Explore the vast range of titles available.

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun 1 – 4 . Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star–black-hole binaries 5 , 6 . When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68 − 13 + 11 solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories. Radial-velocity measurements of a Galactic B-type star show a dark companion that seems to be a black hole of about 68 solar masses, in a widely spaced binary system.

The double revolving fiber positioning unit (FPU) is one of the key technologies of The Large Sky Area Multi-Object Fiber Spectroscope Telescope (LAMOST). The positioning accuracy of the computer controlled FPU depends on robot accuracy as well as the initial parameters of FPU. These initial parameters may deteriorate with time when FPU is running in non-supervision mode, which would lead to bad fiber position accuracy and further efficiency degradation in the subsequent surveys. In this paper, we present an algorithm based on deep learning to detect the FPU’s initial angle using the front illuminated image of LAMOST focal plane. Preliminary test results show that the detection accuracy of the FPU initial angle is better than 2.°5, which is good enough to distinguish those obvious bad FPUs. Our results are further well verified by direct measurement of fiber position from the back illuminated image and the correlation analysis of the spectral flux in LAMOST survey data.

The double revolving fiber positioning unit (FPU) is one of the key technologies of The Large Sky Area Multi-Object Fiber Spectroscope Telescope (LAMOST). The positioning accuracy of the computer controlled FPU depends on robot accuracy as well as the initial parameters of FPU. These initial parameters may deteriorate with time when FPU is running in non-supervision mode, which would lead to bad fiber position accuracy and further efficiency degradation in the subsequent surveys. In this paper, we present an algorithm based on deep learning to detect the FPU’s initial angle using the front illuminated image of LAMOST focal plane. Preliminary test results show that the detection accuracy of the FPU initial angle is better than 2°.5, which is good enough to distinguish those obvious bad FPUs. Our results are further well verified by direct measurement of fiber position from the back illuminated image and the correlation analysis of the spectral flux in LAMOST survey data.

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.

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.

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.

All stellar mass black holes have hitherto been identified by X-rays emitted by gas that is accreting onto the black hole from a companion star. These systems are all binaries with black holes below 30 M$_{\\odot}$$^{1-4}\\(. Theory predicts, however, that X-ray emitting systems form a minority of the total population of star-black hole binaries\\)^{5,6}\\(. When the black hole is not accreting gas, it can be found through radial velocity measurements of the motion of the companion star. Here we report radial velocity measurements of a Galactic star, LB-1, which is a B-type star, taken over two years. We find that the motion of the B-star and an accompanying H\\)\\alpha\\( emission line require the presence of a dark companion with a mass of \\)68^{+11}_{-13}\\( M\\)_{\\odot}\\(, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. The gravitational wave experiments have detected similarly massive black holes\\)^{7,8}\\(, but forming such massive ones in a high-metallicity environment would be extremely challenging to current stellar evolution theories\\)^{9-11}$.

LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) is a Chinese national scientific research facility operated by National Astronomical Observatories, Chinese Academy of Sciences (NAOC). After two years of commissioning beginning in 2009, the telescope, instruments, software systems and operations are nearly ready to begin the main science survey. Through a spectral survey of millions of objects in much of the northern sky, LAMOST will enable research in a number of contemporary cutting edge topics in astrophysics, such as: discovery of the first generation stars in the Galaxy, pinning down the formation and evolution history of galaxies especially theMilky Way and its central massive black hole, looking for signatures of dark matter distribution and possible sub-structures in the Milky Way halo. To maximize the scientific potential of the facility, wide national participation and international collaboration has been emphasized. The survey has two major components: the LAMOST ExtraGAlactic Survey (LEGAS), and the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE). Until LAMOST reaches its full capability, the LEGUE portion of the survey will use the available observing time, starting in 2012. An overview of the LAMOST project and the survey that will be carried out in next five to six years is presented in this paper. The science plan for the whole LEGUE survey, instrumental specifications, site conditions, the descriptions of the current on-going pilot survey, including its footprints and target selection algorithm, will be presented as separate papers in this volume.

We investigate the non-Gaussian features of the IGM at redshift \\(z\\sim 5 - 6\\) using Ly\\(\\alpha\\) transmitted flux of quasar absorption spectra and cosmological hydrodynamic simulation of the concordance \\(\\Lambda\\)CDM universe. We show that the neutral hydrogen mass density field and Ly\\(\\alpha\\) transmitted flux fluctuations possess all the non-Gaussian features predicted by the log-Poisson hierarchy, which depends only on two dimensionless parameters \\(\\beta\\) and \\(\\gamma\\), describing, respectively, the intermittence and singularity of the random fields. We find that the non-Gaussianity of the Ly\\(\\alpha\\) transmitted flux of quasars from \\(z=4.9\\) to \\(z=6.3\\) can be well reconstructed by the hydrodynamical simulation samples. Although the Gunn-Peterson optical depth and its variance underwent a significant evolution in the redshift range of \\(5 - 6\\), the intermittency measured by \\(\\beta\\) is almost redshift-independent in this range. More interesting, the intermittency of quasar's absorption spectra on physical scales \\(0.1-1\\) h\\(^{-1}\\)Mpc in redshift \\(5 - 6\\) are found to be about the same as that on physical scales \\(1-10\\) h\\(^{-1}\\)Mpc at redshifts \\(2 - 4\\). Considering the Jeans length is less than 0.1 h\\(^{-1}\\)Mpc at \\(z\\sim 5\\), and \\(1\\) h\\(^{-1}\\)Mpc at \\(z\\sim 2\\), these results imply that the nonlinear evolution in high and low redshifts will lead the cosmic baryon fluid to a state similar to fully developed turbulence. The log-Poisson high order behavior of current high redshift data of quasar's spectrum can be explained by uniform UV background in the redshift range considered. We also studied the log-Poisson non-Gaussianity by considering inhomogeneous background. With several simplified models of inhomogeneous background, we found the effect of the inhomogeneous background on the log-Poisson non-Gaussianity is not larger than 1-sigma.

We use a sample of galaxy groups selected from the SDSS DR 4 with an adaptive halo-based group finder to probe how the clustering strength of groups depends on their masses and colors. In particular, we determine the relative biases of groups of different masses, as well as that of groups with the same mass but with different colors. In agreement with previous studies, we find that more massive groups are more strongly clustered, and the inferred mass dependence of the halo bias is in good agreement with predictions for the \\(\\Lambda\\)CDM cosmology. Regarding the color dependence, we find that groups with red centrals are more strongly clustered than groups of the same mass but with blue centrals. Similar results are obtained when the color of a group is defined to be the total color of its member galaxies. The color dependence is more prominent in less massive groups and becomes insignificant in groups with masses \\(\\gta 10^{14}\\msunh\\). We construct a mock galaxy redshift survey constructed from the large Millenium simulation that is populated with galaxies according to the semi-analytical model of Croton et al. Applying our group finder to this mock survey, and analyzing the mock data in exactly the same way as the true data, we are able to accurately recover the intrinsic mass and color dependencies of the halo bias in the model. This suggests that our group finding algorithm and our method of assigning group masses do not induce spurious mass and/or color dependencies in the group-galaxy correlation function. The semi-analytical model reveals the same color dependence of the halo bias as we find in our group catalogue. In halos with \\(M\\sim 10^{12}\\msunh\\), though, the strength of the color dependence is much stronger in the model than in the data.