Group leader: 22070902 Huang Zixuan
Team members: 22070801 Li Yuwei 22070804 Feng Yuhui 22070807 Geng Jie 22070814 He Yang
Abstract
This paper mainly expounds that the white dwarf main sequence binary star is a binary star composed of a white dwarf star and a main sequence star.The importance of star system in the study of stellar evolution. This paper introduces three observation methods in detail: spectrum.Observation, multi band observation, light variation curve and radial velocity observation are used to search for such binary systems.In this paper, a fast and efficient program using wavelet transform method is proposed, which can screen by identifying spectral featuresSelect white dwarf main sequence binary candidates. In the process of research, first conduct preliminary screening through code, and then pass through people.After visual confirmation, 24 new white dwarf main sequence binaries were successfully selected from 10055 data.Although the search efficiency is high, the accuracy of the code still needs to be improved. Future research plans will try to makeUse new methods to improve screening efficiency. This study not only provides a theoretical basis for the mechanism of star evolution and binary star formation.It not only provides valuable observational evidence, but also shows the great potential of cutting-edge technology in the field of astronomical data mining.
1 Introduction
1.1 introduction to white dwarf main sequence binary stars
A binary star system consisting of a white dwarf (WD) as the main star and a main sequence star as the companion star,It is called white dwarf major sequence binary system (WDMS).The journey of star formation begins in the vast nebula. When a protostar is in the interstellar medium, byThe giant molecular cloud composed of gas and dust slowly collapses and forms, and its initial composition is uniform,It contains about 70% hydrogen and 28% helium. At this initial stage, the radiation energy released by the protostarIt mainly comes from the gravitational energy transformed during its contraction. At this time, gravity and gas pressure are almost equal in potentialThe enemy, together, maintains a state called quasi hydrostatic equilibrium. As protostars become increasingly unstableTransparent, radiation can barely escape from its surface, while its internal temperature rises sharply. When the temperature of the star core exceeded 8million Kelvin, the hydrogen nucleus began to fuse into helium at high temperature,This thermonuclear reaction releases enormous energy and pushes the star to complete hydrostatic equilibrium.State, thus officially entering the ranks of the main sequence star.
For those stars with low and medium mass, they have spent a long and stable period in the main sequence phaseAfter years, the hydrogen fusion reaction gradually came to an end. Then the core of the star began to accumulate heliumAnd with this process, it expands into a spectacular red giant star. The outer region of a popular superstar.When it expands outward at an amazing speed, the helium nucleus in its core region is violent under the action of reaction force.Shrink inward. This extreme compression makes the material keep heating up until the core temperature soars by more than 100million.The helium nuclei began to coalesce into carbon. After millions of years, the helium nucleus has been gradually depleted, and the constant.The structure of the star is also becoming more complex: the outer layer is still a mixture dominated by hydrogen, and below it is a layer of helium, while.Deep in the helium layer, there is also a sphere made of carbon. With the increasingly complex nuclear reaction process,.The temperature near the core continues to rise, leading to further conversion of carbon into other heavier elements. Same as above.The original stable main sequence star became extremely unstable and eventually evolved into a huge fireball. When this.When the unstable state reaches the limit, the red giant star will have a violent explosion, and.All matter is ejected, and these substances diffuse in the universe and form nebulae again. And in this.After the spectacular explosion, only one core, which we call a white dwarf, was left.
However, for some main sequence binaries with small initial orbital spacing, when the mass of the main sequence binaries is larger.When leaving the main sequence stage and entering the giant star or progressive giant branch stage, its expanded envelope will swallow up the companion star,Thus, the binary system enters the common envelope (CE) evolution stage.At this stage, the friction inside the common envelope gradually reduces the orbital spacing of the binary stars, accompanied by the channel energy and angular momentum are also reduced accordingly, which eventually leads to the throwing out of the common cladding and the formation of the rear co cladding double.Post common envelope binary (PCEB). Wdms[1] number of Double Satellites with the characteristics of multiple targets and easy observation, it has become the most ideal binary system to explore the evolution mechanism of the common envelope.
1.2 observation and search of white dwarf main sequence binary stars
There are generally three observation methods for white dwarf main sequence binary stars
1. spectrum observation: use large optical telescopes (such as LAMOST) for spectrum observation to obtain the spectral data of stars. By comparing the shape of the characteristic lines in the spectrum and the continuous spectrum, we can preliminarily screen out the possible white dwarf main sequence binary candidates.
2. multi band observation: combined with multi band observation data such as optics, infrared and ultraviolet, the candidates are comprehensively analyzed to determine the existence of the binary system. Multi band observations can provide information of white dwarf main sequence binaries at different wavelengths, which is helpful to understand the physical properties of such binaries more comprehensively.
3. optical curve and radial velocity observation: by observing the optical curve and radial velocity change of the binary system, the orbital parameters of the binary system can be derived, such as orbital period, eccentricity, semi major axis, etc. These parameters are of great significance for understanding the evolution state and interaction mechanism of binary stars.
At present, the international classic search method for white dwarf and main sequence binary stars has spectral decomposition technology: match the observed spectrum with the known spectral template of white dwarf and main sequence stars, and identify the binary star system by comparing the spectral characteristics; Spectral energy distribution (SED) fitting: according to the position in the herogram, the possible candidates for WDMS binaries are preliminarily screened out; Color selection method: select binary candidates according to the color index of celestial bodies in different bands, etc.
2 Data source – LAMOST data
"Large sky area multi-target optical fiber spectrum telescope" (LAMOST), also known as GuoShouJing telescope, is a Zhongxing ceremonial reflection Schmidt telescope with an effective aperture of 3.64.9 m, located at the Xinglong observation base of the National Astronomical Observatory of the Chinese Academy of Sciences in Xinglong County, Chengde City, Hebei Province. The main body is composed of a reflecting Schmidt correction mirror MA in the north, a spherical main mirror MB in the South and a focal plane in the middle. During observation, the spherical primary mirror and focal plane are fixed on the ground. When the target passes near the midheaven, it is tracked by the correction mirror. Due to the creative use of active optical technology, the correction mirror has broken through the technical bottleneck that the telescope cannot have both large aperture and large field of view. It is the largest large field of view Survey Telescope in operation in the world. The focal plane diameter is 1.75 m, and the parallel controllable optical fiber positioning technology is used to simultaneously control the real-time position of 4000 optical fibers. The implementation of the above technologies enables LAMOST to have a large field of view of 20 square degrees, and can simultaneously capture spectra of 4000 targets at both ends of red and blue in one exposure, making it the telescope with the highest spectral acquisition rate in the world. LAMOST low resolution sky survey has 16 spectrometers, each connected with 250 optical fibers and 2 CCD cameras. The wavelength coverage of the red end is 57009000 μ g, the wavelength coverage of the blue end is 37005900 μ g, and the resolution is about 1800. The average exposure time of a single target is 1.5h, and the limit magnitude can reach 17.8 mag. The two-dimensional spectral band image of the star light taken by the spectrometer after being dispersive by the grating is obtained through the processes of spectrum extraction, flat field removal, calibration, sky subtraction, red and blue end data combination by LAMOST 2dpipeline software. After template matching, analysis, spectral classification, red shift measurement, parameter measurement, packaging and other operations by LAMOST 1D pipeline software, data products such as star catalogs are generated. The main scientific objectives of LAMOST low resolution spectral survey include the structure and evolution of the Milky Way galaxy, celestial census, search for special celestial bodies (Li rich giant stars, metal poor stars, hypervelocity stars, white dwarfs, etc.), search for extrasolar planets, star formation, formation and evolution of adjacent galaxies, quasar search, etc. [2]
3 Wavelet transform (WT) based method for searching white dwarf main sequence binary stars method
Wavelet transform (WT) method is a fast and efficient program based on wavelet transform. The analysis unit of wavelet transform is the local flux of the spectrum, that is, the selected spectral characteristics. In other words, WT recognizes spectral features rather than continuous spectral emission or other spectral features different from the spectral features of WDMS binaries. In each iteration, the least important feature (based on its coefficient size in the wavelet transform) is removed from the spectrum until the decomposition level is satisfactory. [3]
3.1 basic principle of wavelet transform
Wavelet transform is a mathematical tool, which can extract the characteristic information of the signal at different scales by scaling and shifting the mother wavelet function. This method is especially suitable for analyzing signals with abrupt points or frequency components varying with time. It is a supplement and extension of the traditional Fourier transform.
3.2 application of wavelet transform in spectral signal processing
In spectral signal processing, wavelet analysis can be used to analyze and process various spectral data, including the spectra of WDMS binaries. Its main applications include denoising, feature extraction, signal compression and so on. For the spectral feature recognition of WDMS binaries, feature extraction is a key step.
3.3 specific process of identifying spectral characteristics of WDMS binaries
Select the appropriate wavelet base and decomposition levels, and perform wavelet transform on the preprocessed spectral data. Wavelet components with different frequencies and scales are extracted and their characteristics are analyzed.
According to the spectral characteristics of white dwarf binary stars, such as specific spectral lines and spectral shapes, a feature extraction algorithm is designed. These features are extracted from the data after wavelet transform and recognized by machine learning algorithms (such as support vector machine, decision tree, etc.). Reasonable thresholds and classification criteria are set to screen out possible white dwarf binary candidates.
The selected candidates were further verified and analyzed, including multi band observation, high-resolution spectral observation, etc. By measuring the orbital period and stellar parameters of the candidate, we can further confirm whether it is a white dwarf main sequence binary star. Carry out follow-up research on the confirmed white dwarf main sequence binaries, such as analyzing their physical properties and evolution process.
Figure 1 wavelet transform (WT) decomposition example of LAMOST da/m binary star (j161713.52+215517.5). The top panel shows the blue (left) and red (right) spectra of the binary star. The vertical gray dotted line indicates the spectral region selected for wavelet transform (the blue region is in the range of 3910-4422a, and the red region is in the range of 6800-8496a). The bottom panel shows the variation of approximation coefficient (CA) with the number of sites after the application of wavelet transform (the left panel in the blue area is the fifth iteration, and the right panel in the red area is the seventh iteration). [3]
4 detailed process of data sample query and cleaning
In this scientific research practice, the dr11 data downloaded from FileZilla is used by our team. First, the data is substituted into the code that can be compiled based on wavelet transform to screen out the candidates, and then the candidates from the code are imported into the expert spectrum recognition platform. After importing, through visual observation, the real white dwarf main sequence binaries are finally selected.
Figure 2 the data spectrum after code filtering is manually and visually screened on the expert spectrum recognition platform. The blue end of this spectrum conforms to the white dwarf spectrum template (purple curve), while the red end conforms to the M-type main sequence star template (blue curve), which is very consistent with the properties of white dwarf main sequence binary stars
The spectra of white dwarf and main sequence binaries usually contain the characteristic spectral lines of both M-type stars and white dwarfs, but they are not a simple coupling of the spectra of two stars. When these two kinds of stars form a binary star system, their spectra may overlap each other or produce specific spectral line changes, which depends on the relative position, motion state, material interaction and other factors of the binary stars.
4.1 result analysis
In this search, our team successfully used the algorithm based on wavelet transform to screen the database, and selected 279 white dwarf main sequence binary candidates from 10055 data. After sorting out the data and conducting strict manual visual screening, a total of 24 new white dwarf main sequence binaries were selected. It is worth mentioning that the efficiency of searching for new white dwarf main sequence binaries is relatively high.
At present, the accuracy of the wavelet transform method used in our code is not high enough, and the subsequent manual screening cost is high. In the future, we can try to use random forest, gradient boosting, catboost and other new methods to write new code for the search of white dwarf main sequence binary stars. By improving the accuracy of the code to reduce the cost of manual screening, and further improve the efficiency of white dwarf main sequence binary star search.
5 Summary
In astronomical research, spectral data mining and analysis has become an important means to promote the discovery of astrophysics. In recent years, the progress of observation technology and the development of large-scale Sky Survey Project enable astronomers to obtain unprecedented massive spectral data. However, it is still a challenging task to efficiently mine the target objects with scientific value from these data. Facing this challenge, our team designed and implemented a systematic large-scale spectral data mining and analysis process based on existing technologies and algorithms. The efficiency and rigor of this process made it possible to select 279 highly credible candidate targets from 10055 spectral data, and finally successfully identified 24 previously unrecorded white dwarf main sequence binaries. This study not only provides new observational evidence for the study of star evolution and binary star formation mechanism, but also shows the potential of cutting-edge technology in the field of astronomical data mining.
As an important celestial body in the process of stellar evolution, the existence and research of white dwarf main sequence binaries play an important role in understanding the process and mechanism of stellar evolution. By observing and analyzing such binary stars, we can deeply understand how stars evolve from the main sequence stage to the white dwarf stage, and how matter is transferred and ejected in this process. This will help to verify and improve the existing theory of stellar evolution and promote the theoretical development in the field of astronomy. Massive spectral data based on SDSS, LAMOST and other telescopes search for WDMS binary samples in large quantities, which has important scientific significance for us to deeply understand the evolution process of close binary stars, especially the physical mechanism of the evolution of the common envelope [4].
Reference
[1] 任娟娟, 罗阿理, and 赵永恒. “ 白矮-主序双星的搜寻及研究进展” . In: 天文学进展 32.04 (2014), pp. 462–480. issn: 1000-8349.
[2] 蔡靖豪 et al. “基于 LAMOST DR8 光谱搜寻白矮星”. In: 天文学进展 42.01 (2024), pp. 102–114. issn: 1000-8349.
[3] J. -J. Ren et al. “White dwarf-main sequence binaries from LAMOST:
the DR5 catalogue”. In: 477.4 (July 2018), pp. 4641–4654. doi: 10. 1093/mnras/sty805. arXiv: 1803.09523 [astro-ph.SR].
[4] A. Rebassa-Mansergas et al. “Post-common envelope binaries from
SDSS - VII. A catalogue of white dwarf-main sequence binaries”. In:
402.1 (Feb. 2010), pp. 620–640. doi: 10. .1365-2966.2009.1111/j 15915.x. arXiv: 0910.4406 [astro-ph.SR].