The EDIBLES survey

VI. Searching for time variations of interstellar absorption features^★,★★

¹ Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
² School of Astronomy, Institute for Research in Fundamental Sciences, 19395-5531 Tehran, Iran
e-mail: a.farhang@ipm.ir
³ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
⁴ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁵ Centre d’Études et de Recherche de Grasse, ACRI-ST, Av. Nicolas Copernic, 06130 Grasse, France
⁶ Institute for Earth and Space Exploration, The University of Western Ontario, London ON N6A 3K7, Canada
⁷ SETI Institute, 339 Bernardo Ave, Suite 200, Mountain View, CA 94043, USA
⁸ Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁹ Lennard-Jones Laboratories, Keele University, Keele ST5 5BG, UK
¹⁰ Astrochemistry Laboratory, NASA Goddard Space Flight Center, Code 691, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
¹¹ Department of Physics, The Catholic University of America, Washington, DC 20064, USA
¹² School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK
¹³ Space Policy Institute, George Washington University, Washington, DC, USA
¹⁴ LUNEX EMMESI, Leiden Observatory, 2300 RA Leiden, The Netherlands
¹⁵ Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
¹⁶ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, bus 2401, 3001 Leuven, Belgium

Received: 26 January 2020
Accepted: 13 August 2023

Abstract

Context. Interstellar absorption observed toward stellar targets changes slowly over long timescales, mainly due to the proper motion of the background target relative to the intervening clouds, such that over time, different parts of the intervening cloud are probed. On longer timescales, the slowly changing physical and chemical conditions in the cloud can also cause variation. Detecting such time variations thus provides an opportunity to study cloud structure.

Aims. We searched for systematic variations in the absorption profiles of the diffuse interstellar bands (DIBs) and interstellar atomic and molecular lines by comparing the high-quality data set from the recent ESO diffuse interstellar bands large exploration survey (EDIBLES) to older archival observations, bridging typical timescales of ~10 yr with a maximum timescale of 22 yr.

Methods. For 64 EDIBLES targets, we found adequate archival observations. We selected 31 strong DIBs, seven atomic lines, and five molecular lines to focus our search on. We carefully considered various systematic effects and used a robust Bayesian quantitative test to establish which of these absorption features could display significant variations.

Results. While systematic effects greatly complicate our search, we find evidence for variations in the profiles of the λλ4727 and 5780 DIBs in a few sightlines. Toward HD 167264, we find a new Ca I cloud component that appears and becomes stronger after 2008. The same sightline furthermore displays marginal, but systematic changes in the column densities of the atomic lines originating from the main cloud component in the sightline. Similar variations are seen toward HD 147933.

Conclusions. Our high-quality spectroscopic observations in combination with archival data show that it is possible to probe interstellar time variations on time scales of typically a decade. Despite the fact that systematic uncertainties as well as the generally somewhat lower quality of older data complicate matters, we can conclude that time variations can be made visible, both in atomic lines and DIB profiles for a few targets, but that generally, these features are stable along many lines of sight. We present this study as an archival baseline for future comparisons, bridging longer periods.