分类： 护理学 >> 护理学 提交时间： 2023-04-22
Wang Bei
Xinglin,xiong
Sheng Lian
Chao Liu
Ming Yang
Jianing Li
Qi Wang
Xining Liu
Ye Mao
Qiongqiong Zang
Ye Wang
Yan Ma
Peijuan Wang
摘要： Objective: To explore the effect of implementing manpower supermarket resourcebank management in the nursing human resource management of Jiangsu ProvinceAcademy of Traditional Chinese medicine. Methods: The concept of supermarket management was first developed and appliedto the administration of manpower services. Next, the structure of nursing nursinghuman resource management was established. By developing the commodity bankof the manpower supermarket, comprising ① general nurse bank, ②special post mobile bank ③ post ability refueling bank. The quality of goods is ensuredbycombining job training and recruitment unit criteria. In parallel, a standardizedselection path is created, including the standardization of the order-sending reviewprocess, the implementation of the commodity maintenance regulations, andthescreening of the conditions of the selection units, ensuring the streamlined operationof the manpower supermarket. Results: A total of 1,284 nurses were dynamically deployed in the hospital fromOctober 2021 to October 2022 in 31 different batches. In addition to boostingthequality of nursing human resource management and the quality of specialized nursingcare, the high frequency of staff deployment and orderly and innovative management decreased the rate of patient complaints and the turnover rate of nurses. Conclusion: It is worth learning from the manpower supermarket management which combines diversified staffing needs, the need for flexible nursing staff management inthe management of routine epidemic prevention and control, as well as nursing staff capacity development to meet the needs of nursing human resource management inthe current state of medical services.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The halo stars on highly radial orbits should inevitably pass the center regions of the Milky Way. Under the assumption that the stellar halo is in dynamical equilibrium and axisymmetric, we integrate the orbits of $\sim 10,000$ halo K-giants at $5\leq r \leq 50$ kpc cross-matched from LAMOST DR5 and $Gaia$ DR3. By carefully considering the selection function, we construct the stellar halo distribution at the entire regions of $r \leq 50$ kpc. We find that a double-broken power-law function well describes the stellar halo density distribution with shallower slopes in the inner regions and the two breaks at $r=10$ kpc and $r=25$ kpc, respectively. The stellar halo becomes flatter from outer to inner regions but has $q\sim 0.5$ at $r \lesssim 5$ kpc. The stellar halo becomes isotropic with a slight prograde rotation in the inner 5 kpc, and reaches velocity dispersions of $\sim 250\rm \ km\ s^{-1}$. We get a weak negative metallicity gradient of $-0.005$ dex kpc$^{-1}$ at $5\leq r \leq 50$ kpc, while there is an excess of relative metal-rich stars with [Fe/H]$>-1$ in the inner 10 kpc. The halo interlopers at $r \leq 5$ kpc from integration of our sample has a mass of $\sim1.2 \times 10^8\ M_{\odot}$ ($\sim 4.7 \times 10^7\ M_{\odot}$ at [Fe/H]$<-1.5$), which can explain 50-100% of the metal-poor stars with [Fe/H]$<-1.5$ directly observed in the Galactic central regions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jianping Xiong
Chao Liu
Jiao Li
Jiadong Li
Bo Zhang
Xiaodian Chen
Changqing Luo
Zihuang Cao
Yongheng Zhao
摘要： High-precision stellar mass and radius measured directly from binaries can effectively calibrate the stellar models. However, such a database containing full spectral types and large range of metallicity is still not fully established. A continuous effort of data collecting and analysis are requested to complete the database. In this work, we provide a catalog containing 184 binaries with independent atmospheric parameters and accurate masses and radii as the benchmark of stellar mass and radius. The catalog contains 56 new detached binaries from LAMOST Medium-resolution spectroscopic (MRS) survey and 128 detached eclipsing binaries compiled from previous studies. We obtain the orbital solutions of the new detached binaries with uncertainties of masses and radii smaller than 5%. These new samples densify the distribution of metallicity of the high-precision stellar mass library and add 9 hot stars with Teff>8000 K. Comparisons show that these samples well agree with the PARSEC isochrones in Teff-logg-mass-radius-luminosity space. We compare mass and radius estimates from isochrone and SED fitting, respectively, with those from the binary orbital solution. We find that the precision of the stellar-model dependent mass estimates is >10% and the precision of the radius estimates based on atmospheric parameters is >15%. These give a general view of the uncertainty of the usual approaches to estimate stellar mass and radius.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jianping Xiong
Chao Liu
Jiao Li
Jiadong Li
Bo Zhang
Xiaodian Chen
Changqing Luo
Zihuang Cao
Yongheng Zhao
摘要： High-precision stellar mass and radius measured directly from binaries can effectively calibrate the stellar models. However, such a database containing full spectral types and large range of metallicity is still not fully established. A continuous effort of data collecting and analysis are requested to complete the database. In this work, we provide a catalog containing 184 binaries with independent atmospheric parameters and accurate masses and radii as the benchmark of stellar mass and radius. The catalog contains 56 new detached binaries from LAMOST Medium-resolution spectroscopic (MRS) survey and 128 detached eclipsing binaries compiled from previous studies. We obtain the orbital solutions of the new detached binaries with uncertainties of masses and radii smaller than 5%. These new samples densify the distribution of metallicity of the high-precision stellar mass library and add 9 hot stars with Teff>8000 K. Comparisons show that these samples well agree with the PARSEC isochrones in Teff-logg-mass-radius-luminosity space. We compare mass and radius estimates from isochrone and SED fitting, respectively, with those from the binary orbital solution. We find that the precision of the stellar-model dependent mass estimates is >10% and the precision of the radius estimates based on atmospheric parameters is >15%. These give a general view of the uncertainty of the usual approaches to estimate stellar mass and radius.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Luqian Wang
Jiao Li
You Wu
Douglas R. Gies
Jin Zhong Liu
Chao Liu
Yanjun Guo
Xuefei Chen
Zhanwen Han
摘要： Be stars are B-type main-sequence stars that display broad Balmer emission lines in their spectra. Identification of Be population is essential to further examine the formation and evolutionary models. We report the detection of classical Be (CBe) stars from observations with the Large sky Area Multi-Object fiber Spectroscopic Telescope Medium Resolution Survey of Date Release 7 (LAMOST MRS DR7). We used a deep convolutional neural network, the ResNet, with an 18-layer module to examine the morphology of the H alpha profile. We identified 1,162 candidate Be stars from the collection of 2,260,387 spectra for 789,918 stars in the database. The ResNet network achieves a Be star classification accuracy of 99.5%. Among the detections, 151 of these are prior known Be stars cross-matched from the literature. By applying a three-step test, we identified 183 new CBe stars. We find that 41 CBe stars are members of known open clusters. Based upon an investigation of the kinematics of the identified CBe stars from the Gaia EDR3 astrometric solutions, we identified 16 new runaways. These new identifications will provide a reference for future follow-ups to further investigate their physical properties.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Massive binary stars play a crucial role in many astrophysical fields. Investigating the statistical properties of massive binary stars is essential to trace the formation of massive stars and constrain the evolution of stellar populations. However, no consensus has been achieved on the statistical properties of massive binary stars, mainly due to the lack of a large and homogeneous sample of spectroscopic observations. We study the intrinsic binary fraction $f_{\rm b}^{\rm in}$ and distributions of mass ratio $f(q)$ and orbital period $f(P)$ of early-type stars (comprised of O-, B-, and A-type stars) and investigate their dependences on effective temperature $T_{\rm eff}$, stellar metallicity [M/H], and the projection velocity $v\sin{i}$, based on the homogeneous spectroscopic sample from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release Eight (DR8). We found that $f_{\rm b}^{\rm in}$ increases with increasing $T_\mathrm{eff}$. The binary fraction is positively correlated with metallicity for spectra in the sample. Over all the $v\sin{i}$ values we considered, the $f_{\rm b}^{\rm in}$ have constant values of $\sim$50\%. It seems that the binary population is relatively evenly distributed over a wide range of $v\sin{i}$ values, while the whole sample shows that most of the stars are concentrated at low values of $v\sin{i}$ (probably from strong wind and magnetic braking of single massive stars) and at high values of $v\sin{i}$ (likely from the merging of binary stars). Stellar evolution and binary interaction may be partly responsible for this.There are no correlations found between $\pi$($\gamma$) and $T_{\rm eff}$, nor for $\pi$($\gamma$) and [M/H]. The uncertainties of the distribution decrease toward a larger sample size with higher observational cadence.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Bo Zhang
Ying-Jie Jing
Fan Yang
Jun-Chen Wan
Xin Ji
Jian-Ning Fu
Chao Liu
Xiao-Bin Zhang
Feng Luo
Hao Tian
Yu-Tao Zhou
Jia-Xin Wang
Yan-Jun Guo
Weikai Zong
Jian-Ping Xiong
Jiao Li
摘要： We developed a convolutional neural network (CNN) model to distinguish the double-lined spectroscopic binaries (SB2s) from others based on single exposure medium-resolution spectra ($R\sim 7,500$). The training set consists of a large set of mock spectra of single stars and binaries synthesized based on the MIST stellar evolutionary model and ATLAS9 atmospheric model. Our model reaches a novel theoretic false positive rate by adding a proper penalty on the negative sample (e.g., 0.12\% and 0.16\% for the blue/red arm when the penalty parameter $\Lambda=16$). Tests show that the performance is as expected and favors FGK-type Main-sequence binaries with high mass ratio ($q \geq 0.7$) and large radial velocity separation ($\Delta v \geq 50\,\mathrm{km\,s^{-1}}$). Although the real false positive rate can not be estimated reliably, validating on eclipsing binaries identified from Kepler light curves indicates that our model predicts low binary probabilities at eclipsing phases (0, 0.5, and 1.0) as expected. The color-magnitude diagram also helps illustrate its feasibility and capability of identifying FGK MS binaries from spectra. We conclude that this model is reasonably reliable and can provide an automatic approach to identify SB2s with period $\lesssim 10$ days. This work yields a catalog of binary probabilities for over 5 million spectra of 1 million sources from the LAMOST medium-resolution survey (MRS), and a catalog of 2198 SB2 candidates whose physical properties will be analyzed in our following-up paper. Data products are made publicly available at the journal as well as our Github website.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Motivated by the astrophysical problems of star formations from molecular clouds,we make the first step on the possible long time behaviors of certain irregularly-shaped molecular clouds. We emphasis the main difficulty of the blowups of the irregular-shaped fluids with vacuum (molecular clouds) comes from the initial irregular configurations of its density (multiple centers of gravity). This inevitably causes far more complicated movements during the evolution than the one with spherical symmetry. The spherical symmetric case has been well studied. However, for the non-spherical symmetric case with the gravity, it is very rare in the references due to a very complicate nonlinear interaction between the gravity and the fluids. This article concludes, under the admissible data (i.e., large scale, irregularly-shaped, expanding and rotational molecular clouds), the developments of the solution (molecular clouds) are either global (the first class) with near-boundary mass accretions (leads to star formations), or blowup at finite time. In addition, certain singularities can be removed from the boundary if the data is strongly admissible. This paper partially answers Makino's conjecture [37] in 1992 on the finite time blowup of any tame solution without symmetries for some data and the model of the molecular clouds and the local wellposedness have been established in the companion article [30].
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Siteng Fan
Peter Gao
Xi Zhang
Danica J. Adams
Nicholas W. Kutsop
Carver J. Bierson
Chao Liu
Jiani Yang
Leslie A. Young
Andrew F. Cheng
Yuk L. Yung
摘要： Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto's haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulations of Titan's haze, this result suggests that haze particles in reducing atmospheres undergo rapid shape change near pressure levels ~0.5Pa and favors a photochemical rather than a dynamical origin for the formation of Titan's detached haze. It also demonstrates that both oxidizing and reducing atmospheres can produce multi-modal hazes, and encourages reanalysis of observations of hazes on Titan and Triton.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Bo Zhang
Jiao Li
Fan Yang
Jian-Ping Xiong
Jian-Ning Fu
Chao Liu
Hao Tian
Yin-Bi Li
Jia-Xin Wang
Cai-Xia Liang
Yu-Tao Zhou
Wei-kai Zong
Cheng-Qun Yang
Nian Liu
Yong-Hui Hou
摘要： Radial velocity (RV) is among the most fundamental physical quantities obtainable from stellar spectra and is rather important in the analysis of time-domain phenomena. The LAMOST Medium-Resolution Survey (MRS) DR7 contains 5 million single-exposure stellar spectra at spectral resolution $R\sim7\,500$. However, the temporal variation of the RV zero-points (RVZPs) of the MRS survey, which makes the RVs from multiple epochs inconsistent, has not been addressed. In this paper, we measure the RVs of the 3.8 million single-exposure spectra (for 0.6 million stars) with signal-to-noise ratio (SNR) higher than 5 based on cross-correlation function (CCF) method, and propose a robust method to self-consistently determine the RVZPs exposure-by-exposure for each spectrograph with the help of \textit{Gaia} DR2 RVs. Such RVZPs are estimated for 3.6 million RVs and can reach a mean precision of $\sim 0.38\,\mathrm{km\,s}^{-1}$. The result of the temporal variation of RVZPs indicates that our algorithm is efficient and necessary before we use the absolute RVs to perform time-domain analysis. Validating the results with APOGEE DR16 shows that our absolute RVs can reach an overall precision of 0.84/0.80 $\mathrm{km\,s}^{-1}$ in the blue/red arm at $50<\mathrm{SNR}<100$, while 1.26/1.99 $\mathrm{km\,s}^{-1}$ at $5<\mathrm{SNR}<10$. The cumulative distribution function (CDF) of the standard deviations of multiple RVs ($N_\mathrm{obs}\geq 8$) for 678 standard stars reach 0.45/0.54, 1.07/1.39, and 1.45/1.86 $\mathrm{km\,s}^{-1}$ in the blue/red arm at 50\%, 90\%, and 95\% levels, respectively. The catalogs of the RVs, RVZPs, and selected candidate RV standard stars are available at \url{https://github.com/hypergravity/paperdata}.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We derive stellar parameters and abundances (`stellar labels') of 40,034 late-B and A-type main-sequence stars extracted from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope Medium Resolution Survey (LAMOST--MRS). The primary selection of our early-type sample was obtained from LAMOST Data Release 7 based on spectral line indices. We employed the Stellar LAbel Machine (SLAM) to derive their spectroscopic stellar parameters, drawing on Kurucz spectral synthesis models with 6000 K $< T_\mathrm{eff} <$ 15,000 K and $-1$ dex $< \mathrm{[M/H]} <$ 1 dex. For a signal-to-noise ratio of $\sim 60$, the cross-validated scatter is $\sim$75 K, 0.06 dex, 0.05 dex, and $\sim 3.5\,\mathrm{km\,s^{-1}}$ for $T_\mathrm{eff}$, $\log g$, [M/H], and $v\sin i$, respectively. A comparison with objects with prior, known stellar labels shows great consistency for all stellar parameters, except for $\log g$. Although this is an intrinsic caveat that comes from the MRS's narrow wavelength coverage, it only has a minor effect on estimates of the stellar rotation rates because of the decent spectral resolution and the profile-fitting method employed. The masses and ages of our early-type sample stars were inferred from non-rotating stellar evolution models. This paves the way for reviewing the properties of stellar rotation distributions as a function of stellar mass and age.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Massive binary stars play a crucial role in many astrophysical fields. Investigating the statistical properties of massive binary stars is essential to trace the formation of massive stars and constrain the evolution of stellar populations. However, no consensus has been achieved on the statistical properties of massive binary stars, mainly due to the lack of a large and homogeneous sample of spectroscopic observations. We study the intrinsic binary fraction $f_{\rm b}^{\rm in}$ and distributions of mass ratio $f(q)$ and orbital period $f(P)$ of early-type stars (comprised of O-, B-, and A-type stars) and investigate their dependences on effective temperature $T_{\rm eff}$, stellar metallicity [M/H], and the projection velocity $v\sin{i}$, based on the homogeneous spectroscopic sample from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release Eight (DR8). We found that $f_{\rm b}^{\rm in}$ increases with increasing $T_\mathrm{eff}$. The binary fraction is positively correlated with metallicity for spectra in the sample. Over all the $v\sin{i}$ values we considered, the $f_{\rm b}^{\rm in}$ have constant values of $\sim$50\%. It seems that the binary population is relatively evenly distributed over a wide range of $v\sin{i}$ values, while the whole sample shows that most of the stars are concentrated at low values of $v\sin{i}$ (probably from strong wind and magnetic braking of single massive stars) and at high values of $v\sin{i}$ (likely from the merging of binary stars). Stellar evolution and binary interaction may be partly responsible for this.There are no correlations found between $\pi$($\gamma$) and $T_{\rm eff}$, nor for $\pi$($\gamma$) and [M/H]. The uncertainties of the distribution decrease toward a larger sample size with higher observational cadence.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Most structural and evolutionary properties of galaxies strongly rely on the stellar initial mass function (IMF), namely the distribution of the stellar mass formed in each episode of star formation. As the IMF shapes the stellar population in all stellar systems, it turns out to become one of the most fundamental concepts of modern astronomy. Both constant and variable IMFs across different environments have been claimed despite a large number of theoretical and observational efforts. However, the measurement of the IMF in Galactic stellar populations has been limited by the relatively small number of photometrically observed stars, leading to high uncertainties. Here we report a star-counting result based on ~93,000 spectroscopically observed M-dwarf stars, an order of magnitude more than previous studies, in the 100--300 parsec (pc) Solar neighbourhood. We find unambiguous evidence of a variable IMF that depends on both metallicity and stellar age. Specifically, the stellar population formed at the early time contains fewer low-mass stars compared to the canonical IMF, independent of stellar metallicities. In present days, on the other hand, the proportion of low-mass stars increases with stellar metallicity. The variable abundance of low-mass stars in our Milky Way establishes a powerful benchmark for models of star formation and can heavily impact results in Galactic chemical enrichment modelling, mass estimation of galaxies, and planet formation efficiency.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Galaxy is found to be in disequilibrium based on recent findings of the North/South (N/S) asymmetry and the phase mixing signatures, such as a phase spiral (snail) structure in the vertical phase space ($z-V_{z}$). We show that the N/S asymmetry in a tracer population of dwarfs may be quantitatively modeled with a simple phase snail model superimposed on a smooth equilibrium background. As the phase snail intersects with the $z$ axis, the number density is enhanced, and the velocity dispersion ($\sigma_{z}$) is decreased relative to the other side of the Galactic plane. Fitting only to the observed asymmetric N/S $\sigma_{z}$ profiles, we obtain reasonable parameters for the phase space snail and the potential utilized in modeling the background, despite the complex dependence of the model on the potential parameters and the significant selection effects of the data. Both the snail shape and the N/S number density difference given by our best-fit model are consistent with previous observations. The equilibrium background implies a local dark matter density of $0.0151^{+0.0050}_{-0.0051}$ ${\rm M}_{\odot}\,{\rm pc}^{-3}$. The vertical bulk motion of our model is similar to the observation, but with a $\sim$1.2 $\rm km\,s^{-1}$ shift. Our work demonstrates the strong correlation between the phase space snail and the N/S asymmetry. Future observational constraints will facilitate more comprehensive snail models to unravel the Milky Way potential and the perturbation history encoded in the snail feature.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jiao Li
Jiang-Dan Li
Yan-Jun Guo
Zhan-Wen Han
Xue-Fei Chen
Chao Liu
Hong-Wei Ge
Deng-Kai Jiang
Li-Fang Li
Bo Zhang
Jia-Ming Liu
Hao Tian
Hao-Tong Zhang
Hai-Long Yuan
Wen-Yuan Cui
Juan-Juan Ren
Jing-Hao Cai
Jian-Rong Shi
摘要： LAMOST-MRS-B is one of the sub-surveys of LAMOST medium-resolution (R~7500) spectroscopic survey. It aims at studying the statistical properties (e.g., binary fraction, orbital period distribution, mass ratio distribution) of binary stars and exotic stars. We intend to observe about 30000 stars (10 mag = 10, respectively. Most of the sources are B-, A-, and F-type stars with 0.6 < [Fe/H] < 0.4 dex. We also obtain 347 identified variable and exotic stars and about 250 stars with [Fe/H] < 1 dex. We measure radial velocities (RVs) by using 892233 spectra of the stars. The uncertainties of RV achieve about 1 km/s and 10 km/s1 for 95% of late- and early-type stars, respectively. The datasets presented in this paper are available at http://www.doi.org/10.57760/sciencedb.j00113.00035.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We combine the kinematics of 159 globular clusters (GCs) provided by the Gaia
Early Data Release 3 (EDR3) with other observational data to classify the GCs,
and to estimate the mass of the Milky Way (MW). We use the age-metallicity
relation, integrals of motion, action space and the GC orbits to identify the
GCs as either formed in-situ (Bulge and Disk) or ex situ (via accretion). We
find that $45.3\%$ have formed in situ, $38.4\%$ may be related to known merger
events: Gaia-Sausage-Enceladus, the Sagittarius dwarf galaxy, the Helmi
streams, the Sequoia galaxy, and the Kraken galaxy. We also further identify
three new sub-structures associated with the Gaia-Sausage-Enceladus. The
remaining $16.3\%$ of GCs are unrelated to the known mergers and thought to be
from small accretion events. We select 46 GCs which have radii $8.0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Based on mathematically rigorous analysis of nonlinear differential equations studied in our companion article [1], we construct a model which describes the \textit{nonlinear} gravitational instability on a local portion of the universe characterized by the expanding Newtonian universe. In this portion, the perturbations are homogeneous and isotropic. This result, to some extent, can be viewed as a nonlinear version of the Jeans instability. The growth rate of the relative density due to the nonlinear effects is much faster (at least $\sim \exp(t^{\frac{2}{3}})$ or blowup at a finite time according to the data) than the one predicted by the classical linear version of the Jeans instability ($\sim t^{\frac{2}{3}}$), and it leads to a better, or potentially substantial impacts on, understanding of the formation of the nonlinear structures in the universe and stellar systems. This article associated with [1] provides a new window into the rigorously mathematical and robust method, instead of the most used approximations and numerical calculations, of the fully nonlinear analysis of the Jeans instability for general cases.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We combine the kinematics of 159 globular clusters (GCs) provided by the Gaia
Early Data Release 3 (EDR3) with other observational data to classify the GCs,
and to estimate the mass of the Milky Way (MW). We use the age-metallicity
relation, integrals of motion, action space and the GC orbits to identify the
GCs as either formed in-situ (Bulge and Disk) or ex situ (via accretion). We
find that $45.3\%$ have formed in situ, $38.4\%$ may be related to known merger
events: Gaia-Sausage-Enceladus, the Sagittarius dwarf galaxy, the Helmi
streams, the Sequoia galaxy, and the Kraken galaxy. We also further identify
three new sub-structures associated with the Gaia-Sausage-Enceladus. The
remaining $16.3\%$ of GCs are unrelated to the known mergers and thought to be
from small accretion events. We select 46 GCs which have radii $8.0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Di-Chang Chen
Ji Wei Xie
Ji-Lin. Zhou
Jia-Yi Yang
Subo Dong
Zi Zhu
Zheng Zheng
Chao Liu
Weikai Zong
Ali Luo
摘要： The radius valley, a dip in the radius distribution of exoplanets at ~1.9 Earth radii separates compact rocky Super-Earths and Sub-Neptunes with lower density. Various hypotheses have been put forward to explain the radius valley. Characterizing the radius valley morphology and its correlation to stellar properties will provide crucial observation constraints on its origin mechanism and deepen the understanding of planet formation and evolution. In this paper, the third part of the Planets Across the Space and Time (PAST) series, using the LAMOST-Gaia-Kepler catalog, we perform a systematical investigation into how the radius valley morphology varies in the Galactic context, i.e., thin/thick galactic disks, stellar age and metallicity abundance ([Fe/H] and [alpha/Fe]). We find that (1) The valley becomes more prominent with the increase of both age and [Fe/H]. (2) The number ratio of super-Earths to sub-Neptunes monotonically increases with age but decreases with [Fe/H] and [alpha/Fe]. (3) The average radius of planets above the valley (2.1-6 Earth radii) decreases with age but increases with [Fe/H]. (4) In contrast, the average radius of planets below the valley (R < 1.7 Earth radii) is broadly independent on age and metallicity. Our results demonstrate that the valley morphology as well as the whole planetary radius distribution evolves on a long timescale of giga-years, and metallicities (not only Fe but also other metal elements, e.g., Mg, Si, Ca, Ti) play important roles in planet formation and in the long term planetary evolution.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jiangdan Li
Jiao Li
Chao Liu
Chunqian Li
Yanjun Guo
Luqian Wang
Xuefei Chen
Lifeng Xing
Yonghui Hou
Zhanwen Han
摘要： Binary evolution leads to the formation of important objects crucial to the development of astrophysics, but the statistical properties of binary populations are still poorly understood. The LAMOST-MRS has provided a large sample of stars to study the properties of binary populations, especially for the mass ratio distributions and the binary fractions. We have devised a Peak Amplitude Ratio (PAR) approach to derive the mass ratio of a binary system based on results obtained from its spectrum. By computing a cross-correlation function (CCF), we established a relationship between the derived mass ratio and the PARs of the binary systems. By utilizing spectral observations obtained from LAMSOT DR6 & DR7, we applied the PAR approach to form distributions of the derived mass ratio of the binary systems to the spectral types. We selected the mass ratio within the range of $0.6-1.0$ for investigating the mass-ratio distribution. Through a power-law fitting, we obtained the power index $\gamma$ values of $-0.42\pm0.27$, $0.03\pm0.12$, and $2.12\pm0.19$ for A-, F-, and G-type stars identified in the sample, respectively. The derived $\gamma$-values display an increasing trend toward lower primary star masses, and G-type binaries tend to be more in twins. The close binary fractions (for $P\lesssim 150\,{\rm d}$ and $q\gtrsim 0.6$) in our sample for A, F and G binaries are $7.6\pm 0.5 \%$, $4.9\pm 0.2 \%$ and $3.7 \pm 0.1 \%$, respectively. Note that the PAR approach can be applied to large spectroscopic surveys of stars.
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