LAMOST Time-Domain Survey: First Results of four $K$2 plates
  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.
