[Paper Review] LAMOST Medium-Resolution Spectroscopic Survey (LAMOST-MRS): Scientific goals and survey plan

Chao Liu, Jian-Ning Fu+39 more|arXiv (Cornell University)|May 14, 2020

Stellar, planetary, and galactic studies5 references44 citations

TL;DR

The paper outlines the scientific goals, survey strategy, and expected performance of the LAMOST-MRS, a 5-year medium-resolution spectroscopic survey aiming to obtain ~2 million spectra at R~7500 and ~200k time-domain spectra for various Galactic and stellar studies.

ABSTRACT

Since September 2018, LAMOST starts a new 5-year medium-resolution spectroscopic survey (MRS) using bright/gray nights. We present the scientific goals of LAMOST-MRS and propose a near optimistic strategy of the survey. A complete footprint is also provided. Not only the regular medium-resolution survey, but also a time-domain spectroscopic survey is being conducted since 2018 and will be end in 2023. According to the detailed survey plan, we expect that LAMOST-MRS can observe about 2 million stellar spectra with ~7500 and limiting magnitude of around G=15 mag. Moreover, it will also provide about 200 thousand stars with averagely 60-epoch observations and limiting magnitude of G~14 mag. These high quality spectra will give around 20 elemental abundances, rotational velocities, emission line profiles as well as precise radial velocity with uncertainty less than 1 km/s. With these data, we expect that LAMOST can effectively leverage sciences on stellar physics, e.g. exotic binary stars, detailed observation of many types of variable stars etc., planet host stars, emission nebulae, open clusters, young pre-main-sequence stars etc.

Motivation & Objective

• Present the scientific goals of the LAMOST-MRS survey across stellar physics, binary stars, star formation, Galactic archaeology, emission nebulae, exoplanet host stars, and open clusters.
• Propose a near-optimistic survey strategy and footprint to achieve ~2 million spectra at R~7500 and ~200k high-cadence observations.
• Discuss synergies with space-based missions (Gaia, Kepler/K2, TESS) and the impact on time-domain astronomy and chemical tagging.
• Describe the survey plan including exposure strategy, S/N expectations, and division into time-domain (TD) and non-time-domain (NT) components.

Proposed method

• Describe the instrumental setup of LAMOST-MRS with R~7500 and specific wavelength coverage for blue (4950–5350 Å) and red (6300–6800 Å) arms.
• Provide exposure strategy: single 1200 s exposures, with NT fields using 3x1200 s co-added exposures to reach S/N~10 in blue at G~14.5 and red at G~15.
• Introduce time-domain observations: multiple 1200 s exposures per field within a night and across multiple nights to achieve RV precision and abundance measurements.
• Explain radial velocity calibration approach: use relatively calibrated differential RVs to reach ~0.2 km/s for late-type stars, with absolute RV calibration via constant stars.
• Outline survey simulations comparing TD/NT ratios to optimize the five-year plan and target distribution.

Experimental results

Research questions

• RQ1 What scientific insights can be gained from a large, medium-resolution spectroscopic survey of FGK stars in the Milky Way?
• RQ2 How can LAMOST-MRS achieve precise radial velocities and elemental abundances to enable chemical tagging and Galactic archaeology?
• RQ3 What is the optimal balance between time-domain and non-time-domain observations to fulfill multiple science goals?
• RQ4 How will LAMOST-MRS synergies with Gaia, Kepler/K2, and TESS enhance exoplanet host-star characterization and time-domain astrophysics?
• RQ5 What open cluster and emission nebulae science can be pursued with the large-field, high-multiplex MRS data?

Key findings

• LAMOST-MRS aims to observe about 2 million stellar spectra at R~7500 and G~15 mag, plus ~200 thousand stars with ~60 epochs.
• The blue camera covers 4950–5350 Å and the red camera covers 6300–6800 Å, enabling ~20 elemental abundances and Hα plus other emission lines.
• Radial velocity precision is expected to be ~1 km/s for late-type stars, with differential RVs reaching ~0.2 km/s for time-domain studies.
• The survey will enable studies in binary evolution, pulsating stars, star formation, emission nebulae, exoplanet host stars, Galactic archaeology, and open clusters.
• Two-phase survey design (non time-domain NT and time-domain TD) and multiple sub-projects (MRS-K, MRS-T, MRS-S, MRS-B, MRS-N, MRS-G, MRS-O) are planned to cover diverse science cases.
• Simulation results suggest ~2220 visits over 5 years for NT+TD fields with varying TD field counts, optimizing the TD/NT balance.