| 其他摘要 | Early-type stars are massive and hot stars with spectral type span from O-type to A-type. They are important contributors to many astronomical mechanisms. Observations show that over 70% of O-type massive stars interact with their companions. Binary interactions have significant impact on the evolution of early-type stars. Early-type stars likely evolve to compact binary systems as potential gravitational-wave sources, such as double black holes, double neutron stars, and neutron star-black hole binaries. Massive early-type stars have significant effects on the interstellar medium, element enrichment, and star formation in the universe through ultraviolet radiation, stellar wind, and supernova explosions. The early-type star population can be used to trace the spiral structure in the Milky Way and provide observational constraints on the dynamics of the Milky Way. Because of the complex evolutionary process involved in the massive stars and the lack of observational constraints to these systems, the subject of massive stars is one of the most uncertain areas in stellar evolution theory. The lack of systematic and consistent study of early-type stars to estimate their atmospheric parameters and statistical properties has altered us to fully picture the evolutionary process of massive stars. Fortunately, thanks to the extensive collection of spectroscopic observations provided by the LAMOST database, this offers us a rare opportunity to study the subject of massive stars. In this thesis work, we have conducted several studies to investigate the atmospheric parameters of early-type stars based on the spectra from LAMOST and their binary statistical properties. The main research achievements accomplished are as follows: 1.We identified 9382 early-type stars from the LAMOST medium-resolution survey (MRS) by adopting the technique of measuring the equivalent widths of several diagnostic spectral lines. We estimated the stellar labels of these stars, including effective temperature (Teff), surface gravity (logg), metallicity ([M/H]), and projected rotational velocity (𝑣 sin 𝑖) via applying the data-driven technique called stellar label machine (SLAM) and the non-local thermal equilibrium TLUSTY synthetic spectra to the observations. The atmospheric parameters of early-type stars obtained from the LAMOST low-resolution survey (LRS) are also given. The errors are 𝜎(𝑇eff) = 2,185 K, 𝜎(log 𝑔) = 0.29 dex, and 𝜎(𝑣 sin 𝑖) = 11 km s−1 for MRS, and 𝜎(𝑇eff) = 1,642 K, 𝜎(log 𝑔) = 0.25 dex, and 𝜎(𝑣 sin 𝑖) = 42 km s−1 for LRS spectra, respectively. 2.Based on a sample of 9382 early-type stars identified from the LAMOST-MRS, we identified stars displaying significant variations in the measured relative radial velocity as spectroscopic binary systems. Monte Carlo simulations were then applied to the observed binary fraction to correct for any observational biases, resulting in a relationship between the intrinsic binary fraction and the spectral type of the sample stars. In the sample of 886 early-type stars with more than six observations for each of them, we found that the intrinsic binary fraction in the sample displays an increasing trend toward the population with a higher effective temperature. The binary fraction can reach up to 76% for O- and B-type stars while dropping to 48% for B- and A-type stars. A similar trend was found in the relationship between the intrinsic binary fraction and metallicity, in which the ratio achieves 72% for metal-rich stars and degrades to 44% for metal-poor stars in the sample. We also examined the influence of sample size and the number of observational cadences on the results and found that the statistical properties are constrained better towards a bigger sample size and higher number of observations. 3.Based on the large collection of early-type stars identified from the LAMOST-MRS and their derived atmospheric parameters, as noted previously, we have identified 294 OB runaway stars from the final sample of 4618 stars and investigated their kinematic properties based upon proper motions provided by the Gaia DR3. 4.𝛼 element, such as magnesium (Mg), is a useful indicator to trace the nucleosynthesis of core-collapse supernovae. R-process elements (e.g. europium (Eu)) is used to track the neutron star-neutron star merger and constrain the gas-mixing processes during the star formation. One-dimensional (1D) local thermodynamic equilibrium (LTE) models are widely adopted to measure the abundance of Mg and Eu. In this work, we apply 1D non-local thermodynamic equilibrium (NLTE) and average three-dimensional (<3d>) models to measure the abundance of Mg and Eu. The results obtained from the 1D NLTE atmospheric model show that the Eu values are slightly lower than those obtained from LTE by 0.1 dex, while the Mg values are almost consistent between the two models. |
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