分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hailong Yuan
Zhenwei Li
Zhongrui Bai
Yiqiao Dong
Mengxin Wang
Sicheng Yu
Xuefei Chen
Yongheng Zhao
Yaoquan Chu
Haotong Zhang
摘要： The Extremely Low Mass White Dwarfs (ELM WDs) and pre-ELM WDs are helium core white dwarfs with mass $<\sim 0.3M_{\odot}$. Evolution simulations show that a lower mass limit for ELM WDs exists at $\approx0.14M_{\odot}$ and no one is proposed by observation to be less massive than that. Here we report the discovery of a binary system, LAMOST J224040.77-020732.8 (J2240 in short), which consists of a very low mass hot star and a compact companion. Multi-epoch spectroscopy shows an orbital period $P_{orb} =$0.219658$\pm0.000002$ days and a radial velocity semi-amplitude $K1=318.5\pm3.3km/s$, which gives the mass function of 0.74$M_{\odot}$, indicating the companion is a compact star. The F-type low resolution spectra illustrate no emission features, and the temperature ($\sim 7400K$) is consistent with that from Spectral Energy Distribution fitting and multi-color light curve solution. The optical light curves, in ZTF g, r and i bands and Catalina V band, show ellipsoidal variability with amplitudes $\sim30\%$, suggesting that the visible component is heavily tidally distorted. Combining the distance from Gaia survey, the ZTF light curves are modeled with Wilson-Devinney code and the result shows that the mass of the visible component is $M1=0.085^{+0.036}_{-0.024}M_{\odot}$, and the mass of the invisible component is $M2=0.98^{+0.16}_{-0.09}M_{\odot}$. The radius of the visible component is $R1=0.29^{+0.04}_{-0.03}R_{\odot}$. The inclination angle is approximately between 60$^{\circ}$ and 90$^{\circ}$. The observations indicate the system is most likely a pre-ELM WD + WD/NS binary, and the mass of pre-ELM is possibly lower than the $0.14M_{\odot}$ theoretical limit.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hailong Yuan
Zhenwei Li
Zhongrui Bai
Yiqiao Dong
Mengxin Wang
Sicheng Yu
Xuefei Chen
Yongheng Zhao
Yaoquan Chu
Haotong Zhang
摘要： The Extremely Low Mass White Dwarfs (ELM WDs) and pre-ELM WDs are helium core white dwarfs with mass $<\sim 0.3M_{\odot}$. Evolution simulations show that a lower mass limit for ELM WDs exists at $\approx0.14M_{\odot}$ and no one is proposed by observation to be less massive than that. Here we report the discovery of a binary system, LAMOST J224040.77-020732.8 (J2240 in short), which consists of a very low mass hot star and a compact companion. Multi-epoch spectroscopy shows an orbital period $P_{orb} =$0.219658$\pm0.000002$ days and a radial velocity semi-amplitude $K1=318.5\pm3.3km/s$, which gives the mass function of 0.74$M_{\odot}$, indicating the companion is a compact star. The F-type low resolution spectra illustrate no emission features, and the temperature ($\sim 7400K$) is consistent with that from Spectral Energy Distribution fitting and multi-color light curve solution. The optical light curves, in ZTF g, r and i bands and Catalina V band, show ellipsoidal variability with amplitudes $\sim30\%$, suggesting that the visible component is heavily tidally distorted. Combining the distance from Gaia survey, the ZTF light curves are modeled with Wilson-Devinney code and the result shows that the mass of the visible component is $M1=0.085^{+0.036}_{-0.024}M_{\odot}$, and the mass of the invisible component is $M2=0.98^{+0.16}_{-0.09}M_{\odot}$. The radius of the visible component is $R1=0.29^{+0.04}_{-0.03}R_{\odot}$. The inclination angle is approximately between 60$^{\circ}$ and 90$^{\circ}$. The observations indicate the system is most likely a pre-ELM WD + WD/NS binary, and the mass of pre-ELM is possibly lower than the $0.14M_{\odot}$ theoretical limit.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hailong Yuan
Song Wang
Zhongrui Bai
Yue Wang
Yiqiao Dong
Mengxin Wang
Sicheng Yu
Yongheng Zhao
Yaoquan Chu
Jifeng Liu
Haotong Zhang
摘要： We report the discovery of one possible neutron star binary ($P_{\rm orb} =$ 0.8666 day) by using the LAMOST low-resolution spectroscopic data. The visible companion is a late A-type dwarf ($T_{\rm eff} = 7900 \pm 200$ K; log$g$ $=$ 4.3$\pm$0.2; $M =$ 1.7$\pm$0.1 M$_{\odot}$; $R\ =\ 1.7\pm0.2$ R$_{\odot}$), at a distance of 1.11$\pm0.03$ kpc. No double-lined feature can be seen from the GTC/HORuS high-resolution spectra, thus the radial velocity variation indicates an invisible object hiding in the binary. The system's optical light curves show clear ellipsoidal variability, suggesting that the visible companion is tidal distorted. By fitting the multi-band light curves with the ELC and WD codes, we constrain the mass of the invisible star to be 1.1--1.3 M$_{\odot}$. Spectral disentangling shows no additional component with optical absorption spectra, supporting the system contains one compact object. No X-ray or UV emission are detected in the ROSAT archive observations. Therefore, we suspect the invisible object is more likely a neutron star rather than a white dwarf. Our finding suggests the ability of LAMOST spectroscopic survey to discover X-ray quiescent compact objects.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hailong Yuan
Song Wang
Zhongrui Bai
Yue Wang
Yiqiao Dong
Mengxin Wang
Sicheng Yu
Yongheng Zhao
Yaoquan Chu
Jifeng Liu
Haotong Zhang
摘要： We report the discovery of one possible neutron star binary ($P_{\rm orb} =$ 0.8666 day) by using the LAMOST low-resolution spectroscopic data. The visible companion is a late A-type dwarf ($T_{\rm eff} = 7900 \pm 200$ K; log$g$ $=$ 4.3$\pm$0.2; $M =$ 1.7$\pm$0.1 M$_{\odot}$; $R\ =\ 1.7\pm0.2$ R$_{\odot}$), at a distance of 1.11$\pm0.03$ kpc. No double-lined feature can be seen from the GTC/HORuS high-resolution spectra, thus the radial velocity variation indicates an invisible object hiding in the binary. The system's optical light curves show clear ellipsoidal variability, suggesting that the visible companion is tidal distorted. By fitting the multi-band light curves with the ELC and WD codes, we constrain the mass of the invisible star to be 1.1--1.3 M$_{\odot}$. Spectral disentangling shows no additional component with optical absorption spectra, supporting the system contains one compact object. No X-ray or UV emission are detected in the ROSAT archive observations. Therefore, we suspect the invisible object is more likely a neutron star rather than a white dwarf. Our finding suggests the ability of LAMOST spectroscopic survey to discover X-ray quiescent compact objects.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hongliang Yan
Haining Li
Song Wang
Weikai Zong
Haibo Yuan
Maosheng Xiang
Yang Huang
Jiwei Xie
Subo Dong
Hailong Yuan
Shaolan Bi
Yaoquan Chu
Xiangqun Cui
Licai Deng
Jianning Fu
Zhanwen Han
Jinliang Hou
Guoping Li
Chao Liu
Jifeng Liu
摘要： The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), also known as the Guoshoujing Telescope, is a major national scientific facility for astronomical research located in Xinglong, China. Beginning with a pilot survey in 2011, LAMOST has been surveying the night sky for more than 10 years. The LAMOST survey covers various objects in the Universe, from normal stars to peculiar ones, from the Milky Way to other galaxies, and from stellar black holes and their companions to quasars that ignite ancient galaxies. Until the latest data release 8, the LAMOST survey has released spectra for more than 10 million stars, ~220,000 galaxies, and ~71,000 quasars. With this largest celestial spectra database ever constructed, LAMOST has helped astronomers to deepen their understanding of the Universe, especially for our Milky Way galaxy and the millions of stars within it. In this article, we briefly review the characteristics, observations, and scientific achievements of LAMOST. In particular, we show how astrophysical knowledge about the Milky Way has been improved by LAMOST data.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Song Wang
Haotong Zhang
Zhongrui Bai
Hailong Yuan
Maosheng Xiang
Bo Zhang
Wen Hou
Fang Zuo
Bing Du
Tanda Li
Fan Yang
Kaiming Cui
Yilun Wang
Jiao Li
Mikhail Kovalev
Chunqian Li
Hao Tian
Weikai Zong
Henggeng Han
Chao Liu
摘要： From Oct. 2019 to Apr. 2020, LAMOST performs a time-domain spectroscopic survey of four $K$2 plates with both low- and med-resolution observations. The low-resolution spectroscopic survey gains 282 exposures ($\approx$46.6 hours) over 25 nights, yielding a total of about 767,000 spectra, and the med-resolution survey takes 177 exposures ($\approx$49.1 hours) over 27 nights, collecting about 478,000 spectra. More than 70%/50% of low-resolution/med-resolution spectra have signal-to-noise ratio higher than 10. We determine stellar parameters (e.g., $T_{\rm eff}$, log$g$, [Fe/H]) and radial velocity (RV) with different methods, including LASP, DD-Payne, and SLAM. In general, these parameter estimations from different methods show good agreement, and the stellar parameter values are consistent with those of APOGEE. We use the $Gaia$ DR2 RV data to calculate a median RV zero point (RVZP) for each spectrograph exposure by exposure, and the RVZP-corrected RVs agree well with the APOGEE data. The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters, multi-band magnitudes, distances and extinction values. Finally, we construct a binary catalog including about 2700 candidates by analyzing their light curves, fitting the RV data, calculating the binarity parameters from med-resolution spectra, and cross-matching the spatially resolved binary catalog from $Gaia$ EDR3. The LAMOST TD survey is expected to get breakthrough in various scientific topics, such as binary system, stellar activity, and stellar pulsation, etc.
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