arXiv subjects

Bing-Qiu Chen

Publications and source records attributed to Bing-Qiu Chen.

At least 19 recordsLinked to original sources

arXiv2026

Characterising the Kinematics and Evolution of Young Stellar Groups within 1 kpc of the Sun Using Gaia DR3

Star-forming regions are key to understanding the formation and early evolution of stars. Young stellar objects (YSOs) form groups with distinct kinematic and spatial properties, inherited from the turbulent dynamics of their parent molecular clouds. The high-precision astrometry and photometry from Gaia Data Release 3 (DR3) enable detailed studies of these groups' three-dimensional motions and their evolutionary stability. This study aims to investigate the kinematic properties and evolutionary consistency of YSO associations in the solar neighbourhood. Here, we show that HDBSCAN clustering of Gaia DR3 data yields 145 YSO groups comprising 5713 stars within 1 kpc, with a derived Larson's relation of $σ_v = (1.10 \pm 0.13) \times r^{0.38 \pm 0.03}$, consistent across age bins up to 20 Myr. This slope aligns with the canonical value of 0.38 and typical ranges of 0.4--0.5. The stable Larson's relation across ages indicates that the inherited turbulent structure from parent clouds persists without significant disruption. These findings establish a benchmark for studying the kinematic legacy of star-forming regions.

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arXiv2025

Kinematics of the interstellar medium using Gaia: A catalogue of 102 YSO-MC associations within 3.5 kpc from the Sun with 3D velocities

Kinematic information is crucial for understanding the evolution of complex systems, such as interstellar gas. Obtaining full 3D kinematic information is a crucial final step for modeling and interpretation. Molecular clouds are nurseries where stars are born. Stars at a very early stage, like young stellar objects (YSOs), inherit the spatial and kinematic structure of the gas patches they originate from. In this paper, we combine measurements of radial velocities towards the gas and the kinematic information of YSOs from Gaia DR3 to derive 3D velocities of a sample of YSO (Young Stellar Object)-MC (Molecular Cloud) complexes at d$\lesssim$3.5kpc from the Sun. We find that the molecular interstellar medium traced by the YSO-MC complexes generally follows Galactic rotation, with an additional peculiar velocity of 8.6 km s$^{-1}$. The random motion of these complexes in the Galactic XY plane is more energetic than motion along the Z direction. A catalogue containing the 3D velocities of the YSO-MC complexes at different reference frames is available, and the distances and 3D velocities of well-known molecular clouds are presented. Our results set the foundation for exploring the interplay between the Galaxy, the molecular ISM, and star formation. Data available at https://doi.org/10.5281/zenodo.16364877.

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arXiv2025

A recent re-acceleration of the Local Bubble revealed by kinematics of young star associations

The low-density region of the interstellar medium (ISM) where the Sun is located is known as the Local Bubble, a cavity filled with high-temperature and low-density plasma that may be created by a series of supernova (SN) explosions over the past 14 Myr. However, the effects of these SN explosions on the formation and evolution of the Local Bubble, as well as on nearby star formation, remain not fully understood. To study the expansion history of the Local Bubble, we use the kinematic data of the young stars obtained by cross-matching the pre-main-sequence (PMS) star catalog of \citet{Zari2018} with the high-precision astrometric and photometric data from the {\it Gaia} DR3 database. We perform a three-dimensional spatial clustering analysis on these young stars to identify star associations. We discover three unique star associations that exhibit a wiggle-like velocity pattern. The distances of these star associations are 108.5308, 141.5284, and 176.0318 pc, respectively. Their radial velocities in the Local Standard of Rest (LSR) are 10.0622, 5.4982, and 9.0581 km/s, showing a pattern of decreasing and then increasing. This velocity pattern, as predicted by \citet{Krause&Diehl2014}, is caused by a recent re-acceleration affected by the SN explosion, reinforcing the picture of the Local Bubble as an evolving entity.

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arXiv2025

Empirically Predicted Absolute Magnitudes for Red Clump Stars in Mephisto and CSST Filters

Red clump (RC) stars are reliable standard candles for studying the structure and evolution of the Milky Way. In this study, we present empirical calibrations of RC absolute magnitudes in the Mephisto (v, g, r, i) and CSST (g, r, i) photometric systems using a high-purity sample of 25,059 RC stars cross-matched between APOGEE and Gaia DR3 XP spectra. Through synthetic photometry and polynomial fitting, we find that RC absolute magnitudes exhibit strong dependencies on effective temperature and metallicity, with the strongest variations observed in bluer bands and progressively decreasing towards redder wavelengths. In particular, the Mephisto v band exhibits the highest sensitivity, with variations reaching up to 2.0 mag across the metallicity range (-1.0 dex <[Fe/H] <0.5 dex) and the temperature range (4500-5200 K). The calibrations achieve high precision for all bands, enabling accurate determination of RC absolute magnitudes and distances. Furthermore, we evaluate the metallicity estimation capabilities of both systems using a Random Forest-based method, achieving a precision of 0.12 dex for Mephisto and 0.14 dex for CSST under typical photometric uncertainties (< 0.01 mag). These results provide robust tools for distance and metallicity determinations, supporting future Galactic structure studies with Mephisto and CSST data.

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arXiv2025

Photometric metallicities of 0.8 million KiDS stars

Accurate determinations of metallicity for large, complete stellar samples are essential for advancing various studies of the Milky Way. In this paper, we present a data-driven algorithm that leverages photometric data from the KiDS and the VIKING surveys to estimate stellar absolute magnitude, effective temperature and metallicities. The algorithm is trained and validated using spectroscopic data from LAMOST, SEGUE, APOGEE, and GALAH, as well as a catalog of very metal-poor stars from the literature, and Gaia EDR3 data. This approach enables us to estimate metallicities, effective temperatures, and g-band absolute magnitudes for approximately 0.8 million stars in the KiDS dataset. The photometric metallicity estimates exhibit an uncertainty of around 0.28 dex when compared to spectroscopic studies, within the metallicity range of -2 dex to 0.5 dex. The photometric effective temperature estimates have an uncertainty of around 149 K, while the uncertainty in the absolute magnitude is approximately 0.36 mag. The metallicity estimates are reliable for values down to about -2 dex. This catalog represents a valuable resource for studying the structure and chemical properties of the Milky Way, offering an extensive dataset for future investigations into Galactic formation and evolution.

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arXiv2024

The Red Supergiant Progenitor of the Type II Supernova 2024abfl

Linkage between core-collapse supernovae (SNe) and their progenitors is not fully understood and ongoing effort of searching and identifying the progenitors is needed. $\mathrm{SN\,2024abfl}$ is a recent Type II supernova exploded in the nearby star-bursting galaxy $\mathrm{NGC\,2146}$, which is also the host galaxy of $\mathrm{SN\,2018zd}$. From archival Hubble Space Telescope (HST) data, we have found a red source ($\mathrm{m_{F814W} \sim 25}$) near the location (angular distance $\leq 0.2"$) of $\mathrm{SN\,2024abfl}$ before its explosion. With F814W and F606W photometry, we found that the properties of this source matched a typical red supergiant (RSG) moderately reddened by interstellar dust at the distance of the host galaxy. We conclude that the $\mathrm{SN\,2024abfl}$ had an RSG progenitor with initial mass of $\mathrm{10M_{\odot}}$--$\mathrm{16\,M_{\odot}}$.

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arXiv2024

Little time for oscillation: Fast disruption of the Radcliffe Wave by Galactic motions

The Radcliffe wave \cite{2020Natur.578..237A} is a 2.7 kpc long, 100 pc wide-like structure in the Galactic disk with a wave-like velocity structure \cite{2022MNRAS.517L.102L,2024arXiv240212596K}. A referent Nature paper \cite{2024arXiv240212596K} treated the Wave as a solid body in the disk plane, modeled its oscillation along the vertical direction, and derived the local Galactic mass distribution from the oscillation pattern. In reality, Galactic shear can stretch gas through differential rotation, whereas gas clouds experience epicyclic motions. We simulate the 3D evolution of the local interstellar gas and find shear and encyclic motion stretches the Radcliffe wave to almost twice its current length at the timescale of 45 Myr, within which only half a cycle of the proposed vertical oscillation occurs. The simulation also reveals the formation of new filaments and filament-filament mergers. Treating the Radcliffe wave as a solid body in the Galactic disk and an oscillating structure in the vertical direction is thus an oversimplification. Our data-driven simulation reveals the 3D evolution of the local interstellar gas with several processes at play, strengthening the role of the Solar Neighborhood as a unique test ground for theories of interstellar gas evolution.

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arXiv2024

The Correlation Between Dust and Gas Contents in Molecular Clouds

Molecular clouds are regions of dense gas and dust in space where new stars and planets are born. There is a strong correlation between the distribution of dust and molecular gas in molecular clouds. The present work focuses on the three-dimensional morphological comparisons between dust and gas within 567 molecular clouds identified in a previously published catalog. We confirm a sample of 112 molecular clouds, where the cloud morphology based on CO observations and dust observations displays good overall consistency. There are up to 334 molecular clouds whose dust distribution might be related to the distribution of gas. We are unable to find gas structures that correlate with the shape of the dust distribution in 24 molecular clouds. For the 112 molecular clouds where the dust distribution correlates very well with the distribution of gas, we use CO observational data to measure the physical properties of these molecular clouds and compare them with the results derived from dust, exploring the correlation between gas and dust in the molecular clouds. We found that the gas and dust in the molecular clouds have a fairly good linear relationship, with a gas-to-dust ratio of $\mathrm{GDR}=(2.80_{-0.34}^{+0.37})\times10^{21}\mathrm{\,cm^{-2}\, mag^{-1}}$. The ratio varies considerably among different molecular clouds. We measured the scale height of dust-CO clouds exhibiting strong correlations, finding $h_{Z} = 43.3_{-3.5}^{+4.0}\mathrm{\,pc}$.

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arXiv2024

Morphology of molecular clouds at kiloparsec scale in the Milky Way: Shear-induced alignment and vertical confinement

The shape of the cold interstellar molecular gas is determined by several processes, including self-gravity, tidal force, turbulence, magnetic field, and galactic shear. Based on the 3D dust extinction map derived by Vergely et al., we identify a sample of 550 molecular clouds (MCs) within $3\hspace{0.2em}\rm kpc$ of the solar vicinity in the Galactic disk. Our sample contains clouds whose size ranges from pc to kiloparsec, which enables us to study the effect of Galactic-scale processes, such as shear, on cloud evolution. We find that our sample clouds follow a power-law mass-size relation of $M\propto 32.00\hspace{0.2em}{R_{\rm{max}}}^{1.77}$, $M\propto 20.59\hspace{0.2em}{R_S}^{2.04}$ and $M\propto 14.41\hspace{0.2em}{R_V}^{2.29}$, where $R_{\rm{max}}$ is the major axis-based cloud radius, $R_S$ is the area-based radius, and $R_V$ is the volume-based radius, respectively. These clouds have a mean constant surface density of $\sim 7 \hspace{0.2em} \rm {M_{\odot}pc^{-2}}$, and follow a volume density-size relation of $ρ\propto 2.60\hspace{0.2em}{R_{\rm{max}}}^{-0.55}$. As cloud size increases, their shapes gradually transition from ellipsoidal to disk-like to bar-like structures. Large clouds tend to have a pitch angle of $28^{\circ} - 45^{\circ}$, where the angle is measured concerning the Galactic tangential direction. These giant clouds also tend to stay parallel to the Galactic disk plane and are confined within the Galactic molecular gas disk. Our results show that large molecular clouds in the Milky Way can be shaped by Galactic shear and confined in the vertical direction by gravity.

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arXiv2024

The wave-like disk oscillations of mono-age stellar populations in the Solar neighbourhood from Gaia DR3

The North-South asymmetry in the number density and bulk velocity of stars in the solar neighborhood provides valuable insights into the formation and evolution of the Milky Way disk. Our objective is to investigate the wave-like disk oscillations of mono-age stellar populations in the Solar neighbourhood using data from Gaia Data Release 3. We have selected a comprehensive sample of main sequence turn off stars. The ages of these stars can be accurately determined using isochrone fitting methods. Our findings indicate that the north-south density and mean vertical velocity asymmetries remain consistent across all age groups.The uniformity of perturbations across all subsamples suggests that all populations are responding to the same external influence, which likely affects them irrespective of their age. Moreover, the fact that these perturbations appear consistently implies they could be either ongoing or recent. Regarding vertical velocity dispersions, we observe that older stars exhibit larger dispersions.

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arXiv2024

Photometric Re-calibration of VPHAS+ $u$-band Photometry with the Stellar Colour Regression Method and Gaia DR3

The u band magnitude is vital for determining stellar parameters and investigating specific astronomical objects. However, flux calibration in the u band for stars in the Galactic disk presents significant challenges. In this study, we introduce a comprehensive re-calibration of $u$-band photometric magnitudes of the VPHAS+ Data Release 4 (DR4), employing the Stellar Colour Regression (SCR) technique. By leveraging the expansive set of XP spectra and $G_{\rm BP}$ photometry from Gaia Data Release 3 (DR3), as well as the individual stellar extinction values provided by the literature, we have obtained precise model magnitudes of nearly 3 million stars. Our analysis identifies systematic magnitude offsets that exhibit a standard deviation of 0.063 mag across different observational visits, 0.022 mag between various CCDs, and 0.009 mag within pixel bins. We have implemented precise corrections for these observational visits, CCD chips, and pixel bins-dependent magnitude offsets. These corrections have led to a reduction in the standard deviation between the observed magnitudes and the model magnitudes from 0.088 mag to 0.065 mag, ensuring that the calibrated magnitudes are independent of stellar magnitude, colour, and extinction. The enhanced precision of these magnitudes substantially improves the quality of astrophysical research and offers substantial potential for furthering our understanding of stellar astrophysics.

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arXiv2024

Gas content and evolution of a sample of YSO associations at $d \lesssim$ 3.5 kpc from the Sun

Young Stellar Objects (YSO) are newly formed stars from molecular clouds. They stay close to where they were born and serve as good tracers to study gas and star formation. During cloud evolution, young massive stars can disrupt the surrounding gas through stellar feedback, changing the gas distribution. We study the distribution of the gas around a sample of YSO associations located at $d \lesssim 3.5 \;\rm kpc$ from the Sun by comparing the location and morphology between $^{12}$CO (J = 1$-$0) emission, Planck 870 $μ$m maps and YSO associations. Based on the spatial distribution of the gas compared to that of the YSOs, we classify the YSO associations into six types: direct, close, bubble, complex, diffuse, and clean associations. The complex associations are large structures consisting of both gas-rich and gas-poor segments. We study the velocity dispersion-size relation toward different association types. From the ratio between different types, we estimate a feedback time of $\approx$ 1.7 Myr in the solar neighborhood. The sample sets a solid foundation to explore the relationship between interstellar medium evolution, star formation, and Galaxy structure.

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arXiv2022

Weather Forecast of the Milky Way: Shear and Stellar feedback determine the lives of Galactic-scale filaments

The interstellar medium (ISM) is an inseparable part of the Milky Way ecosystem whose evolutionary history remains a challenging question. We trace the evolution of the molecular ISM using a sample of Young Stellar Objects (YSO) association --molecular cloud complex (YSO-MC complex). We derive their three-dimensional (3D) velocities by combining the Gaia astrometric measurements of the YSO associations and the CO observations of the associated molecular clouds. Based on the 3D velocities, we simulate the motions of the YSO-MC complexes in the Galactic potential and forecast the ISM evolution by tracing the motions of the individual complexes, and reveal the roles of shear and stellar feedback in determining ISM evolution: Galactic shear stretches Galactic-scale molecular cloud complexes, such as the G120 Complex, into Galactic-scale filaments, and it also contributes to the destruction of the filaments; while stellar feedback creates interconnected superbubbles whose expansion injects peculiar velocities into the ISM. The Galactic-scale molecular gas clumps are often precursors of the filaments and the Galactic-scale filaments are transient structures under a constant stretch by shear. This evolutionary sequence sets a foundation to interpret other gas structures. Animations are available at https://gxli.github.io/ISM-6D/movie.html.

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arXiv2022

Discovery of a coherent, wave-like velocity pattern for the Radcliffe Wave

Recently studies discovered that part of the Gould Belt belongs to a 2.7 kpc-long {coherent, thin} wave consisting of a chain of clouds, where a damped undulation pattern has been identified from the spatial arrangement of the clouds. We use the proper motions of Young Stellar Objects (YSOs) anchored inside the clouds to study the kinematic structure of the Radcliffe Wave in terms of $v_z$, and identify a damped, wave-like pattern from the $v_z$ space, which we call "velocity undulation". We propose a new formalism based on the Ensemble Empirical Mode Decomposition (EEMD) to determine the amplitude, period, and phase of the undulation pattern, and find that the spatial and the velocity undulation share an almost identical spatial frequency of about 1.5 kpc, and both are damped when measured from one side to the other. Measured for the first cycle, they exhibit a phase difference of around $2π/3$. The structure is oscillating around the midplane of the Milky Way disk with an amplitude of $\sim\,130\,\pm\,20\,\rm pc$. The vertical extent of the Radcliffe Wave exceeds the thickness of the molecular disk, suggesting that the undulation of the undulation signature might originate from a perturbation, e.g. the passage of a dwarf galaxy.

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arXiv2022

Kinematics of the molecular interstellar medium probed by Gaia: steep velocity dispersion-size relation, isotropic turbulence, and location-dependent energy dissipation

The evolution of the molecular interstellar medium is controlled by processes such as turbulence, gravity, stellar feedback, and Galactic shear. AL a part of the ISM-6D https://gxli.github.io/ISM-6D/ project, using Gaia astrometric measurements towards a sample of young stellar objects (YSOs), we study morphology and kinematic structure of the associated molecular gas. We identify 150 YSO associations with distance $d \lesssim 3 \;\rm kpc$. The YSO associations are elongated, with a median aspect ratio of 1.97, and are oriented parallel to the disk midplane, with a median angle of 30$^{\circ}$. The turbulence in the molecular clouds as probed by the YSOs is isotropic, and the velocity dispersions are related to the sizes by $σ_{v,{\rm 2D}} = 0.74\;(r/{\rm pc})^{0.67} \;({\rm km/s})\;$. The slope is on the steeper side, yet consistent with previous measurements. The energy dissipation rate of turbulence $\dotε = σ_{v,{\rm 3D}}^3 /L$ decreases with the Galactocentric distance, with a gradient of 0.2 $\rm dex \; kpc^{-1}$, which can be explained if turbulence is driven by cloud collisions. In this scenario, the clouds located in the inner Galaxy have higher chances to accrete smaller clouds and are more turbulent. Although the density structures of the complexes are anisotropic, the turbulence is consistent with being isotropic. If the alignment between density structures and the Galactic-disk mid-plane is due to shear, we expect $t_{\rm cloud} \gtrsim t_{\rm shear}\approx 30\; \rm Myr$. This cloud lifetime is longer than the turbulence crossing time, and a continuous energy injection is required to maintain the turbulence.

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arXiv2021

Identifications of RR Lyrae stars and Quasars from the simulated data of Mephisto-W Survey

We have investigated the feasibilities and accuracies of the identifications of RR Lyrae stars and quasars from the simulated data of the Multi-channel Photometric Survey Telescope (Mephisto) W Survey. Based on the variable sources light curve libraries from the Sloan Digital Sky Survey (SDSS) Stripe 82 data and the observation history simulation from the Mephisto-W Survey Scheduler, we have simulated the $uvgriz$ multi-band light curves of RR Lyrae stars, quasars and other variable sources for the first year observation of Mephisto-W Survey. We have applied the ensemble machine learning algorithm Random Forest Classifier (RFC) to identify RR Lyrae stars and quasars, respectively. We build training and test samples and extract ~ 150 features from the simulated light curves and train two RFCs respectively for the RR Lyrae star and quasar classification. We find that, our RFCs are able to select the RR Lyrae stars and quasars with remarkably high precision and completeness, with $purity$ = 95.4 per cent and $completeness$ = 96.9 per cent for the RR Lyrae RFC and $purity$ = 91.4 per cent and $completeness$ = 90.2 per cent for the quasar RFC. We have also derived relative importances of the extracted features utilized to classify RR Lyrae stars and quasars.

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arXiv2020

Astronomical Site Monitoring System at Lijiang Observatory

We installed two sets of Astronomical Site Monitoring System(ASMS) at Lijiang Observatory(GMG), for the running of the 2.4-meter Lijiang optical telescope(LJT) and the 1.6-meter Multi-channel Photometric Survey Telescope (Mephisto). The Mephistro is under construction. ASMS has been running on robotic mode since 2017. The core instruments: Cloud Sensor, All-Sky Camera and Autonomous-DIMM that are developed by our group, together with the commercial Meteorological Station and Sky Quality Meter, are combined into the astronomical optical site monitoring system. The new Cloud Sensor's Cloud-Clear Relationship is presented for the first time, which is used to calculate the All-Sky cloud cover. We designed the Autonomous-DIMM located on a tower, with the same height as LJT. The seeing data have been observed for a full year. ASMS's data for the year 2019 are also analysed in detail, which are valuable to observers.

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arXiv2018

An Investigation of the Interstellar Environment of Supernova Remnant CTB 87

We present a new millimeter CO-line observation towards supernova remnant (SNR) CTB 87, which was regarded purely as a pulsar wind nebula (PWN), and an optical investigation of a coincident surrounding superbubble. The CO observation shows that the SNR delineated by the radio emission is projectively covered by a molecular cloud (MC) complex at V$_{\rm {LSR}}$ = $-60$ to $-54$ km s$^{-1}$. Both the symmetric axis of the radio emission and the trailing X-ray PWN appear projectively to be along a gap between two molecular gas patches at $-58$ to $-57$ km s$^{-1}$. Asymmetric broad profiles of $^{12}$CO lines peaked at $-58$ km s$^{-1}$ are found at the eastern and southwestern edges of the radio emission. This represents a kinematic signature consistent with an SNR-MC interaction. We also find that a superbubble, $\sim 37'$ in radius, appears to surround the SNR from HI 21cm (V$_{\rm {LSR}} \sim -61$ to $-68$ km s$^{-1}$), WISE mid-IR, and optical extinction data. We build a multi-band photometric stellar sample of stars within the superbubble region and find 82 OB star candidates. The likely peak distance in the stars' distribution seems consistent with the distance previously suggested for CTB 87. We suggest the arc-like radio emission is mainly the relic of the part of blastwave that propagates into the MC complex and is now in a radiative stage while the other part of blastwave has been expanding into the low-density region in the superbubble. This scenario naturally explains the lack of the X-ray emission related to the ejecta and blastwave. The SNR-MC interaction also favours a hadronic contribution to the γ-ray emission from the CTB 87 region.

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