分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As groups of coeval stars born from the same molecular cloud, an Open cluster (OC) is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way. The release of High-Precision Gaia Early Data Release 3 (Gaia EDR3) and modern machine-learning methods offer unprecedented opportunities to identify OCs. In this study, we extended conventional HDBSCAN (e-HDBSCAN) for searching for new OCs in Gaia EDR3. A pipeline was developed based on the parallel computing technique to blindly search for open clusters from Gaia EDR3 within Galactic latitudes \left| b \right| <25 ^\circ. As a result, we obtained 3787 star clusters, of which 83 new OCs were reported after cross-match and visual inspection. At the same time, the main star cluster parameters are estimated by colour-magnitude diagram fitting. The study significantly increases the sample size and physical parameters of open clusters in the catalogue of OCs. It shows the incompleteness of the census of OCs across our Galaxy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As groups of coeval stars born from the same molecular cloud, an Open cluster (OC) is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way. The release of High-Precision Gaia Early Data Release 3 (Gaia EDR3) and modern machine-learning methods offer unprecedented opportunities to identify OCs. In this study, we extended conventional HDBSCAN (e-HDBSCAN) for searching for new OCs in Gaia EDR3. A pipeline was developed based on the parallel computing technique to blindly search for open clusters from Gaia EDR3 within Galactic latitudes \left| b \right| <25 ^\circ. As a result, we obtained 3787 star clusters, of which 83 new OCs were reported after cross-match and visual inspection. At the same time, the main star cluster parameters are estimated by colour-magnitude diagram fitting. The study significantly increases the sample size and physical parameters of open clusters in the catalogue of OCs. It shows the incompleteness of the census of OCs across our Galaxy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We identify and investigate a possible correlation between the \rm{[CII]} 158{\mu}m luminosity and linewidth in the \rm{[CII]}-detected galaxies. Observationally, the strength of the \rm{[CII]} 158{\mu}m emission line is usually stronger than that of the CO emission line and this \rm{[CII]} line has been used as another tracer of the galactic characteristics. Moreover, many \rm{[CII]}-detected galaxies are identified in z > 4. Motivated by previous studies of the CO luminosity - FWHM correlation relation (LFR) and the available new \rm{[CII]} measurements, we compile samples of the \rm{[CII]}-detected galaxies in the literature and perform the linear regression analysis. The \rm{[CII]} LFR is confirmed at a robust level. We also demonstrate the possible application of the \rm{[CII]} LFR by utilizing it on the distance measurement of the high-z galaxy. As a result, we extend the cosmic spatial scale beyond the redshift z of 7. With the outcome of the distance measurement, we constrain the cosmology parameters in the Chevallier-Polarski-Linder model, which considers the evolution of dark energy. Consequently, the uncertainties of the \textit{w}_{0} and \textit{w}_{a} are reduced significantly when the measured distance data of the \rm{[CII]}-detected galaxies are included in the cosmological parameter constraint, exemplifying the potential of using the \rm{[CII]}-detected galaxies as a tracer to constrain the cosmological parameters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We identify and investigate a possible correlation between the \rm{[CII]} 158{\mu}m luminosity and linewidth in the \rm{[CII]}-detected galaxies. Observationally, the strength of the \rm{[CII]} 158{\mu}m emission line is usually stronger than that of the CO emission line and this \rm{[CII]} line has been used as another tracer of the galactic characteristics. Moreover, many \rm{[CII]}-detected galaxies are identified in z > 4. Motivated by previous studies of the CO luminosity - FWHM correlation relation (LFR) and the available new \rm{[CII]} measurements, we compile samples of the \rm{[CII]}-detected galaxies in the literature and perform the linear regression analysis. The \rm{[CII]} LFR is confirmed at a robust level. We also demonstrate the possible application of the \rm{[CII]} LFR by utilizing it on the distance measurement of the high-z galaxy. As a result, we extend the cosmic spatial scale beyond the redshift z of 7. With the outcome of the distance measurement, we constrain the cosmology parameters in the Chevallier-Polarski-Linder model, which considers the evolution of dark energy. Consequently, the uncertainties of the \textit{w}_{0} and \textit{w}_{a} are reduced significantly when the measured distance data of the \rm{[CII]}-detected galaxies are included in the cosmological parameter constraint, exemplifying the potential of using the \rm{[CII]}-detected galaxies as a tracer to constrain the cosmological parameters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Open clusters (OCs) are regarded as tracers to understand stellar evolution theory and validate stellar models. In this study, we presented a robust approach to identifying OCs. A hybrid method of pyUPMASK and RF is first used to remove field stars and determine more reliable members. An identification model based on the RF algorithm built based on 3714 OC samples from Gaia DR2 and EDR3 is then applied to identify OC candidates. The OC candidates are obtained after isochrone fitting, the advanced stellar population synthesis (ASPS) model fitting, and visual inspection. Using the proposed approach, we revisited 868 candidates and preliminarily clustered them by the friends-of-friends algorithm in Gaia EDR3. Excluding the open clusters that have already been reported, we focused on the remaining 300 unknown candidates. From high to low fitting quality, these unrevealed candidates were further classified into Class A (59), Class B (21), and Class C (220), respectively. As a result, 46 new reliable open cluster candidates among classes A and B are identified after visual inspection.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasi-periodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 years of observational data, we systematically analyzed the quasi-periodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time-frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 years, and 3.3-4.3 years. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2(+-0.01) months, 3.1(+-0.04) months, ~6.1(+-0.4) months, 1.2(+-0.1) years, and 2.4(+-0.4) years. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1(+-0.2) months and 4.1(+-0.2) years in the northern hemisphere, 1(+-0.004) months, 5.9(+-0.2) months, 1(+-0.1) years, 1.4(+-0.1) years, and 2.4(+-0.4) years in the southern hemisphere, 6.1(+-0.4) months in solar cycle 23 (SC23) and 6.1(+-0.4) months, 1.2(+-0.1) years, and 3.7(+-0.2) years in solar cycle 24 (SC24). The analysis shows that quasi-periodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasi-periodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 years of observational data, we systematically analyzed the quasi-periodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time-frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 years, and 3.3-4.3 years. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2(+-0.01) months, 3.1(+-0.04) months, ~6.1(+-0.4) months, 1.2(+-0.1) years, and 2.4(+-0.4) years. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1(+-0.2) months and 4.1(+-0.2) years in the northern hemisphere, 1(+-0.004) months, 5.9(+-0.2) months, 1(+-0.1) years, 1.4(+-0.1) years, and 2.4(+-0.4) years in the southern hemisphere, 6.1(+-0.4) months in solar cycle 23 (SC23) and 6.1(+-0.4) months, 1.2(+-0.1) years, and 3.7(+-0.2) years in solar cycle 24 (SC24). The analysis shows that quasi-periodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.
分类： 天文学 >> 天文学 提交时间： 2024-12-06 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The double neutron star PSR J1846–0513 is discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Commensal Radio Astronomy FAST Survey. The pulsar is revealed to be harbored in an eccentric orbit with e = 0.208 and an orbital period of 0.613 day. The total mass of the system is constrained to be 2.6287(35)M⊙, with a mass upper limit of 1.3455 M⊙ for the pulsar and a mass lower limit of 1.2845 M⊙ for the companion star. To reproduce its evolution history, we perform a 1D model for the formation of PSR J1846–0513 whose progenitor is assumed to be neutron star—helium (He) star system via MESA code. Since the large eccentricity is widely believed to originate from an asymmetric supernova explosion, we also investigate the dynamical effects of the supernova explosion. Our simulated results show that the progenitor of PSR J1846–0513 could be a binary system consisting of a He star of 3.3–4.0 M⊙ and a neutron star in a circular orbit with an initial period of ∼0.5 day.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The infall of the Sagittarius (Sgr) Dwarf Spheroidal Galaxy in the Milky Way halo is an unique opportunity to understand how the different components of a dwarf galaxy could be tidally removed. In this work, we reconstruct the Sgr core morphology and kinematics on the basis of a model that has already successfully reproduced the Sgr stream. Here we use a very high resolution model that almost resolves individual stars in the Sgr core. It reproduces most of the observed morphology and kinematic properties, without specific fine-tuning. We also show that the dark matter may have been almost entirely stripped by Milky Way tides after two passages at pericenter. Finally the model predicts that the Sgr core will be fully disrupted within the next 2 Gyr.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As a dedicated solar radioheliograph, the MingantU SpEctral RadioHeliograph (MUSER) has a maximum baseline of more than 3000 meters and a frequency range of 400 MHz -- 15 GHz. According to the classical radio interferometry theory, the non-coplanar baseline effect (i.e., w-term effect) would be considered and calibrated for such a radio instrument. However, little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph in-depth. This study proposes a complete quantitative analysis of w-term effects for the MUSER. After a brief introduction of the MUSER, we systematically investigate the baseline variations over a year and analyze the corresponding variations of w-term. We further studied the effects of the w-term in the imaging for the specified extended source, i.e., the Sun. We discussed the possible effects of the w-term, such as image distortion and so on. The simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： LISA and Taiji are expected to form a space-based gravitational-wave (GW) detection network in the future. In this work, we make a forecast for the cosmological parameter estimation with the standard siren observation from the LISA-Taiji network. We simulate the standard siren data based on a scenario with configuration angle of 40^{\circ} between LISA and Taiji. Three models for the population of massive black hole binary (MBHB), i.e., pop III, Q3d, and Q3nod, are considered to predict the events of MBHB mergers. We find that, based on the LISA-Taiji network, the number of electromagnetic (EM) counterparts detected is almost doubled compared with the case of single Taiji mission. Therefore, the LISA-Taiji network's standard siren observation could provide much tighter constraints on cosmological parameters. For example, solely using the standard sirens from the LISA-Taiji network, the constraint precision of H_0 could reach 1.3\%. Moreover, combined with the CMB data, the GW-EM observation based on the LISA-Taiji network could also tightly constrain the equation of state of dark energy, e.g., the constraint precision of w reaches about 4\%, which is comparable with the result of CMB+BAO+SN. It is concluded that the GW standard sirens from the LISA-Taiji network will become a useful cosmological probe in understanding the nature of dark energy in the future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Many modeling of the Sagittarius (Sgr) stream have been attempted, but they still have difficulties to reproduce its full 6D space-phase properties. Using N-body simulation with a Milky Way mass of 5.2\times10^{11} M_{\odot} and a Sgr mass of 9.3\times10^{8} M_{\odot}, we have been able to reproduce well all 3D spatial features of Sgr stream, including its core, leading and trailing arms, and their associated bifurcations. Moreover, all reported 3D kinematics properties of the Sgr stream have been qualitatively reproduced without the need for a massive LMC, although the latter can not be ruled out from this work. Moreover, we also find that our model fails in reproducing the exact behaviors of the stream arms in the energy-angular momentum plane. It let us to suggest that significant further progress can be only achievable after introducing a major component in the Sgr progenitor, which is the gas that dominates all Irregular dwarf galaxies in the Sgr mass range.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We apply a statistical deconvolution of the parallax errors based on Lucy's inversion method (LIM) to the Gaia-DR3 sources to measure their three dimensional velocity components in the range of Galactocentric distances R between 8 kpc and 30 kpc with their corresponding errors and root mean square values. We find results that are consistent with those obtained by applying LIM to the Gaia-DR2 sources, and we conclude that the method gives convergent and more accurate results by improving the statistics of the data-set and lowering observational errors. The kinematic maps reconstructed with LIM up to R \approx 30 kpc show that the Milky Way is characterized by asymmetrical motions with significant gradients in all velocity components. Furthermore, we determine the Galaxy rotation curve V_C(R) up to \approx 27.5 kpc with the cylindrical Jeans equation assuming an axisymmetric gravitational potential. We find that V_C(R) is significantly declining up to the largest radius investigated. Finally, we also measure V_C(R) at different vertical heights, showing that, for R <15 kpc, there is a marked dependence on Z, whereas at larger R the dependence on Z is negligible.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The statistical study of the Coronal Mass Ejections (CMEs) is a hot topic in solar physics. To further reveal the temporal and spatial behaviors of the CMEs at different latitudes and heights, we analyzed the correlation and phase relationships between the occurrence rate of CMEs, the Coronal Brightness Index (CBI), and the 10.7-cm solar radio flux (F10.7). We found that the occurrence rate of the CMEs correlates with CBI relatively stronger at high latitudes (>=60) than at low latitudes (<=50). At low latitudes, the occurrence rate of the CMEs correlates relatively weaker with CBI than F10.7. There is a relatively stronger correlation relationship between CMEs, F10.7, and CBI during Solar Cycle 24(SC24) than Solar Cycle 23 (SC23). During SC23, the high-latitude CME occurrence rate lags behind F10.7 by three months, and during SC24, the low-latitude CME occurrence rate leads to the low-latitude CBI by one month. The correlation coefficient values turn out to be larger when the very faint CMEsare removed from the samples of the CDAW catalog. Based on our results, we may speculate that the source regions of the high/low-latitude CMEs may vary in height, and the process of magnetic energy accumulation and dissipation is from the lower to the upper atmosphere of the Sun. The temporal offsets between different indicators could help us better understand the physical processes responsible for the solar-terrestrial interactions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Improving the performance of solar flare forecasting is a hot topic in solar physics research field. Deep learning has been considered a promising approach to perform solar flare forecasting in recent years. We first used the Generative Adversarial Networks (GAN) technique augmenting sample data to balance samples with different flare classes. We then proposed a hybrid convolutional neural network (CNN) model M for forecasting flare eruption in a solar cycle. Based on this model, we further investigated the effects of the rising and declining phases for flare forecasting. Two CNN models, i.e., Mrp and Mdp, were presented to forecast solar flare eruptions in the rising phase and declining phase of solar cycle 24, respectively. A series of testing results proved: 1) Sample balance is critical for the stability of the CNN model. The augmented data generated by GAN effectively improved the stability of the forecast model. 2) For C-class, M-class, and X-class flare forecasting using Solar Dynamics Observatory (SDO) line-of-sight (LOS) magnetograms, the means of true skill statistics (TSS) score of M are 0.646, 0.653 and 0.762, which improved by 20.1%, 22.3%, 38.0% compared with previous studies. 3) It is valuable to separately model the flare forecasts in the rising and declining phases of a solar cycle. Compared with model M, the means of TSS score for No-flare, C-class, M-class, X-class flare forecasting of the Mrp improved by 5.9%, 9.4%, 17.9% and 13.1%, and the Mdp improved by 1.5%, 2.6%, 11.5% and 12.2%.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ultra-low-frequency gravitational waves (GWs) generated by individual inspiraling supermassive black hole binaries (SMBHBs) in the centers of galaxies may be detected by pulsar timing arrays (PTAs) in the future. These GW signals encoding absolute cosmic distances can serve as bright and dark sirens, having potential to be developed into a precise cosmological probe. Here we show that an SKA-era PTA consisting of 100 millisecond pulsars may observe about 20 bright sirens and 90 dark sirens during a 10-year observation. The bright sirens, together with the CMB data, have comparable capabilities to current mainstream data for measuring the equation of state of dark energy. The dark sirens could make the measurement precision of the Hubble constant far beyond the standard of precision cosmology. Our results indicate that ultra-low-frequency GWs from individual SMBHBs are of great significance in exploring the nature of dark energy and measuring the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ultra-low-frequency gravitational waves (GWs) generated by individual inspiraling supermassive black hole binaries (SMBHBs) in the centers of galaxies may be detected by pulsar timing arrays (PTAs) in the future. These GW signals encoding absolute cosmic distances can serve as bright and dark sirens, having potential to be developed into a precise cosmological probe. Here we show that an SKA-era PTA consisting of 100 millisecond pulsars may observe about 20 bright sirens and 90 dark sirens during a 10-year observation. The bright sirens, together with the CMB data, have comparable capabilities to current mainstream data for measuring the equation of state of dark energy. The dark sirens could make the measurement precision of the Hubble constant far beyond the standard of precision cosmology. Our results indicate that ultra-low-frequency GWs from individual SMBHBs are of great significance in exploring the nature of dark energy and measuring the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We investigate the kinematic-chemical distribution of Red Giant Branch (RGB) stars from the LAMOST survey crossed matched with Gaia DR2 proper motions, and present time tagging for the well-known ridge structures (diagonal distributions for V_R in the R, V_\phi plane) in the range of Galactocentric distance R = 8 to 15 kpc. We detect six ridge structures, including five ridges apparent in the radial velocity distribution and three ridges apparent in the vertical velocity, the sensitive time of which to the perturbations are from young population (0-3 Gyr) to old population (9-14 Gyr). Based on an analysis of the evolution of angular momentum distribution, we find that four ridges are relatively stationary, while another is evolving with time, which is confirmed by the difference analysis at different populations and supporting that there might be two kinds of dynamical origins. Furthermore, ridge features are also vividly present in the chemical properties ([Fe/H], [\alpha/Fe]). The comparison between the north and south hemispheres of the Galaxy does show some differences and the ridge features are asymmetrical. Moreover, we find that diagonal ridge structures may affect the shape of the rotation curve, which is manifested as fluctuations and undulations on top of a smooth profile. Finally we speculate that the bar dynamics should be not enough to explain all ridge properties including the break feature in the V_Z-L_Z plane.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Interacting dark energy (IDE) scenario assumes that there exists a direct interaction between dark energy and cold dark matter, but this interaction is hard to be tightly constrained by the current data. Finding new cosmological probes to precisely measure this interaction could deepen our understanding of dark energy and dark matter. Fast radio bursts (FRBs) will be seen in large numbers by future radio telescopes, and thus they have potential to become a promising low-redshift cosmological probe. In this work, we investigate the capability of future FRBs of constraining the dimensionless coupling parameter \beta in four phenomenological IDE models. We find that in the IDE models with the interaction proportional to the energy density of dark energy, about 10^5 FRB data can give constraint on \beta tighter than the current cosmic microwave background data. In all the IDE models, about 10^6 FRB data can constrain the absolute errors of \beta to less than 0.10, providing a way to precisely measure \beta by only one cosmological probe. The reconstruction of the interaction term also shows that the FRB data could help constrain the redshift evolution of interaction.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The identification and analysis of different variable sources is a hot issue in astrophysical research. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic survey has accumulated massive spectral data but contains no information about variable sources. Although a few related studies present variable source catalogs for the LAMOST, the studies still have a few deficiencies regarding the type and number of variable sources identified. In this study, we presented a statistical modeling approach to identify variable source candidates. We first crossed the Kepler, Sloan Digital Sky Survey (SDSS), and Zwicky Transient Facility (ZTF) catalogs to obtain light curves data of variable and non-variable sources. The data are then modeled statistically using commonly used variability parameters, respectively. And then, an optimal variable source identification model is determined using the Receiver Operating Characteristic (ROC) curve and four credible evaluation indices such as precision, accuracy, recall, and F1score. Based on this identification model, a catalog of LAMOST variable sources (including 631,769 variable source candidates with a probability greater than 95% and so on) is obtained. To validate the correctness of the catalog, we performed a two-by-two cross-comparison with the GAIA catalog and other published variable source catalogs. We achieved the correct rate ranging from 50% to 100%. Among the 123,756 sources cross-matched, our variable source catalog identifies 85,669 with a correct rate of 69%, which indicates that the variable source catalog presented in this study is credible.
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