Phase II of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)-Kepler/K2 survey (LK–MRS), initiated in 2018, aims at collecting medium-resolution spectra (R ∼ 7500; hereafter MRS) for more than 50,000 stars with multiple visits (∼60 epochs) over a period of 5 yr (2018 September to 2023 June). We selected 20 footprints distributed across the Kepler field and six K2 campaigns, with each plate containing a number of stars ranging from ∼2000 to ∼3000. During the first year of observations, the LK–MRS has already visited 13 plates 223 times over 40 individual nights, and collected ∼280,000 and ∼369,000 high-quality spectra in the blue and red wavelength ranges, respectively. The atmospheric parameters and radial velocities for ∼259,000 spectra of 21,053 targets were successfully calculated by the LAMOST stellar parameter pipeline. The internal uncertainties for the effective temperature, surface gravity, metallicity, and radial velocity are found to be 100 K, 0.15 dex, 0.09 dex, and 1.00 km s⁻¹, respectively, when derived from a medium-resolution LAMOST spectrum with a signal-to-noise ratio (S/N) in the g band of 10. All of the uncertainties decrease as S/N increases, but they stabilize for S/N > 100. We found 14,997, 20,091, and 1514 stars in common with the targets from the LAMOST low-resolution survey (LRS), Gaia, and the Apache Point Observatory Galactic Evolution Experiment (APOGEE), respectively, corresponding to fractions of ∼70%, ∼95%, and ∼7.2%. In general, the parameters derived from LK–MRS spectra are consistent with those obtained from the LRS and APOGEE spectra, but the scatter increases as the surface gravity decreases when comparing with the measurements from APOGEE. A large discrepancy is found with the Gaia values of the effective temperature. Comparisons of the radial velocities of LK–MRS to Gaia and LK–MRS to APOGEE nearly follow a Gaussian distribution with means of μ ∼ 1.10 and 0.73 km s⁻¹, respectively. We expect that the results from the LK–MRS spectra will shed new light on binary stars, asteroseismology, stellar activity, and other research fields.

The LAMOST-Kepler (LK-) project was initiated to use the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to make spectroscopic follow-up observations for the targets in the field of the Kepler mission. The Kepler field is divided into 14 subfields that are adapted to the LAMOST circular field with a diameter of 5°. During the regular survey phase of LAMOST, the LK-project took data from 2012 June to 2017 June and covered all 14 subfields at least twice. In particular, we describe in this paper the second Data Release of the LK-project, including all spectra acquired through 2015 May–2017 June together with the first round observations of the LK-project from 2012 June to 2014 September. The LK-project now counts 227,870 spectra of 156,390 stars, among which we have derived atmospheric parameters ( , T _eff, and [Fe/H]) and heliocentric radial velocity for 173,971 spectra of 126,172 stars. These parameters were obtained with the most recent version of the LAMOST Stellar Parameter Pipeline v 2.9.7. Nearly one half, namely 76,283 targets, are observed both by the LAMOST and Kepler telescopes. These spectra, establishing a large spectroscopy library, will be useful for the entire astronomical community, particularly for planetary science and stellar variability on Kepler targets.

Until recently, black holes (BHs) could be discovered only through accretion from other stars in X-ray binaries, or in merging double compact objects. Improvements in astrometric and spectroscopic measurements have made it possible to detect BHs also in noninteracting BH binaries (nBHBs) through a precise analysis of the companion’s motion. In this study, using an updated version of the StarTrack binary-star population modeling code and a detailed model of the Milky Way (MW) galaxy, we calculate the expected number of detections for Gaia and LAMOST surveys. We develop a formalism to convolve the binary population synthesis output with a realistic stellar density distribution, star formation history (SFH), and chemical evolution for the MW, which produces a probability distribution function of the predicted compact-binary population over the MW. This avoids the additional statistical uncertainty that is introduced by methods that Monte Carlo sample from binary population synthesis output to produce one potential specific realization of the MW compact-binary distribution, and our method is also comparatively fast to such Monte Carlo realizations. Specifically, we predict ∼41–340 nBHBs to be observed by Gaia, although the numbers may drop to ∼10–70 if the recent (≲100 Myr) star formation is low (∼1 M _⊙ yr⁻¹). For LAMOST we predict ≲14 detectable nBHBs, which is lower partially because its field of view covers just ∼6% of the Galaxy.