochs of phase-referencing observations were conducted with the Very Long Baseline Array for Sgr A* at 22 and 43 GHz in 2019 and 2020. Using extragalactic radio sources with submilliarcsecond-accurate positions as reference, we determined the absolute position of Sgr A* at a reference epoch 2020.0 to be at α (J2000) = 17 h 45 m 40.ˢ032863 ± 0.ˢ000016 and δ (J2000) = − 29 ° 00 ′ 28 .″ 24260 ± 0.″00047, with an updated proper motion −3.152 ± 0.011 and −5.586 ± 0.006 mas yr −1 in the easterly and northerly directions, respectively.