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The EDIBLES survey V: Line profile variations in the λλ5797, 6379, and 6614 diffuse interstellar bands as a tool to constrain carrier sizes

MacIsaac, Heather; Cami, Jan; Cox, Nick L.J.; Farhang, Amin; Smoker, Jonathan; Elyajouri, Meriem; Lallement, Rosine; Sarre, Peter J.; Cordiner, Martin A.; Fan, Haoyu; Kulik, Klay; Linnartz, Harold; Foing, Bernard H.; van Loon, Jacco Th.; Mulas, Giacomo; Smith, Keith T.

The EDIBLES survey V: Line profile variations in the λλ5797, 6379, and 6614 diffuse interstellar bands as a tool to constrain carrier sizes Thumbnail


Authors

Heather MacIsaac

Jan Cami

Nick L.J. Cox

Amin Farhang

Jonathan Smoker

Meriem Elyajouri

Rosine Lallement

Peter J. Sarre

Martin A. Cordiner

Haoyu Fan

Klay Kulik

Harold Linnartz

Bernard H. Foing

Giacomo Mulas

Keith T. Smith



Abstract

Context. Several diffuse interstellar bands (DIBs) have profiles with resolved sub-peaks that resemble rotational bands of large molecules. Analysis of these profiles can constrain the sizes and geometries of the DIB carriers, especially if the profiles exhibit clear variations along lines of sight probing different physical conditions.

Aims. Using the extensive data set from the ESO Diffuse Interstellar Bands Large Exploration Survey we searched for systematic variations in the peak-to-peak separation of these sub-peaks for three well-known DIBs in lines of sight with a single dominant interstellar cloud.

Methods. We used the spectra of twelve single-cloud sight lines to examine the lambda lambda 5797, 6379, and 6614 DIB profiles. We measured the peak-to-peak separation in the band profile substructures for these DIBs. We adopted the rotational contour formalism for linear or spherical top molecules to infer the rotational constant for each DIB carrier and the rotational excitation temperature in the sight lines. We compared these to experimentally or theoretically obtained rotational constants for linear and spherical molecules to estimate the DIB carrier sizes.

Results. All three DIBs have peak separations that vary systematically between lines of sight, indicating correlated changes in the rotational excitation temperatures. The rotational constant B of the lambda 6614 DIB was determined independently of the rotational excitation temperature; we derived B-6614 = (22.2 +/- 8.9) x 10(-3 )cm(-1), consistent with previous estimates. Assuming a similar rotational temperature for the lambda 6614 DIB carrier and assuming a linear carrier, we found B-5797(linear) = (5.1 +/- 2.0) x 10(-3) cm(-1) and B-5797(linear) = (2.3 +/- 0.9) x 10(-3) cm(-1). If the carriers of those DIBs are spherical species, on the other hand, their rotational constants are half that value, B-5797(spherical) = (2.6 +/- 1.0) x 10(-3) cm(-1) and B-5797(spherical) = (1.1 +/- 0.4) x 10(-3) cm(-1).

Conclusions. Systematic variations in the DIB profiles provide the means to constrain the molecular properties. We estimate molecule sizes that range from 7-9 carbon atoms (lambda 6614 carrier, linear) to 77-114 carbon atoms (lambda 6379, spherical).

Acceptance Date Jan 28, 2022
Publication Date Mar 22, 2022
Publicly Available Date Mar 28, 2024
Journal Astronomy & Astrophysics
Print ISSN 0004-6361
Publisher EDP Sciences
DOI https://doi.org/10.1051/0004-6361/202142225
Keywords ISM: lines and bands; ISM: molecules; ISM: clouds; line: profiles
Publisher URL https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/202142225

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