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20 pages, 701 KB

Open AccessArticle

Parallaxes and Proper Motions of Long Period Variable Stars Determined from VLBI and Gaia DR3

by Akiharu Nakagawa, Tomoharu Kurayama, Hiroshi Sudou and Gabor Orosz

Galaxies 2026, 14(2), 26; https://doi.org/10.3390/galaxies14020026 - 30 Mar 2026

Viewed by 784

Abstract

Annual parallaxes of Galactic long period variable stars (LPVs) are essential for determining their distances and intrinsic properties, but their measurement remains challenging because of their large stellar sizes, circumstellar matter, and time-variable surface brightness asymmetry. In this study, we compare astrometric measurements [...] Read more.

Annual parallaxes of Galactic long period variable stars (LPVs) are essential for determining their distances and intrinsic properties, but their measurement remains challenging because of their large stellar sizes, circumstellar matter, and time-variable surface brightness asymmetry. In this study, we compare astrometric measurements obtained from very long baseline interferometry (VLBI) and Gaia Data Release 3 (DR3) for 43 Galactic LPVs. The parallaxes from the two methods are generally consistent within uncertainties for about half of the sample, although Gaia DR3 parallaxes tend to be slightly smaller than the VLBI values. This is consistent with previously reported systematic offsets. The behavior of parallax uncertainties differs between the two techniques: VLBI parallax errors increase with increasing parallax, whereas Gaia DR3 errors remain nearly constant. Consequently, VLBI measurements are more effective for LPVs with parallaxes smaller than approximately 2 mas, corresponding to distances beyond 500 pc. Proper motions are also compared, showing general agreement with a 2-sigma dispersion of approximately 13 km s⁻¹, consistent with typical AGB outflow velocities. These results demonstrate the complementarity between VLBI and Gaia astrometry. We also find that the dispersion of parallax residuals becomes slightly larger for sources with pulsation periods around one year, suggesting a coupling of timescales between the stellar pulsation and the annual parallax. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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25 pages, 2977 KB

Open AccessArticle

Implementation of Deep Reinforcement Learning for Radio Telescope Control and Scheduling

by Sarut Puangragsa, Tanawit Sahavisit, Popphon Laon, Utumporn Puangragsa and Pattarapong Phasukkit

Galaxies 2025, 13(6), 137; https://doi.org/10.3390/galaxies13060137 - 17 Dec 2025

Viewed by 1216

Abstract

The proliferation of terrestrial and space-based communication systems introduces significant radio frequency interference (RFI), which severely compromises data acquisition for radio telescopes, necessitating robust and dynamic scheduling solutions. This study addresses this challenge by implementing a Deep Recurrent Reinforcement Learning (DRL) framework for [...] Read more.

The proliferation of terrestrial and space-based communication systems introduces significant radio frequency interference (RFI), which severely compromises data acquisition for radio telescopes, necessitating robust and dynamic scheduling solutions. This study addresses this challenge by implementing a Deep Recurrent Reinforcement Learning (DRL) framework for the control and dynamic scheduling of the X-Y pedestal-mounted KMITL radio telescope, explicitly trained for RFI avoidance. The methodology involved developing a custom simulation environment with a domain-specific Convolutional Neural Network (CNN) feature extractor and a Long Short-Term Memory (LSTM) network to model temporal dynamics and long-horizon planning. Comparative evaluation demonstrated that the recurrent DRL agent achieved a mean effective survey coverage of 475 deg²/h, representing a 72.7% superiority over the non-recurrent baseline, and maintained exceptional stability with only 1.0% degradation in median coverage during real-world deployment. The DRL framework offers a highly reliable and adaptive solution for telescope scheduling that is capable of maintaining survey efficiency while proactively managing dynamic RFI sources. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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11 pages, 936 KB

Open AccessArticle

ASKAP Detection of the Ultra-Long Spin Period Pulsar PSR J0901-4046

by Emil Lenc, Philip G. Edwards, Susmita Sett and Manisha Caleb

Galaxies 2025, 13(6), 131; https://doi.org/10.3390/galaxies13060131 - 1 Dec 2025

Viewed by 1209

Abstract

A radio source with a period of 75.88 s, suspected of being an ultra-long period pulsar, was discovered in 2020 with the MeerKAT radio telescope. Here, we report the detection of radio pulses from this object in multi-epoch ASKAP image data at frequencies [...] Read more.

A radio source with a period of 75.88 s, suspected of being an ultra-long period pulsar, was discovered in 2020 with the MeerKAT radio telescope. Here, we report the detection of radio pulses from this object in multi-epoch ASKAP image data at frequencies between 744 MHz and 1800 MHz and a search for pulses made in Murchison Widefield Array data at 154 MHz. The ASKAP detections pre-date and extend other published observations and so support the belief the pulsar emission has been persistent. The non-detection of the pulsar in MWA data is consistent with a recent report that the spectrum turns over at low frequencies. An ASKAP image of the field centred at 943 MHz confirms the MeerKAT detection of diffuse emission surrounding the pulsar. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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21 pages, 69632 KB

Open AccessArticle

A Morphological Identification and Study of Radio Galaxies from LoTSS DR2 II. Strange and Odd Morphology Extragalactic Radio Sources ‘STROMERSs’

by Tapan K. Sasmal, Soumen Kumar Bera, Xuelei Chen, Yougang Wang, Soumen Mondal and Taotao Fang

Galaxies 2025, 13(6), 128; https://doi.org/10.3390/galaxies13060128 - 14 Nov 2025

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Abstract

STRange and Odd Morphology Extragalactic Radio Sources (STROMERSs) is a new category of radio galaxies that shows extremely peculiar anatomy. A purely manual visual search is carried out for the identification of such interesting sources. We reported a total of 108 STROMERS sources [...] Read more.

STRange and Odd Morphology Extragalactic Radio Sources (STROMERSs) is a new category of radio galaxies that shows extremely peculiar anatomy. A purely manual visual search is carried out for the identification of such interesting sources. We reported a total of 108 STROMERS sources from the LOFAR Two-meter Sky Survey second data release (LoTSS DR2) at 144 MHz. The host galaxies are found ∼94% of the sources. We studied the radio and optical properties of the sources. Redshifts were found in 76% of sources with known host galaxies. The redshifts of STROMERS range from 0.0015 to 1.6599 and peak at 0.15. Among the reported STROMERS sources, there are 17 giant radio galaxies (GRG) with a linear size of greater than 700 kpc. Among them, only five GRGs are new, which is a small fraction of the population of GRGs from LoTSS DR2 data. The source ILTJ164117.44 +380208.4 has the highest linear size, approximately 1.8 Mpc. To study the reasons behind these interesting morphologies, we studied the galaxy cluster environment of each candidate within a 1 Mpc search radius. We found that 53% of STROMERS candidates are associated with cluster environments with known redshifts. The source ILTJ150956.65+332642.9 is associated with a high mass galaxy cluster Abell 2034 with mass a 7.57

\times 10^{14} M_{⊙}

. We also propose that the merger scenario is one of the reasons for the formation of STROMERS in the paper. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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20 pages, 7428 KB

Open AccessArticle

Reinforcement Learning-Driven Framework for High-Precision Target Tracking in Radio Astronomy

by Tanawit Sahavisit, Popphon Laon, Supavee Pourbunthidkul, Pattharin Wichittrakarn, Pattarapong Phasukkit and Nongluck Houngkamhang

Galaxies 2025, 13(6), 124; https://doi.org/10.3390/galaxies13060124 - 31 Oct 2025

Cited by 1 | Viewed by 1823

Abstract

Radio astronomy requires precise target localization and tracking to ensure accurate observations. Conventional regulation methodologies, encompassing PID controllers, frequently encounter difficulties due to orientation inaccuracies precipitated by mechanical limitations, environmental fluctuations, and electromagnetic interferences. To tackle these obstacles, this investigation presents a reinforcement [...] Read more.

Radio astronomy requires precise target localization and tracking to ensure accurate observations. Conventional regulation methodologies, encompassing PID controllers, frequently encounter difficulties due to orientation inaccuracies precipitated by mechanical limitations, environmental fluctuations, and electromagnetic interferences. To tackle these obstacles, this investigation presents a reinforcement learning (RL)-oriented framework for high-accuracy monitoring in radio telescopes. The suggested system amalgamates a localization control module, a receiver, and an RL tracking agent that functions in scanning and tracking stages. The agent optimizes its policy by maximizing the signal-to-noise ratio (SNR), a critical factor in astronomical measurements. The framework employs a reconditioned 12-m radio telescope at King Mongkut’s Institute of Technology Ladkrabang (KMITL), originally constructed as a satellite earth station antenna for telecommunications and was subsequently refurbished and adapted for radio astronomy research. It incorporates dual-axis servo regulation and high-definition encoders. Real-time SNR data and streaming are supported by a HamGeek ZedBoard with an AD9361 software-defined radio (SDR). The RL agent leverages the Proximal Policy Optimization (PPO) algorithm with a self-attention actor–critic model, while hyperparameters are tuned via Optuna. Experimental results indicate strong performance, successfully maintaining stable tracking of randomly moving, non-patterned targets for over 4 continuous hours without any external tracking assistance, while achieving an SNR improvement of up to 23.5% compared with programmed TLE-based tracking during live satellite experiments with Thaicom-4. The simplicity of the framework, combined with its adaptability and ability to learn directly from environmental feedback, highlights its suitability for next-generation astronomical techniques in radio telescope surveys, radio line observations, and time-domain astronomy. These findings underscore RL’s potential to enhance telescope tracking accuracy and scalability while reducing control system complexity for dynamic astronomical applications. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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21 pages, 4883 KB

Open AccessArticle

VERA’s 20 yr Evolution in Science and Technology

by Mareki Honma, Tomoya Hirota, Tomoaki Oyama and Akiharu Nakagawa

Galaxies 2025, 13(6), 120; https://doi.org/10.3390/galaxies13060120 - 27 Oct 2025

Cited by 1 | Viewed by 1477

Abstract

We review the past 20 yr evolution of VERA (VLBI Exploration of Radio Astrometry) in both science and techinology. VERA is a VLBI array in Japan which consists of four 20 m-diameter telescopes, originally dedicated to phase-referencing VLBI astrometry. Its main observing bands [...] Read more.

We review the past 20 yr evolution of VERA (VLBI Exploration of Radio Astrometry) in both science and techinology. VERA is a VLBI array in Japan which consists of four 20 m-diameter telescopes, originally dedicated to phase-referencing VLBI astrometry. Its main observing bands are K (22 GHz) and Q (43 GHz) for conducting astrometry observations of H₂O and SiO maser sources. In its 20 yr history, VERA has conducted astrometry observations of ∼100 maser sources, revealing the three-dimensional structure of the Milky Way Galaxy. Its long-term observations of Sgr A* resulted in the first parallax detection of the super-massive black hole at the Galaxy center. Observations of maser sources also revealed physical properties of star-forming regions and provided calibration of AGB stars’ distances and their Period–Luminosity relation. In parallel, several upgrades have been carried out in receivers as well as digital back-ends and correlator to extend the frequency bands and the data rate. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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14 pages, 247 KB

Open AccessArticle

The Murchison Widefield Array Enters Adolescence: A Personal Review of the Early Years of Operations

by Steven J. Tingay

Galaxies 2025, 13(5), 107; https://doi.org/10.3390/galaxies13050107 - 11 Sep 2025

Cited by 1 | Viewed by 1431

Abstract

The Murchison Widefield Array (MWA) is a low frequency radio interferometer designed and developed by an international consortium, operated on behalf of the consortium by Curtin University. The MWA is a Precursor for the low frequency Square Kilometre Array (SKA) and is located [...] Read more.

The Murchison Widefield Array (MWA) is a low frequency radio interferometer designed and developed by an international consortium, operated on behalf of the consortium by Curtin University. The MWA is a Precursor for the low frequency Square Kilometre Array (SKA) and is located at the SKA site in Western Australia, Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory. Commencing science operations in 2013 after an extended development period, the MWA has performed observations over a wide set of science objectives, has been upgraded multiple times, and has played a fundamental role in the development of the low frequency SKA. As MWA Program Manager from 2008 to 2011, as Director from 2011 until 2015, and then again from 2021 to the present, I describe some personal reflections on the MWA’s activities and successes in these different dimensions, as well as my view of some of the approaches that have enabled these successes. I offer some of the lessons I’ve perceived over the last 17+ years in the project. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

18 pages, 30275 KB

Open AccessArticle

RAD@home Citizen Science Discovery of Two Spiral Galaxies Where the 30–220 kpc Radio Lobes Are Possibly Shaped by Ram Pressure Stripping

by Prakash Apoorva, Ananda Hota, Pratik Dabhade, P. K. Navaneeth, Dhruv Nayak and Arundhati Purohit

Galaxies 2025, 13(5), 98; https://doi.org/10.3390/galaxies13050098 - 22 Aug 2025

Cited by 1 | Viewed by 2112

Abstract

We report the RAD@home citizen science discovery of two rare spiral-host radio galaxies (NGC 3898 and WISEA J221656.57-132042434.1 or RAD-“Thumbs up” galaxy), both exhibiting asymmetric radio lobes extending over 30 to 220 kiloparsec scales. We present a multi-wavelength image analysis of these two [...] Read more.

We report the RAD@home citizen science discovery of two rare spiral-host radio galaxies (NGC 3898 and WISEA J221656.57-132042434.1 or RAD-“Thumbs up” galaxy), both exhibiting asymmetric radio lobes extending over 30 to 220 kiloparsec scales. We present a multi-wavelength image analysis of these two sources using radio, optical, and ultraviolet data. Both host galaxies are young, star-forming systems with asymmetric or distorted stellar disks. These disks show similarities to those in galaxies undergoing ram pressure stripping, and the radio morphologies resemble those of asymmetric or bent FR-II and wide-angle-tailed radio galaxies. We suggest that non-uniform gas density in the environment surrounding the ram pressure-stripped disks may contribute to the observed asymmetry in the size, shape, and brightness of bipolar radio lobes. Such environmental effects, when properly accounted for, could help explain many of the non-standard radio morphologies observed in Seyfert galaxies and in recently identified populations of galaxies with galaxy-scale radio jets, which are now being revealed through deep and sensitive radio surveys with uGMRT, MeerKAT, LOFAR, and, in the future, SKAO. These findings also underscore the potential of citizen science to complement professional research and data-driven approaches involving machine learning and artificial intelligence in the analysis of complex radio sources. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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18 pages, 16328 KB

Open AccessReview

Radio Astronomy with NASA’s Deep Space Network

by T. Joseph W. Lazio and Stephen M. Lichten

Galaxies 2025, 13(6), 123; https://doi.org/10.3390/galaxies13060123 - 31 Oct 2025

Viewed by 2509

Abstract

The Deep Space Network (DSN) is the spacecraft tracking and communication infrastructure for NASA’s deep space missions. At three sites, approximately equally separated in (terrestrial) longitude, there are multiple radio antennas outfitted with cryogenic microwave receiving systems both for receiving transmissions from deep [...] Read more.

The Deep Space Network (DSN) is the spacecraft tracking and communication infrastructure for NASA’s deep space missions. At three sites, approximately equally separated in (terrestrial) longitude, there are multiple radio antennas outfitted with cryogenic microwave receiving systems both for receiving transmissions from deep space spacecraft and for conducting radio astronomical observations, particularly in the L band (1350 MHz–1800 MHz), X band (8200 MHz–8600 MHz), and K band (18 GHz–27 GHz). In particular, the 70 m antennas at the Canberra and Madrid DSN Complexes are well-equipped to participate in international very long baseline interferometry (VLBI) observations. Over the past five years, there has been an effort to refurbish and modernize equipment such as receiving and signal transport systems for radio astronomical observations. We summarize current capabilities, on-going refurbishment activities, and possible future opportunities. Full article

(This article belongs to the Special Issue Recent Advances in Radio Astronomy)

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