Measuring the diffuse interstellar bands at 5780, 5797, and 6614 Å in low-resolution spectra of cool stars from LAMOST

Abstract

Context. The limited number of high-resolution spectra of hot stars is inadequate for statistical studies of diffuse interstellar bands (DIBs). In contrast, the vast quantity of low-resolution spectroscopic surveys on cool stars holds great potential for investigating the relationship between DIBs and the known interstellar medium (ISM), as well as the spatial distribution of their unidentified carriers. Aims. We attempt to measure the DIBs λ5780, λ5797, and λ6614 in over two million low-resolution spectra of cool stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Based on these DIB measurements, we reviewed and investigated the correlation between DIBs and extinction; the kinematics of DIBs; and the Galactic distribution of DIBs from a statistical perspective. Methods. We developed a pipeline to measure the DIBs λ5780, λ5797, and λ6614 in the LAMOST low-resolution spectra. Four modules in the pipeline consist of building the target and reference dataset; extracting the ISM residual spectra from the target spectra; measuring the DIBs in the residual spectra; and quality control of the measurements. Results. We obtained DIB measurements of spectra of late-type stars from LAMOST, and selected 176 831, 13 473, and 110 152 high-quality (HQ) measurements of the DIBs λ5780, λ5797, and λ6614, respectively, corresponding to 142074, 11 480, and 85 301 unique sources. Using these HQ measurements, we present Galactic maps of the DIBs λ5780 and λ6614 in the northern sky for the first time. The central wavelengths of the DIBs λ5780, λ5797, and λ6614 in air are determined to be 5780.48 ± 0.01, 5796.94 ± 0.02, and 6613.64 ± 0.01 Å, respectively, based on their kinematics. A statistical fit of the equivalent widths of these three DIBs per unit extinction provides values of 0.565, 0.176, and 0.256 Å mag−1. As a result of this work, three catalogs of the HQ measurements for the DIBs λ5780, λ5797, and λ6614 are provided via https://nadc.china-vo.org/res/r181484/. Conclusions. To the best of our knowledge, this is the largest number of measurements of these three DIBs to date. It is also the first time that Galactic maps of the DIBs λ5780 and λ6614 in the northern hemisphere are presented, and that the central wavelengths of the DIBs λ5780, λ5797, and λ6614 are estimated from kinematics.