The EDIBLES Survey

VIII. Band profile alignment of diffuse interstellar bands

¹ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstr. 25/8, 6020 Innsbruck, Austria
e-mail: Alexander.Ebenbichler@uibk.ac.at
² European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
³ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁴ GEPI, Observatoire de Paris, PSL Research University, CNRS, Université Paris-Diderot, Sorbonne Paris Cité, Place Jules Janssen, 92195 Meudon, France
⁵ School of Astronomy, Institute for Research in Fundamental Sciences, 19395-5531 Tehran, Iran
⁶ Centre d’Etudes et de Recherche de Grasse, ACRI-ST, Av. Nicolas Copernic, Grasse 06130, France
⁷ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université Toulouse III – Paul Sabatier, CNRS, CNES, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 04, France
⁸ Lennard-Jones Laboratories, Keele University, Keele ST5 5BG, UK
⁹ Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁰ Department of Physics and Astronomy, The University of Western Ontario, London ON N6A 3K7, Canada
¹¹ Institute for Earth and Space Exploration, The University of Western Ontario, London ON N6A 3K7, Canada
¹² SETI Institute, 189 Bernardo Ave, Suite 100, Mountain View, CA 94043, USA
¹³ Astrochemistry Laboratory, NASA Goddard Space Flight Center, Code 691, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
¹⁴ Department of Physics, The Catholic University of America, Washington, DC 20064, USA

Received: 7 December 2023
Accepted: 16 February 2024

Abstract

Context. There have been many attempts to identify families of diffuse interstellar bands (DIBs) with perfectly correlating band strengths. Although major efforts have been made to classify broadly based DIB families and important insights have been gained, no family has been identified with sufficient accuracy or statistical significance to prove that a series of selected DIBs originates from the same carrier. This can be attributed in part to the exclusive use of equivalent widths to establish DIB families.

Aims. In a change of strategy, we search for DIBs that are highly correlated in both band strength and profile shape. This approach increases the chance of correlating DIBs being members of one family and originating from the same carrier molecule. We also search for correlations between DIB profile families and atomic interstellar lines, with the goal of further chemically constraining possible DIB carriers.

Methods. We adapted the well-known method of time-series alignment to perform a spectral alignment; that is, DIB alignment. In a second step, we analysed the alignment results using a clustering analysis. This method required a statistically significant data set of DIB sight lines. The ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) data were perfectly suited for this application.

Results. We report eight DIB families with correlating strengths and profiles, as well as four previously unreported DIBs in the visual range, found using DIB alignment. All profile family members show Pearson correlation coefficients in band strength higher than 0.9. In particular, we report the 6614–6521 Å DIB pair, in which both DIBs show the same triple-peak substructure and an unprecedented band strength Pearson correlation coefficient of 0.9935. The presented approach opens up new perspectives that can guide the laboratory search for DIB carriers.