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
Wei Zhang
Hong Wu
Chaojian Wu
Juanjuan Ren
Jianjun Chen
Chih-Hao Hsia
Yuzhong Wu
Hui Zhu
Jianrong Shi
Zhongrui Bai
Zhaoxiang Qi
Yongheng Zhao
Yonghui Hou
摘要： We introduce a method of subtracting geocoronal Halpha emissions from the spectra of LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N). The flux ratios of the Halpha sky line to the adjacent OH lambda6554 single line do not show a pattern or gradient distribution in a plate. More interestingly, the ratio is well correlated to solar altitude, which is the angle of the sun relative to the Earth's horizon. It is found that the ratio decreases from 0.8 to 0.2 with the decreasing solar altitude from -17 to -73 degree. Based on this relation, which is described by a linear function, we can construct the Halpha sky component and subtract it from the science spectrum. This method has been applied to the LAMOST-MRS-N data, and the contamination level of the Halpha sky to nebula is reduced from 40% to less than 10%. The new generated spectra will significantly improve the accuracy of the classifications and the measurements of physical parameters of Galactic nebulae.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ling-Lin Zheng
Mouyuan Sun
Wei-Min Gu
Tuan Yi
Zhi-Xiang Zhang
Pei Wang
Junfeng Wang
Jianfeng Wu
Song Wang
Jia Zhang
Chun-Qian Li
Jian-Rong Shi
Yong Shao
Xiang-Dong Li
Jin-Bo Fu
Fan Yang
Zhongrui Bai
Yu Bai
Haotong Zhang
Jifeng Liu
摘要： Recent studies have revealed the global deposition on Earth of radioactive elements (e.g., $^{60}$Fe) resulting from the metal-enriched ejecta of nearby (within $\sim 100$ pc) supernova explosions. The majority of neutron stars in our Solar neighborhood remain to be discovered. Here we report the discovery of the nearest ($127.7 \pm 0.3$ pc) neutron star candidate in the single-lined spectroscopic binary LAMOST J235456.76+335625.7 (hereafter J2354). Utilizing the multi-epoch spectra and high-cadence periodic light curves, we measure the mass of the visible star ($M_{\rm vis}=0.70\pm 0.05\ M_{\odot}$) and determine the mass function of the invisible object $f(M)=0.525 \pm 0.004\ M_{\odot}$, i.e., the mass of the unseen compact object is $M_{\rm inv} \geq 1.26 \pm 0.03M_{\odot}$. The excess UV emission due to a hot supramassive white dwarf is absent. Hence, it is likely that J2354 harbors a neutron star. J2354 is X-ray dim (the $0.1$--$2.4$ keV luminosity $<10^{30}\ {\rm erg\ s^{-1}}$) since it is not detected in the ROSAT all-sky surveys in X-ray. One-hour exceptionally sensitive radio follow-up observations with FAST, the largest single-dish radio telescope, failed to reveal any radio pulsating signals (the potential pulse power at $1.4$ GHz is $<6.8\times 10^{23}\ {\rm erg\ s^{-1}}$). Hence, the neutron star candidate in J2354 can only be discovered via our time-resolved observations. The alternative scenario involving a nearby supramassive cold white dwarf cannot be fully excluded. Our discovery demonstrates a promising way to unveil the missing population of backyard inactive neutron stars or supramassive cold white dwarfs in binaries by exploring the optical time domain, thereby facilitating understanding of the supernovae explosion and metal-enrichment history in our Solar neighborhood.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Tuan Yi
Wei-Min Gu
Zhi-Xiang Zhang
Ling-Lin Zheng
Mouyuan Sun
Junfeng Wang
Zhongrui Bai
Pei Wang
Jianfeng Wu
Yu Bai
Song Wang
Haotong Zhang
Yize Dong
Yong Shao
Xiang-Dong Li
Jia Zhang
Yang Huang
Fan Yang
Qingzheng Yu
Hui-Jun Mu
摘要： Optical time-domain surveys can unveil and characterize exciting but less-explored non-accreting and/or non-beaming neutron stars (NS) in binaries. Here we report the discovery of such a NS candidate using the LAMOST spectroscopic survey. The candidate, designated LAMOST J112306.9+400736 (hereafter J1123), is in a single-lined spectroscopic binary containing an optically visible M star. The star's large radial velocity variation and ellipsoidal variations indicate a relatively massive unseen companion. Utilizing follow-up spectroscopy from the Palomar 200-inch telescope and high-precision photometry from TESS, we measure a companion mass of $1.24_{-0.03}^{+0.03}~M_{\odot}$. Main-sequence stars with this mass are ruled out, leaving a NS or a massive white dwarf (WD). Although a massive WD cannot be ruled out, the lack of UV excess radiation from the companion supports the NS hypothesis. Deep radio observations with FAST yielded no detections of either pulsed or persistent emission. J1123 is not detected in numerous X-ray and gamma-ray surveys. These non-detections suggest that the NS candidate is not presently accreting and pulsing. Our work exemplifies the capability of discovering compact objects in non-accreting close binaries by synergizing the optical time-domain spectroscopy and high-cadence photometry.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ling-Lin Zheng
Mouyuan Sun
Wei-Min Gu
Tuan Yi
Zhi-Xiang Zhang
Pei Wang
Junfeng Wang
Jianfeng Wu
Song Wang
Jia Zhang
Chun-Qian Li
Jian-Rong Shi
Yong Shao
Xiang-Dong Li
Jin-Bo Fu
Fan Yang
Zhongrui Bai
Yu Bai
Haotong Zhang
Jifeng Liu
摘要： Recent studies have revealed the global deposition on Earth of radioactive elements (e.g., $^{60}$Fe) resulting from the metal-enriched ejecta of nearby (within $\sim 100$ pc) supernova explosions. The majority of neutron stars in our Solar neighborhood remain to be discovered. Here we report the discovery of the nearest ($127.7 \pm 0.3$ pc) neutron star candidate in the single-lined spectroscopic binary LAMOST J235456.76+335625.7 (hereafter J2354). Utilizing the multi-epoch spectra and high-cadence periodic light curves, we measure the mass of the visible star ($M_{\rm vis}=0.70\pm 0.05\ M_{\odot}$) and determine the mass function of the invisible object $f(M)=0.525 \pm 0.004\ M_{\odot}$, i.e., the mass of the unseen compact object is $M_{\rm inv} \geq 1.26 \pm 0.03M_{\odot}$. The excess UV emission due to a hot supramassive white dwarf is absent. Hence, it is likely that J2354 harbors a neutron star. J2354 is X-ray dim (the $0.1$--$2.4$ keV luminosity $<10^{30}\ {\rm erg\ s^{-1}}$) since it is not detected in the ROSAT all-sky surveys in X-ray. One-hour exceptionally sensitive radio follow-up observations with FAST, the largest single-dish radio telescope, failed to reveal any radio pulsating signals (the potential pulse power at $1.4$ GHz is $<6.8\times 10^{23}\ {\rm erg\ s^{-1}}$). Hence, the neutron star candidate in J2354 can only be discovered via our time-resolved observations. The alternative scenario involving a nearby supramassive cold white dwarf cannot be fully excluded. Our discovery demonstrates a promising way to unveil the missing population of backyard inactive neutron stars or supramassive cold white dwarfs in binaries by exploring the optical time domain, thereby facilitating understanding of the supernovae explosion and metal-enrichment history in our Solar neighborhood.
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
Ling-Lin Zheng
Wei-Min Gu
Mouyuan Sun
Zhixiang Zhang
Tuan Yi
Jianfeng Wu
Junfeng Wang
Jin-Bo Fu
Sen-Yu Qi
Fan Yang
Song Wang
Liang Wang
Zhongrui Bai
Haotong Zhang
Chun-Qian Li
Jian-Rong Shi
Weikai Zong
Yu Bai
Jifeng Liu
摘要： We report a single-lined white dwarf-main sequence binary system, LAMOST J172900.17+652952.8, which is discovered by LAMOST's medium resolution time-domain surveys. The radial velocity semi-amplitude and orbital period of the optical visible star are measured by using the Palomar 200-inch telescope follow-up observations and the light curves from TESS. Thus the mass function of the invisible candidate white dwarf is derived, $f(M_{\rm{2}}) = 0.120\,\pm\,0.003\,M_{\odot}$. The mass of the visible star is measured based on the spectral energy distribution fitting, $M_{\mathrm{1}}$ = $0.81^{+0.07}_{-0.06}\,M_{\odot}$. Hence, the mass of its invisible companion is $M_{\rm{2}}\,\gtrsim\,0.63\,M_{\odot}$. The companion ought to be a compact object rather than a main-sequence star owing to the mass ratio $q = M_{\rm{2}} / M_{\rm 1} \gtrsim 0.78$ and the single-lined spectra. The compact object is likely to be a white dwarf except for small inclination angle, $i\,\lesssim\,40^{\circ}$. By using the GALEX NUV flux, the effective temperature of the white dwarf candidate is constrained as $T_{\rm eff}^{\rm WD}\,\lesssim\,12000-13500$ K. It is difficult to detect white dwarfs which are outshone by their bright companions via single-epoch optical spectroscopic surveys. Therefore, the optical time-domain surveys can play an important role in unveiling invisible white dwarfs and other compact objects in binaries.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ling-Lin Zheng
Wei-Min Gu
Mouyuan Sun
Zhixiang Zhang
Tuan Yi
Jianfeng Wu
Junfeng Wang
Jin-Bo Fu
Sen-Yu Qi
Fan Yang
Song Wang
Liang Wang
Zhongrui Bai
Haotong Zhang
Chun-Qian Li
Jian-Rong Shi
Weikai Zong
Yu Bai
Jifeng Liu
摘要： We report a single-lined white dwarf-main sequence binary system, LAMOST J172900.17+652952.8, which is discovered by LAMOST's medium resolution time-domain surveys. The radial velocity semi-amplitude and orbital period of the optical visible star are measured by using the Palomar 200-inch telescope follow-up observations and the light curves from TESS. Thus the mass function of the invisible candidate white dwarf is derived, $f(M_{\rm{2}}) = 0.120\,\pm\,0.003\,M_{\odot}$. The mass of the visible star is measured based on the spectral energy distribution fitting, $M_{\mathrm{1}}$ = $0.81^{+0.07}_{-0.06}\,M_{\odot}$. Hence, the mass of its invisible companion is $M_{\rm{2}}\,\gtrsim\,0.63\,M_{\odot}$. The companion ought to be a compact object rather than a main-sequence star owing to the mass ratio $q = M_{\rm{2}} / M_{\rm 1} \gtrsim 0.78$ and the single-lined spectra. The compact object is likely to be a white dwarf except for small inclination angle, $i\,\lesssim\,40^{\circ}$. By using the GALEX NUV flux, the effective temperature of the white dwarf candidate is constrained as $T_{\rm eff}^{\rm WD}\,\lesssim\,12000-13500$ K. It is difficult to detect white dwarfs which are outshone by their bright companions via single-epoch optical spectroscopic surveys. Therefore, the optical time-domain surveys can play an important role in unveiling invisible white dwarfs and other compact objects in binaries.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Tuan Yi
Wei-Min Gu
Zhi-Xiang Zhang
Ling-Lin Zheng
Mouyuan Sun
Junfeng Wang
Zhongrui Bai
Pei Wang
Jianfeng Wu
Yu Bai
Song Wang
Haotong Zhang
Yize Dong
Yong Shao
Xiang-Dong Li
Jia Zhang
Yang Huang
Fan Yang
Qingzheng Yu
Hui-Jun Mu
摘要： Optical time-domain surveys can unveil and characterize exciting but less-explored non-accreting and/or non-beaming neutron stars (NS) in binaries. Here we report the discovery of such a NS candidate using the LAMOST spectroscopic survey. The candidate, designated LAMOST J112306.9+400736 (hereafter J1123), is in a single-lined spectroscopic binary containing an optically visible M star. The star's large radial velocity variation and ellipsoidal variations indicate a relatively massive unseen companion. Utilizing follow-up spectroscopy from the Palomar 200-inch telescope and high-precision photometry from TESS, we measure a companion mass of $1.24_{-0.03}^{+0.03}~M_{\odot}$. Main-sequence stars with this mass are ruled out, leaving a NS or a massive white dwarf (WD). Although a massive WD cannot be ruled out, the lack of UV excess radiation from the companion supports the NS hypothesis. Deep radio observations with FAST yielded no detections of either pulsed or persistent emission. J1123 is not detected in numerous X-ray and gamma-ray surveys. These non-detections suggest that the NS candidate is not presently accreting and pulsing. Our work exemplifies the capability of discovering compact objects in non-accreting close binaries by synergizing the optical time-domain spectroscopy and high-cadence photometry.
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.
点击量
待评议
点击量
下载量
评论
