arXiv subjects

Z. H. Lin

Publications and source records attributed to Z. H. Lin.

8 recordsLinked to original sources

arXiv2026

Compact Objects Revealed by SKA and SKA-VLBI

Compact objects represent a crucial interdisciplinary frontier between astronomy and fundamental physics.The SKA/SKA-VLBI, with exceptional sensitivity (at $\mu$Jy levels) and ultrahigh positional precision (at $\mu$as levels), will enable direct, precise measurements of orbital dynamics in compact objects including black holes and neutron stars. This facility is expected to achieve at least three breakthroughs: (1) Developing effective methodologies for detecting and identifying black hole-neutron star binaries to construct observational catalogues, thus advancing investigations into the equation of state of ultra-dense nuclear matter and strong-field relativistic effects; (2) Determining critical parameters such as orbital elements and component masses in compact binaries, yielding insights into stellar structures and evolutionary mechanisms under extreme conditions; (3) Identifying intermediate-mass black holes and measuring their masses to deepen understanding of black hole formation and evolution.

astro-ph.HE↗

arXiv2026

Gravitational Light Deflection with SKA-VLBI and Its Application to Precision Tests of General Relativity

Experimental test of general relativity remains an ongoing endeavour. Radio astrometry provides a vital tool for precisely measuring the light deflection caused by the Sun, testing general relativity, and discriminating between gravitational theories. The best accuracy for the post-Newtonian relativistic parameter, $\gamma$, achieved with very long baseline interferometry is $9 \times 10^{-5}$. With 300-sec integration, SKA-VLBI can achieve a sensitivity of $\sim$15 $\mu$Jy at 15 GHz over a bandwidth of 0.256 GHz. This enables detection of $\sim$36 extragalactic radio sources per square degree with flux densities of $\sim$1.5 mJy, and potentially detecting in-beam radio sources. Single-epoch SKA-VLBI observations may achieve an astrometric precision of $\sim$2 $\mu$as. Utilising the Sun as a gravitational lens, 10-epoch positional tracking of extragalactic sources could improve $\gamma$ accuracy to $\sim$10$^{-7}$. Even with Jupiter as a lens, SKA-VLBI can measure $\gamma$ to $\sim$10$^{-4}$. Critically, it may conduct the first measurement of quadrupolar deflection of light caused by Jupiter, determining the physical oblateness of Jupiter, $J_{\mathrm{2, J}}$, to within $\sim${}$10^{-3}$. These advances are expected to rigorously test and improve gravitational theories or high-order parameterized post-Newtonian formalisms, while laying the foundations for (sub)$\mu$as astrometry.

astro-ph.IM↗

arXiv2024

Probing the nature of rotation in the Pleiades, Alpha Persei, and Hyades clusters

Unraveling the internal kinematics of open clusters is crucial for understanding their formation and evolution. However, there is a dearth of research on this topic, primarily due to the lack of high-quality kinematic data. Using the exquisite-precision astrometric parameters and radial velocities provided by Gaia data release 3, we investigate the internal rotation in three of the most nearby and best-studied open clusters, namely the Pleiades, Alpha Persei, and Hyades clusters. Statistical analyses of the residual motions of the member stars clearly indicate the presence of three-dimensional rotation in the three clusters. The mean rotation velocities of the Pleiades, Alpha Persei, and Hyades clusters within their tidal radii are estimated to be 0.24 (0.04), 0.43 (0.08), and 0.09 (0.03) km s-1, respectively. Similar to the Praesepe cluster that we have studied before, the rotation of the member stars within the tidal radii of these three open clusters can be well interpreted by Newton's theorem. No expansion or contraction is detected in the three clusters either. Furthermore, we find that the mean rotation velocity of open clusters may be positively correlated with the cluster mass, and the rotation is likely to diminish as open clusters age.

astro-ph.GA↗

arXiv2023

Unveiling the initial conditions of open star cluster formation

Open clusters (OCs) are infrequent survivors of embedded clusters gestated in molecular clouds. Up to now, little is known about the initial conditions for the formation of OCs. Here, we studied this issue using high-precision astrometric parameters provided by Gaia data release 3. The statistics show that the peculiar motion velocities of OCs vary little from infancy to old age, providing a remarkable opportunity to use OCs to trace their progenitors. Adopting a dynamical method, we derived the masses of the progenitor clumps where OCs were born, which have statistical characteristics comparable to previously known results for clumps observed in the Galaxy. Moreover, the masses of the progenitor clumps of OCs indicate they should be capable of gestating massive O-type stars. In fact, after inspecting the observed OCs and O-type stars, we found that there are many O-type stars in OCs. The destructive stellar feedback from O-type stars may disintegrate the vast majority of embedded clusters, and only those sufficiently dense ones can survive as OCs.

astro-ph.GA↗

arXiv2023

What Does the Milky Way Look Like?

In spite of much work, the overall spiral structure morphology of the Milky Way remains somewhat uncertain. In the last two decades, accurate distance measurements have provided us with an opportunity to solve this issue. Using the precise locations of very young objects, for the first time, we propose that our galaxy has a multiple-arm morphology that consists of two-arm symmetry (the Perseus and Norma Arms) in the inner parts and that extends to the outer parts, where there are several long, irregular arms (the Centaurus, Sagittarius, Carina, Outer, and Local Arms).

astro-ph.GA↗

arXiv2022

On the nature of rotation in the Praesepe cluster

Although a large number of Galactic open clusters (OCs) have been identified, the internal kinematic properties (e.g., rotation) of almost all the known OCs are still far from clear. With the high-precision astrometric data of Gaia EDR3, we have developed a methodology to unveil the rotational properties of the Praesepe cluster. Statistics of the three-dimensional residual motions of the member stars reveal the presence of Praesepe's rotation and determine its spatial rotation axis. The mean rotation velocity of the Praesepe cluster within its tidal radius is estimated to be 0.2 $\pm$ 0.05 km s$^{-1}$, and the corresponding rotation axis is tilted in relation to the Galactic plane with an angle of 41 $\pm$ 12 degree. We also analysed the rms rotational velocity of the member stars around the rotation axis, and found that the rotation of the member stars within the tidal radius of Praesepe probably follows the Newton's classical theorems.

astro-ph.GA↗

arXiv2022

Open clusters housing classical Cepheids in Gaia DR3

The latest Gaia Data Release 3 provides an opportunity to expand the census of Galactic open clusters harboring classical Cepheid variables, thereby bolstering the cosmic distance scale. A comprehensive analysis yielded a total of 50 classical Cepheids associated with 45 open clusters, of which 39 open cluster-classical Cepheid pairs are considered probable, with the remaining 11 pairs considered improbable but worth following up. Two previously identified clusters by us possibly host classical Cepheids (OC-0125/V1788 Cyg and OC-0675/OGLE-BLG-CEP-114). In addition, we identify 38 new open cluster candidates within the Galactic disk.

astro-ph.SR↗

arXiv2022

Newly detected open clusters in the Galactic disk using Gaia EDR3

The astrometric satellite Gaia recently released part of its third data set, which provides a good opportunity to hunt for more open clusters in the Milky Way. In this work, we conduct a blind search for open clusters in the Galactic disk using a sample-based clustering search method with high spatial resolution, which is especially suited to finding hidden targets. In addition to confirming 1930 previously known open clusters and 82 known globular clusters, 704 new stellar clusters are proposed as potential open clusters at Galactic latitudes of $|$b$|$ < 20 {deg}. For each of these new open clusters, we present the coordinates, detailed astrometric parameters, and ages, as well as the radial velocity, if available. Our blind search greatly increases the number of Galactic open clusters as objects of study and shows the incompleteness of the open cluster census across our Galaxy

astro-ph.GA↗