Diffuse interstellar band λ6614 as a distance tracer for the Perseus, Taurus, and Orion molecular clouds: Feasibility and limitations

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
² School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
³ Purple Mountain Observatory and Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 10 Yuanhua Road, Nanjing 210033, PR China

^★ Corresponding authors: jjchen@nao.cas.cn; he.zhao@oca.eu

Received: 1 January 2025
Accepted: 22 July 2025

Abstract

Context. Diffuse interstellar bands (DIBs) are absorption features in the optical-to-near-infrared spectra of stars and they are associated with interstellar medium (ISM) carriers. They are valuable in studying the ISM, offering insights into its physical and chemical conditions, while tracing the distribution and kinematics of interstellar material.

Aims. We employed DIB λ6614 as a tracer to probe the distances and spatial distributions of interstellar material in the Perseus, Taurus, and Orion molecular clouds. These key star-forming regions in the solar neighborhood were analyzed to evaluate the feasibility and limitations of using DIB λ6614 as a tracer for distance and kinematic measurements.

Methods. We obtained stellar spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope medium-resolution survey within 600 pc. For hot stars (T_eff ≥ 7500 K), DIB λ6614 was directly measured due to minimal contamination by stellar lines near the wavelength of 6614 Å. For cool stars (T_eff < 7500 K), a template subtraction method was applied to isolate the ISM spectrum. Molecular cloud boundaries were identified based on ¹²CO emission maps integrated over velocity ranges, with 315, 684, 281, and 275 sources selected for Perseus, Taurus, Orion A, and Orion B, respectively.

Results. The DIB λ6614-derived distances to the molecular clouds are 297.2 ± 1.7 pc, 150.2 ± 1.2 pc, 421. 1 ± 0.7 pc, and 409.8 ± 0.7 pc for Perseus, Taurus, Orion A, and Orion B, respectively. These results are consistent with extinction-based distances, with discrepancies of 3–15 pc. In Perseus, two significant jumps in DIB λ6614 equivalent width are detected along the distance direction, with the first at ~152 pc, likely corresponding to the boundary of the Local Bubble.

Conclusions. DIB λ6614 is a robust tracer for molecular cloud distances, with estimates closely matching extinction-based measurements. DIB λ6614 is particularly effective for tracing diffuse regions and provides complementary insights into the structural details of molecular clouds.