arXiv subjects

Olga Bayandina

Publications and source records attributed to Olga Bayandina.

8 recordsLinked to original sources

arXiv2026

Advancing Astrophysics with the SKA II

Advancing Astrophysics with the SKA II (AASKAII), written by our science community, outlines the transformative scientific advances that will be enabled by the SKA telescopes. In the decade since the publication of the previous edition, telescope designs have matured, construction has commenced, and the SKA Organisation has evolved into the SKA Observatory (SKAO). At the same time, observations from SKA precursor and pathfinder telescopes have provided new insights into longstanding scientific challenges while revealing entirely new phenomena. Published in advance of the first science verification campaign for the SKA Observatory, this volume looks ahead to the coming decades of discovery and innovation in radio astronomy. AASKAII spans the broad range of scientific research enabled by the SKA telescopes, SKA-Mid and SKA-Low. The contributions are organised into six thematic categories according to their scientific focus. The opening section presents overview chapters from the SKA Science Working Groups, around which our community is organised. Each overview provides the broader context that connects the contributions in this volume to the key scientific questions being pursued by their respective communities.

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arXiv2026

Cosmic Rulers: Masers as Tools for Probing Structure in the Galaxy and Beyond, from AU to kpc

Maser emission provides an unique window into astronomical sources across vast spatial scales - from tens to hundreds of astronomical units around protostars and evolved stars up to kiloparsecs in distant galaxies. These natural microwave amplifiers penetrate dust shells in star-forming regions, revealing the dynamics of accretion disks and outflows, trace envelopes and winds of evolved stars, map Galactic structure, while also allowing us to follow the evolution of all these systems. Owing to their compactness and brightness masers provide precise astrometry as cosmic rulers: measuring positions, structures and kinematics in dense regions, not easily accessible at other wavelengths. SKA-Mid will observe hydroxyl, methanol, and formaldehyde masers using bands 2, 5a and 5b, and later methylidyne radical masers in band 4. SKA-Mid's sensitivity and broad frequency coverage will support discoveries of new maser types and allow for simultaneous multi-transition and multi-species maser observations. In addition, bright masers can serve in the science verification of the SKA-Mid array during the deployment phase.

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arXiv2026

Extending the SKA Across Africa: The Case for a Continental African VLBI Network

The African continent holds the key to unlocking the full potential of global Very Long Baseline Interferometry (VLBI). Strategic placement of radio telescopes across Africa provides the crucial north-south and intermediate baselines that are currently missing from the global VLBI network. This expansion will dramatically enhance imaging fidelity and resolution. In this chapter, we propose a vision for a continental African VLBI Network (AVN) that will operate in close synergy with SKA-Mid, enabling transformational science across all cosmic scales. While only the Hartebeesthoek Radio Astronomy Observatory (HartRAO) in South Africa and the Ghana Radio Astronomy Observatory (GRAO) are currently operational, several partner countries are in the process of refurbishing or converting existing antennas. Here, we advocate for the expansion of this network through the deployment of a limited number of SKA-Mid-type telescopes across the continent, creating an "African arm" of SKA-VLBI. With a maximum baseline of ~ 9000 km (from Rabat, Morocco to Cassis, Mauritius), the proposed continental facility will surpass for example, the resolution that will be achieved by the next generation Very Large Array (ngVLA) by ~ 10 % at similar observing frequencies and significantly enhance global VLBI coverage. Beyond the scientific and technical gains, the AVN represents a unique opportunity for sustainable growth in human capital, education, and innovation across Africa. Developing and operating a continental VLBI array will train the next generation of engineers, data scientists, and astronomers, stimulate local industry, and inspire public engagement in science and technology. We outline the current status, challenges, and potential roadmap towards realizing this vision, and we highlight how a continental African VLBI network will position Africa at the forefront of global radio astronomy.

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arXiv2025

Detections of Compact Radio Continuum toward Methanol Maser Rings Using the VLA

High-mass protostars are deeply embedded in dust inside their natal cores and are not easily detectable. However, maser emission at centimeter wavelengths, owing to its high brightness, enables us to study gas kinematics in protostars' circumstellar regions. We aim to understand the origin of the ring-like structures outlined by the 6.7 GHz methanol maser emission in six high-mass young stellar objects by performing a sensitive search of the associated radio-continuum emission and derive its properties. We used the Karl G. Jansky Very Large Array in the A configuration at C and K bands in order to image radio-continuum as well as 6.7 GHz methanol and 22 GHz water maser emission. We present the first images of the thermal jets towards four targets in our sample, G23.389+00.185, G23.657-00.127, G28.817+00.365, and G30.400-00.296. In a further target, G23.207-00.377, the complex K band continuum emission makes it unclear whether the detected peaks trace jet knots from a single young protostar or mark multiple compact young protostars. The remaining source G31.047+00.356 shows radio continuum emission associated with an evolved H II region.

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arXiv2025

Protostellar Outflows at the EarliesT Stages (POETS). VIII. The jets in the intermediate-mass star-forming region G105.42+9.88 (alias LkHα 234)

Our aim is to investigate the protostellar jets inside the young stellar object (YSO) cluster G105.42+9.88 (alias LkH$α$ 234). This is one of the least luminous targets of the Protostellar Outflows at the EarliesT Stages (POETS) survey, which has been recently carried out to study young outflow emission on scales of 10-100 au. The combination of multi-epoch water maser very long baseline interferometry (VLBI) observations with sensitive Jansky Very Large Array (JVLA) continuum and Large Binocular Telescope (LBT) H$_2$ 2.12 $μ$m observations, allows us to study the protostellar outflows from the intermediate-mass binary system VLA 3A and 3B, separated by ~0.22", and from VLA 2, an intermediate-mass YSO placed ~1" to northwest of VLA 3. Toward VLA 2, the 2001 and 2011 Very Long Baseline Array (VLBA) observations consistently show that the water masers are tracing a jet. The analysis of the 3D flow velocities proves that the jet is magneto-centrifugally launched in a magnetohydrodynamic (MHD) disk wind (DW). We infer launch radii in the range 10-50 au for the streamlines traced by the water masers. The global VLBI 2023 water maser observations indicate that the jet propagation can be hindered by a very dense clump placed northeast of VLA 2 and that is consistent with the large-scale LBT H$_2$ emission, tracing only the southwest lobe of the VLA 2 jet. Instead, the parallel jets emitted by the nearby YSOs VLA 3A and 3B can be reliably tracked with the H$_2$ emission at scales of a few 10" to both the southwest and the northeast. In particular, northeast of VLA 3 the direction of these two jets crosses a linear chain of spaced H$_2$ knots, which is a clear signature of an episodic jet. The variable ejection from VLA 3B, witnessed by the water masers at scales of ~10 au, could be the origin of the episodic jet observed at larger scales.

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arXiv2024

Protostellar Outflows at the EarliesT Stages (POETS) V. The launching mechanism of protostellar winds via water masers

Understanding the launching mechanism of winds and jets remains one of the fundamental challenges in astrophysics. The Protostellar Outflows at the EarliesT Stages (POETS) survey has recently mapped the 3D velocity field of the protostellar winds in a sample (37) of luminous young stellar objects (YSOs) at scales of 10-100 au via very long baseline interferometry (VLBI) observations of the 22 GHz water masers. In most of the targets, the distribution of the 3D maser velocities can be explained in terms of a magnetohydrodynamic (MHD) disk wind (DW). We have performed Very Long Baseline Array observations of the 22 GHz water masers in IRAS 21078+5211, the most promising MHD DW candidate from the POETS survey, to determine the 3D velocities of the gas flowing along several wind streamlines previously identified at a linear resolution of ~1 au. Near the YSO at small separations along ($xl \le 150$ au) and across ($R \le 40$ au) the jet axis, water masers trace three individual DW streamlines. By exploiting the 3D kinematic information of the masers, we determined the launch radii of these streamlines with an accuracy of $\sim$1 au, and they lie in the range of 10-50 au. At increasingly greater distances along the jet (110 au $\le xl \le 220$ au), the outflowing gas speeds up while it collimates close to the jet axis. Magneto-centrifugal launching in a radially extended MHD DW appears to be the only viable process to explain the fast (up to 60 km/s) and collimated (down to 10 degree) velocities of the wind in correspondence with launch radii ranging between 10 and 50 au. At larger separations from the jet axis ($R \ge 100$ au), the water masers trace a slow ($\le$20 km/s), radially expanding arched shock-front with kinematics inconsistent with magneto-centrifugal launching. Our resistive-magnetohydrodynamical simulations indicate that this shock-front could be driven by magnetic pressure.

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arXiv2019

Online Database of Class I Methanol Masers

In this paper, we present a database of class I methanol masers. The compiled information from the available literature provides an open and fast access to the data on class I methanol maser emission, including search, analysis and visualization of the extensive maser data set. There is information on individual maser components detected with single-dish observations and maser spots obtained from interferometric data. At the moment the database contains information from ~100 papers, i.e. ~7500 observations and ~650 sites of class I methanol masers. Analysis of the data collected in the database shows that the distribution of class I methanol maser sources is similar to that of class II methanol masers. They are mostly found in the Molecular Ring, where majority of the OB stars are located. The difference between class I and II distributions is the presence of many class I methanol masers in the Nuclear Disk region (Central Molecular Zone). Access to the class I methanol maser database is available online at http://maserdb.net

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arXiv2018

Multi-epoch VLBI of a double maser super burst

In a rare and spectacular display, two well-known massive star forming regions, W49N and G25.65+1.05, recently underwent maser 'super burst' - their fluxes suddenly increasing above 30,000 and 18,000 Jy, respectively, reaching several orders of magnitude above their usual values. In quick-response, ToO observations with the EVN, VLBA and KaVA were obtained constituting a 4 week campaign - producing a high-cadence multi-epoch VLBI investigation of the maser emission. The combination of high-resolution, polarisation and flux monitoring during the burst provides one of the best accounts, to date, of the maser super burst phenomenon, aiding their use as astrophysical tools. These proceedings contain the preliminary results of our campaign.

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