Unveiling Vela - Time Variability of Na I D lines in the Direction of the Vela Supernova Remnant

TL;DR

This study presents high-resolution Na I D line spectra towards 64 stars near the Vela supernova remnant, revealing significant changes in interstellar absorption features over 15-18 years, indicating dynamic interstellar medium processes.

Contribution

It provides the first long-term comparison of Na I D line profiles, uncovering notable temporal variability in interstellar clouds associated with the Vela SNR.

Findings

Disappearance of low-velocity absorption components in three stars.

Detection of changes in high-velocity Na D components.

Evidence of dynamic evolution of interstellar clouds over 15-18 years.

Abstract

High-resolution spectral profiles of Na I D lines from the interstellar medium towards 64 stars in the direction of the Vela supernova remnant are presented. This survey conducted mostly between 2011-12 complements an earlier survey of the same stars by Cha & Sembach done in the 1993-96 period. The interval of 15 to 18 years provides a base line to search for changes in the interstellar profiles. Dramatic disappearance of strong absorption components at low radial velocity is seen towards three stars - HD 63578, HD 68217, HD 76161 - over 15-18 years; HD 68217 and HD 76161 are associated with the Vela SNR but HD 63578 is likely associated with the wind bubble of g2 Velorum. The vanishing of these cold neutral clouds in the short time of 15 to 18 years needs some explanation. Other changes are seen in high-velocity Na D components.